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Comprehensive water analysis: combining titration, IC, and direct measurement in one setup

Comprehensive water analysis: combining titration, IC, and direct measurement in one setup

If you perform water analyses on a regular basis, then you know that analyzing different parameters for drinking water can be quite time-consuming, expensive, and it requires significant manual labor. In this article, I’d like to show you an example of wider possibilities in automated sample analysis when it comes to combining different analytical techniques, especially for our drinking water.

Water is the source and basis of all life. It is essential for metabolism and is our most important foodstuff.

As a solvent and transporting agent it carries not only the vital minerals and nutrients, but also, increasingly, harmful pollutants, which accumulate in aquatic or terrestrial organisms.

Within the context of quality control and risk assessment, there is a need in the water laboratory for cost-effective and fast instruments and methods that can deal with the ever more complex spectrum of harmful substances, the increasing throughput of samples, and the decreasing detection limits.

Comprehensive analysis of ionic components in liquid samples such as water involves four analytical techniques:

  • Direct measurement
  • Titration
  • Ion chromatography
  • Voltammetry

Each of these techniques has its own particular strengths. However, applying them one after the other on discrete systems in the laboratory is a rather complex task that takes up significant time.

Back in 1998, Metrohm accepted the challenge of combining different analytical techniques in a single fully automated system, and the first TitrIC system was introduced.

What is TitrIC?

The TitrIC system from Metrohm combines direct measurement, titration, and ion chromatography in a fully automated system.

Direct measurements include temperature, conductivity, and pH. The acid capacity (m and p values) is determined titrimetrically. Major anions and cations are quantified by ion chromatography. Calcium and magnesium, which are used to calculate total hardness, can be determined by titration or ion chromatography.

The results are displayed in a common table, and a shared report is given out at the end of the analysis. All methods in TitrIC utilize the same liquid handling units and a common sample changer.

For more detailed information about the newest TitrIC system, which is available in two predefined packages (TitrIC flex I and TitrIC flex II), take a look at our informative brochure:

Efficient: Titrations and ion chromatography are performed simultaneously with the TitrIC flex system.

Figure 1. Flowchart of TitrIC flex II automated analysis and data acquisition.

How does TitrIC work?

Each water sample analysis is performed fully automated at the push of a button—fill up a sample beaker with the sample, place it on the sample rack, and start the measurement. The liquid handling units transfer the required sample volume (per measurement technique) for reproducible results. TitrIC carries out all the work, and analyzes up to 175 samples in a row without any manual intervention required, no matter what time the measurement series has begun. The high degree of automation reduces costs and increases both productivity and the precision of the analysis.

Figure 2. The Metrohm TitrIC flex II system with OMNIS Sample Robot S and Dis-Cover functionality.

To learn more about how to perform comprehensive water analysis with TitrIC flex II, download our free application note AN-S-387:

Would you like to know more about why automation should be preferred over manual titration? Check out our previous blog post on this topic:

Calculations with TitrIC

With the TitrIC system, not only are sample analyses simplified, but the result calculations are performed automatically. This saves time and most importantly, avoids sources of human error due to erroneously noting the measurement data or performing incorrect calculations.

Selection of calculations which can be automatically performed with TitrIC: 

  • Molar concentrations of all cations
  • Molar concentrations of all anions
  • Ionic balance
  • Total water hardness (Ca & Mg)
  • … and more

Ionic balances provide clarity

The calculation of the ion balance helps to determine the accuracy of your water analysis. The calculations are based on the principle of electro-neutrality, which requires that the sum in eq/L or meq/L of the positive ions (cations) must equal the sum of negative ions (anions) in solution.

TitrIC can deliver all necessary data required to calculate the ion balance out of one sample. Both anions and cations are analyzed by IC, and the carbonate concentration (indicative of the acid capacity of water) is determined by titration.

If the value for the difference in the above equation is almost zero, then this indicates that you have accurately determined the major anions and cations in your sample.

Advantages of a combined system like TitrIC

  • Utmost accuracy: all results come from the same sample beaker

  • Completely automated, leaving analysts more time for other tasks

  • One shared sample changer saves benchtop space and costs

  • Save time with parallel titration and IC analysis

  • Flexibility: use titration, direct measurement, or IC either alone or combined with the other techniques

  • Single database for all results and calculation of the ionic balance, which is only possible with such a combined system, and gives further credibility to the sample results

Even more possibility in sample analysis

TitrIC has been developed especially for automated drinking water analysis but can be adapted to suit any number of analytical requirements in food, electroplating, or pharmaceutical industries. Your application determines the parameters that are of interest.

If the combination of direct measurement, titration, and IC does not suit your needs, perhaps a combination of voltammetry and ion chromatography in a single, fully automatic system might be more fitting. Luckily, there is the VoltIC Professional from Metrohm which fulfills these requirements.

Check out our website to learn more about this system:

As you see, the possibility of combining different analysis techniques is almost endless. Metrohm, as a leading manufacturer of instruments for chemical analysis, is aware of your analytical challenges. For this reason, we offer not only the most advanced instruments, but complete solutions for very specific analytical issues. Get the best out of your daily work in the laboratory!

Discover even more

about combined analytical systems from Metrohm

Post written by Jennifer Lüber, Jr. Product Specialist Titration/TitrIC at Metrohm International Headquarters, Herisau, Switzerland.

Dissolved oxygen measurement – easier than ever

Dissolved oxygen measurement – easier than ever

Do you know why your drinking water becomes flat after you leave it untouched for a few hours? Or why your orange juice changes its color and darkens a bit when the bottle is left open for a longer time?

One of the key driving factors behind these changes is the amount of oxygen in your beverage.

I would like to share some information with you about the effects (both positive and negative) oxygen has when dissolved in liquids, which parameters affect the dissolved oxygen (DO) content, as well as how to accurately assess the DO concentration.

Why is DO concentration important?

Next to pH and conductivity, dissolved oxygen is one of the most important water quality indicators. Oxygen dissolves in surface water according to its partial pressure (Henry’s law), but also due to aeration processes (e.g., wind, rapids). Additionally, oxygen is introduced into water as byproduct of photosynthesis by plants and phytoplankton. Dissolved oxygen is essential for the survival of fish and any other aquatic organism that breathes oxygen.

The DO content may be reduced when too many bacteria or algae contaminate the water. Bacteria feed on dead algae and other organic material, consuming oxygen and producing carbon dioxide. If all DO is consumed by bacteria, it is called eutrophication. When the DO content in water drops below 5 mg/L, aquatic life is put under stress, and if the concentration is even lower, a large amount of aquatic life can die. Dissolved oxygen can be directly assessed, in-situ in surface water, by the direct measurement technique.

Learn more about dissolved oxygen measurement in surface water by downloading our free application note:

Getting back to the example of your drinking water or orange juice:

Water only tastes good to us when there is a certain amount of oxygen is dissolved into it. When your glass or water bottle is standing around, DO is released as it equilibrates with the atmosphere and additionally it will warm up to the ambient temperature, releasing even more oxygen. This is why the taste of your water turns flat over time.

If you would like an overview of how dissolved oxygen in your water supply can be determined, download our free application note:

Orange juice exhibits the contrary situation. Orange juice (and other fruit and vegetable juices) are kept almost DO free. The reasoning is because oxygen, as an oxidizing agent, has a negative influence on the overall quality, taste, nutritional value, and color of a beverage. The longer you keep your orange juice open to the atmosphere, the more oxygen will dissolve into your juice, until a point. Furthermore, this DO will start to react with other ingredients of your juice. For example, DO will oxidize any present Vitamin C (ascorbic acid, an antioxidant) to dehydroascorbic acid. To prevent quick browning, as well as the flavor and quality of your juice, keep it in a closed bottle.

Do you want to know more about the determination of dissolved oxygen in fruit juices? Download our free application note:

What affects the dissolved oxygen concentration? 

Temperature

The temperature has a large influence on DO concentration. The higher the temperature, the less oxygen is dissolved in the liquid phase. Why? I will explain it to you a bit more visually:

When the temperature of a solution increases, the ions and molecules therein move and vibrate due to the increased energy. This leads to more and more collisions between particles and thus, some of the bonds that hold them together break. As more particles vibrate, more collisions occur, and even more bonds are broken. That also means that the bonds which hold oxygen molecules in the liquid will break, and oxygen will be released from the solution. This results in a decrease in the DO content. The opposite happens if the temperature decreases: particle motion decreases, and therefore the DO concentration increases.

Pressure

For our purpose, here «pressure» refers to the atmospheric pressure. Perhaps you’ve been on the top of a mountain, or inside of an airplane flying at altitude, and had a drink from your water bottle up there. When you were back on the ground, or at the base of your hike, and checked the bottle again, maybe you noticed that it was compressed slightly, or had a suction noise as you opened it again. This is due to the difference in atmospheric pressure, which is inversely proportional to altitude.

As atmospheric pressure decreases, the partial pressure of oxygen also decreases. Therefore at higher altitudes, less oxygen is dissolved in the liquid since the pressure does not hold it there. Oxygen diffuses out of the liquid, the higher we get. When we go to lower altitudes, the DO concentration increases as the atmospheric pressure increases.

Salinity

The salinity also plays a part in the amount of dissolved oxygen which is available in a liquid.

Again consider the ions and molecules present in the solution. When we have a dissolved salt present in the water, these charged ions are very much attracted to the water molecules. Dissolved oxygen has no charge, and is therefore not attracted to anything. The higher the salinity content, the more ions are present. This increased density of particles coerces oxygen to leave the solution as its interaction with water is not so strong.

How can we assess the DO concentration?

There are two possibilities to determine the dissolved oxygen content in liquids, either by direct measurement or by titration. We have summarized the pros and cons for each of the methods in a free white paper which you can download below.

However, I will only cover direct measurement using an optical sensor here. Why? Because you can measure the DO content online or in-situ without tedious sampling and sample preparation and your equipment is almost maintenance-free – you will be surprised how easy it is to use!

The O2-Lumitrode, the optical sensor for DO measurement from Metrohm, is the fastest of its kind on the market. It measures the DO content in liquids in less than 30 seconds! The working principle is based on luminescence quenching.

Let me explain how this works: the sensor cap contains a membrane with an embedded luminophore that is excited by red light. When there is no oxygen present, the luminophore returns to its ground state via emission of luminescence.

If oxygen is present, and these molecules collide with the excited luminophore, the luminophore returns to its ground state emission-free, because the energy is transferred to the oxygen molecule. By evaluating the lifetime of the excited state of the luminophore (by using the phase shift), it is possible to determine the DO content.

The O2-Lumitrode does not need much maintenance—a regular one-point calibration with 100% air saturation is enough. From time to time, we recommend performing a two-point calibration with 100% and 0% air saturation.

Our 913 pH/DO Meter or 914 pH/DO/Conductometer can be equipped with the O2-Lumitrode. Both of these are combined instruments, meaning you can additionally measure pH and/or conductivity alongside dissolved oxygen.

As stated earlier, temperature, pressure, and salinity impact the dissolved oxygen content in liquids. Therefore, the O2-Lumitrode is equipped with a temperature sensor and a pressure sensor so automatic temperature and pressure compensation can be applied for the most reliable results. If you are measuring DO in a saline solution or in seawater, you can measure the conductivity in parallel to DO and switch the automatic salinity compensation on.

The O2-cap must be replaced from time to time, as the luminophore becomes less reactive. This effect is called photo bleaching. However, the sensor will tell you when this is necessary due to its active performance monitoring. Never worry again about inaccurate DO measurements due to poor quality instrumentation.

To summarize, depending on the application and matrix, a wide range of dissolved oxygen can be found. The determination of the DO content fast and accurately is extremely important. Using an optical sensor with a mobile device makes it very easy to assess the DO content in-situ. For the most reliable data, additionally measure the temperature and pressure (and eventually the salinity) in parallel to minimize the effect of these physical parameters on your results.

Want to learn more?

Download our free White Paper:

Determining dissolved oxygen in water: Titration or direct measurement?

Post written by Dr. Sabrina Gschwind, Jr. PM Titration (Sensors) at Metrohm International Headquarters, Herisau, Switzerland.