Determination of arsenic and selenium in environmental and agricultural samples by hydride generation atomic absorption spectrometry.

Agricultural and environmental samples are digested with acid, and arsenic and selenium are determined using hydride generation atomic absorption spectrometry. Interelement interferences are eliminated by high acid concentrations or cation-exchange resins. Agreement with standard reference material is excellent. The technique is also applied to actual samples.

Continued investigation of the diazotization and coupling spectrophotometric technique for the determination of aromatic amines with 8-amino-1-hydroxynaphthalene-3,6-disulphonic acid and N-(1-naphthyl)ethylenediamine as coupling agents.

Twenty more aromatic amines are determined by the diazotization and coupling spectrophotometric technique, with 8-amino-1-hydroxynaphthalene-3,6-disulphonic acid (H-acid) and N-(1-naphthy)ethylenediamine (N-na) as coupling agents. The following are determined by both methods: 2,4-diaminotoluene, 2-aminobenzotrifluoride, 4-benzoxyaniline, 2,4-dimethyl-6-nitroaniline, 4,5-dimethyl-2-nitroaniline, 2-amino-9-fluorenone, naphthionic acid (sodium salt), 3-aminonaphthalene-2, 7-disulphonic acid (monosodium salt), 2-aminonaphthalene-1-sulphonic acid, 4-aminonaphthalene-1-sulphonic acid and 2,4-dibromoaniline. The following are determined only by the N-na method: 5-aminosalicylic acid, 2-amino-4-nitrophenol, 4-amino-2,6-dichlorophenol hydrochloride, 2,5-dimethoxy-aniline, 4-aminothiophenol, 4,4'-diaminodiphenylmethane, 1-naphthylamine, 4,4'-diaminobiphenyl-2,2'-disulphonic acid and 4,4'-diaminostilbine-2,2'-disulphonic acid. The optimum acidities for the different aromatic amines for the N-na method vary considerably. A number of aromatic amines cannot be determined by either method.

Further application of the diazotizationcoupling spectrophotometric technique to the determination of aromatic amines with 8-amino-1 -hydroxynaphthalene-3,6-disulphonic acid and N-(1-naphthyl)-ethylenediamine as coupling agents.

Twenty-two aromatic amines are determined by the diazotization-coupling spectrophotometric technique, using 8-amino-1-hydroxynaphthalene-3,6-disulphonic acid (H-acid) and N-(1-naphthyl) ethylenediamine (N-na) as coupling agents. The following are determined by both methods: 2-and 4-ethylaniline, 4-aminobenzonitrile, 3- and 4-aminoacetophenone, 4-aminobenzophenone, 4-iodoaniline, 2,5-dichloroaniline, 4-aminohippuric acid, 2-aminobenzyl alcohol, 3-aminobenzamide, sulphathiazole, 2-, 3- and 4-methoxyaniline and 2,4-, 3,4- and 3,5-dimethylaniline. It is possible to determine 2,3- and 2,5-dimethylaniline only by the H-acid method, but 2,6-dimethylaniline cannot be determined by either method. 2-Aminobenzamide can only be determined by the N-na method. In the application of the H-acid method to the methoxyanilines and dimethylanilines, the colour is developed by adding a large excess of sodium bicarbonate and H-acid. In the application of the N-na method to the ethylanilines, methoxyanilines and 2,4-, 3,4- and 3,5-dimethylanilines, the colour is developed by addition of a large excess of N-na reagent and allowing the solution to stand overnight.

Spectrophotometric determination of trace amounts of aniline by diazotization coupling with N-(1-naphthyl)ethylenediamine and extraction.

A spectrophotometric procedure is proposed for the determination of trace amounts of aniline by diazotization, coupling with N-(1-naphthyl)ethylenediamine in sodium acetate medium, extraction of the yellow dye with chloroform, and conversion into a reddish purple dye. Two methods are available for the conversion. In the first, the chloroform extract is shaken with hydrochloric acid and the dye is converted and transferred into the aqueous phase. In the other, the chloroform extract is evaporated to dryness and the residue is dissolved in glacial acetic acid. The hydrochloric acid extraction method is the more rapid. The minimum detection limits for the two methods are 0.8 and 0.6 mug/ml respectively. Both methods show satisfactory accuracy and precision.

Study of the behaviour of various phenolic compounds in the 4-aminoantipyrine and ultraviolet-ratio spectrophotometric methods without and with distillation.

It is customary in industrial analysis in the determination of phenols by the 4-aminoantipyrine (4-AAP) and ultraviolet-ratio spectrophotometric methods to report the total of phenolic compounds as phenol. A study was therefore made of the behaviour of 36 representative phenolic compounds in the 4-AAP and UV-ratio methods, with and without distillation, to ascertain the apparent recoveries relative to that for phenol. The Fisher phenol analyser was used for the UV-ratio method, which depends upon the bathochromic shift (from about 270 to about 290 nm) usually obtained when the solution of the phenol is made alkaline. The apparent recoveries by the 4-AAP method both with and without distillation varied from 0 to 100%. The apparent recoveries by the UV-ratio method without distillation varied from 0 to 148%, and those with distillation varied from 0 to 110%. Sixteen of the compounds tested without distillation gave less than 10% recovery by the 4-AAP method and eleven gave less than 10% recovery by the UV-ratio method. The results after distillation indicated that several of the compounds did not distil completely.

Spectrophotometric determination of tetrazene in primers and primer mixes by use of resorcinol.

A spectrophotometric method is proposed for the determination of tetrazene (tetracene) in primers and primer mixes that involves treatment of the tetrazene with resorcinol solution and measurement of the intensity of the yellow colour of the diazo-dye produced. In the application of the method, lead styphnate and barium nitrate are first removed by extraction with ammonium acetate solution and then nitrocellulose and PETN are removed by extraction with acetone. The insoluble matter containing the tetrazene is boiled with resorcinol reagent, the solution filtered, and the absorbance measured at 400 nm. Conditions for optimum colour development are studied and the nature of the reaction is considered.

Semimicro spectrophotometric determination of nitroglycerine in propellants by use of 2,4-xylenol.

A semimicro spectrophotometric method using 2,4-xylenol is proposed for the determination of nitroglycerine in propellants. The propellant is extracted with methylene chloride, the extract is diluted, and a 10-ml aliquot is evaporated just to dryness. Then 2,4-xylenol reagent and 63% v/v sulphuric acid are added to hydrolyse the nitroglycerine to nitrate and form 6-nitro-2,4-xylenol which is steam-distilled in a Parnas-Wagner Kjeldahl distillation apparatus into a water-ammonia-isopropyl alcohol mixture. The absorbance of the yellow solution of the anion of the 6-nitro-2,4-xylenol is measured. The calibration curve is prepared from potassium nitrate and an empirical factor (5.50) is used to convert from nitrogen content to nitroglycerine (the theoretical factor is 5.40). The 2,4-xylenol should be added before the sulphuric acid in order to prevent interference from diphenylamine and ethyl centralite. The method is designed for the usual nitrocellulose double-base propellants containing 8-50% of nitroglycerine.