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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]

Abstract: A rapid, simple, accurate, and highly selective spectrophotometric method is proposed for the determination of periodate in water samples. This method is based on the reaction of methylene green with periodate in the presence of iodide. The decrease in the absorbance of methylene green is used to monitor the reaction spectrophotometrically at 613nm. Under the optimum conditions, periodate could be determined in the concentration range 0.18–6.0μgmL−1. The detection limit for the method is 0.010μgmL−1. The influence of various foreign species was studied, and it was found that iodate did not interfere with the determination even in the presence of 200-fold of periodate. The relative standard deviations for six replicate determinations of 0.30, 0.50, 1.0, 1.5, 4.0, and 5.5μgmL−1 of periodate were 3.33, 2.0, 1.6, 1.33, 0.50, and 0.55%, respectively. The proposed method was applied to the determination of periodate in water samples and indirect determination of ethylene glycol in antifreeze and glycerol in vegetable oil via malaprade reaction, and satisfactory results were obtained. [Copyright &y& Elsevier]

Abstract: This paper describes a new, simple, sensitive, and selective catalytic–kinetic-spectrophotometric method for the determination of trace amounts of oxalate in vegetable and water samples. The method is based upon the catalytic effect of oxalate on the oxidation of crystal violet (CV) by dichromate in sulfuric acid media. The reaction was followed by measuring the decrease in absorbance of CV at 630nm (λ max of CV). The dependence of sensitivity on the reaction variables was studied and discussed. Under the optimum conditions, a fixed time procedure was used to obtain a linear calibration curve in the oxalate concentration ranges of 0.20–5.5μgmL−1 of oxalate. The calculated detection limit was 0.050μgmL−1. The relative standard deviations for ten replicate determinations of 0.40, 1.8, and 2.5μgmL−1 of oxalate were 6.0%, 2.5%, and 1.8%, respectively. The effect of the presence of various species commonly associated with real samples was also investigated. The proposed method was successfully applied for the determination of oxalate in vegetable and spiked water samples. [Copyright &y& Elsevier]

Abstract: A new, simple and sensitive kinetic spectrophotometric method with no need for removing of interfering substances is proposed for the determination of thiocyanate ion in biological and water samples. The procedure is based on the inhibiting effect of thiocyanate on the sodium periodate–potassium bromide–meta cresol purple (MCP) system in acidic media. The induction period of the reaction is proportional to the SCN− concentration. The decolorization of meta cresol purple by the reaction products was used to monitor the reaction spectrophotometrically at 525nm. Under optimum conditions, thiocyanate can be determined in the range of 0.02–0.8μgml−1 with a 3σ detection limit of 5ngml−1. The relative standard deviations for 10 replicate determinations of 0.060, 0.10 and 0.50μgml−1 thiocyanate are 3.7, 2.4 and 1.0%, respectively. This method has been successfully used to the determination of thiocyanate content in smokers and non-smokers saliva and spiked water sample. [Copyright &y& Elsevier]

Abstract: A simple, sensitive and selective spectrophotometric method for the simultaneous determination of Co(II) and Pd(II) using partial least square (PLS) calibration and H-point standard addition method is described. The method is based on the complex formation of Co(II) and Pd(II) with 4-(2-pyridylazo) resorcinol (PAR) in acidic media and in the presence of sodium dodecyl sulfate (SDS) as a micellizing agent. Acidic media and the presence of a micellar system improve selectivity and sensitivity, respectively. By applying PLS calibration, Co(II) and Pd(II) can be determined in the range of 0.20–2.0 and 0.40–4.0μgml−1, respectively. The relative errors of prediction for the determination of Co(II) and Pd(II) in the 10 prediction samples were 1.69 and 1.72%, respectively. The results of applying H-point standard addition method show that Co(II) and Pd(II) can be determined simultaneously with concentration ratio of Co(II) to Pd(II) varying between 7:1 and 1:8 in the mixed samples. Both proposed methods (PLS and HPSAM) were applied to the determination of Co(II) and Pd(II) in several alloy solutions with satisfactory results. [Copyright &y& Elsevier]

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]

• Determination of nitroaniline isomers in binary mixtures by four spectrophotometric methods. • Similar precision and accuracy of CC and RD methods compared to PLS and PCR methods. • Selection of best pair of wavelengths and divisor in proposed methods was studied. • No need to computer programs or sophisticated equipment in suggested methods. In the present work, four simple and economic spectrophotometric methods, namely constant center (CC), ratio difference (RD), H-point standard addition method (HPSAM), and ratio H-point standard addition method (RHPSAM) were employed for the simultaneous determination of meta and para -nitroaniline with severely overlapping spectra without unitizing the preliminary physical separation techniques. In each method, the parameters affecting the resolution of the spectra were optimized to determine the cited isomers in a binary mixture with a high accuracy. Under the optimized conditions, the results obtained showed that from cited methods used, the CC and RD methods have the least errors in determination of the concentration of highly spectral overlapping species. The mean percentage recovery values for the binary mixture of meta- and para -nitroaniline were found to be 95.98 and 98.78 using the RD method, and 101.85 and 100.23 using the CC method, respectively. For comparison of the powerful multivariate methods including the principal component regression (PCR) and partial least squares (PLS) were also applied. The mean percentage recovery values for the binary mixtures of the cited isomers were found to be 101.62 and 101.47 using the PCR method, and 101.00 and 101.36 using the PLS method, respectively. A statistical comparison of the methods demonstrated that there was no significant difference between the RD, CC, PCR, and PLS methods and the reported HPLC method regarding both accuracy and precision. The proposed methods have an admissible precision and accuracy for determination of the two isomers in their binary mixtures in tap water as a real sample. [ABSTRACT FROM AUTHOR]