Select Page
Best practice for separation columns in ion chromatography (IC) – Part 3

Best practice for separation columns in ion chromatography (IC) – Part 3

This is the third and final post in our series providing you with tips and tricks on the proper use of ion chromatography columns. In the first part, we mostly discussed the standard operation conditions as well as operational limits for columns, while in the second post, we focused on application related topics and what elution parameters can be changed to modify the separation performance. In the conclusion of this series we will take a closer look at the ways to assess the column performance during its lifetime and offer some troubleshooting tips which can help in fixing issues that may appear. 

Essential column parameters

Let’s begin by looking at the main parameters that can be used to judge the column performance. Most of these reference values can be extracted from the certificate of analysis. The separation column certificates can be found in the Metrohm Certificate Finder. Reproducing the certificate chromatogram periodically to verify the column performance can be helpful to detect changes in performance early and to avoid irreversible damage of the column.

Below, we will consider the most important parameters one by one.
Retention time and column capacity

The retention time of the individual analytes is a good measure of the column selectivity and capacity. When the retention times of the analytes do not match the retention times of the certificate, there are many possible reasons for this behavior.

Possibly, the eluent composition is wrong, e.g., because the eluent components are not present in the correct concentrations. In case the eluent strength is too high, the retention times will be reduced. This phenomenon usually occurs for all ions simultaneously and shifts all the peaks closer together. Thereby, the multivalent ions are accelerated to a stronger extent than the monovalent ions. This issue can be fixed by preparing a fresh eluent with the correct composition.

The eluent may not be fresh or not sufficiently protected from the surrounding atmosphere, e.g., with a CO2 adsorber. Carbon dioxide from the ambient air can change the eluent composition (i.e., strength, pH, etc.) over time and this will affect the retention times of the analytes. Weak hydroxide eluents are particularly affected by this issue, since the elution strength of carbonate ions is much stronger than the one of hydroxide ions, leading to strong shifts in retention times. Therefore, multivalent ions are more affected by this than monovalent ones. This issue can be fixed by preparing a fresh eluent and by using a CO2 adsorber. When working with hydroxide eluents, it is also important to verify the status of the hydroxide stock solution as it can absorb CO2 from the air. Figure 1 shows the effect of CO2 uptake from the air on the retention times of common anions.

Effect of eluent absorption of carbon dioxide in the air on ion separation.
Figure 1. Example chromatograms showing the effect of eluent absorption of carbon dioxide in the air for seven standard anions measured on a Metrosep A Supp 5 – 250/4.0 column under standard conditions. Red: unprotected eluent. Black: eluent protected with a carbon dioxide adsorber.
Some samples may contain constituents that occupy the ion exchange groups of the column material. In that case, the number of available ion exchange groups on the column is reduced compared to the initial state, leading to an apparent smaller column capacity and shorter retention times. Depending on the type of contaminant(s), there are possibilities to reverse this effect and wash them from the column surface. These regeneration procedures are adapted individually to the different stationary phases and should be used as a last option to save a column.
The procedures as well as the operation limits are described in the respective leaflets of the column and can be found on our website. Please consult your Metrohm dealer before performing a regeneration procedure.
  • In case the contamination is from a multivalent ion, it is usually possible to wash them off by flushing the column with an eluent of a higher concentration. When doing so, do not forget the operation limits of the column, particularly regarding the eluent pH.
  • Sometimes, organic molecules can adsorb to the column stationary phase because of their strong affinity to it. This can lead to a blockage of the ion exchange groups and reduced retention times along with increased operating pressure. When this happens, it can help to wash the stationary phase with an eluent containing a fraction of an organic modifier. This will increase the affinity of the contaminant to the mobile phase and help to detach it from the stationary phase.

Usually, after such a regeneration procedure, the original column capacity can be restored.

An even better way to extend the lifetime of the separation column is by regularly exchanging the guard column. One of its purposes is to protect the separation column from contaminants by retaining them.

Make sure to exchange the guard column three to four times over the lifetime of the separation column, or even more frequently when dealing with very complex sample matrices such as dyes or food matrices. In these situations, we suggest using the Metrosep RP 2 Guard/3.5.

The chromatogram overlay in Figure 2 shows the effect of a defective guard column on the peak shape.
Effect of eluent absorption of carbon dioxide in the air on ion separation.
Figure 2. Example chromatograms showing the effect of a damaged guard column. Black: analysis of standard anions when using a defective guard column. Red: identical analysis without a guard column installed. In this case, the replacement of the guard column is strongly recommended.
In some cases, the column capacity is reduced due to chemical modification of the stationary phase. This happens when a column is used in conditions outside of the operation limits—e.g., extreme pH situations. Extreme pH conditions can alter the chemical bonds of the ion exchange groups to the base particle substrate. This irreversible process leads to permanent column capacity loss. In this case, no regeneration procedure can restore the original column capacity.

Please note that this loss of ion exchange groups also happens slowly during the regular use of ion exchange columns. The strength of the chemical bond of the ion exchange groups is thoroughly tested during the development of Metrohm columns to provide a long column lifetime.

Theoretical plates and peak symmetry

The number of theoretical plates (TP) can be a useful tool to judge the column packing status. The higher the TP value, the better the packing of the column. For a meaningful judgement of the column packing bed, choose an analyte that does not elute too early in the chromatogram (these peaks can be affected by extra-column effects, in particular on 2 mm systems) and that is not affected by secondary interactions (i.e., avoid using nitrate). For cations, potassium is a good choice, while for anions, sulfate is a suitable choice.

Although the columns are packed at pressures higher than the normal operating pressure, the packing bed continues to further densify throughout the column lifetime with the continuous application of flowing mobile phase (eluent). While the packing bed of the stationary phase improves due to this effect, it may also lead to some dead volume at the entrance of the separation column. This dead volume can be responsible for peak broadening and reduced theoretical plates, particularly at the beginning of the chromatogram.

While this is a regular aging process of the column, it is possible to slow it down by taking good care of the column. Preventive actions include the slow initiation of the eluent flow rate and temperature at start-up as well as the proper and complete shutdown of the high-pressure pump before removing the column, as mechanical stress can be detrimental to the packing bed. Exchanging the guard column can often have a positive impact on the theoretical plates and peak shapes (see Figure 2).

Issues with the column packing bed often also become visible in the asymmetry factor values and the overall peak shapes. More pronounced fronting as well as peak broadening can be warning signs for channeling in the column or the guard column. Unfortunately, this kind of damage on the column is irreversible and requires an exchange of the separation column.

Before column replacement, it is important to check if the issues originated from the column or another connection in the IC system whenever peak broadening is observed in the chromatogram. Make sure that all capillaries in the high-pressure path have a diameter of ≤0.25 mm and that all capillaries have been installed and connected correctly without additional dead volume. Systems equipped with small inner diameter (2 mm, microbore) columns are more strongly affected by dead volume than those with 4 mm columns. This means that when using microbore columns, less dead volume is required for the peak broadening effect to become visible compared to when using 4 mm columns.

Column pressure

Another important parameter to regularly check throughout the column lifetime is the system pressure. High pressure is among the most frequent reasons leading to a column replacement. Whenever a pressure increase is noted, it is important to verify what part of the IC system is the cause.

If the sample contains particles and insufficient sample preparation is applied, the particles will accumulate at the entrance of the protective guard column and eventually lead to increased system pressure. In this case, the guard column performs its intended use of protecting the separation column and needs to be replaced. If the guard column is not replaced soon enough, then particulate contamination may break through and load onto the separation column. While there is no regeneration procedure for a guard column loaded with particles, separation columns contaminated with particles may be regenerated by rinsing the column at low flow rates in the reverse flow direction.

Please note that these regeneration procedures may not always be successful.

Avoiding particles from being injected into the high-pressure path of the IC system is a good way of protecting the guard and separation columns. Metrohm provides several automated sample preparation techniques which result in a positive impact on the column lifetime. The most common techniques for this purpose are Inline Ultrafiltration (Figure 3) and Inline Dialysis.

Effect of eluent absorption of carbon dioxide in the air on ion separation.
Figure 3. Inline Ultrafiltration is a useful automated sample preparation technique that protects the separation column from particle accumulation.
Learn more about Metrohm Inline Ultrafiltration in our related blog post.

Column end of life

All of the parameters described above should be considered to judge the column (and the IC system) performance. Many of these parameters can be monitored closely in the MagIC Net software so that a potential issue can be detected as early as possible.

Even though Metrohm IC columns are designed and manufactured to have very long lifetimes, at some point performance will decrease and even regeneration procedures may not be able to restore the required column performance to solve the application needs. This represents the end of the column life and makes the exchange of the separation column unavoidable.

Metrohm separation columns cannot be recycled and can be disposed with normal waste. However, depending on the samples measured as well as the used chemical types and their associated hazards, it may be necessary to consider a proper disposal option.

Irrespective of the sample nature, do not open the column at any time. 

Troubleshooting overview

Table 1 gives an overview about certain troubleshooting strategies when looking at your column performance behavior.

Table 1. Preventing and correcting performance loss in IC columns

 

Indicator Cause Preventive and corrective measures
Increasing counterpressure Particles on the guard column Replace the guard column.
Particles on the separation column

Rinse out the separation column in the reverse flow direction

  • Place the column inlet (i.e., the opening next to the intelligent chip) in a beaker, as this is now the outlet path for the contaminants.
  • Rinse out the separation column for approx. one hour.
  • Reinstall the separation column in the flow direction.
Particles in the sample Sample preparation, e.g., remove particles through lnline Ultrafltration
Shortened retention time Carbonate in the eluent

Carbon dioxide from the air affects the carbonate/hydrogen carbonate balance in the eluent. A carbonate/hydrogen carbonate eluent weakens over time; a hydroxide eluent strengthens.

  • Always tightly seal eluent bottles and bottles containing eluent concentrate.
  • Always use a CO2 adsorber.
Air bubbles in the eluent

Air bubbles make the eluent flow unstable. The counterpressure is an indicator of unstable flow. lt should remain stable
within a range of ± 0.1 MPa.

 

  • Deaerate the high-pressure pump.
  • Use an eluent degasser.
Capacity loss in the column due to high- valency ions Regenerate the column as per the column leaflet to remove any inorganic deposits.
Resolution loss Eluent too old or produced incorrectly Eluents should be freshly prepared. Make sure that they are produced correctly and particularly that carbonate and hydrogen carbonate are not confused.
Adsorptive effect of the contamination deposited in the guard column Replace the guard column.
Adsorptive effect of the contamination deposited in the separation column Regenerate the column as per the column leaflet to remove any organic or inorganic deposits.
Loss of theoretical plates Guard column contaminated Replace the guard column.
Separation column contaminated Regenerate the column as per the column leaflet to remove any organic or inorganic deposits.
Separation column overloaded

The separation column can be overloaded by factors such as a high salt content in the sample matrix.

  • Dilute the sample.
  • Inject less sample.
Dead volume in the IC system
  • Check that all capillaries have a diameter ≤0.25 mm; if they don’t, replace the capillaries.
  • Check that all of the capillaries have been installed correctly. The installation process is described step by step in the «IC Maintenance» multimedia guide.
Asymmetry Dead volume or contamination on the guard column Replace the guard column.
Separation column contaminated Regenerate the column as per the column leaflet to remove any organic or inorganic deposits.

 

Conclusion

This article explained how IC column performance can be assessed and monitored throughout the column lifetime and what measures can be taken to ensure a long column lifetime. With that, we now conclude the series «Best practice for separation columns in ion chromatography». If you have more questions, do not hesitate to contact your local Metrohm IC salesperson.

Get free tips and tricks

for your IC columns 
Post written by Dr. Vincent Diederich (Product Manager IC Columns) and Dr. Anne Katharina Riess (Head of Column Division) at Metrohm International Headquarters, Herisau, Switzerland.
Best practice for separation columns in ion chromatography (IC) – Part 3

Best practice for separation columns in ion chromatography (IC) – Part 2

The second part of this blog series about best practice for IC separation columns focuses on application related topics that have an impact on the column suitability and stability. First, there is the proper choice of the column that best suits the intended application. Then we turn to the operating parameters which can be modified in order to optimize the separation between analytes, and what the respective effects and possibilities are.

Choice of column length and diameter

Metrohm offers a broad range of columns that contain different stationary phases, have different lengths and/or inner diameters. The choice of the stationary phase has a great impact on the selectivity between the individual analytes on the one hand, as well as the stability against different sample matrices on the other hand. Instead, the column length has no impact on the selectivity, but rather on the separation efficiency between the individual peaks.

Find out more about Metrohm’s wide selection of separation columns for ion chromatography in our Column Catalog.
Effects of column length

In the following chromatograms (Figure 1), the effect of the column length on the separation efficiency for the Metrosep A Supp 17 column series is shown. Whenever choosing a column length, you should take the complexity of the intended separation and the presence of matrix components that could disturb the ions of interest into account.

Figure 1. Effect of column length on the retention times of the standard anions on the Metrosep A Supp 17 column (1: fluoride, 2: chloride, 3: nitrite, 4: bromide, 5: nitrate, 6: sulfate, 7: phosphate). Click image to enlarge.
Effects of column diameter

In addition to providing different lengths of IC separation columns, Metrohm also offers most columns in both in 4 mm inner diameter and 2 mm inner diameter (known as «microbore») versions. With regard to this, there are several criteria to distinguish:

  • If you use online systems in a continuous mode (i.e. systems which run unattended for several days in a row such as the Metrohm Process Analytics MARGA system – Monitor for AeRosols and Gases in Ambient air), we recommend using 2 mm IC columns. Due to the reduced flowrate for microbore columns (only 25% of the flowrate for 4 mm columns), the eluent and the regenerant solutions last much longer, which increases the time the instrument can be left unattended.
  • There are applications that require hyphenated techniques such as IC-MS for higher analyte selectivity and sensitivity. In this case, the use of 2 mm columns is ideal. The low flowrate is optimal for the electrospray process, and thus no flow splitter is required before entering the mass spectrometer.
  • Sometimes, only a limited amount of sample is available for injection. In these situations, 2 mm columns are preferred. This is because less dilution/diffusion occurs during the separation process and therefore higher signals are obtained.
  • On the other hand, if your sample contains a high load of matrix components, then selecting a suitable 4 mm IC columns will be a better choice because of the higher capacity available to separate the desired analytes from the matrix.
Find out more about MARGA and its capabilities for continuous air quality monitoring in our blog post.

Optimizing the analyte separation

Next to the column itself, several other parameters can be modified to optimize the selectivity of the separation. These parameters include temperature, eluent components and strength, and organic modifiers.

Effects of modifying the temperature

One of the simplest ways to fine tune the separation selectivity in IC is by modifying the temperature of the analysis. This is accomplished by using the integrated column oven in the instrument (if available). Multiple effects can be observed, for instance in anion analysis. As an example, the impact of the temperature on the selectivity is shown in the chromatogram overlay (Figure 2) for the Metrosep A Supp 17 column line.

Figure 2. Effect of temperature variation on the retention times of a suite of standard anions on the Metrosep A Supp 17 column (1: fluoride, 2: chloride, 3: nitrite, 4: bromide, 5: nitrate, 6: sulfate, 7: phosphate). Click image to enlarge.
  • The monovalent ions such as fluoride, chloride, nitrite, bromide, and nitrate are all accelerated with increasing temperature, indicating that fewer interactions with the stationary phase happen.
  • The behavior of multivalent ions such as phosphate or sulfate is more complicated to describe and will vary with each stationary phase. In general, multivalent ions are retarded more at higher temperatures, which causes the retention times to increase, as can be seen for sulfate. Phosphate on the other hand behaves differently, because of the temperature induced change of the eluent pH in a range close to the pKa value of phosphate. Due to this pH change, the effective charge of the phosphate ion changes as well (in this example, the effective charge is reduced with increasing temperature).
  • The peak shape of the polarizable ions such as nitrite, bromide, and in particular nitrate, is significantly improved at higher temperatures. The reason for this behavior is the reduction of secondary interactions with the stationary phase.
Effects of modifying the eluent composition and strength

Eluent composition and strength can be used to change the elution order of several analytes while using the same separation column. In cation chromatography, a retention model was developed by P.R. Haddad and P.E. Jackson, which allows researchers to predict retention times when changing the eluent composition [1].

Considering that the column remains identical in each determination, no change of ion exchange equilibrium and column capacity is to be expected. Therefore, when changing only the eluent concentration, the following correlation can be used:
Where:

  • k’ is the retention factor of the analyte of interest
  • c is a constant
  • x is the charge of the analyte
  • y is the charge of the eluent
  • Ey+M is the concentration of the eluent in the mobile phase
If nitric acid is used as the eluent, y = 1, and the model can be simplified to:
Applying this formula to practical situations in the laboratory means the following: with increasing the eluent strength, alkaline earth metals are accelerated much faster (x = 2) in comparison with alkali metals (x = 1), and thus it is possible to elute magnesium before potassium. This effect is called electroselectivity.

Multivalent metal ions are capable of forming complexes with dedicated complexing agents. Therefore, selectivities can be modified by adding complexing agents to the eluent. As an example, dipicolinic acid (DPA) is often used to complex calcium, which leads to a reduction of the effective charge of calcium. As a consequence, the retention time of calcium is reduced and calcium elutes before magnesium in the chromatogram (Figure 3).

The retention of monovalent cations can be influenced by the addition of crown ether to the mobile phase.

Figure 3. Effect of DPA concentration in the eluent on the retention times of several cations measured using the Metrosep C 6 column.
Anion systems are more complex regarding the retention time model, although the same electroselectivity effect can be observed to some extent for anions. However, when changing the eluent strength, the eluent pH also frequently changes, leading to different deprotonation equilibria of multivalent anions (e.g. phosphate). This influences the effective charge of the analyte, and by doing so, also influences its retention in a similar way as previously described for the effects of changing temperature.

In some cases, the use of a small amount of an organic modifier such as methanol, acetonitrile, or acetone in the eluent can make sense:

  • If bacterial contamination has been an issue before, the addition of 5% methanol to the eluent can help prevent future bacterial growth.
  • When samples containing a lot of organic solvent(s) need to be injected and no sample pretreatment such as extraction or matrix elimination (MiPCT-ME) is possible, it is recommended to add a suitable organic modifier to the eluent to ensure that the organic solvent(s) can be properly flushed out of the chromatographic column.
  • When using IC-MS, it is also recommended to add an organic modifier to the eluent to improve the electrospray process.

Be aware that the addition of organic modifiers will also affect the separation selectivities. For the standard anions, the effect is similar to that observed with increased temperatures: the peak shapes of the polarizable ions such as nitrite, bromide, and nitrate are improved.

Organic acids on the other hand may react very differently compared to the standard anions, and their reaction also strongly depends on the type of organic modifier used. Sample chromatograms that show the effect of the organic modifier on retention of analytes are shown in the manual for the Metrosep A Supp 10 column.

Download the Metrosep A Supp 10 column manual here to see example chromatograms showing the effects of organic modifier on analyte retention time.
For more information about column care, check out our blog post for different tips and tricks.

The History of Metrohm IC

Metrohm ion chromatography: bringing top quality and exceptional analytical performance to the lab since 1987. 
Reference

[1Haddad, P. R.; Jackson, P. E. Ion Chromatography: Principles and Applications; Journal of chromatography library; Elsevier; Distributors for the U.S. and Canada, Elsevier Science Pub. Co: Amsterdam, Netherlands; New York: New York, NY, USA, 1990.

Post written by Dr. Vincent Diederich (Product Manager IC Columns) and Dr. Anne Katharina Riess (Head of Column Division) at Metrohm International Headquarters, Herisau, Switzerland.

Frequently asked questions for beverage analysis with ion chromatography

Frequently asked questions for beverage analysis with ion chromatography

A brief overview of beverage analysis with ion chromatography

The analysis of beverages is extremely important for the general health of the population. Why is this so? Our bodies are composed of about 60% water, depending on several factors like weight and sex. Hydration is one of our basic physiological needs, as noted in Maslow’s hierarchy of needs. When we are dehydrated, a number of problems occur, from irritability to confusion leading to severe kidney problems and even low blood volume shock in extreme cases. Therefore it is incredibly important for standards to be set by regulatory agencies regarding the contents of the beverages we choose to drink, whether this is water, milk, coffee, juice, soft drinks, beer, wine, or any other number of items. Reliable beverage analysis is critical for many reasons: product monitoring and quality control, general content determination, and to avoid health issues.

Depending on the regulations regarding the concentration limit for a compound as well as on the complexity of the analysis and the detection limit of the determination, different instruments and analysis techniques can be applied for the analysis. For single analyte determination, mostly in a higher concentration range (e.g., sugar determination in wine) instruments like titrators, refractometers, or enzymatic kits can be applied for analysis. For analyte qualification and quantification in complex matrices (e.g., lactose determination in dairy products) instruments like ion chromatographs (IC), high-performance liquid chromatographs (HPLC), gas chromatographs with mass spectrometers (GC-MS), or hyphenated liquid chromatographic techniques (LC-MS/MS) are necessary.

Ion chromatography is a simple and robust analysis technique that is able to measure several components in beverages with relative ease compared to these other technologies.

Typically, conductivity detection is used for IC analysis. Other options are available including UV/VIS and amperometric detectors for more specialized analyses (e.g., carbohydrate analysis). Find out more on our website.

When analyzing complex beverage matrices like milk, coffee, or wine, sample preparation steps are normally required to protect the instrument (e.g., from contamination or blockages due to particles). Performing these steps manually is a very time-consuming and costly process that is also prone to human errors. Metrohm offers a time-saving solution for this with «MISP»: Metrohm Inline Sample Preparation specifically developed for difficult sample matrices. Several options are available including Inline Ultrafiltration, Inline Dialysis, Inline Dilution, and much more.

Watch our LabCast video below about to learn more about the benefits of using Inline Ultrafiltration in IC.

With fully automated sample preparation, analysts can be sure that every sample is treated in the exact same manner, leaving time for other more important tasks. Not only does this increase sample throughput, but it also improves accuracy and reproducibility of analyses and results. Discover the variety of Metrohm Inline Sample Preparation techniques on our website.

FAQ about beverage analysis with IC

Now that you know a bit more about the capabilities of ion chromatography for quality control in beverage analysis, it’s time to answer some frequently asked questions in this field. Dr. Gabriele Zierfels, Senior Product Specialist Ion Chromatography at Metrohm, has given a webinar hosted by New Food Magazine discussing how IC can help modern quality control labs from the beverage industry comply with official quality and labelling standards and make their daily routine analytics more efficient, which you can watch on-demand for free.

The webinar begins with an overview of the latest analytical techniques used by the beverage industry to comply with quality standards and labelling requirements such as EU regulation 1169/2011 and US regulation 21CFR101. Then the focus shifts to the versatility of ion chromatography for beverage testing and how it can help modern QC labs increase the efficiency of their daily routine analytics, which is exemplified in the main part of the webinar by numerous application examples.

Here we answer the top five questions asked by participants regarding beverage analysis with ion chromatography after the webinar.

1. What are the differences between HPLC and ion chromatography (IC) when it comes to beverage analysis? What are the main benefits of using IC?

High-performance liquid chromatography (HPLC) is typically used to separate complex mixtures with large organic (nonpolar) molecules by utilizing their affinities for different solvents and interactions with modified stationary phases. Many analytes required for food and beverage testing are either ions or polar molecules, some of which cannot be measured using reversed-phase HPLC.

IC on the other hand is a simple and robust analysis technique which allows determination of similar chemical substances in a single chromatographic run. With IC, ionic or polar analytes can be determined in very complex matrices with superior sensitivity and reproducibility using analytical separation columns made of ion exchange resins. The analytes undergo chemical/electrostatic interactions with the column resin. Due to such interactions these analytes are retained stronger than on reversed-phase columns. This allows excellent separation from the matrix components.

Check out the benefits of using IC over HPLC in our video.

2. How easy or difficult is it to switch between applications with a single instrument setup (e.g., analyzing different beverages like coffee and juices)?

Switching between different sample types can be simple, but every sample requires preparation before injection into the chromatographic system. In most cases this means sample dilution or filtration. This procedure can be done manually (which is time consuming) or completely unattended utilizing automated Metrohm Inline Sample Preparation (MISP) techniques. Therefore, several different sample types (e.g., tea, coffee, or juices) can be analyzed one after another for the same analyte profile, such as sugar content. The sample matrices can vary widely, as Metrohm offers various MISP techniques to get the cleanest possible extract for injection and subsequent separation and quantification of the target analytes.

Visit our website to download free IC Application Notes for the analysis of a variety of analytes in multiple beverage types.

3. How robust is IC when it comes to analytes that require stabilization, for example, sulfite?

Determination of samples containing analytes that must be stabilized prior to analysis (e.g. sulfite) is even more robust when using IC for the task. Even if samples have been stabilized, the detection can be disturbed by electrode fouling in the amperometric detector. To avoid this process (which is common in Direct Current mode), a short automatic cleaning method was applied between the sample analyses for stabilization of the signal and results that lasts for up to three weeks. This means no manual polishing steps and no disposable accessories are required.

To learn more about simplified sulfite analysis with Metrohm ion chromatography, download our free White Paper, check out our previous blog post, and download our free article featured in LC/GC’s The Column.

4. If a series of different samples are analyzed for the same parameter, will the instrument automatically calculate the dilution factor for each individual sample, or does it need to be predetermined for each sample?

When working with the logical Inline Dilution setup, samples containing analytes in different concentration ranges can be determined automatically with correct results. Because every single sample can contain varying concentrations of analytes, the software calculates the dilution factors individually for each sample. The summary report then gives the correct results from the first and second determinations.

5. Are the results traceable?

In short, yes. The MagIC Net software has been developed by Metrohm to intelligently operate the instruments and provide full traceability of results. All parameters of the system components e.g. the series number or the separation column are documented thanks to the intelligent chip technology integrated into various working parts of the instrument. This also permits the monitoring of the inline sample preparation and automation steps, improving the reliability of the analysis. The results are traceable for repeatability and audit control, fulfilling GLP and FDA standards.

Read more about the MagIC Net software and its capabilities on the Metrohm website.

Thirsty for more knowledge?

Download our free application ebook made in cooperation with with SelectScience:

Ion chromatography for food & beverage analysis

Post written by Dr. Alyson Lanciki (Scientific Editor) and Dr. Gabriele Zierfels (Senior Product Specialist Ion Chromatography) at Metrohm International Headquarters, Herisau, Switzerland.

Best practice for separation columns in ion chromatography (IC) – Part 3

Best practice for separation columns in ion chromatography (IC) – Part 1

The high performance ion chromatography (IC) separation column is often referred to as the «heart» of the ion chromatograph. The reason for this denomination is straightforward: the column is responsible for the separation of the analytes of interest from each other as well as from interfering sample matrix ions. The unique separation capabilities of IC columns allow the determination of multiple analytes within one run. In this blog series, we will share what is required to ensure the proper operation of an IC column and how to maximize the column lifetime.

Standard operating conditions

To begin with, the standard operating conditions should be considered, such as the eluent (mobile phase) composition, the eluent flow rate, the column oven temperature, and the detection method. These standard conditions are specific for each individual column type and correspond to the conditions that work best with the application the column is intended for. Every analytical column sold by Metrohm is delivered with a certificate of analysis (CoA) which is recorded under standard operating conditions. In the following table, you can find the standard operating conditions for three different Metrohm IC columns.

Column Metrosep C 6 – 150/4.0 Metrosep A Supp 17 – 150/4.0 Metrosep Carb 2 – 150/4.0
Eluent composition 1.7 mmol/L nitric acid

1.7 mmol/L dipicolinic acid

5.0 mmol/L sodium carbonate

0.2 mmol/L sodium bicarbonate

100 mmol/L sodium hydroxide

10 mmol/L sodium acetate

Flow rate 0.9 mL/min 0.6 mL/min 0.5 mL/min
Oven Temperature 30 °C 25 °C 30 °C
Detection Non-suppressed conductivity Suppressed conductivity Amperometric detection
Analytes Lithium, sodium, ammonium, potassium, calcium, magnesium Fluoride, chloride, nitrite, bromide, nitrate, sulfate, phosphate Inositol, arabitol, sorbitol, glucose, xylose, fructose, lactose, sucrose

Equilibration

Next to the standard operating conditions, the start-up parameters play an important role for the lifetime of the separation column. High mechanical and thermal stress is a frequent reason for decreased column lifetime. It is therefore recommended to slowly increase the eluent flow rate to the column and to avoid thermal and pressure shocks. For more information regarding specifics, please refer to the recommended equilibration conditions in the corresponding column leaflet.

Operating limits

Based on the different stationary phase designs that are required to achieve different selectivities and guarantee a wide range of IC applications, the chemical and physical properties of the ion exchangers can vary. Therefore, different operating limits are recommended for various column types and set according to stress tests performed during the development of a product. Before beginning to optimize an application, please refer to the respective column leaflet for the corresponding operating limits to achieve optimal results and guarantee a long column lifetime.

The chemistry of the ion exchanger defines the limits of operating temperature, eluent pH, and organic modifiers that can be present in the eluent. These values are valid for every dimension of a column type (e.g., the Metrosep C 6). Exceeding these limits can strongly affect column performance and, in the worst case, lead to irreversible damage. Tolerated flow rates and maximum pressure correlate with physical properties and of course column dimension—therefore these limits are set for every column dimension (e.g., Metrosep C 6 – 100/4.0 vs. Metrosep C 6 – 250/2.0).

Are you searching for a specific IC column for your research? Then check out the Metrohm Column Finder!

Information leaflet

In addition to the CoA, a lot of necessary valuable information can be found in the respective column leaflet. Instructions about equilibration, regeneration, operating limits, and much more can be found in the column leaflet which is provided for every IC column type offered by Metrohm.

You can download an example of a column leaflet here, where the information is provided in several different languages (DE, EN, FR, and ES).

Storage

Depending on the operation conditions and the properties of the ion exchanger material, different storage conditions are recommended for different column types. These conditions (storage temperature and storage eluent) are described on the respective column leaflet and should be strictly followed.

Please note that storing a new column for long time periods as well as frequently switching between storage and operation can actually be more stressful to the column than operating it 24/7! It is therefore not recommended to stock a column for a long time without using it.

Column guards

To protect your separation column from sample contamination and to extend its lifetime, it is critical to use a guard column. The guard column should be exchanged at regular intervals—a general rule of thumb is that about four guard columns will be used over the lifetime of an IC column.

Guard columns are offered in two designs: «on column» (e.g. Metrosep A Supp 17 Guard/4.0, on the left) and as a separate guard that is connected to the IC column with a capillary (e.g. Metrosep A Supp 17 S-Guard/4.0, on the right). For microbore separation columns, the corresponding microbore column guards are recommended (e.g. Metrosep A Supp 10 Guard/2.0).

By default, a guard column with the same material as the column should be used. However, for special applications, combining different ion exchange materials by using a different guard column can help to optimize the separation. One such example is in the case of sulfate and sulfite, as shown below.

Pulsation absorber

With the exception of the Eco IC product line, all Metrohm ion chromatography instruments are equipped with a pulsation absorber. For the Eco IC, it is strongly recommended to add the pulsation absorber as an option. As mentioned earlier, IC columns do not like repeated mechanical stress, especially those based on polyvinyl alcohol or polymethacrylate stationary phases. Therefore, the pulsation absorber is a useful tool to protect the column from possible pressure fluctuations in the system and enhance the column lifetime.

Find out more about the full line of Metrohm ion chromatography products and accessories on our website!

Chemical quality

In ion chromatography, the ratio between the volume of sample and the volume of eluent that flows through the column is very small, usually in the range of 1:1000. Therefore the quality of the chemical reagents used in the eluent preparation plays a crucial role for the column lifetime. To guarantee optimal performance, use chemicals denominated as «for IC» whenever possible as they are tested particularly on impurities (e.g. metals) that could harm the chromatographic column.

For dilution of the eluent components, ultrapure water is typically used in ion chromatography. To ensure good chromatographic results, the ultrapure water should have a specific resistance greater than 18 MΩ · cm and be free from particles. The ultrapure water is filtered through a 0.45 µm filter and treated with UV. Modern ultrapure water sources for laboratory use guarantee this level of water quality (Type I).

Sample preparation

With the Metrohm Inline Sample Preparation (MISP) options, Metrohm provides a large number of sample preparation techniques that are beneficial to the separation column, as well as analysts. Instead of loading the full sample onto the column, these techniques ensure the reduction of several sample matrix effects, thus avoiding potential harm to the column.

One of the most prominent MISP techniques is Inline Ultrafiltration (illustrated here), which efficiently removes particles from the sample in a fully automated way, before they ever reach the column. In that way, column blockage from dirty samples can be avoided without any manual effort.

iColumn features

All Metrosep columns offered by Metrohm are equipped with an intelligent chip containing useful information about various column operation conditions (e.g., equilibration, standard operation conditions, operation limits, and more) and tracks certain parameters (e.g., set to work, number of injections, number of working hours, and maximum working values such as pressure and flow rate) over the column lifetime. It is beneficial to attach the column chip to the chip reader as illustrated here for proper monitoring as well as support.

Column shelf life

How many injections are possible on a specific column? Unfortunately, it is not possible to deliver an exact answer to this question. This is because the column lifetime strongly depends on the sample matrix and elution conditions. Due to the multitude of different applications and samples that can be covered with a single IC column, it is not possible to predict the column life for every application and sample type.

During column development, several endurance tests are performed under standard conditions with a guard column using appropriate standards. Under these conditions, the column must withstand at least 2000 injections.

The History of Metrohm IC

Metrohm ion chromatography: bringing top quality and exceptional analytical performance to the lab since 1987. 

Post written by Dr. Vincent Diederich (Product Manager IC Columns) and Dr. Anne Katharina Riess (Head of Column Division) at Metrohm International Headquarters, Herisau, Switzerland.

Chemistry of Fireworks

Chemistry of Fireworks

Developed nearly two millennia ago in ancient China, fireworks are increasingly used in cultural celebrations around the world and enjoyed by nearly all ages. As one of the most entertaining forms of chemistry, fireworks appeal to our senses of sight and sound, offering a staggering variety of colors, sizes, shapes, sounds, and so on. We love to watch fireworks because they take our breath away with their magnificence and mystery.

However it is not all fun and games. The business of fireworks (and the field of pyrotechnics in general) is very serious since they should be made as safe as possible to use and also environmentally friendly. Beyond fireworks, other pyrotechnics are found in all kinds of entertainment, like in concerts, movies, and more serious applications for defense and security (e.g., safety measures like flares and signal lights).

What are fireworks made of?

Early fireworks were quite dangerous and were used for protection rather than for celebrations, and hardly resemble the ones we are now familiar with.

It all began back in Ancient China with the invention of gunpowder, which was created from a mixture of charcoal, sulfur, and saltpeter (potassium nitrate). Eventually, as new developments were made to increase the safety and predictability of using these early fireworks, experimentation with colors began and people started using them more for nonviolent purposes. Now there is an entire industry devoted to the development of all kinds of fireworks for consumers and professionals alike.

Learn more about the history of fireworks in the links below:

A firework, or aerial shell as it is also known, basically consists of three main parts aside from the housing: gunpowder and an igniter to make the rocket explode, and inside of the transported capsule on the top there are small garniture pods usually called «stars» (despite being shaped like spheres or cylinders) that include various chemicals for the desired effects. Stars consist of a colorant, a fuel, an oxidizer (oxygen providing substance, e.g., chlorates or nitrates), and a binder to hold the ingredient mixture together in a compact briquette.

The industry has spent a significant amount of time in development to make fireworks explode in shapes like stars and stripes, hearts, or even more complex forms like a cartoon figure, or letters and numbers if timed correctly.

Cross-sectional diagram of a firework capsule filled with star garnitures (72) and igniter (70). [1]

Forming a rainbow of colors

The vibrant colors of fireworks come from the combustion of metal ions which make up to 20% of the components. Metals have been used to color flames even before the invention of modern fireworks (e.g. Bengal fire). Chemically speaking, these metal ions change their electronic state by heating (addition of energy) and then going back to a lower energy state before emitting light of a certain color.

Table 1. List of metals used in pyrotechnics and their colors [2].

Color

Metal

Example compounds

Red

Strontium (intense red)

SrCO3 (strontium carbonate)

Lithium (medium red)

Li2CO3 (lithium carbonate)

LiCl (lithium chloride)

Orange

Calcium

CaCl2 (calcium chloride)

Yellow

Sodium

NaNO3 (sodium nitrate)

Green

Barium

BaCl2 (barium chloride)

B3N3 (boron nitride)

Blue

Copper halides

CuCl2 (copper chloride), at low temperature

Indigo

Cesium

CsNO3 (cesium nitrate)

Violet

Potassium

KNO3 (potassium nitrate)

Rubidium (violet-red)

RbNO3 (rubidium nitrate)

Gold

Charcoal, iron, or carbon black

 

White

Titanium, aluminum, beryllium, or magnesium powders

 

Very prominent here is the yellow color from sodium which is also seen in older street lightbulbs in some countries. Unfortunately, the most vibrant colors formed are also the most toxic for the environment, like strontium (red) and barium (green). These contaminants can be measured in the air, water, and even in the soil—but more on that later.

Find out more information about how fireworks get their colors in the links below:

Safety first

Safety is always a critical issue when discussing fireworks, whether concerning their construction, their use, or their storage. Too many serious accidents have happened over the years involving fireworks.

Learn more about how to handle fireworks in a safe manner here:

Among one of the largest fireworks disasters recorded in Europe was in Enschede (The Netherlands) in 2000. This explosion occurred in the warehouse of the S.E. Fireworks factory, which was located in the center of a residential area as the city grew and continued to build homes around it. An entire neighborhood was razed and the largest of the explosions was felt up to 30 kilometers away.

Because of this incident, sales of larger fireworks in most European countries is only allowed outdoors. Accumulating fireworks at home in preparation for celebrations should be avoided at least in confined environments like basements or apartments. It is better to store them in a ventilated shed or car parking to avoid problems in the case of a fire. Also do not store fireworks for long periods, since most of commercial fireworks are meant to be used within 3–6 months after production because the paper contents can get humid, ionic substances can dissolve and recrystallize, and therefore the likelihood of a failure increases.

In the event of a firework failure: Never have a look immediately! Wait at least 15 minutes at a proper distance and then use a tool to confine it afterwards—never touch it with your bare hands, especially when dealing with exploding fireworks or rockets.

Having said this, fireworks have integrated some safety features over the last several years to work more properly and reliably. For instance, the propellants have been modified from containing black powder to using technology from rockets such as plasticizers for better burning performance during launch, also resulting in less smoke and dust on the ground. A dedicated chain of reactions has to be followed, otherwise it will burn in a harmless way.

Knowledge is power: Prevent accidents with proper analytical testing

In order to help prevent fireworks accidents such as the one in Enschede and countless others, it is crucial to closely monitor different quality parameters including the water content of paper-based fireworks, grain size of the metal particles, and the purity and composition of the colorant, just to mention a few. Adequate quality control provides an entertaining, but safe fireworks experience even in the hands of the general public, when proper protocols are followed.

Metrohm offers several analytical technologies and related applications for this area of research. Analyses can be performed for a wide variety of substances and quality parameters as well as trace materials in the laboratory, on the street, and in the air either via wet chemical methods (e.g., Karl Fischer titration, ion chromatography, voltammetry) or spectroscopic techniques (e.g., near-infrared spectroscopy [NIRS] and Raman spectroscopy).

As mentioned earlier, moisture is an important quality parameter when discussing the safety of explosive materials. Metrohm offers two different techniques for accurate analysis of water content in a variety of matrices which are outlined in the following blog posts.

When it comes to determining the individual concentrations of the main constituents, some wet chemical techniques really stand out. Suppressed anion chromatography is ideal for measuring the ionic components of e.g., firecracker powder, other explosive material, and even in explosion residues for forensic purposes. Coupling an ion chromatograph to a mass spectrometer (IC-MS) opens up even more analysis possibilities. Read more about these studies (and more) by downloading our free Application Notes.

The use of several different metal salts to create the vibrant colors of fireworks can be beautiful but also harmful to our health and that of our environment. Voltammetry (VA) is an electrochemical method suitable for the determination of trace and ultratrace concentrations of heavy metals and other electrochemically active substances. Not only is VA excellent at determining these substances in the laboratory, but also in the field such as for measuring the after effects of a fireworks display or an undesired event. Check out our selection of VA instruments and applications on our website.

Spectroscopic techniques like Raman can help to determine the presence of dangerous explosive materials even when keeping a safe distance by using different instrument attachments. Read our free White Paper about how to use MIRA DS from Metrohm Raman for the purpose of identifying explosives safely.

Environmentally friendly fireworks – a contradiction?

Although fireworks are a very spectacular form of entertainment, there is quite an environmental impact after big cultural events or national holidays. The general atmospheric pollution after a fireworks display has been set off can be seen in an increase of dust and smoke, but also heavy metal content in the air as most contemporary fireworks use these for coloring.

The unburnt material still contains a significant amount of heavy metals. After falling to the ground, this material can dissolve and enter the ground water after it rains. Plastics materials that covered the fireworks for safety reasons are found again as broken shell shrapnel or as microplastics. The combustion of the compounds inside the fireworks leads to increased air pollution in form of aerosols that can be measured and evaluated resulting in heavy metals in the air, fine dust, and even nanoparticles which are extremely harmful for our lungs.

Metrohm Process Analytics has developed the 2060 MARGA (Monitor for AeRosols and Gases in ambient Air) which is used by official agencies and research bodies worldwide to monitor the air quality fully autonomously. This instrument is based on the analytical technique of ion chromatography and can be used as a dedicated continuous air monitoring device that can be left unattended for several weeks at a time, or as a research instrument that can be used for other projects when not monitoring the air quality.

Learn more about the 2060 MARGA and its capabilities in our blog post.

To find out more about the use of Metrohm instruments to monitor the air quality, check out this selection of peer-reviewed articles.

A new «green» firework generation is being developed for both professional and indoor use to try to minimize the heavy metal content and also reduce aerosol forming agents. This makes them more suitable for indoor pyrotechnic shows and for movie production. In regular outdoor shows (e.g. at theme parks), the gunpowder for transport of the capsule has mostly been substituted with an air pressure gun mechanism.

A significant amount of research has gone into substituting heavy metal-based colorants with more environmentally benign substances by increasing the luminosity of lithium derivatives by substituting them for strontium, or by using boron instead of barium or chlorinated compounds.

Finally, the plastic parts commonly used to surround fireworks are planned to be substituted by microcrystalline cellulose mixtures with better plasticizing binders. This leads to a similar stability compared to the current plastic materials, but the cellulose-based containers burn up completely and do not leave harmful materials scattered on the ground.

The future of fireworks shows

All safety measures increase the joy of fireworks not only during, but also after the event—being green and being safe. Foretelling the future, some of these celebrations may now use a cadre of lighted drones in a choreographed dance. This has been happening more steadily as drones fall in price and increase in their handling and programming capabilities. However, fireworks have already been with us for a couple of thousand years, and probably will not disappear any time soon.

Download our free Application Notes

and White Papers related to explosives and propellants

Post written by Dr. Norbert Mayr (Ph.D. in the field of HEDM, pyrotechnics, propellants, and oxidizers), Marketing Specialist & Product Training at Metrohm International Headquarters, Herisau, Switzerland.