Sulphamic acids analysis

No satisfactory direct gravimetric procedure is available but nitrite can be oxidised to nitrate by permanganate or cerium(IV) and then determined in that form. The determination of total nitrate + nitrite is an important analysis, e.g. for soil samples. Nitrite may be destroyed using urea, sulphamic acid or hydrazine sulphate the reaction with the former is ... 

The application of CFD methods also makes it possible to carry out the analysis of such inorganic substances as anions and metals. As an example let us consider the analysis of trace amounts of nitrates in water. Tan [44] proposed a simple and sensitive method for determining nitrates in aqueous solutions using GC—mass spectrometry (MS) with an ionic detector-multiplier. The method is based on the nitration of 1,3,5-trimethoxy-benzene (TMB) in sulphuric acid. In this medium the nitration follows the hydrolysis of the ether groups of TMB, and nitrobenzene is formed as the final product [44]. The reaction mixture is analysed by GC and detected with a mass spectrometer. Hexamethyl-benzene (HMB) is used as an internal standard. To avoid interference from nitrates and chlorides, sulphamic acid and mercury(ll) sulphate are used. 

A convenient synthesis of the triethylamine-sulphur trioxide complex Et3NS03 (129) has been reported by Nair and Bernstein177. A 75% yield of 129 was obtained by the reaction of triethylamine with chlorosulphonic acid. Reaction of quinuclidine N-oxide with SO2 yield a stable colourless, non-hygroscopic material which was identified by X-ray and elemental analysis to be the quinuclidine-sulphur trioxide complex 130178. The complex was exceedingly stable and its hydrolysis in water even at 86 °C was very slow, 280 times slower than the analogous rate for triethylamine-sulphur trioxide (129). A single X-ray structure determination of the complex showed a sulphamic acid type coordination of SO3 to the quinuclidine nucleus [N-S =1.831 (6) A]. 

Air sample analysis Glass impingers are used to obtain air samples. A separate bubbler is carried through all the steps except the actual air sampling in order to act as a blank. To each bubbler, 0-5 ml of 3% sodium nitrite solution is added and allowed to stand for about 90s. 1 ml of 10% sulphamic acid solution is added, mixed and allowed to stand for about 2 min to destroy all the excess nitrous acid present. 1ml of 0-1% N-naphthylethylene diamine is added, mixed and the colour allowed to develop for about 5 min. A reddish blue colour indicates the presence of TDI. The final volume is adjusted to 20 ml with water. The transmittance is read at 550 nm using a 1-cm or 5-cm cuvet. The sample absorbance, after allowing for the absorbance of the blank, is compared with the calibration curve, and the concentration of TDI in ppm is calculated as above. 

The standard method for the determination of nitrite in seawater is based on the reaction of nitrite with an aromatic amine leading to the formation of a diazonium compound which couples with a second aromatic amine. The product is an azo dye which is quantified by spectrophotometry. Early methods were modifications of the Griess-Ilosvay procedure where the nitrite diazotized with sulphamic acid. The diazonium salt then coupled with 1-naphthylamine. The method described below is generally accepted for seawater analysis and is based on the method proposed by Shinn (1941) and adapted for seawater by Bendschnei-der and Robinson (1952). This method is very sensitive and is unaffected by the presence of other constituents normally occurring in seawater. Sulphanilamide hydrochloride is used as the amino compound, which after diazotization is coupled with N-(l-naphthyl)-ethylene-diamine dihydrochloride. 

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