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The analysis described in this poster dicusses thermometric titration as a promising method for the straightforward sodium determination in foodstuffs. Thermometric sodium titration was tested for its applicability to various food matrices such as soups, gravy and several salty snacks. Enthalpy change can be monitored as a change in temperature of the solution using a sensitive digital thermometer. The sodium determination described here relies on the exothermic precipitation of elpasolite (NaK2AlF6). The titrant is a standard aluminum solution which contains an excess of potassium ions. The titration is performed directly on a suspension of the food sample and is completed in under two minutes. The method is robust, can be fully automated and due to the highly reproducible high-frequency homogenization, copes with a variety of challenging food matrices (ketchup, instant soups, pretzels, etc.). In addition to this application note, you can find more information on thermometric sodium determination in foods in our application video available on YouTube: https://youtu.be/lnCp9jBxoEs

The photometric determination of nitrate is limited by the fact that the respective methods (salicylic acid, brucine, 2,6-dimethyl phenol, Nesslers reagent after reduction of nitrate to ammonium) are subject to interferences. The direct potentiometric determination using an ion-selective nitrate electrode causes problems in the presence of fairly large amounts of chloride or organic compounds with carboxyl groups. The polarographic method, on the other hand, is not only more rapid, but also practically insensitive to chemical interference, thus ensuring more accurate results. The limit of quantification depends on the matrix of the sample and is approximately 1 mg/L.

This Application Bulletin describes the voltammetric determination of the elements antimony, bismuth, and copper. The limit of detection for the three elements is 0.5 ... 1 µg/L.

The determination of sodium with the sodium ISE represents a selective, rapid, accurate, and favorably-priced method which is described in this Bulletin. Examples are used to show how determinations can be carried out with the 692 pH/Ion Meter using either direct measurement or the standard addition technique. The sodium concentration has been determined in standard solutions, water samples (tap water, mineral water, wastewater), foodstuffs (spinach, baby food), and urine. The construction, working principles, and areas of application of the two Metrohm ion-selective sodium electrodes – the 6.0501.100 Glass membrane ISE and the 6.0508.100 Polymer membrane ISE – are explained in detail.

This Application Bulletin describes the determination of mercury by anodic stripping voltammetry (ASV) at the rotating gold electrode. With a deposition time of 90 s, the calibration curve is linear from 0.4 to 15 μg/L; the limit of quantification is 0.4 μg/L.The method has primarily been drawn up for investigating water samples. After appropriate digestion, the determination of mercury is possible even in samples with a high load of organic substances (wastewater, food and semi-luxuries, biological fluids, pharmaceuticals).

Cadmium, lead, and copper can be determined simultaneously in oxalate buffer by anodic stripping voltammetry (ASV) after digestion with sulfuric acid and hydrogen peroxide. Tin present in the sample does not interfere with the determination of lead.For the voltammetric determination of tin please refer to Application Bulletin no. 176.

Cu2+, Co2+, Ni2+, Zn2+, and Fe2+/Fe3+ are determined simultaneously. Interference due to the presence of other metals is mentioned, and methods given to eliminate it. The threshold of determination is ρ = 20 µg/L for Co and Ni, and ρ = 50 µg/L each for Cu, Zn, and Fe.

Bromide is removed from the sample as BrCN by distillation. The BrCN is absorbed in sodium hydroxide solution and decomposed with concentrated sulfuric acid, then the released bromide ions are determined by potentiometric titration with silver nitrate solution. Iodide does not interfere with the determination.Iodide is oxidized to iodate by hypobromite. After destruction of the excess hypobromite, the potentiometric titration (of the iodine released from iodate) is carried out with sodium thiosulfate solution. Bromide does not interfere, even in great excess.The described methods allow the determination of bromide and iodide in the presence of a large excess of chloride (e.g., in brine, seawater, sodium chloride, etc.).

Nitrite can be determined polarographically after its conversion to diphenylnitrosamine (C6H5)2NNO. Potassium thiocyanate is used as a catalyst in order for the conversion to proceed rapidly and quantitatively. The reaction takes place in acid solution at a pH value of approx. 1.5. The limit of quantification is 5 μg/L NO2-.

Potentiometric titration is an accurate method for determining chloride content. For detailed instructions and troubleshooting tips, download our Application Bulletin.