Sodium rhodizonate

Analysis. The bright scarlet flame color of Sr indicates that atomic emission and absorption methods wiU be good for its analysis. Sr is quantitatively determined by colorimetry down to 200 ppm using chloranrlic acid, by atomic absorption spectroscopy (AAS) to 100 ppb, to 1 ppb by electrothermal absorption spectroscopy (ETAS), and to 0.1 ppb by inductively-coupled plasma emission spectroscopy (ICPES) and inductively-coupled plasma mass spectroscopy (ICPMS). A spot test for Sr which extends to 40 ppm is provided by K2Cr04 and sodium rhodizonate. 

Sodium rhodizonate Strontium (II), Sr2 Ammonium carbonate Dilute sulfuric acid Saturated calcium sulfate Potassium chromate Ammonium oxalate... 

J. H. Dillon, Sodium Rhodizonate Test A Chemically Specific Test for Lead in Gunshot Residues, AFTE Journal 22, no. 3 (October 1990) 251. 

The reagent consists of a 0 5 per cent aqueous solution of sodium rhodizonate. It does not keep well so only small quantities should be prepared at a time. 

Sodium rhodizonate reagent reddish-brown precipitate of strontium rhodi-zonate in neutral solution. The test is applied to the elements of Group IV. Barium reacts similarly and a method for the detection of barium in the presence of strontium has already been described (Section III.31, reaction 7). To detect strontium in the presence of barium, the latter is converted into the insoluble barium chromate. Barium chromate does not react with sodium rhodizonate, but the more soluble strontium chromate reacts normally. 

Sodium rhodizonate test Barium salts yield a reddish-brown precipitate with sodium rhodizonate (see under Barium, Section III.31, reaction 7). Sulphates and sulphuric acid cause immediate decolourization because of the formation of insoluble barium sulphate. This test is specific for sulphates. 

Group IV. Ca, Sr, and Ba This is a difficult separation. The metals are present as chlorides. The solvent used is pyridine containing 20 per cent (v/v) water and 1 per cent (w/v) potassium thiocyanate. The elution is allowed to proceed for 5-6 hours in an atmosphere saturated with respect to pyridine and also with a relative humidity of between 65 and 80 per cent the latter is attained by the use of a saturated aqueous solution of ammonium nitrate or chloride. The solvent front moves about 20 cm. The strip is dried, and then sprayed with a saturated alcoholic solution of alizarin to identify Ca, and with 0 5 per cent (w/v) aqueous sodium rhodizonate (freshly prepared) to reveal Ba and Sr. The RF values are Ca, 0-95 Sr, 0-75 Ba, 0-15 (see Fig. VI.5c). 

Sodium rhodizonate (0-5 %). Dissolve 0-5 g sodium rhodizonate (rhodizonic acid, sodium salt C6OeNa2) in 100 ml water. The solution decomposes rapidly. 

In Inorganic Chemistry, typical spray reagents for cations include potassium iodine (0.2%, aqueous), hydrogen sulphide (saturated aqueous solution), ammonium sulphide (0.2 N, aqueous), quercetin (0.1%, alcoholic), l-(2-pyridylazo)-2-naphthol (PAN) (0.2%, methanolic), oxine (8-hydroxyquinoline) (1% methanolic, view under visible and UV light), and sodium rhodizonate (0.5%, aqueous). Reaction with dithizone to produce coloured dithizonate chelates of many metals is particularly suitable if quantitative spectrometric analysis (in situ or after elution) is to be carried out. Anions are detected with bromocresol purple (0.1%, alcoholic), 1% ammoniacal silver nitrate + 0.1% alcoholic fluorescein/UV light, zirconium alizarin lake (0.1% in HC1 solution), and ammonium molybdate (1%, aqueous) followed by SnCl2 (1%) and HC1 (10%). Typical detection limits range from 10 ng (10 9g) to several pg (10 6g). 

Sodium Rhodizonate. 5,6-Dihydroxy-5-cyctohex-ene-l, 2,3,4-tetrone disodium salt [(3,4,3,6-tetraoxo-I-eyefo-hexen-I,2-ytene)dioxy disodium. C Na.O mot wt 214.05. 

Sodium rhodizonate (rhodizonic acid, sodium salt) reagent... 

Place a drop of barium chloride solution upon filter or drop-reaction paper, followed by a drop of a freshly prepared 0.5% aqueous solution of sodium rhodizonate. Treat the reddish-brown spot with a drop of the acid or alkaline test solution. The coloured spot disappears. 

Sodium rhodizonate Sodium hydroxide Sodium peroxide Sodium nitrite Sodium acetate Sodium thiosulfate... 

Sodium rhodizonate 0.2% aqueous soln Morin+ EDTA... 

Sodium rhodizonate soln, filter paper impregnated with saturated soln of potassium chromate... 

Spray reagent I 1% aqueous solution of sodium rhodizonate. 

Figure 10.11 The sodium rhodizonate test An example is shown in the color insert. 

The detection of cations on chromatoplates is performed by spraying the solutions of the detection reagents at an appropriate concentration level, followed by visualization of the separated zones. The spraying reagents used as detectors include, 0.04-1 % dithizone in chloroform or carbon tetrachloride, 1% ethanolic solution of dimethylglyoxime, 1% aqueous solution of potassium ferrocyanide, 1% aqueous aluminon containing sufficient amount of ammonium acetate, 1% alcoholic solution of alizarine Red S, freshly prepared 0.1% solution of stannous chloride in 2 M HCl, hydrogen sulfide gas, aqueous saturated solution of ammonium sulfide, aqueous solution of ammonium thiocyanate and dilute solutions of diphenylcarbazide, p-nitroso-yV,A -dimethylaniline and sodium rhodizonate. 

The yellow aqueous solution of sodium rhodizonate (I) produces colored precipitates (II) with neutral solutions of the salts of bivalent heavy metals. 2... 

The precipitation capacity of sodium rhodizonate is particularly interesting within the group of the alkaline earth metals. Barium gives a red-brown precipitate of barium rhodizonate. Strontium salts react in the same way with rhodizonates, but calcium salts do not. Under suitable conditions, however, barium may be identified in the presence of strontium. The rhodizonate test is thus recommended for the detection of barium within the ammonium carbonate (alkaline earth) group, or for its detection when bivalent heavy metals are known to be absent. 

Procedure. A drop of the neutral or slightly acid test solution is placed on filter paper and then a drop of an aqueous 0.2 % solution of sodium rhodizonate. According to the amount of barium present, a more or less intense red-brown stain is formed. 

The paper may be impregnated with sodium rhodizonate. It must be dried in vacuo (over concentrated H2SO4) and stored in the dark. Otherwise, the finely divided rhodizonate is oxidatively decomposed. ... 

Strontium salts react similarly to barium salts with sodium rhodizonate. However, strontium rhodizonate is easily soluble in dilute hydrochloric acid in the cold, whereas the barium compound is converted into an insoluble bright red acid salt. It must be noted that small amounts of barium rhodizonate prepared in a test tube in neutral solution, and then treated with hydrochloric acid, seem to dissolve, because the red barium salt is formed in a fine state of division and is hard to see. If, however, the reaction is carried out on paper, the brown-red stain of barium rhodizonate is turned to a... 

If no brown fleck is formed on treating a drop of the test solution with a drop of sodium rhodizonate on filter paper, the absence of both barium and strontium is indicated a brown fleck may mean that either ion is present, or both. If the fleck disappears on treatment with dilute hydrochloric acid, only strontium is present if it turns red, barium (or barium and strontium) is present. 

If neutral or weakly acid solutions are to be examined, the following procedure may be used for the detection of barium and strontium in a micro drop. One drop of 0.5 % sodium rhodizonate solution is placed on Whatman filter paper No. 1. After the liquid has soaked in, the center of the yellow spot is treated with a drop of the test solution. A brownish or reddish-brown stain appears at once if barium or strontium is present. The fleck is then spotted with 1 or 2 drops of a mixture of equal parts of a saturated water solution of dimethylamine hydrochloride and 95 % ethanol. 

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