No abstract

A new sensitive and simple kinetic method is developed for determination of traces of ascorbic acid based on its activated effect on oxidation of trisodium-2-hydroxy-1-(4-sulphonato-1-naphthylazo)naphthalene-6,8-disulphonato (red artificial color Ponceau 4R) by hydrogen peroxide, in the presence of Cu(II) as catalyst, in borate buffer. The reaction is followed spectrophotometrically by tracing the oxidation product at 478.4 nm within 1 min after addition of H 2 O 2 . The optimum reaction conditions are: borate buffer (pH = 11.00), Ponceau 4R (9.6·10 -6 mol/L), H 2 O 2 (2·10 -2 mol/L), Cu(II) (8·10 -7 mol/L) at 22°C. Following this procedure, ascorbic acid can be determined with a linear calibration graph up to 1.76 ng/mL and a detection limit of 0.28, based on 3S criterion. The relative error ranges between 6.77-1.66% for the concentration interval of ascorbic acid 1.76-17.61 ng/mL. The effects of certain foreign ions upon the reaction rate were determined for an assessment of the selectivity of the method. The method was applied for determination of ascorbic acid in pharmaceutical samples, and spectrophotometric method was used like an comparative method.

In the present study, a new sensitive and simple kinetic-spectrophotometric method for the determination of the insecticide diflubenzuron [1-(4-chlorophenyl)-3-(2,6-diflubenzoil)urea] is proposed. The method is based on the inhibited effect of diflubenzuron on the oxidation of sulphanilic acid (SA) by hydrogen peroxide in phosphate buffer in presence Cu(II) ion. Diflubenzuron was determined with linear calibration graph in the interval from 0.31 to 3.1 μg mL⁻¹ and from 3.1 to 31.0 μg mL⁻¹. The optimized conditions yielded a theoretical detection limit of 0.18 μg mL⁻¹ corresponding to 0.036 mg kg(-1)mushroom sample based on the 3S(b) criterion. The RSD is 5.03-1.83 % and 2.81-0.71 % for the concentration interval of diflubenzuron 0.31-3.1 μg mL⁻¹ and 3.1-31.0 μg mL⁻¹, respectively. The reaction was followed spectrophotometrically at 370 nm. The kinetic parameters of the reaction are reported, and the rate equations are suggested. The developed procedure was successfully applied to the rapid determination of diflubenzuron in spiked mushroom samples of different mushroom species. The HPLC method was used like a comparative method to verify results.

The purpose of this paper is to present a new kinetic-spectrophotometric method which involve inexpensive equipment and which can be applied by all analyst who have to determine difenzoquate methyl sulfate (DFQ) residues in citruses and baby juices. The method is based on the inhibited effect of DFQ on the oxidation of sulfanile acid (SA) by hydrogen peroxide in phosphate buffer in presence Cu(II) ion. The reaction was monitored spectrophotometrically by measuring the increase in absorbance of the reaction product at 370 nm. The proposed inhibited method permits determination of DFQ over the range 0.36 to 1.80 mg/mL and 1.80 to 7.20 mg/mL, with quantification limit of 0.184 mg/mL. The relative standard deviations are 0.73-2.90% for the concentration interval of DFQ 1.80-0.36 mg/mL. The method was successfully applied to determination of DFQ residues in citruses and baby juices. The HPLC method is used to verify the results. The results obtained for the same samples by the two methods are quite comparable.

In the present study, a new sensitive and simple kinetic‐spectrophotometric method for the determination of the insecticide dimethoate[O,O‐dimethyl‐S‐(N‐methyl‐carbomoylmethyl)‐phosphoro‐dithioate] is developed. The method is based on the inhibited effect of dimethoate on the oxidation of sulphanilic acid (SA) by potassium periodate in acetate buffer in presence Fe(III) ion and 1,10‐phenantroline. Dimethoate was determined with linear calibration graph in the interval from 28.10 to 196.70 ng/mL. The optimized conditions yielded a theoretical detection limit of 21.64 ng/mL based on the 3Sb criterion. The RSD is 4.85‐1.2% for the concentration interval of dimethoate 28.10‐196.70 ng/mL. The reaction was followed spectrophotometrically at 368 nm. The kinetic parameters of the reaction are reported, and the rate equations are suggested. The developed procedure was successfully applied to the rapid determination of dimethoate in spiked milk and water samples. Liquid‐liquid extraction and solid‐phase extraction (SPE) was used for extraction of dimethoate from milk and water samples with Chromabond® (Macherey‐Nagel) C18 cartridges. The HPLC method was used like an comparative method to verify the results. The results obtained by two different methods showed good agreement.