Magnesium, flame photometric determination

Flame photometric determination cannot be recommended except for solutions containing upwards of 10 p.p.m. of magnesium because the resonance line occurs at 2852 A in the middle of an intense OH molecular band system and correction for this background is difficult even when a recording spectrophotometer is used. A hot flame is required and it has been reported by Knutson that some increase in sensitivity is obtained if an oxy-acetylene flame containing 55 per cent by volume of acetylene is used instead of the stoichiometric level of 29 per cent by volume. The resonance line suffers no serious spectral interference from other elements present in the sample solution but aluminium, chromium and molybdenum cause varying degrees of depression. Silicate, phosphate and sulphur ions depress the emission seriously and other anions less seriously and so standards should be made up to contain the same acids in the same concentrations as the samples. 

Muller [76] has described a gas chromatographic method for the determination of tributyltin compounds in sediments. The tributyltin compounds are first converted to tributylmethyltin by reaction with ethyl magnesium bromide, and then analysed using capillary gas chromatography with flame photometric detection and gas chromatography-mass spectrometry. Tributyltin was found in samples of sediment and these results demonstrated that the technique has detection limits of less than 0.5pg L 1. 

Unger et al. [217] determined butyltins in non saline water by gas chromatography with flame photometric detection and confirmation by mass spectrometry. The sample was extracted with tropalone in //-hexane and organotin compounds derivatised with n-hexyl magnesium bromide to form tetraalkyltins. The n-hexyl derivatives of methyltin and butyltin species were easily separated and quantified relative to an internal standard (triphenyltin chloride) which was not found to be present in environmental samples and did not interfere. 

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