Phosphorus, analytical determination

The estabhshed method for phosphorus analysis using a heated block involves a lengthy digestion with sulphuric acid. Furthermore, it is labour and space intensive and requires the digested sample to undergo a second stage for the final analytical determination. 

The analysis of phosphates and phosphonates is a considerably complex task due to the great variety of possible molecular structures. Phosphorus-containing anionics are nearly always available as mixtures dependent on the kind of synthesis carried out. For analytical separation the total amount of phosphorus in the molecule has to be ascertained. Thus, the organic and inorganic phosphorus is transformed to orthophosphoric acid by oxidation. The fusion of the substance is performed by the addition of 2 ml of concentrated sulfuric acid to — 100 mg of the substance. The black residue is then oxidized by a mixture of nitric acid and perchloric acid. The resulting orthophosphate can be determined at 8000 K by atom emission spectroscopy. The thermally excited phosphorus atoms emit a characteristic line at a wavelength of 178.23 nm. The extensity of the radiation is used for quantitative determination of the phosphorus content. 

Plant samples are homogenized with sodium hydrogencarbonate aqueous solution to prevent decomposition of the analytes during homogenization. Imibenconazole and its primary metabolite, imibenconazole-debenzyl, are extracted from plan materials and soil with methanol. After evaporation of methanol from the extracts, the residues are extracted with dichloromethane from the residual aqueous solution. The dichloromethane phase is cleaned up on Florisil and Cig columns. Imibenconazole and imibenconazole-debenzyl are determined by gas chromatography/nitrogen-phosphorus detection (GC/NPD). 

Biological and Analytical Applications. - Phosphorus-31 n.m.r. continues to expand its application in the medical and biological fields20 and is now being applied to soil analysis.21 The problems involved in the use of FT 31P n.m.r. for quantitative determinations have been discussed.22 Samples of phosphinic carboxylic acids were cooled to -40°Cfor quantitative estimations.23... 

Of course, not all dissolved ions produce colored solutions, and therefore not all ions in solution can be quantified by colorimetry. Noncolored solutions can sometimes, however, be converted to colored solutions by introducing chromophore species which complex with (i.e., attach themselves to) the target ion to produce a colored solution, which may then be measured by UV/visible colorimetry. An important archaeological example of this is the determination of phosphorus in solution (which is colorless) by com-plexation with a molybdenum compound, which gives a blue solution (see below). The term colorimetry applies strictly only to analytical techniques which use the visible region of the spectrum, whereas spectrophotometry may be applied over a wider range of the electromagnetic spectrum. 

Simmons, W. R. and Robertson, J. H. (1950). Spectrophotometric determination of phosphorus in organic phosphates. Analyt. Chem. 22, 1177. 

Sun, L., Gao, Z., Li, L., Yu, X. and Fang, Z. (1981) Determination of soil available phosphorus by flow injection analysis [in Chinese, English translation]. Fenxi Fluaxue (Analytical Chemistry) 9, 585. 

Due to the lack of suitable standard reference material for quantification purposes in phospho-proteomics and metallomics, reliable calibration strategies were developed for the direct microlocal analysis of phosphorus and metals in protein spots and in thin sections of brain tissue using LA-ICP-MS.16,17,116 For quantification of analytical data, the application of a solution based calibration strategy was proposed with LA-ICP-MS6 and the simultaneous determination of P, S, Si, Al, Cu and Zn concentrations in human brain proteins (Alzheimer s disease) or for imaging thin... 

A number of instrumental analytical techniques can be used to measure the total phosphorus content of organophosphorus compounds, regardless of the chemical bonding of phosphorus within the molecules, as opposed to the determination of phosphate in mineralized samples. If the substances are soluble, there is no need for their destruction and for the conversion of phosphorus into phosphate, a considerable advantage over chemical procedures. The most important methods are flame photometry and inductively coupled plasma atomic emission spectrometry the previously described atomic absorption spectrometry is sometimes useful. 

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