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A simple and sensitive double injection/single detector flow injection analysis (FIA) method is proposed for the simultaneous kinetic determination of ascorbic acid (AA) and uric acid (UA). This method is based upon the difference between the rates of the AA and UA reactions with Fe 3 + in the presence of 1, 10-phenanthroline (phen). The absorbance of Fe 2 + /1, 10-phenanthroline (Fe-phen) complex obtained as the product was measured spectrophotometrically at 510 nm. To reach a good accuracy in the differential kinetic determination via the mathematical manipulations of the transient signals, different criteria were considered in the selection of the optimum conditions. The multi criteria decision making (MCDM) approach was applied for the selection of the optimum conditions. The importance weights of the evaluation criteria were determined using the analytic hierarchy process, entropy method, and compromised weighting (CW). The experimental conditions (alternatives) were ranked by the technique for order preference by similarity to an ideal solution. Under the selected optimum conditions, the obtained analytical signals were linear in the ranges of 0.50–5.00 and 0.50–4.00 mg L − 1 for AA and UA, respectively. The 3σ detection limits were 0.07 mg L − 1 for AA and 0.12 mg L − 1 for UA. The relative standard deviations for four replicate determinations of AA and UA were 2.03% and 3.30% respectively. The method was also applied for the analysis of analytes in the blood serum, Vitamine C tablets, and tap water with satisfactory results. [ABSTRACT FROM AUTHOR]

In this work, a flow injection analysis (FIA) method was introduced for the determination of trace amounts of thiourea in tap water. This method is based upon the inhibition effect of thiourea on the reaction between meta-cresol purple (MCP) and potassium bromate catalyzed by bromide ions in a sulfuric acid medium. In the presence of thiourea, an induction period appears in the reaction system, and as a result, the absorbance of MCP increases at 525 nm in the FIA manifold. The chemical and FIA variables are studied and optimized using the univariate and Simplex optimization methods. Under the optimum conditions, thiourea can be determined in the range of 0.100–13.0 μg mL −1 . The limit of detection (3 σ ) for thiourea was found to be 0.0310 μg mL −1 . The relative standard deviations (RSDs) for six replicate determinations of 0.500, 5.00, and 12.0 μg mL −1 of thiourea were 4.0%, 1.8%, and 1.2%, respectively. The proposed method was also applied for the determination of thiourea in orange juice and orange peel samples with recoveries in the range of 98.0–101%. The analytical speed of the method was calculated to be about 120 sample per hour. [ABSTRACT FROM AUTHOR]

A flow injection (FI) system is described for the sequential determination of periodate and iodate based on their reaction with iodide at pH 3.5. Two sample plugs were injected into the same carrier stream sequentially. One injection is for the iodate determination and the other for the sum of iodate and periodate determination. For iodate determination, molybdate solution buffered at pH of 3.5 was used for selective masking of periodate. The influences of reagent concentrations were studied by a univariable method and the influence of FI manifolds was studied using univariable and simplex method. Periodate and iodate can be determined in the range of 0.050–5.0 and 0.050–10 μg/ml, respectively. The 3σ limit of detection was 0.030 and 0.050 μg/ml for periodate and iodate, respectively. The proposed method has been applied for the sequential determinations of periodate and iodate in water samples. [Copyright &y& Elsevier]

A simple and efficient flow-injection method was used with good results to determine periodate and iodate in water. The method is based on the reaction of periodate or iodate with pyrogallol red in sulfuric acid media. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of pyrogallol red at 470 nm. The chemical and FIA variables were established using the univariate and simplex optimization methods. The calibration curve was linear over the concentration ranges of 0.8–73.0 and 2.0–100.0 μM for IO4− and IO3−, respectively. The detection limits were 0.7 and 1.0 μM for IO4− and IO3−, respectively. The sample throughput was 20±5 h−1. The influence of potential interfering ions in the determination of the anions was tested. The relative standard deviations for 4.20 and 5.73 μM periodate and iodate were 1.8 and 2.2%, respectively. [ABSTRACT FROM AUTHOR]