Photometric flow injection analysis of As(III) by using a homemade, LED-based flow-cell device and methyl orange reagent.

Inorganic arsenic especially As(III) is considered a carcinogenic substance and its measurement is important in water samples. In this work, an inexpensive flow injection analysis system was designed for the photometric determination of As(III) at low concentrations. For this purpose, a light-emitting diode (LED) based photometer with a miniaturized detector, was fabricated and used as a determination apparatus and methyl orange was used as a detecting reagent. The fabricated photometer employed the LEDs, as a light source and the light detector. The λmax of emission for emitter and detector LEDs were 525 and 625 nm, respectively. Determination of As (III) was based on its inhibition effect on the redox reaction between methyl orange and X2 (Cl2 or Br2). The decolorization of the reaction products in the FIA system was monitored using the homemade flow cell detector. Analytical figures of merit including linear responses ranging from 0.03 to 3.0 mg/l of As(III) (r = 0.994), detection limits of 0.007 mg/l As(III), RSD% of 1.5% (n = 7), low reagent consumption per determination, and sampling throughput of 50 determinations per hour were achieved.

Development of flow injection spectrofluorimetric detection system for the determination of homocysteine.

In this work, a new simple and sensitive flow injection method is developed for the determination of homocysteine with spectrofluorimetric detection technique. This method is based on the oxidation of homocysteine with Tl (III) in acidic media, producing fluorescence reagent, TlCl(3)(2-) (λ(ex) = 237 nm, λ(em) = 419 nm). The effects of chemical parameters (including pH of the solutions, the buffer, Tl (III) and potassium chloride concentrations), instrumental parameters (such as flow rate of the solutions, reaction coil length, and sample loop volume) and temperature on the fluorescence intensity as an analytical signal are studied and optimized. In the optimum conditions of the above variables, homocysteine can be determined in the range 4.0 × 10(-7)-40.0 × 10(-6) M with the LDR from 4.0 × 10(-7) to 25.0 × 10(-6) M. The detection limit (with S/N = 3) is 6.0 × 10(-8) M of homocysteine and precision for the injection of 5.0, 10.0 and 15.0 µM of homocysteine are 0.8%, 1.5% and 2.5% (n = 10) respectively. The rate of analysis is 90 samples per hour. The influence of potential interfering substances, including amino acids and carbohydrates is also studied. The proposed method has been successfully used for the determination of homocysteine in the real sample (blood serum and tap water) matrix.

Flow injection kinetic spectrophotometric method for the determination of trace amounts of nitrite.

In this work, a new, simple and sensitive flow injection catalytic kinetic spectrophotometric determination of nitrite is reported based on catalytic effect of nitrite on the redox reaction between sulfonazo III and potassium bromate in acidic media. The reaction was monitored by measuring the decrease in the absorbance of sulfunazo III at 570 nm. Various chemical (such as the effect of acidity, reagents concentrations) and instrumental parameters (flow rate, reaction coil length, injection volume and temperature) were studied and were optimized. Under the optimum conditions calibration graph was linear in the nitrite concentration ranges of 8.00 x 10(-3)-3.00 x 10(-1) microg/ml (with slope of 2.40) and 3.50 x 10(-1)-1.80 microg/ml (with slope of 0.42). The detection limit was 6.00 x 10(-3) microg/ml of nitrite, the relative standard deviation (n=10) was 1.25% and 0.88% for 5.00 x 10(-2) and 2.00 x 10(-1)microg/ml of nitrite respectively. About 60 samples in 1h can be analyzed. The interfering effects of various chemical species were studied. The method was successfully applied in the determination of nitrite in food and environmental samples.

Flow-injection determination of ascorbic acid and cysteine simultaneously with spectrofluorometric detection.

A simple and sensitive spectrofluorometric method was developed for the simultaneous determination of ascorbic acid and cysteine by a flow-injection system. This method is based on the reduction of Tl(III) with ascorbic acid or cysteine in acidic media, producing fluorescence reagent, TlCl3(2-) (lambdaex = 227 nm, lambdaem = 419 nm). The injected sample solution was divided into two separate streams. The first stream was treated with Tl(III) at pH 3.0 and then passed through a 270 cm reaction coil to the flow cell of the spectrofluorometer, where the fluorescence intensity was measured. This signal is related to ascorbic acid and cysteine concentration. The second part of the injected sample solution was treated with Tl(III) in HCl solution and then passed through a 50 cm reaction coil to the flow cell and the fluorescence intensity was measured. This signal is related only to cysteine. Thus, the ascorbic acid content was determined directly by the difference according to the calibration curve. Ascorbic acid and cysteine can be determined in the range of 1 x 10(-6) to 5.0 x 10(-5) M, at a rate of 16 samples per hour. The limits of detection (S/N = 3) were 8 x 10(-7) M for ascorbic acid and 7 x 10(-7) M for cysteine. The influence of potential interfering substances was studied. The proposed method was successfully applied to the simultaneous determination of both analytes in real samples.