Dithizone method

Discussion. For the determination of small amounts of lead (0.005-0.25 mg) advantage is taken of the fact that when a sulphide is added to a solution containing lead ions a brown colour, due to the formation of colloidal lead sulphide, is produced. However, for general use the dithizone method (see Section 6.13) is to be preferred and this will be described. 

EatonAD, Clescer LS, Greenberg AE. 1995a. Method 3500-Pb D. Dithizone Method, Standard Methods for the Examination of Water and Wastewater, American Public Health Association, Washington, DC. 

When samples are dry ashed for Sn determination, it is theoretically possible to volatilize the metal during the process, just as for Cd and Pb. This does not seem to be the case in practical work, though. Results from dry ashing have compared very well with results obtained with other techniques, such as HC1 extraction or the dithizone method. It is crucial, however, that the ashes are dissolved in HC1 and not HNO3. 

Assay Transfer about 1.2 g of sample, accurately weighed, into a 250-mL beaker, and dissolve in 75 mL of water. Add 25 mL of 1 N acetic acid and 1.0 mL of diphenylcarbazone TS, and titrate slowly with 0.1 M mercuric nitrate to the first appearance of a purple color. Each milliliter of 0.1 M mercuric nitrate is equivalent to 37.43 mg of C1oH12CaN2Na208. Lead Determine as directed for the Dithizone Method under Lead Limit Test, Appendix MB, using a Sample Solution prepared as directed for organic compounds, but use 70%... 

Note Unless otherwise specified in the monograph, use the Dithizone Method to determine lead levels. 

The other techniques used are less sensitive and could require preconcentration by extraction by the chloroform-dithizone method (6, 45, 64), non-boiling evaporation (39) or by adsorption on W wire loops (44, 65). Preconcentration and extraction methods require great care to be taken in order to avoid contamination and are often time-consuming, and require a fairly large volume of samples. 

Food (total) Digestion of sample with HNOs and H2S04 under reflux isolation of mercury by dithizone extraction Colorimetric dithizone method No data No data AOAC 1984 (methods 25.138-25.145)... 

Unless otherwise indicated, metal content is given in micrograms per gram of protein. All zinc determinations by the dithizone method in duplicate, and in quadruplicate for the crystalline enzyme preparations. Copper determined by the sodium dithiocarbamate method. Spectrographic analyses were done in duplicate, and separately on two different instruments. 

The sensitivity of the dithizone method for determination of copper (Xmax = 550, molar mass of Cu = 63.54 g/mole) may be expressed as follows ... 

Trace amounts of Bi are determined conveniently by the dithizone method. The Xylenol Orange method is less sensitive. The diethyldithiocarbamate method is not very sensitive, but it is specific for Bi. 

The dithizone method has been applied for determining bismuth in natural waters [9], platinum [12], gold [15], silver [5], tin [60], and tellurium [61],... 

Two sensitive methods for determining cadmium are presented in detail the classical dithizone method, and a new method with use of the chelating azo reagent 5-Br-PADAP. 

The dithizone method has been applied in determining cadmium in food products [12], natural waters [19], organic materials [76], zinc sulphide [23], beryllium [17], zirconium alloys [8], uranium compounds [77], Cd-Se and Cd-Te thin films [78]. The flow-injection technique (FIA) has also been applied in determining Cd with dithizone [79,80]. 

Cu(Il) has been determined by the dithizone method, without the extraction, in the presence of Triton X-100 [14,15] and hydroxylammonium chloride [16],... 

The dithizone method has been applied for determining copper in biological materials [12,16], water [94], tin [3], titanium and its alloys [95]. Copper has been determined in sea sediments (in the presence of Hg and Pb) by derivative spectrophotometry [96]. 

The dithizone method is the most frequently applied extractive spectrophotometric method for determining lead. The convenient PAR or Pyrocatechol Violet methods (in the presence of a surfactant) can also be recommended, after extractive separation of lead as the iodide complex. 

The dithizone method has been applied for determining lead in biological samples [44,89,90], waters [8,15,91], soils [92],organic materials [93], plant materials [94,95], air (inorganic lead and organolead compounds) [96-98], silicate minerals [99], steel [2], molybdenum and tungsten [100], silver [34], cadmium [101], cobalt [11,13], boron [45], telluric acid [102], antimony sulphide [103], and gasoline [104],... 

Two methods are presented in detail an extractive dithizone method and the thio-Michler s ketone method. Both of them have good selectivity but the latter is more sensitive. Methods based on ion-associates formed by anionic mercury complexes with basic dyes are also noteworthy. 

A number of organic sulphur compounds are recommended as reagents for mercury. The thio-Michler s ketone and the dithizone methods have been described above. Other, less sensitive reagents include, thiodibenzoylmethane [59], thiobenzoylacetone (e = 1.7-10 ) [60], l-salicylidene-5-(2-pyridylmethylidene)-isothiocarbonehydrazide (40% DMF, e = 1.7-10 at 400 nm) [61], and 1-(2-thienyl)benzothiazoline [62]. 

The dithizone method has been used in determination of mercury in natural waters [80], coal and its products [81], sulphide minerals [82], silver [12], tin [10], cadmium [83], uranium compounds [84] selenium [85], Hg-Cd-Te thin films [86], foodstuffs [87,88], and water... 

A dithizone method, a very sensitive thio-Michler s ketone method, and a less sensitive iodide method are discussed below. A simple modification of the iodide method gives a very sensitive method involving the formation of the blue starch-iodine complex. 

Traces of Pt in palladium were determined by the dithizone method after separation of the macro-amounts of Pd as the sparingly soluble Pd(NH3)l2 [50]. Simultaneous determination of Pt and Pd is possible in the 5 order derivative spectrophotometry technique [51]. Trace amounts of Pt in larger amounts of Pd have been determined by means of the 2" order derivative of Pt(HDz)2 absorption curve [52]. 

Silver is often separated from other metals by extraction with dithizone. The details of this separation are discussed below in the dithizone method for determining silver. 

Among the many spectrophotometric methods for determining silver, the dithizone method is particularly important. Some newer methods, such as that using thio-Michler s ketone, and methods based on ion-associates with dyes, can be recommended. 

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