L.M.Polo Díez

Determination of tert-butylhydroxyanisole and tert-butylhydroxytoluene by flow injection with amperometric detection

Abstract Two flow-injection methods are described for the determination of the antioxidants tert-butylhydroxyanisole (BHA) and tert-butylhydroxytoluene (BHT) based on their oxidation at a glassy carbon electrode. In both instances, the analytical solution is injected into a carrier stream consisting of a solution of perchloric acid and 5% (v/v) methanol. Calibration graphs are linear in the concentration ranges 1.0–10.0, 0.1–1.0 and 0.01–0.1 mg l−1 for BHA and 1.0–8.0, 0.1–1.0 and 0.02–0.1 mg l−1 for BHT. Detection limits for BHA and BHT are 2.5 and 6.0 μg l−1, respectively. The determination of BHA in the presence of BHT is possible because the former is more easily oxidized than the latter. Other compounds usually present in commercial antioxidant mixtures, such as citric acid or propylene glycol, do not interfere, although propyl gallate does. Good results were obtained by applying the proposed flow-injection methods to determine BHA in spiked corn oil and BHT in stabilized diethyl ether samples after extraction of the analytes.

Determination of paraquat by flow-injection spectrophotometry

Abstract The flow-injection determination of Paraquat (1,1′-dimethyl-4,4′-bipyridinium) is based on its reduction with sodium dithionite in alkaline medium and detection at 605 nm. Linear calibration plots are obtained for 0.1–1.0, 1.0–10 and 5.0–30.0 mg l −1 Paraquat, the lower limit being 40 times less than that of the usual spectrophotometric method. The method is applied to determine Paraquat in spiked potable water and potatoes after preconcentration by column ion-exchange. The determination of Paraquat in different herbicide samples yielded results in good agreement with those obtained by polarographic and manual spectrophotometric methods.

Electroanalytical study of sulphamerazine at a glassy-carbon electrode and its determination in pharmaceutical preparations by HPLC with amperometric detection

An electroanalytical study of the oxidation of sulphamerazine at a glassy-carbon electrode has been made by use of different voltammetric techniques. The limiting current is diffusion-controlled, at pH 7.0, for sulphamerazine in the concentration range 2.0 x 10(-5)-1.0 x 10(-4)M. The limits of determination found for differential pulse voltammetry at a stationary electrode and at a rotating electrode were 5.9 x 10(-6) and 3.3 x 10(-6)M respectively. A reversed-phase HPLC method with amperometric detection for the analysis of sulphamerazine, sulphadiazine and phthalylsulphathiazole mixtures has been developed, and applied to a commercial pharmaceutical preparation.

Electroanalytical study of sulphadiazine at solid electrodes: determination in pharmaceutical preparations

An electroanalytical study of the sulphadiazine oxidation process at solid electrodes using different voltammetric techniques was carried out. Limiting current is diffusion-controlled in the concentration range studied. dpv at a glassy carbon electrode allows the determination of sulphadiazine within the range 1.5 × 10−5−6.0 × 10−5 mol l−1. The dpv method was applied to determine sulphadiazine in a commercial pharmaceutical preparation.

Determination of coumarins by voltammetric techniques in micellar and emulsified media

Abstract An electroanalytical study of the oxidation processes of umbelliferone and hymecromone at a glassy carbon electrode in micellar solution and emulsified medium by different voltammetric techniques is described. The non-ionic surfactant Triton X-405 in acetate-buffered medium at pH 4.8 was found to be the most suitable. Different ranges of linearity were obtained in the micellar solutions, depending on the technique used; the limits of determination for differential pulse voltammetry (DPV) at a stationary electrode were 2.9×10 −6 mol l −1 and 3.3×10 −6 mol l −1 for umbelliferone and hymecromone, respectively. In the emulsified medium formed with a mixture of toluene and ethyl acetate (3:2), the oxidation processes yielded similar results. With DPV, linear calibration plots were obtained in the ranges 1.0×10 −5 –9.0×10 −7 mol l −1 umbelliferone and 1.0×10 −5 –2.0×10 −6 mol l −1 hymecromone. The media used are predominantly aqueous so that special reference electrodes and solvent purification are not needed.

Spectrophotometric determination of carbaryl by flow injection analysis

Abstract A flow injection analysis is described for the determination of carbaryl, based on its reaction with diazotized sulfanilic acid in alkaline medium and Spectrophotometric detection at 515 nm. Calibration plots are linear within the ranges 10.0–40.0, 1.0–10.0, and 0.1 – 1.0 ppm of carbaryl. The determination and detection limits are 0.27 and 0.08 ppm of insecticide, respectively, with a coefficient of variation of 3.8% at the 0.5 ppm level. Sampling frequency is about 27 hr −1 for triplicate analysis. The method has been applied to determine carbaryl in spiked potable water, in the absence and presence of 1-naphthol, as well as in a commercial preparation, yielding good results in both samples.

Voltammetric determination of indole in micellar and emulsified media

Abstract An electroanalytical study of the indole oxidation process at a Pt electrode in micellar solution and emulsified medium was carried out using different voltammetric techniques. The non-ionic surfactant Triton X-405 was found suitable for solubilizing indole. By voltammetry at a Pt rotating disc electrode in the micellar solution formed by Triton X-405 and KNO3, indole showed one or two oxidation waves depending on both rotation rate of the electrode and indole concentration. The limiting current is diffusion-controlled in the concentration range 2.0×10−4 to 5.0×10−4 mol 1−1. In the emulsified medium formed from aliquots of indole dissolved in an ethyl acetate+n-hexane (1:49) mixture, the indole oxidation process yielded similar results. Using DPV at ΔE = 50 mV, determination of indole in micellar solutions is possible in the range 4.0×10−4 to 3.0×10−6mol 1−1, with a detection limit of 85 ppb of indole. In emulsified medium linear ip vs. indole concentration plots were obtained in the ranges 1.0×10−4 to 1.0×10−5 and 1.0×10−5 to 1.0×10−6 mol 1−1 with a detection limit of 40 pph of indole.

Polarographic study of the 1-(2,4-dimethylphenylazo)-2-naphthol (sudan II) in hydroalcoholic medium

Abstract The polarographic behaviour of the Sudan II azo-dye in a 60% hdyroalcoholic medium has been studied using different polarographic techniques. The electrochemical reaction involves a four-electron exchange in both acid and basic media, yielding the formation of 1-amino-2-naphthol and 2,4-dimethyl-aniline. The reduction process is irreversible and the limiting current is diffusion-controlled. The E 1 2 is strongly dependent on pH, involving mechanism changes, passing from acid catalysis, up to pH 5, to basic catalysis, between pH 6.3 and 10.4, and finally above pH 12 to the direct reduction of Sudan II without a previous protonation reaction. The proportionality between diffusion current and Sudan II concentration allows its polarographic determination over a wide concentration range. The determination limit using differential pulse polarography is 3.0 × 10 −7 M, with a variation coefficient of about 4% at a 6.50 × 10 −7 M concentration level.

A rapid extractive spectrophotometric method for the determination of tin in canned foods with 5,7-dichloro-8-quinolinol

A rapid method for the spectrophotometric determination of tin in canned foods, based on formation of the binary Sn(IV)-5,7-dichloro-8-quinolinol complex and extraction into chloroform has been developed. The absorption maximum at 390nm ( = 1.26 x 10(4) l.mole(-1).cm(-1)) is used for the determination. Beers law is obeyed up to 6mug of tin per ml. Organic matter is destroyed by digestion with acid. Potential interferences have been studied. The detection limit for tin is 2.5mg kg .

Separation Study of PAHs by HPLC Using A Micellar SDS Mobile Phase and Short Chain Columns

Abstract The possibility of using micellar sodium dodecyl sulfate mobile phase modified with n-propanol to separate six PAHs on apolar columns was examined. The large capacity factors found in large-chain stationary phases made the analysis impractical. The use of short-chain stationary phases and the presence of n-propanol in the mobile phase, as a modifier, significantly decreased the capacity factors but also decreased resolution, allowing separation of five PAHs in reasonable analysis times. Conditioning of the column was easy and reproducible but the effect of temperature was quite critical. The gradient technique decreased peak width significantly.