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Trace metal analysis with solid-state electrodes – Part 5

Trace metal analysis with solid-state electrodes – Part 5

In the last part of our series of articles about trace metal analysis using solid-state electrodes, we will have a look at the glassy carbon rotating disc electrode (GC RDE) and its application possibilities.

Did you read the other parts in this series? Find them here!

The Glassy Carbon Rotating Disc Electrode

A rotating disc electrode (RDE) consists of two parts: the electrode tip which is made available in different materials, and a driving axle. The electrode tip is simply screwed onto the axle (Figure 1) to assemble the complete working electrode.

Figure 1. The two parts which make up the RDE. Left: driving axle for RDE. Right: glassy carbon electrode tip, with shaft made of glass.

Glassy carbon (GC) has a long history as solid electrode material for trace metal analysis. In general, GC is carbon with an amorphous structure which is similar to glass or ceramics, but different from graphite or diamond which both have a crystalline structure.

Aside from properties including a high temperature stability and a hardness similar to quartz, glassy carbon is very chemically inert and has a low electrical resistance, making it a versatile electrode material.

In the Metrohm GC electrode tip (Figure 1), the glassy carbon rod is fused within a glass shaft—another inert material. This design creates an electrode tip that is inert against most chemicals and solvents and guarantees measurements with excellent reproducibility due to the seamless intersection between the electrode material and glass shaft.

Modification with a metal film

For trace metal applications, the GC electrode is modified with a metal film, usually mercury or bismuth. The film is plated ex-situ from an acid plating solution which contains about 20 mg/L Hg2+ or Bi3+. Such a solution can easily be prepared from commercially available metal standard solutions and can be used for the plating of several films.

Once the film is deposited on the glassy carbon electrode, multiple determinations can be carried out with the same film. When the performance deteriorates, the exhausted film is simply wiped off and a fresh film is plated. Since only the renewable film is affected by aging processes, the GC electrode itself can be used for a very long time.

Applications using glassy carbon electrodes exhibit excellent reproducibility and stability in combination with very low detection limits.

Figure 2. Glassy carbon rotating disc electrode in a 884 Professional VA instrument from Metrohm.

Applications

Cadmium and lead determinations

The risk of cadmium and lead poisoning from drinking water and the significance of the determination of these two elements has already been discussed in previous posts in this series. To monitor the guideline values of 3 µg/L for cadmium and 10 µg/L for lead, recommended by the WHO (World Health Organization), a detection limit of β(Cd) = 0.3 µg/L and β(Pb) = 1 µg/L would be sufficient.

With the glassy carbon electrode the determination is far more sensitive, featuring a ten-fold improvement on the limit of detection of β(Cd) = 0.02 µg/L and β(Pb) = 0.05 µg/L with a deposition time of 30 s. This limit can be lowered even more with an increased deposition time.

For this extremely sensitive determination, a mercury film is plated on the glassy carbon electrode. The determination of cadmium and lead is carried out by anodic stripping voltammetry (ASV).

To learn more about this application, please check our website.

Free Application Note download: AN-V-225 Cadmium and lead in drinking water – Simultaneous determination on a mercury film modified glassy carbon electrode.

The very low detection limit makes this application especially interesting when it is not only required to monitor limit values but to actually detect concentrations in the ppt (parts per trillion, ng/L) range, e.g. in environmental analysis such as for seawater research.

Nickel and cobalt measurements

Another application with very low detection limits using the GC electrode is the determination of nickel and cobalt. This electrode allows the detection of concentrations down to β(Ni) = 0.05 µg/L and β(Co) = 0.03 µg/L. For this application, the electrode is modified with a bismuth film. The determination of nickel and cobalt is carried out by adsorptive stripping voltammetry (AdSV) using the complexing agent DMG (dimethylglyoxime).

Figure 3. Determination of β(Ni) = 0.34 µg/L and β(Co) < LOD in tap water (30 s deposition time) using the GC RDE.

For decades, this method was successfully executed with the mercury drop electrode. The use of a bismuth film on a glassy carbon electrode offers a non-toxic alternative with a similar sensitivity as the established method. Besides the high sensitivity, this application also shows excellent repeatability.

20 consecutive determinations of β(Ni) = 0.5 µg/L and β(Co) = 0.5 µg/L, carried out on the same bismuth film, showed an average recovery of 105% for nickel, with a relative standard deviation (RSD) of 2.0%. The recovery for cobalt was 112% with a RSD of 3.3%. This makes this method a viable tool in environmental analysis when natural background concentrations, which are often in the ppt (ng/L) range, should be investigated.

For further details about this application, please refer to Application Note AN-V-224: Nickel and cobalt in drinking water – Simultaneous determination in low ng/L range on the GC RDE modified with a bismuth film.

Chromium(VI) monitoring

Legal limits for chromium are relatively high. For example, the guideline value of the World Health Organization (WHO) is 50 µg/L for drinking water. These values usually refer to the total chromium concentration, but there are significant differences in toxicity between Cr(III) and Cr(VI). Even miniscule doses of Cr(VI) are toxic as well as carcinogenic.

Since the beginning of this century, there have been ongoing discussions in the scientific community about whether an additional limit value only for Cr(VI) is required, and what this value should be.

Measuring techniques are needed which allow the determination of Cr(VI) in the ng/L range. Using the glassy carbon electrode modified with a mercury film it is possible to detect Cr(VI) concentrations down to 0.05 µg/L. Cr(VI) is determined by adsorptive stripping voltammetry (AdSV) with DTPA (diethylenetriaminepentaacetic acid) as complexing agent. The recovery of a concentration of β(Cr(VI)) = 0.1 µg/L is 111% with a relative standard deviation of 4.4% (triplicate determination).

If you are interested to learn more, download our free Application Note V-277: Chromium(VI) in drinking water – Ultra-sensitive determination on the mercury film modified glassy carbon electrode (DTPA method).

All the above-mentioned applications can be carried out manually with a 884 Professional VA system (Figure 4), but it is also possible to run small sample series with an automated setup.

Figure 4. 884 Professional VA with two 800 Dosinos for automatic addition of electrolyte and standard solution.

Summary

This was the last post in our five-part series on heavy metal analysis with solid state electrodes. If this or one of the previous posts sparked your interest in one of the applications, do not hesitate to contact your local Metrohm representative.

For a complete overview of the different applications that can be performed with the SSEs exhibited in this series, check out the table below. Click on each application note or bulletin for a free download! 

Overview: Applications with Metrohm SSEs
Element Electrode Application Document Lab Portable
Ag GC RDE Application Bulletin 207

As scTRACE Gold Application Note V-210
Application Note V-211

Bi scTRACE Gold Application Note V-218

Cd, Pb GC RDE (Hg film) Application Note V-225

Cd, Pb SPE (Hg film) Application Note V-231

Cd, Pb Bi drop Application Note V-221

Cr(VI) GC RDE (Hg film) Application Note V-227

Cr(VI) scTRACE Gold (Hg film) Application Note V-230

Cu scTRACE Gold Application Note V-213

Fe scTRACE Gold Application Note V-216

Fe Bi drop Application Note V-222

Hg scTRACE Gold Application Note V-212

Ni, Co scTRACE Gold (Bi film) Application Note V-217

Ni, Co GC RDE (Bi film) Application Note V-224

Ni, Co SPE (Bi film) Application Note V-232

Ni, Co Bi drop Application Note V-223

Pb scTRACE Gold (Ag film) Application Note V-214

Sb(III) scTRACE Gold Application Note V-229

Se(IV) scTRACE Gold Application Note V-233

Te(IV) scTRACE Gold Application Note V-234

Tl scTRACE Gold (Ag film) Application Note V-228

Zn scTRACE Gold Application Note V-215

Post written by Barbara ZumbrägelProduct Manager VA/CVS at Metrohm International Headquarters, Herisau, Switzerland.

History of Metrohm IC – Part 4

History of Metrohm IC – Part 4

In the fourth installment in our series about the history of ion chromatography development at Metrohm over the years, we now focus on some of our combined analysis techniquesThese are unique combinations of Metrohm instruments from different product groups which broaden application possibilities beyond what IC could accomplish alone. Here we will discuss the TitrIC and VoltIC systems.

Did you miss the other parts in this series? Find them here!

TitrIC: combining titration, direct measurement, and IC in one

The combination of titration, pH, and conductivity measurement, as well as ion chromatography in a single analytical system was introduced in the late 1990s. This TitrIC system consisted of a Titrino for the determination of the p- and m-value (alkalinity), pH and conductivity meters, as well as a modular IC from the 732 IC Detector generation.

Figure 1. The first-generation TitrIC system from the late 1990s, including an autosampler for higher sample throughput.

Depending on the analysis requirements, either a second Titrino (for the Ca/Mg water hardness determination) or a second IC channel (for alkali and alkaline earth metal cations as well as ammonium) was selected. The latter enabled an automatic determination of the ion balance for the first time.

The central unit is the autosampler, which directs the water sample to the titration/metering section and to the ion chromatographs. The respective titration software controls the titrators and pH/temperature meters, calculates the results, and transfers them to the IC software (at the time, IC Net). The IC software controls the ion chromatograph and creates the final report. The user only communicates with the master software, making comprehensive analysis a simple task. This combination was available in all Metrohm IC generations (Figures 1 and 2). The most current setup (TitrIC Flex I and II) combines the 930 Compact IC Flex instruments with OMNIS titration.

Figure 2. TitrIC has evolved: TitrIC 7 system with 850 Professional IC series and Robotic Titrosampler has now become the TitrIC Flex (I and II), based on OMNIS titration and the 930 Compact IC Flex series.

Do you want to learn more about the combination of titration, direct measurement, and IC analysis and what it can do for your laboratory efficiency? Take a look at our previous blog post, download a free application note, or check out our brochure full of important information.

VoltIC – Voltammetry and IC

Just as with titration, it also is possible to combine IC and voltammetry in order to further expand application capabilities for enhanced trace measurement of analytes in water. VoltIC Professional integrates these techniques in a single, fully automatic system that is controlled via a common software, providing users with the strengths of both IC and voltammetry. Anions, major cations as well as trace cations may be detected in one determination. 

Back in 2012, the original VoltIC pro system was launched to bridge the gap between these two techniques and to offer a unique solution to the market. In 2013, the new line of 940 Professional IC Vario instruments came along. A few years later in 2016, the 884 Professional VA analyzer was brought to the market, and thus VoltIC on the next level: the current VoltIC Professional system (Figure 3).

Figure 3. VoltIC Professional system developed in 2016 for the enhanced analysis of trace impurities in water samples.

Is VoltIC the right choice for your laboratory? We offer free application notes for download, or check out the Metrohm website and download our brochure!

Next topic:

In Part 5 of our series, we will move on the use of ion chromatography for continuous air monitoring with the MARGA from Metrohm Process Analytics!

Don’t miss out – subscribe to our blog for weekly updates from the experts!

Download our free monograph:

Practical Ion Chromatography – An Introduction

Post written by Dr. Markus Läubli, Manager Marketing Support IC at Metrohm International Headquarters, Herisau, Switzerland.

Trace metal analysis with solid-state electrodes – Part 4

Trace metal analysis with solid-state electrodes – Part 4

In this series of articles featuring various solid state electrodes, we have introduced the new Bi drop electrode and the scTRACE Gold electrode and their potential in the determination of heavy metals in drinking water. In Part 4, we introduce the next type of sensors available for heavy metal analysis: the screen-printed electrode (SPE) together with two applications for the simultaneous determination of cadmium and lead as well as nickel and cobalt.

Catch up on the series «Trace metal analysis with solid-state electrodes» here:

Screen-printed electrodes (SPEs)

Screen printing microfabrication technology is well established for the manufacture of thick film electrochemical sensors. This technology enables the mass production of reproducible and mechanically robust solid electrodes. The possibility of mass production has great impact on the price and makes the SPEs inexpensive and convenient for the determination of heavy metals.

Printing technology allows production of a maintenance-free reference electrode, making the preparation of the analytical system for the analysis of heavy metals faster and more straightforward. Here, you do not need to refill the reference electrode or clean the sensor after a finished determination. The integration of three electrodes (working, reference, and auxiliary – see Figure 1) on a single platform, with the simultaneous miniaturization of their size and the corresponding device, both supports and facilitates transportation of the equipment to the sampling point and the determination of heavy metals on-site.

Figure 1. Screen-printed electrode (SPE) from Metrohm DropSens.

The simplest and the fastest way to modify the properties of these screen-printed electrodes for heavy metal detection is to deposit (in situ or ex situ) a metal film (either bismuth or mercury) electrochemically on the working electrode. This approach allows flexible use of single sensor type (e.g. carbon) SPEs for a wide range of applications.

Mercury film modified SPEs

The mercury film on the carbon working electrode consists of a very thin layer of mercury adsorbed onto the electrode surface. The mechanisms of accumulation and the stripping are the same as those which occur at a conventional mercury drop electrode.

Bismuth film modified SPEs

Because bismuth is not toxic, there are two environmental friendly methods for the preparation of the bismuth film: in situ plating and ex situ plating. With ex situ plating, a bismuth film is prepared in a separate solution before the first determination. Then the modified electrode is rinsed with ultrapure water and can be further used for the analysis.

Screen-printed electrodes can only be used for a limited number of measurements and have to be replaced at regular intervals. The lifetime and the frequency of replacement depend on the type of electrode and the application.

Figure 2. 946 Portable VA Analyzer (SPE version).

For further information about the 946 Portable VA Analyzer, visit the Metrohm website!

Currently, screen printed electrodes allow the on-site, simultaneous determination of cadmium and lead. Therefore, below I will present a method for the cadmium and lead determination using the ex situ modification of the Metrohm DropSens 11L carbon screen printed electrodes with a mercury film.

In addition to the cadmium and lead determination, a method using an ex situ bismuth film for nickel and cobalt will be introduced. Both measurements (cadmium and lead, as well as nickel and cobalt) can be carried out with the 946 Portable VA Analyzer (version for screen printed electrodes (SPE), see Figure 2) or with any Metrohm VA Stand using the electrode shaft (see Figure 3).

Figure 3. Electrode shaft for screen-printed electrodes (SPE).

With the electrode shaft, you can now use screen-printed electrodes in any Metrohm VA Stand. Whether you are performing voltammetric trace analysis or you want to explore new application fields with your own modified sensor, the electrode shaft allows simple use of SPEs.

To download our free informative flyer, click the button below!

This leaflet explains even more about the handling and troubleshooting of the electrode shaft for screen-printed electrodes.

Applications

Anodic stripping voltammetric determination of cadmium and lead

Cadmium and lead are toxic elements, and their concentration in drinking water has to be monitored. The provisional guideline values in the World Health Organization’s «Guidelines for Drinking-water Quality» are set to a maximum concentration of 3 µg/L for cadmium and 10 µg/L for lead. The Metrohm DropSens 11L carbon screen printed electrode modified with an ex situ mercury film allows the simultaneous determination of cadmium and lead in drinking water samples (Figure 4).

Figure 4. Example for determination of cadmium and lead in tap water spiked with β(Cd) = 2 µg/L and β(Pb) = 2 µg/L.

Using the 946 Portable VA Analyzer with a 90 s deposition time, a limit of detection (LOD) of 0.3 µg/L for both elements can be achieved. This is more than sufficient to monitor the provisional WHO guideline values.

For more information about this application, download our free application note:

The relative standard deviation for 5 measurements in a check standard solution with β(Cd) = 2 µg/L and β(Pb) = 2 µg/L is 14% and 12%, and the recovery rate is 88% and 82% for cadmium and lead, respectively.

Adsorptive stripping voltammetric determination of nickel and cobalt

Nickel and cobalt can be released either directly, or via the wastewater–river pathway, into drinking water systems. In the EU, the legislation specifies 20 µg/L as the limit value for the nickel concentration in drinking water.

The simultaneous and straightforward determination of nickel and cobalt is based on adsorptive stripping voltammetry (AdSV) using dimethylglyoxime (DMG) as a complexing agent. Prior to the first determination, the Metrohm DropSens 11L carbon SPE has to be modified with an ex situ bismuth film. The unique properties of the non-toxic Bi film combined with AdSV results in an excellent performance in terms of sensitivity. When using the 946 Portable VA Analyzer the limit of detection for 30 s deposition time is approximately 0.4 µg/L for nickel and 0.2 µg/L for cobalt, and can be lowered further by increasing the deposition time.

The disposable sensor does not need maintenance such as mechanical polishing or mechanical cleaning. This method is best suited for manual systems.

Figure 5. Example determination of nickel and cobalt in tap water with the modified Metrohm DropSens 11L carbon SPE.

The relative standard deviation for 3 subsequent measurements in a check standard solution (β(Ni) = 2 µg/L β(Co) = 2 µg/L) is 7% and 8% respectively, and the recovery rate is 100% for nickel and 94% for cobalt.

For more information about this application, download our free application note:

Key features of the screen-printed electrodes

  • Mechanically robust, inexpensive, maintenance-free, miniaturized solid electrodes
  • Electrode holder fits all Metrohm VA Stands
    • 884 Professional VA, 797 VA Computrace, 663 VA Stand
  • Solution-proof electrode holder
  • Fast and easy exchange of SPEs
  • Simultaneous determination of Ni and Co, as well as Cd and Pb
  • Limit of detection in low μg/L and even high ng/L range
  • Suitable for on-site diagnostics

What’s next?

In the next part of this series on solid state electrodes, we will have a look at an ultra-sensitive and robust sensor for heavy metal detection: the glassy carbon electrode with some of its associated applications.

Post written by Dr. Jakub TymoczkoApplication Specialist VA/CVS at Metrohm International Headquarters, Herisau, Switzerland.

Exposing secrets of ancient Greek civilization through chemistry

Exposing secrets of ancient Greek civilization through chemistry

This week, learn the story of how analytical instrumentation from Metrohm helps underwater archaeology locate hidden treasures beneath the seafloor.

 

Antikythera Mechanism: a machine lost to time

One of the most fascinating items ever salvaged from an ancient shipwreck is the so-called «Antikythera Mechanism». More than 2000 years old, this magnificent piece of mechanical engineering forced the scientific community to rewrite the history of science as it became clear that its unknown maker must have possessed knowledge and skills that were believed to simply not exist in the 1st century BC.

Figure 1. Digital reconstruction of the Antikythera Mechanism.

The Antikythera Mechanism was a complex and highly precise lunar and solar calendar that could also predict solar and lunar eclipses as well as the future dates of the Panhellenic Games. The complexity and precision of this machine inspired not only scientists but also Hublot, the Swiss brand famous for their luxury watches. Not only did Hublot recreate the Antikythera Mechanism in a wristwatch but they also started their own underwater archaeology program. This project of Hublot is fascinating—and we from Metrohm are part of it on every dive.

 The device was retrieved from an ancient shipwreck (70 BC) found off the coast of the Greek island of Antikythera in 1901. Since then, researchers have tried to get to the bottom of its mysteries. Dated to approximately 100 BC, the Antikythera Mechanism was a shockingly complex piece of machinery, the likes of which were not seen elsewhere for at least another millennium.

One of the challenges faced by underwater archeology is the fact that the cargo and debris of ancient shipwrecks is often randomly scattered across vast areas on the seafloor and also often covered by sediments. Because only fragments of the mechanism have been found and recovered, retrieving the missing pieces of the Antikythera Mechanism would be a scientific sensation.

Figure 2. Location where the Antikythera Mechanism was found in 1901 at a shipwreck in Greece.

As divers can only operate for very limited time spans at depths below 50 meters, drones are needed to investigate larger areas on the seafloor at such depths. Hublot’s engineers have built drones for this purpose, known as «Bubblots», and have equipped them with miniaturized voltammetric measuring stands from Metrohm.

«With a metal detector, all you get is «beep-beep-beep», which means there is metal around. However, in a bronze statue, there is copper, there is tin, and you have to detect the oxides of them, the exact kind of material you are facing. We have decided for Metrohm, because you are the most competent for the measuring technology we need in our drones.»

Mathias Buttet

R&D Director, Hublot

The Bubblots are utilized to perform real-time analyses of the seawater for unusual concentrations of dissolved metal salts typically associated with corroding bronze artefacts. Thus, the systematic and highly selective investigation of larger areas of seafloor for historical bronze artefacts becomes feasible.

Figure 3. Hublot’s underwater drones, known as «Bubblots», and the voltammetric measuring stand from Metrohm.

Voltammetry to the rescue

Due to its selectivity regarding different metals and their oxidation states, voltammetry is ideally suited for such investigations, as it is also very fast and robust technique. In the case of Hublot’s drones, results are obtained in a few seconds and this information can be immediately processed.

«We use this Metrohm instrument for voltammetric measurements. We take a water sample and do a live measurement of the aspirated water. The voltammetric measurement takes only a few seconds. This is enough to give us an idea of the different metals present in the solution. This allows us to do highly selective measurements very fast to cover different regions of the archaeological site.»

Sébastien Recalcati

Materials Engineer, Hublot

For a selection of free Metrohm Application Notes related to voltammetric measurements in seawater, visit our website!

Figure 4. The 910 PSTAT mini from Metrohm used in the study.
Figure 5. One of Metrohm’s disposable screen printed electrodes (SPEs) utilized in Hublot’s drone analysis of the seafloor.

Giving the Antikythera Mechanism a second life

The maker of this mechanism was far ahead of his time. He must have had skills and possessed scientific knowledge that are mind-boggling even today. The watchmakers from Hublot were inspired by this to a very special project: they rebuilt the Antikythera Mechanism in a wristwatch.

«The original Antikythera Mechanism has the size of a shoe box. Reducing the size of the mechanism and putting it into a wrist watch was not so easy. Because the Antikythera Mechanism was not a clock, it was a machine with a driving crank to show the position of the moon and the sun in relation to the stars at any given date. The absolute dream is to find the missing parts of the machine. But the debris is hidden below the seafloor, covered by sediments, one meter, sometimes two meters.»

Mathias Buttet

R&D Director, Hublot

Figure 6. The Antikythera Mechanism miniaturized and captured in a Hublot wristwatch.

We are glad to support Hublot’s archaeological mission with our analytical instruments and our expertise in chemical analysis. Metrohm wishes the Hublot team all the best.

Visit our website to learn more

about this fascinating project and to discover more related applications from Metrohm

Post written by Dr. Alyson Lanciki, Scientific Editor at Metrohm International Headquarters, Herisau, Switzerland.

Trace metal analysis with solid-state electrodes – Part 3

Trace metal analysis with solid-state electrodes – Part 3

In Part 2 of this series on trace metal analysis with solid-state electrodes, we introduced the scTRACE Gold electrode. The third part of this series explains even more applications which can be performed with this electrode, but this time after modifying the gold micro-wire with a thin layer of another metal.

Catch up on the series «Trace metal analysis with solid-state electrodes» here:

Why modify the electrode material?

As explained for the Bi drop electrode in Part 1 of this series, stripping voltammetry is a two-step measurement.

In the first step, the analyte is deposited on the working electrode. In the case of anodic stripping voltammetry (ASV), the analyte is reduced and forms an alloy with the electrode material (Fig. 1). In the case of adsorptive stripping voltammetry (AdSV), the analyte forms a complex which is adsorbed to the working electrode.

In the subsequent stripping step, the deposit is brought back into solution, giving the analytical signal which is proportional to the deposited amount of analyte. In the case of ASV, the electrochemical reaction is the re-oxidation of the analyte during an anodic scan (Fig. 2). In the case of AdSV, the adsorbed metal complex is reduced during a cathodic scan.

Figure 1. Anodic stripping voltammetry (ASV) with Ag film modified scTrace Gold electrode – deposition of lead (solution stirred).

Figure 2. Anodic stripping voltammetry (ASV) with Ag film modified scTrace Gold electrode – stripping of lead (solution not stirred).

Both steps, deposition as well as stripping, are subject to the principles of kinetics and thermodynamics. Without going into detail, the result is simply that some analytes cannot be determined with certain electrode materials. One way to solve this problem is to modify an existing working electrode with a different material that is more suitable.

Applications

Lead in drinking water

Most of the lead which is present in surface and ground water is of anthropogenic origin, resulting from the leaching of contaminated soils. Lead in tap water, however, often originates from the household plumbing system. Pipes from lead metal were popular in some countries until the 1970s. Although Pb is barely soluble in water, it slowly dissolves in the presence of oxygen. As a result, the allowed limit for lead in tap water can be easily exceeded by a significant amount. Now lead pipes for municipal water transport are forbidden, but there are still houses with old installations intact. The WHO (World Health Organization) recommends a limit value for lead in drinking water of 10 µg/L. In the European Union, the upcoming limit is as low as 5 µg/L.

For the determination of lead, the scTRACE Gold electrode is modified with a silver film. The film is plated ex situ from a separate plating solution. Once plated, it can be used for multiple determinations. When the film is depleted, it can be removed, and then a fresh film is plated again. A side effect of the silver film is that the scTRACE Gold electrode lasts longer, since aging processes mainly affect the renewable silver film. In a repeatability study, determining 10 µg/L Pb with 3 different electrodes on 4 different days (total number of determinations = 10) the average recovery of Pb was 96% with a relative standard deviation of 5%.

Using the 884 Professional VA it is possible to measure lead concentrations in water down to 0.4 µg/L, allowing a simple and reliable determination of even the future limit in the European Union.

With the 946 Portable VA Analyzer, the limit of detection is only slightly higher: 0.6 µg/L. However, the mobile use offers the possibility for close monitoring of individual installations without the need to preserve samples and send them in to a central lab. Furthermore, the concerned resident gets an immediate result on the spot.

Free Application Note download: AN-V-214 Lead in drinking water – Straightforward determination by voltammetry using a gold microwire electrode.

If you want to learn more about our voltammetry product lines, lab as well as mobile, check out our website!

Nickel and cobalt in drinking water

Similar to lead, nickel concentrations present in water sources can be increased by human influence as well. Plumbing fixtures and faucets are often plated with a thin layer of nickel for protection against corrosion, even if the finish is made of chromium. Furthermore, nickel is part of many alloys from stainless steel to nickel brasses and bronze. Nickel steel alloy cookware or nickel pigmented dishes can also cause increased nickel levels. The maximum allowed level in drinking water in the European Union is 20 µg/L whereas the WHO recommends a limit of 70 µg/L.

For the voltammetric determination of nickel and cobalt, an ex situ plated bismuth film on the scTRACE Gold electrode is used as working electrode. Nickel as well as cobalt are determined in the form of their DMG (dimethylglyoxime) complex. This method had already proven its reliability with the mercury electrode, and therefore this application can now be transferred to a mercury-free electrode. With a detection limit of 1 µg/L with the 946 Portable Analyzer, and even lower at 0.2 µg/L with the 884 Professional VA lab instrument, the method is surely sufficient to monitor the compliance with legal requirements. The recovery for 1 µg/L Ni in a standard solution is about 99% (mean of 10 determinations) with a relative standard deviation of 5%.

Free Application Note download: AN-V-217 Nickel, cobalt in drinking water – Straightforward determination by voltammetry using a gold microwire electrode.

Chromium(VI) in drinking water

The problem of chromium(VI) in drinking water was brought to the attention of the general public with the movie «Erin Brockovich» in 2000, starring Julia Roberts. The plot is based on a true story, which happened in the small community of Hinkley, California, where the local energy provider contaminated the groundwater with the carcinogenic hexavalent chromium. The company attempted to cover up the incident, but an increased number of tumors and other health problems among the residents could finally be traced back to the contaminated drinking water.

Contamination with Cr(VI) in the environment is usually the result of improper handling of various industrial processes, especially abandoned waste dumped from galvanic chromium plating. The WHO recommends a maximum limit of 50 µg/L total chromium for drinking water

After modifying the scTRACE Gold electrode with an ex situ plated mercury film, Chromium(VI) can be determined as a complex with DTPA (diethylenetriaminepentaacetic acid). The recovery of a standard containing 30 µg/L Cr(VI) is 115% (mean of 3 determinations) with a relative standard deviation of 2%. Using the 946 Portable VA Analyzer it possible to determine concentrations down to 2 µg/L Cr(VI), allowing the on-site determination, providing immediate results without delay.

Free Application Note download: AN-V-230 Chromium(VI) in drinking water – Sensitive determination on the mercury film modified scTRACE Gold (DTPA method).

Summary

Talking about all of the applications that are possible with the scTRACE Gold electrode would go beyond the scope of this blog. The table here gives an overview of several elements for which methods with the scTRACE Gold are currently available from Metrohm. Your local Metrohm representative can assist in case of questions regarding the determination of one of the elements, or analysis in a specific matrix.

Figure 3. The scTRACE Gold electrode from Metrohm is suitable for trace analysis of several elements in water.

Overview: Applications with the scTRACE Gold
Element Application document
As(total) Application Note V-210
As(III) Application Note V-211
Hg Application Note V-212
Cu Application Note V-213
Pb Application Note V-214
Zn Application Note V-215
Tl Application Note V-228
Fe Application Note V-216
Ni, Co Application Note V-217
Bi Application Note V-218
Sb(III) Application Note V-229
Cr(VI) Application Note V-230

What’s next?

In Part 4 of this series, I will discuss the use of screen-printed electrodes (SPEs) which had already been introduced in the blog post «Virus detection using screen-printed electrodes». However, this time the focus will be on the determination of heavy metals using these disposable electrodes.

Post written by Barbara ZumbrägelProduct Manager VA/CVS at Metrohm International Headquarters, Herisau, Switzerland.