Phosphate spectrophotometric determination

SPECTROPHOTOMETRIC DETERMINATION OF PHOSPHATE AND ARSENATE IONS BY MEANS OF IONIC ASSOCIATES OF CYANINE DYES WITH POLYOXOMETALATES... 

EXTRACTION-SPECTROPHOTOMETRIC DETERMINATION OF PHOSPHATE AND ARSENATE USING IONIC ASSOCIATES OF POLYOXOMETALATES WITH BASIC DYES... 

ELUCIDATION OF THE HETEROPOLYBLUE NATURE AND EXTRACTION-SPECTROPHOTOMETRIC DETERMINATION OF PHOSPHATE USING MIXED HETEROPOLYANIONS... 

Ln(II) in LnFj Ln(II) were determined after samples dissolution in H PO in the presence of a titrated solution of NFI VO, which excess was titrated with the Fe(II) salt. It was found that dissolution of the materials based on CeF CeFj in H PO does not change the oxidation state of cerium, thus phosphate complexes of Ce(III, IV) can be used for quantitative spectrophotometric determination of cerium valence forms. The contents of Ln(II, III) in Ln S LnS may be counted from results of the determination of total sulfur (determined gravimetric ally in BaSO form) and sum of the reducers - S and Ln(II) (determined by iodometric method). 

Vishwavidyalaya et al. [22] used a difference-spectrophotometric method for the estimation of primaquine phosphate in tablets. One portion of powdered tablets, equivalent to 7.5 mg of primaquine phosphate, was extracted with hydrochloric acid-potassium chloride buffer (pH 2) and a second portion was extracted with phosphate buffer (pH 10). Primaquine phosphate was determined from the difference in absorbance of the acid and alkaline extracts at 254.2 nm. The calibration graph was rectilinear from 2 to 14 pg/mL of primaquine phosphate. Recovery was 98.6% and no interference was observed from excipients. Results compared with those by the British Pharmacopoeial method. 

Isaeva [181] described a phosphomolybdate method for the determination of phosphate in turbid seawater. Molybdenum titration methods are subject to extensive interferences and are not considered to be reliable when compared with more recently developed methods based on solvent extraction [182-187], such as solvent-extraction spectrophotometric determination of phosphate using molybdate and malachite green [188]. In this method the ion pair formed between malachite green and phosphomolybdate is extracted from the seawater sample with an organic solvent. This extraction achieves a useful 20-fold increase in the concentration of the phosphate in the extract. The detection limit is about 0.1 ig/l, standard deviation 0.05 ng-1 (4.3 xg/l in tap water), and relative standard deviation 1.1%. Most cations and anions found in non-saline waters do not interfere, but arsenic (V) causes large positive errors. 

Shulka et al. [75] investigated interference by arsenic in the spectrophotometric determination of inorganic phosphate in lake sediments. 

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

Vinnikova [22, 23] described the spectrophotometric determination of mefenamic acid at 490 nm after conversion to its colored complex with Fast Red B salt at pH 6.60 (phosphate buffer). The method was applied for the determination of free and bound mefenamic acid, and found to be useful for studying the blood plasma protein binding, absorption, distribution, metabolism, and excretion of mefenamic acid. 

Tris buffers Tris is also a much used buffer. However, it has one great disadvantage its pH is highly dependent on temperature and concentration. The pH of a Tris buffer will increase from 8.0 at 25 °C to 8.6 on cooling to 5 °C and on dilution of a 0.1 M solution at pH 8.0 to 0.01 M, the pH will fall to 7.9. This problem can only really be avoided by adjusting the pH of the buffer under the conditions of temperature and concentration where it is to be used. In addition, Tris has been shown, like phosphate discussed above, to interfere with many enzymic reactions, particularly those which have aldehyde intermediates. It also interferes with many chemical reactions, like the coupling of proteins to activated surfaces, and the Bradford assay for spectrophotometric determination of proteins. 

Vucic, N., and Ilic, Z., Extraction and spectrophotometric determination of uranium in phosphate fertilizers. J. Radioanal. Nucl. Chem. Articles 129 (1989) 113-120. 

If higher sensitivities are desired then the ammonium phosphomolybdate product may be reduced with stannous chloride or ascorbic acid in order to give soluble molybdenum blue [24]. Spectrophotometric determination of the blue absorbance at 885 nm gives a detection limit of 0.003 mg/L phosphate, stated as phosphorus (3 ppb in freshwater) or 0.0092 mg/L as expressed phosphate [24]. 

By use of releasing agents Considering the reaction M-X-i-R = R- Xh-M, it becomes evident that an excess of the releasing agent (R) will lead to an enhanced concentration of the required gaseous metal atoms (M) which will be of special significance if the product R-X is a stable compormd. Hence in the determination of calcium in presence of phosphate the addition of excess of strontium chloride to the test solution will lead to the formation of strontium phosphate and the calcium can then be determined in an acetylene-air flame without any interference due to phosphate. Also addition of EDTA to a calcium solution before analysis may increase the sensitivity of the subsequent flame spectrophotometric determination which may be due to the formation of an EDTA complex of calcium which is readily dissociated in the flame. 

Worked example 4. A confluence flow injection system with a very low confluent stream flow rate is designed for the spectrophotometric determination of phosphate in plant digests. The linearity of the analytical calibration graph is good and the recorded absorbance corresponding to a 100.0 mg L 1 P (as phosphate) standard solution is 0.21. Replacing the sample carrier stream by this standard solution (sample infinite volume) yields a steady state situation and the related absorbance is 0.68. The pump is then turned off and an asymptotic increase in absorbance towards 0.95 is observed determine the sensitivity improvement that in principle could be attained simply by increasing the sample volume and the mean sample residence time in the analytical path. 

The sample is inserted simultaneously with the reagents required for a given determination thereafter, it is inserted again but with the reagents required for the second determination. In this way, sequential determinations are performed in the same manifold. This approach was exploited initially in the spectrophotometric determinations of ammonium and phosphate in plant digests [20], which required rather different reaction conditions the ammonium determination was carried out in a highly alkaline medium, whereas the phosphate determination was performed... 

For simultaneous determinations and /or speciation, different separation/ concentration steps can be implemented in the same manifold, as in, e.g., the determination of nitrogen, phosphorus and potassium in fertilisers [314]. The sample was inserted and passed successively through a dialysis unit and a gas diffusion unit to a flow cell for the spectrophotometric determination of phosphate. The dialysed potassium ions and the diffused gaseous ammonia were collected in specific streams and determined by flame photometry and potentiometry, respectively. 

This innovation generally involves modifications to the operation of the sampler and random access reagent selection, and can be implemented in both segmented and unsegmented flow analysers. For unsegmented flow analysis, the spectrophotometric determination of zinc and phosphate in soil extracts [368] is a good example. Zinc was determined only when phosphate was present at concentrations above a threshold level. The number of determinations required was reduced by 30%. Analogously, an expert flow system was proposed for the turbidimetric determination of chloride and sulphate in natural waters [369]. Both methods were implemented in the same manifold, and the need for sulphate determination was dependent on the chloride concentration determined. 

EXPERIMENT 38 THREE-LINE FIA SPECTROPHOTOMETRIC DETERMINATION OF PHOSPHATE... 

Nagai, M., Sugiyama, M. and Hori, T. (2004) Sensitive spectrophotometric determination of phosphate using silica-gel collectors. Anal Sci, 20 (2), 341-344. 

Figure 6.3. (a) FIA manifold for spectrophotometric determination of phosphate. The two reagents are premixed in the first coil, whereupon sample is injected (30 ixL). All tubes are 0.5 mm ID. (b) Left record obtained by injecting standards in quadruplicate, containing 5-40 ppm P-PO4 the record to the right shows a scan where the time scale is expanded to show the peak shape when injecting 20 and 40 ppm solutions. Note that it takes only 15 s between sample injection 5 and peak maximum readout / , and another 15 s until the next sample (52) can be injected. Hence, the signal will be below the 1% level before the next readout will be taken, and therefore there is no carryover even at a rate of 120 samples/h. 

W. Cheng and Y. Li, The Flow Injection Spectrophotometric Determination of Phosphate in Power Plant Boilers [in Chinese]. Gongye Shui Chuli, 3 (1986). 

Fig.9.2 FI manifold for the spectrophotometric determination of codeine by solvent extraction. P, pump DB. displacement bottle for delivery of chloroform C. carrier, 0.065 M phosphate buffer, pH 6.5 PR, picrate reagent S, sample SG, phase segmentor, EC, extraction coil SP, phase separator, R, restrictor or impediuice coil D, detector, W, waste (233 ] ...

Spectrophotometric determination after hydrolysis to hydrogen phosphate ions... 

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