Phosphorus intensity measurements

The proton-coupled spectrum is much more informative. We can see immediately which protons show a measurable coupling with the phosphorus atom, because the pattern is clearly identifiable as two triplets separated by 28.7 Hz. This, as we have already seen in Table 1, is the two-bond coupling between the phosphorus and the methine proton. The triplets (intensity 1 2 1)... 

Figure 9.21 Depth profiling of phosphorus and sulfur in protein spots of a 2D gel measured by LA-ICP-MS. Transient signals show decreasing ion intensity with increasing replication number (proportional to measurement time).

More recent flame photometric methods rely on direct measurement of the phosphorus emission. If organophosphorus compounds are injected into a hydrogen flame, a continuous emission is obtained in the 490-650 nm region. A broad band system, with an intensity maximum at 526 nm, is superimposed on this background139 it is attributed to the HPO species formed in the flame. An early determination of phosphorus at 0.01-0.04 m concentrations was based on examination of the continuous emission standard and sample solutions were injected into the burner and the intensities were measured at 540 nm the calibration graph was linear down to the detection limit of 10 4 M phosphorus sodium or calcium, if present in the sample, interfered with the results140. 

A numerical matrix correction technique is used to linearise fluorescent X-ray intensities from plant material in order to permit quantitation of the measurable trace elements. Percentage accuracies achieved on a standard sample were 13% for sulfur and phosphorus and better than 10% for heavier elements. The calculation employs all of the elemental X-ray intensities from the sample, relative X-ray production probabilities of the elements determined from thin film standards, elemental X-ray attenuation coefficients, and the areal density of the sample cm2. The mathematical treatment accounts for the matrix absorption effects of pure cellulose and deviations in the matrix effect caused by the measured elements. Ten elements are typically calculated simultaneously phosphorus, sulfur, chlorine, potassium, calcium, manganese, iron, copper, zinc and bromine. Detection limits obtained using a rhodium X-ray tube and an energy-dispersive X-ray fluorescence spectrometer are in the low ppm range for the elements manganese to strontium. 

If a water sample contains both soluble and insoluble manganese (Mn) compounds and ions, and it is filtered to separate the dissolved and insoluble fractions, and the filtrate and insoluble residue are analyzed separately, the results can be expressed as total dissolved Mn and total suspended or insoluble Mn. Phosphorus (P) can be determined colorimet-rically as the ortho-phosphate ion, P043, in aqueous samples after a reaction that forms an intensely blue-colored derivative. However polyphosphate ions and other ions and compounds containing P do not form this derivative. Total P in a sample can be determined with the same colorimetric procedure after acid hydrolysis and oxidation of all ions and compounds containing P to P04 3. In some elemental analyses the sample is treated with reagents designed to make available for measurement some fraction of an element or elements but not the total amount. For example, a soil sample may be treated with water at pH 3 to simulate the leaching process of acid rain. A total elemental analysis of the filtrate provides information about just those elements solubilized by the mild acid treatment. This can be called the determination of total mild acid leachable elements. 

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