Application Finder

A high throughput automated system was developed to determine pH of culture media using a pH module equipped with an external flow cell. A custom septum-piercing, vented needle was developed to accommodate the shape and size of the customer sample vials. For this application, both accurate and precise pH measurements were required. The data presented in this document was collected by a customer as a part of their validation process and was provided for use with their consent.

Two electrometric methods for determining the pH value of papers with homogeneous and heterogeneous pH cross-sections are described.

The pH value and oxidation reduction potential (ORP) of soil provide important information about soil properties, such as solubility of minerals and ion mobility. Knowledge of these properties allows making predictions concerning plant growth, bacterial activity, nutrients that may be needed, possible corrosive effects on buildings, etc.Here, the determination of the pH value is described according to ISO 10390, EN 15933 and ASTM D4972. Th oxidation reduction potential determination is carried out in a suspension.

This Bulletin describes fluoride determination in various matrices with the help of the ion-selective fluoride electrode (F-ISE). The F-ISE is comprised of a lanthanum fluoride crystal and exhibits a response in accordance with the Nernst equation across a wide range of fluoride concentrations.The first part of this Bulletin contains notes regarding the handling and care of the electrode and the actual fluoride determination itself. The second part demonstrates the direct determination of fluoride with the standard addition technique in table salt, toothpaste and mouthwash.

This document explains how to measure Na ion concentration in diverse matrices with a sodium ion-selective electrode (Na-ISE) using direct measurement and standard addition.

The quality of a vinegar depends on various factors. Since the contents of the individual components vary widely even from bottle to bottle, it is impossible to give average values. This Bulletin describes the determination of the following parameters in vinegar: pH value, total titratable acid, volatile, and non-volatile acid, free mineral acid as well as free and total sulfurous acid.

This Bulletin describes analysis methods for determining the following parameters: pH value, total titratable acid, ash alkalinity, formol number, total sulfurous acid, chloride, sulfate, calcium, and magnesium. These methods are suitable for the analysis of jams, fruit and vegetable juices, and their concentrates.

This Bulletin describes methods for measuring the pH value of dairy products. Particular attention has been paid to the handling, maintenance, and storage of the pH electrodes.

This bulletin contains two parts. The first part gives a short theoretical overview while more details are offered in the Metrohm Monograph Conductometry. The second, practice-oriented part deals with the following subjects:Conductivity measurements in general; Determination of the cell constant; Determination of the temperature coefficient; Conductivity measurement in water samples; TDS – Total Dissolved Solids; Conductometric titrations;

Wine sometimes contains heavy metals which can be precipitated out by the addition of potassium ferrocyanide. Generally, these are quantities of iron ranging between 1 and 5 mg, and exceptionally up to 9 mg Fe/L. Zinc, copper, and lead – in descending order of content – may also be present. To estimate the quantity of potassium ferrocyanide necessary for the «décassage of the wine», only very complicated and relatively inaccurate methods have been described until now.This Bulletin permits accurate results to be obtained easily with a simple instrumentation. The results are available in a short time.

It has been known for years that consuming too much nitrates from foodstuffs can result in cyanosis, particularly for small children and susceptible adults. According to the WHO standard, the hazard level lies at a mass concentration c(NO3-) ≥ 50 mg/L. However, more recent studies have shown that when nitrate concentrations in the human body are too high, they can (via nitrite) result in the formation of carcinogenic and even more hazardous nitrosamines.Known photometric methods for the determination of the nitrate anion are time-consuming and prone to a wide range of interferences. With nitrate analysis continually increasing in importance, the demand for a selective, rapid, and relatively accurate method has also increased. Such a method is described in this Application Bulletin. The Appendix contains a cselection of application examples where nitrate concentrations have been determined in water samples, soil extracts, fertilizers, vegetables, and beverages.

Although the known photometric methods for the determination of ammonia/ammonium are accurate, they require a considerable amount of time (Nessler method 30 min, indophenol method 90 min reaction time). A further disadvantage of these methods is that only clear solutions can be measured. Opaque solutions must first be clarified by time-consuming procedures. These problems do not exist with the ion-selective ammonia electrode. Measurements can be easily performed in waste water, liquid fertilizer, and urine as well as in soil extracts. Especially for fresh water and waste water samples several standards, such as ISO 6778, EPA 350.2, EPA 305.3 and ASTM D1426, describe the analysis of ammonium by ion measurement. In this Application Bulletin, the determination according to these standards is described besides the determination of other samples as well as some general tips and tricks on how to handle the ammonia ion selective electrode. Determination of ammonia in ammonium salts, of the nitric acid content in nitrates, and of the nitrogen content of organic compounds with the ion-selective ammonia electrode is based on the principle that the ammonium ion is released as ammonia gas upon addition of excess caustic soda:NH4+ + OH- = NH3 + H2OThe outer membrane of the electrode allows the ammonia to diffuse through. The change in the pH value of the inner electrolyte solution is monitored by a combined glass electrode. If the substance to be measured is not present in the form of an ammonium salt, it must first be converted into one. Organic nitrogen compounds, especially amino compounds are digested according to Kjeldahl by heating with concentrated sulfuric acid. The carbon is oxidized to carbon dioxide in the process while the organic nitrogen is transformed quantitatively into ammonium sulfate.

Potassium is one of the most common elements and can be found in many different minerals and other potassium compounds. It is of importance for humans, animals and plants as it is an essential mineral nutrient and involved in many cellular functions like cell metabolism and cell growth. For these reasons, it is important to be able to declare the potassium content of food or soil to reduce problems that may arise by a potassium deficiency or extensive consumption.This bulletin describes an alternative to flame photometric method using an ion selective electrode and direct measurement or standard addition technique. Several potassium determinations in different matrices using the combined potassium ion-selective electrode (ISE) are presented here. Additionally, general hints, tips and tricks for best measurement practice are given.

The determination of the physical and chemical parameters as electrical conductivity, pH value, p and m value (alkalinity), chloride content, the calcium and magnesium hardness, the total hardness, as well as fluoride content are necessary for evaluating the water quality. This bulletin describes how to determine the above mentioned parameters in a single analytical run.Further important parameters in water analysis are the permanganate index (PMI) and the chemical oxygen deman (COD). Therefore, this Bulletin additionally describes the fully automated determination of the PMI according to EN ISO 8467 as well as the determination of the COD according to DIN 38409-44.

The formol number represents a further parameter for the characterization of fruit and vegetable juices. As this is merely an index (the formalin number does not deal with the molecular size, nor with the quantity of amino acids), the conditions of the titration can be adapted to meet practical needs. This concerns mainly the pH value of the endpoint of the SET titration (pH = 8.5, pH = 9.0, pH = 9.2, etc.).

This Bulletin, using practical examples, indicates how the user can achieve optimum pH measurements. As this Bulletin is intended for actual practice, the fundamentals - which can be found in numerous books and publications - are treated only briefly.

This Bulletin gives a survey of standard methods from the field of water analysis. You will also find the analytical instruments required for the respective determinations and references to the corresponding Metrohm Application Bulletins and Application Notes. The following parameters are dealt with: electrical conductivity, pH value, fluoride, ammonium and Kjeldahl nitrogen, anions and cations by means of ion chromatography, heavy metals by means of voltammetry, chemical oxygen demand (COD), water hardness, free chlorine as well as a few other water constituents.

The Bulletin describes the determination of the following parameters in wine: pH value, total titratable acid, free sulfurous acid, total sulfurous acid as well as ascorbic acid (vitamin C) and other reductones.

This Bulletin describes the automatic measurement of conductivity in water samples with low electrical conductivity in accordance with USP<645>. Conductivity measurement is demonstrated on the example of ultrapure water, which is used, among other things, to produce injection solutions in the pharmaceutical sector.

This document describes the recommended equipment, installation, and software handling instructions for the TitrIC flex I system combining IC and titration.

This document describes the recommended equipment, installation, and software handling instructions for the TitrIC flex II system combining IC and titration.

Fluoride protects dental enamel and is an important trace element in toothpaste. A rapid and precise determination is made via standard addition with the help of an ion-selective fluoride electrode (F-ISE).

Determination of ammonia (ammonium) in distilled water by direct potentiometry using the NH3-ISE.

Determination of nitrate in a copper plating bath after conversion of nitrate to ammonium. Direct potentiometric measurement using the NH3-ISE.

Determination of fluoride in a chromium plating bath by direct potentiometry using the F-ISE.

Determination of chloride in water by direct potentiometry using the Cl-ISE.

Determination of fluoride in cement or clinker by direct potentiometry with the F-ISE.

Determination of sulfide in wastewater by direct potentiometry with the Ag/S ion-selective electrode.

Cyanides are used in some industrial processes, but if not handled carefully, they could contaminate the wastewater. In an acidic or neutral environment, this contaminated wastewater can form highly toxic hydrogen cyanide gas. Furthermore, the cyanide salts could also poison the environment and enter the ground water system. Therefore, it is essential to monitor the content of cyanide in effluent water. Cyanides can be easily determined with a cyanide ion-selective electrode. This application note presents a method for cyanide analysis according to APHA Method 4500-CN and ASTM D2036.

Nitrate is present in all common agricultural products and due to an extensive use of fertilizers, the nitrate content can be disconcertingly high in vegetables and their fabricated products, like juices. The nitrate content is regulated in many countries because it can form nitrosamines within the human body. Nitrosamines can potentially cause cancer and therefore, the World Health Organization (WHO) has defined an accepted daily intake (ADI) for nitrate of 3.7 mg/kg. To control the nitrate content e.g., in juices, a quick and inexpensive assessment of its concentration is performed via standard addition with a nitrate ion selective electrode . The method can be automated and is faster and less expensive compared to competing chromatographic or spectroscopic methods.

Fluoride content in drinking water can be determined quickly and conveniently with the help of potentiometric titration and the ion-selective fluoride electrode (F-ISE). The F-ISE is calibrated with suitable standard solutions before the measurement.

Ammonia determination via NH3 ISE requires precise calibration. Details on this are provided by the present Application Note.

Even in low concentration, sulfide ions cause odor and corrosion problems in ground water and waste water. They can release hydrogen sulfide in acidified water, which is toxic in even minuscule amounts. This Application Note describes the determination of sulfide concentration in water via direct measurement with the Ag/S-ISE in accordance with ASTM D4658.

Bromide is ubiquitous in sea water, where it is present in concentrations of around 65 mg/L. By contrast, the maximum bromide concentration in drinking and ground water is usually less than 0.5 mg/L. A higher bromide content may indicate a contamination of the water caused by fertilizer, road salt or industrial waste water. This Application Note describes the determination of the bromide content in water via direct measurement with a Br ion-selective electrode in accordance with ASTM D1246.

In the synthesis of certain dyes, sodium chloride is a byproduct. The content of chloride is therefore an important parameter. This Application Note describes the determination of the chloride content in dye by standard addition using a Cl- ion-selective electrode.

Determination of the potassium content plays a major role in the food and beverage industry. Potassium is an essential mineral nutrient for humans. It is an important intracellular cation and also plays an important role in processes withincells, where it is involved in the regulation of numerous body functions like blood pressure, cell growth and muscle control.To declare the potassium content of drinks and food, it is usually determined by flame photometric method. However, flame photometry is linear only over a limited concentration range, and often sample dilution is necessary. Furthermore, the instrumentation is rather complex and expensive to buy and maintain. The ion measurement method presented here is a fast, less expensive, and reliable alternative to determine potassium content in beverages.

The determination of the potassium content in foodstuffs plays a major role in the food and dietary supplement industry, as potassium is an essential mineral nutrient for humans. It is an important intracellular cation and also plays a important role in processes within cells, where it is involved in the regulation of numerous body functions like blood pressure, cell growth and muscle control.As a dietary supplement, potassium is present in e.g., electrolyte powder, electrolyte drinks and food supplements. To quantify the potassium content in such products, e.g. flame photometry can be used. In this work, an alternative, ion measurement by standard addition, is described, which is fast, inexpensive and simple to use.

As nitrogen is essential nutrient for plants, it is an essential constituent of many fertilizers. It is present there in different forms, mainly as ammonium or nitrate. Knowing the nitrogen concentration and the form in which is present helps to select the right fertilizer for the plants. For producers of fertilizers, it is therefore necessary to indicate the concentration of ammonium nitrogen in their product.This Application Note shows how to determine ammonium in liquid fertilizers by means of a standard addition.

Nitrogen is essential for plant growth. In soil, it can be present in the form of nitrate, ammonium, or urea. Knowing the nitrogen content of soil and in which form it is present helps selecting the right kind of fertilizer to stimulate plant growth.This Application Note shows a fast and reliable way to determine the ammonium concentration in soil by using standard addition.

NPK fertilizers are mainly comprised of three primary nutrients required for a healthy plant growth (nitrogen, phosphorous, potassium). They are available as liquid, or granular form, whereof the last is the most common used one. Knowing the quality and content of a fertilizer allows an optimal utilization for a planned culture and optimizing the amount of used fertilizer. This helps to reduce costs and to improve plant growth and with it, a better harvest follows.To assess potassium, several methods like flame photometry, titration, or ion measurement can be used. In this work, the potassium content is measured by standard addition which is a fast, inexpensive, and easy to use method.

To assess the quality of a soil it is necessary to know its nutrients. For example, it is necessary that the level of bio-available ions is known as a deficiency might negatively affect plant growth. One of the most important ions is potassiumwhich is directly absorbed in its ionic form by plants roots. It is an essential nutrient and required for proper growth and reproduction.One commonly used method to assess the K content is the extraction of phosphorous and potassium from soil with an acidic, to pH 4.1 buffered solution of calcium acetate, calcium lactate, and glacial acetic acid. This test is called calcium acetate lactate test (CAL-test). Commonly, the extract is analyzed by flame photometric method. In this application note we present a fast and inexpensive alternative using the potassium ion selective electrode.

Potassium is naturally occurring in surface water caused by weathering of stones and soil. As potassium in drinking water is regulated and should not exceed a certain threshold value, it is necessary to assess the potassium concentration.This can easily be done by direct measurement using a potassium selective electrode. First, a calibration is performed, afterwards, the samples are measured within tens of seconds. This is a fast, inexpensive and reliable method to determine the potassium content in various water samples.

One of the major sources of fluoride intake for humans comes from foodstuff, such as tea. Tea actually has one of the highest potentials to increase the daily fluoride intake. Excessive fluoride intake may lead to dental or skeletal fluorosis. The World Health Organization does not recommend consuming water with a fluoride content higher than 1.5 mg/L. In the presented method according to DIN 10807, the fluoride content can be assessed quickly with an ion selective electrode.

Nitrate is naturally present in the environment. However, excessive concentrations of nitrate in surface and ground water are problematic as such concentrations have a negative effect on the water quality. Usually, excessive levels of nitrate area direct result of extensive usage of fertilizers in agriculture. Nitrate is easily washed from soils and can end up in surface or ground water. As the nitrate content is regulated in many countries, a quick and inexpensive assessment of its concentration is required to monitor the water quality.The nitrate concentration can easily be obtained by direct measurement using a nitrate ion selective electrode. First, a calibration is performed, afterwards, the samples are measured in less than a minute.This is a fast, inexpensive and reliable method to determine the nitrate content in various water samples.

Lucigenin is one of the most often used chemiluminescent reagents and might be used for e.g., the indication of the presence of superoxide anion radicals.Lucigenin is rather expensive to buy, however, its synthesis only includes a two stage synthesis starting from acridanone. The first stage includes an Nmethylation, the second forms the lucigenin chloride, which is finally transformed into lucigenin nitrate. To check the purity of the synthesized lucigenin, ion measurement can be applied using a nitrate selective electrode. This is a fast and inexpensive method compared to competing methods such as ion chromatography.

Increased fluoride concentrations in water may cause tooth damage, growth disorders, and bone deformation. According to the World Health Organization (WHO), concentrations above 1.5 mg/L are critical.One possible source of fluoride is landfills. Rain washes out harmful substances from landfills which can enter the groundwater. The leachate from landfills should thus be monitored for the fluoride concentration.Ion measurement is a fast and inexpensive method to determine the fluoride content in water samples compared to other methods such as ion chromatography. This Application Note describes a reproducible and accurate measurement of the fluoride content using the fluoride ion-selective electrode with an OMNIS system.

Dissolved oxygen (DO), incorporated into juices during processing, affects quality parameters of the beverage during storage such as Vitamin C concentration, color, and aroma. Various oxygen removal methods are used during juice production, such as vacuum-deaeration or gas sparging to increase product quality and extend shelf life. However, these methods have the drawback that the aroma might be affected since the volatile compounds are also removed. By assessing the DO content in fruit juices, manufacturers can improve the overall product quality. This application note describes a fast and accurate determination of dissolved oxygen in juices by using an optical sensor.

Oxygen diffuses into water sources from the air via aeration, however several factors can reduce the dissolved oxygen (DO) content in water. First, as water warms up, oxygen is released into the atmosphere. Secondly, oxygen is consumed by bacteria and other microorganisms which feed on organic material. Finally, plants can also consume oxygen in certain situations.Human-induced alterations can have a negative influence on surface water when DO values fall below crucial limits for maintaining the life supporting capacity of freshwater ecosystems. Therefore, monitoring the DO content in surface water by an optical sensor to assess its quality is important.

Dissolved oxygen (DO) is generally considered detrimental to wine quality, especially if introduced after fermentation, storage, or bottling. The presence of oxygen after primary fermentation and during the later stages of winemaking can enhance browning reactions, chemical and microbiological instability, and the formation of off-flavors such as acetaldehyde. Knowing the DO content in wine is important through the entire wine production process, because oxidation is a common fault in bottled wines. With the 913 pH/DO meter and the 914 pH/DO/Conductometer, the oxygen content of wine can be determined quickly and easily directly on site.

In municipal water supplies, higher dissolved oxygen (DO) content is desirable because it improves the taste of drinking water. However, high DO levels also speed up corrosion in water pipes. For this reason, industries utilize water with as little DO as possible, and add scavengers such as sodium sulfite to remove any oxygen from a water supply. Municipal water supply pipes are normally coated inside with polyphosphates to protect the metal from contact with oxygen, thus allowing higher DO contents. Therefore, monitoring the DO content online in a water supply is important to assess its DO content to either improve taste or minimize pipe corrosion. Using an optical sensor, such as the O2-Lumitrode, allows a fast and reliable determination according to ISO 17289.