Gutzeit method

The limitations of the Gutzeit method for determining arsenic are well-known. The spectrophotometric molybdenum blue or silver diethyldithio-carbamate procedures tend to suffer from poor precision. Sandhu [34] has described a spectrophotometric method for the direct determination of hydrochloric acid-releasable inorganic arsenic in soils and sediments. The method provides reliable data on the quantitative recovery of 2.0 xg of arsenic(V) added to 5.0 g (0.4 mg/kg) of soil, clay, sand and sediment samples. The method is simple, reliable and relatively rapid 24 samples can be analysed in about an hour. It does not require elaborate equipment and can be routinely used for the quantitative determination of arsenic in soil and soil-like material. The detection limit has been established as 0.5 xg of arsenic. The extent of ionic interference when this method is used for arsenic determination in soil was also quantitatively evaluated. 

Early colorimetric methods for arsenic analysis used the reaction of arsine gas with either mercuric bromide captured on filter paper to produce a yellow-brown stain (Gutzeit method) or with silver diethyl dithiocarbamate (SDDC) to produce a red dye. The SDDC method is still widely used in developing countries. The molybdate blue spectrophotometric method that is widely used for phosphate determination can be used for As(V), but the correction for P interference is difficult. Methods based on atomic absorption spectrometry (AAS) linked to hydride generation (HG) or a graphite furnace (GF) have become widely used. Other sensitive and specihc arsenic detectors (e.g., AFS, ICP-MS, and ICP-AES) are becoming increasingly available. HG-AES, in particular, is now widely used for routine arsenic determinations because of its sensitivity, reliability, and relatively low capital cost. 

Field-test kits. A large number of wells need to be tested (and retested) for arsenic worldwide. Hence, there is a need for reliable field-test kits that can measure arsenic concentrations down to 10 p,g the WHO guideline value for arsenic in drinking water. Some of the more recently developed kits based on the Gutzeit method can achieve this semiquantitatively (Kinniburgh and Kosmus, 2002). 

Gutzeit Method, Modified by Sanger and Blacks This method depends on the change of colour, from white to brown, of a paper impregnated with mercuric chloride solution when it is exposed to the action of hydrogen arsenide. 

The method of taking a sample depends on whether the substance to be examined is diffused in the air as vapour or as an aerosol. If the substance is in the vapour state, a part of the sample is passed through a U tube filled with dry, finely divided silica gel. Then the material absorbed on the silica is decomposed by one of the methods described on p. 329 et seq., and the solution obtained is tested by the Gutzeit method. 

The solution obtained by method (a), or the material obtained by method (6) or (c), is treated by one of the methods described on p. 329 et seq. to convert the arsenic present to the oxide, and then the Gutzeit method is used. It is simpler, however, to treat the solution from (a), or an alcoholic extract of the materials from (6), or (c) directly in the Gutzeit apparatus with zinc and sulphuric acid, in presence of copper sulphate or better a few drops of platinic chloride solution. 

The separation of traces is done in a closed system and involves absorbing the traces in a suitable sorbent, for example hydrogen sulphide in a zinc acetate solution, ammonia in dilute HCl, and methyl borate in dilute NaOH. In the Gutzeit method traces of arsenic, liberated in the form of AsHa, are absorbed by a strip of paper saturated with a reagent giving a colour effect with AsHa. In all such procedures a carrier gas, such as hydrogen, nitrogen, chlorine, or steam is indispensable... 

The arsenomolybdenum blue method is the most widely used. The method using the reaction of AsHs with Ag-DDTC is less sensitive. In certain cases, the classical Gutzeit method is convenient. Methods based on ion-associates of molybdoarsenate with basic dyes are very sensitive. 

The functions of the reagents used in the reduction of arsenic compounds, such as Zn, HCl, NiCla, SnCh, and KI are discussed below in connection with the Gutzeit method. Sodium borohydride also has been proposed as the reducing agent [39-42]. Sequential spectrophotometric determination of As(III) and As(V) is possible by using borohydride [40]. Hydrogen sulphide, which interferes in the reaction, is separated from arsine on cotton wool impregnated with lead acetate. 

The Gutzeit method was applied in determinations of arsenic i.a. in germanium and its compounds [49], silicon [49,50], and petroleum products [48]. 

Reduction Methods. Early methods used a zinc-hydrochloric acid reduction (Gutzeit method), together with some kind of collecting device for the hydrides formed ... 

Arsenic is best tested for by the Gutzeit method. About 5 c.c. is placed in a test-tube, a few fragments of granulated zinc free from arsenic, and 10 c.c. dilute hydrochloric acid added, and the mouth of the tube covered with a small filter paper, moistened three successive times with an alcoholic solution of mercury bichloride and dried. 

Traces of arsenic may be determined either by the molybdenum blue or Gutzeit methods. For determination of arsenic contents from T5 to 15 //g in the sample taken the molybdenum blue method is recommended by the Analytical Methods Committee of the S.A,C. the details are as follows ... 

In the opinion of the Analytical Methods Committee of the S,A,C. the molybdenum-blue method is considered to have inherent advantages over the Gutzeit method, which may be regarded as an estimation rather than a determination, since it depends on the evaluation of the intensity of a stain on a test-paper and the judgments of individual analysts may differ slightly. Nevertheless, within this limitation and provided that the details of the method are strictly observed, the Gutzeit method is adequate in many circumstances, particularly when it is necessary to ascertain whether or not an arsenic content exceeds a certain limit. It is also less intricate and time-consuming than the molybdenum-blue method. 

Analysis of zinc solutions at the purification stage before electrolysis is critical and several metals present in low concentrations are monitored carefully. Methods vary from plant to plant but are highly specific and usually capable of detecting 0.1 ppm or less. Colorimetric process-control methods are used for cobalt, antimony, and germanium, turbidimetric methods for cadmium and copper. Alternatively, cadmium, cobalt, and copper are determined polarographicaHy, arsenic and antimony by a modified Gutzeit test, and nickel with a dimethylglyoxime spot test. 

The Gutzeit Test.3—This test is as accurate as the Marsh test and the apparatus necessary is comparatively simple. It consists in allowing the arsine to react with strips or discs of dry filter paper impregnated with silver nitrate or, in the more recent modifications of the method, mercuric chloride or bromide. 

Estimation Gravimetrically as Sulphide as Magnesium Pyroarsenate—Volu-metrically by Iodometric Methods with Potassium Bromate, etc.—The Marsh Test—The Gutzeit Test—Fleitmann s Test—Colorimetric Methods— Microohemioal Methods—Determination of Arsenic in Gases. 

Fleitmann s test this test depends upon the fact that nascent hydrogen generated in alkaline solution, e.g. from aluminium or zinc and sodium hydroxide solution, reduces arsenic(III) compounds to arsine, but does not affect antimony compounds. A method of distinguishing arsenic and antimony compounds is thus provided. Arsenates must first be reduced to the tervalent state before applying the test. The modus operandi is as for the Gutzeit test, except that zinc or aluminium and sodium hydroxide solution... 

Determinations of very small amoxmts of arsenic, such as 0.1 mg or less, were traditionally done with the Marsh test or the Gutzeit test invented in the late nineteenth century. Method (a) of the European Pharmacopoeia can be considered a modified Gutzeit test, but whereas this originally used silver nitrate or mercury(II)chloride to detect any arsenic present, method (a) uses mercury(II)bromide. 

Gutzeit test n. Method for testing and estimating small quantities of arsenic and antimony in other materials. Details are given in the British pharmacopoeia. 

The fluorescence enhancement of flavonols upon binding to biomolecules has been recently exploited for the development of analytical methods and in microfluorescence studies using flavonols as endogenous fluorophores." In particular, the use of quercetin and other flavonols as probes in vim for target proteins has been reported by Gutzeit et... 

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