Tetrachloromercurate sodium

The method of tetrachloromercurate sodium is perfectly specific. It requires the use of a molecular absorption spectrometer UV-Visible as well as firequent and regular inspections of the calibration curve and it is effective in terms of sampling and precisely because it can measure the quantities of sulphur dioxide to very low absolute value, less than 100 pg/m, with very short periods of sampling 5 min to 6h. 

This method relies on the absorption of sulphur dioxide by a flow of air into a solution of tetrachloromercurate sodium where it forms a stable bisulfitomercurate. The assessment of sulphur dioxide amount is done from the obtained colour by adding to the solution a dye fuchsine (hydrochloride para-rosaline). The colour... 

A method suitable for analysis of sulfur dioxide in ambient air and sensitive to 0.003—5 ppm involves aspirating a measured air sample through a solution of potassium or sodium tetrachloromercurate, with the resultant formation of a dichlorosulfitomercurate. Ethylenediaminetetraacetic acid (EDTA) disodium salt is added to this solution to complex heavy metals which can interfere by oxidation of the sulfur dioxide. The sample is also treated with 0.6 wt % sulfamic acid to destroy any nitrite anions. Then the sample is treated with formaldehyde and specially purified acid-bleached rosaniline containing phosphoric acid to control pH. This reacts with the dichlorosulfitomercurate to form an intensely colored rosaniline—methanesulfonic acid. The pH of the solution is adjusted to 1.6 0.1 with phosphoric acid, and the absorbance is read spectrophotometricaHy at 548 nm (273). 

The earliest detectors of S02 in the atmosphere were automated calorimetric wet chemical devices. The reference technique for determining the SOz content of atmospheric air is based on the absorption of S02 from an air sample by a solution of sodium tetrachloromercurate, which, upon the addition of formaldehyde and a pararosaniline dye, forms a strong purple dye complex. Several manufacturers have automated this procedure. Properly maintained, these units provide an excellent record of S02 concentration in the air, because they operate on the basis of a chemical reaction that is specific for S02. 

The CEA 555 continuous monitor(17) is used for real-time monitoring of chamber and actual field survey formaldehyde determinations. The monitor is a useful instrument in field surveys because it is one method that provides real time formaldehyde measurements which is useful in tracing and iden tifying usually high formaldehyde sources. The monitor s analytical method is based on the modified Schiff procedure developed by Lyles, Dowling and Blanchard (18). Formaldehyde is absorbed in a sodium tetrachloromercurate solution that contains a fixed quantity of sodium sulfite. Acid bleached pararosaniline is added, and the intensity of the resultant dye is measured at 500 nm. Both formaldehyde in air and liquid standards can be analyzed. 

Sodium tetrachloromercurate Na2HgCl4, 0.1 M solution. Dissolve 27.2 g of HgCh and 11.7 g of NaCl in water and dilute the solution with water to 1 litre. 

Place 10-15 ml of the sodium tetrachloromercurate solution containing not more than 25 pg of SO2 (after absorption of SO2 from a gas mixture, or separation by distillation from an acidified solution) in a 25-ml standard flask. Add 2.5 ml of the bleached pararosaniline solution and 2.5 ml of formaldehyde solution. Dilute to the mark with Na2HgCl4 solution, mix, and allow to stand for 30 min. Measure the absorbance of the solution at 560 nm, using a reagent blank solution as reference. 

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