Phosphate determination reverse flow-injection analysis

Johnson and Petty [177] adapted reverse flow injection analysis to the well-known Murphy and Riley [178] colorimetric phosphomolybdate reduction method for the determination of phosphate. 

Figure 2.5a and b show flow sheets for the determination of phosphate by flow injection analysis and reversed flow injection analysis, respectively. 

Figure 2.5. Analytical manifolds for the determination of phosphate by flow injection analysis (a) and reverse flow injection (b). The symbols S, M, and A are the seawater, mixed reagent, and the ascorbic acid solutions. The pump injection valve and detector are represented by P, I, and D, respectively. W = waste. From [177]... 

Kritsunankul et al. [76] proposed flow injection online dialysis for sample pretreatment prior to the simultaneous determination of some food additives by HPLC and UV detection (FID-HPLC). For this, a liquid sample or mixed standard solution (900 pL) was injected into a donor stream (5%, w/v, sucrose) of a FID system and was pushed further through a dialysis cell, while an acceptor solution (0.025 mol/L phosphate buffer, pH 3.75) was held on the opposite side of the dialysis membrane. The dialysate was then flowed to an injection loop of the HPLC valve, where it was further injected into the HPLC system and analyzed under isocratic reversed-phase HPLC conditions and UV detection (230 nm) (Figure 24.6). The order of elution of five food additives was acesulfame-K, saccharin, caffeine, benzoic acid, and sorbic acid, with an analysis time of 14 min. This system has advantages of high degrees of automation for sample pretreatment, that is, online sample separation and dilution and low consumption of chemicals and materials. 

Nemutlu et al. [22] determined lomoxicam in pharmaceutical preparations by a liquid chromatographic method. The separation was achieved on a reversed phase (Nucleosil 100-5 Cis 25 cm x 4.6 mm, 5 gm) column kept at room temperature. The flow rate of mobile phase was 1 ml / min. The mobile phase consisted of 0.1 M phosphate buffer (pH 6)-acetonitrile (60 40) and UV detection at 293 nm. The retention times for the drug and the internal standard, metronidazole, were 5.65 and 3.95 min, respectively. Quantitative analysis of the drug in tablets and injections were performed. The method is fast, simple, inexpensive and applicable over a wide range of concentrations with high precision and accuracy. 

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