Determination of quinclorac by adsorptive stripping voltammetry in rice samples without sample pretreatment.

A novel voltammetric method with practically no sample pretreatment was developed for determination of Quinclorac (QNC) in rice samples by using a working Carbon Paste Electrode (CPE) modified with ionic liquid, with deposition potential (ED) of -1.43 V for 30 s in NaOH 0.01 mol L-1. The systematic influence of cations and anions of imidazole ionic liquids on the composition of CPE has evaluated. The best electrode composition was 65% (w/w) of graphite powder, 30% (w/w) of mineral oil and 5.0% (w/w) of C4min+BF4- ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate). The matrices analyzed were deionized water and extracts of upland rice: white, brown, peel and seed. The limits of quantification ranged between 0.954 mg kg-1 and 3.61 mg kg-1. The recovery percentages of QNC in rice samples ranged between 90% and 121%. The simplicity and good analytical frequency enable the proposed method to be used to obtain preliminary information on the presence of QNC, prior to the implementation of more detailed, costly and elaborate quantitative analyses. The technique can be applied in the study and evaluation of sorption mechanisms, metabolization of the herbicide in plants and its persistence and degradation in the environment.

Forensic Investigation of Formaldehyde in Illicit Products for Hair Treatment by DAD-HPLC: A Case Study.

The illegal use of formalin (commercial formaldehyde) in cosmetic products harms the health of individuals exposed to this substance. Over the last years, the commercial availability of these products, especially those containing irregular dosage of formaldehyde, has increased in Brazil. This work analyzes some products for hair treatment available in the Brazilian market and verifies their safety. The adopted analytical methodology involved sample derivatization with 2,4-dinitrophenylhydrazine, followed by high-performance liquid chromatography with ultraviolet detection (UV-VIS) at λ = 365 nm. The limit of quantification is 2.5 × 10-3% w/w, and the recovery tests were around 93%. Some of the samples contained high and illegal formaldehyde levels ranging from 9% to 19% (w/w) and others presented suitable concentrations of the analyte. On the basis of the results, this work discusses the efficiency and practicality of this analytical method for forensic purposes.

Cathodic stripping voltammetric determination of arsenic in sugarcane brandy at a modified carbon nanotube paste electrode.

We have developed an eletroanalytical method that employs Cu(2+) solutions to determine arsenic in sugarcane brandy using an electrode consisting of carbon paste modified with carbon nanotubes (CNTPE) and polymeric resins. We used linear sweep (LSV) and differential-pulse (DPV) voltammetry with cathodic stripping for CNTPE containing mineral oil or silicone as binder. The analytical curves were linear from 30 to 110µgL(-1) and from 10 to 110µgL(-1) for LSV and DPV, respectively. The limits of detection (L.O.D.) and quantification (L.O.Q.) of CNTPE were 10.3 and 34.5µgL(-1) for mineral oil and 3.4 and 11.2µgL(-1) for silicone. We applied this method to determine arsenic in five commercial sugarcane brandy samples. The results agreed well with those obtained by hydride generation combined with atomic absorption spectrometry (HG AAS).

Simultaneous determination of neutral nitrogen compounds in gasoline and diesel by differential pulse voltammetry.

The presence of trace neutral organonitrogen compounds as carbazole and indole in derivative petroleum fuels plays an important role in the car's engine maintenance. In addition, these substances contribute to the environmental contamination and their control is necessary because most of them are potentially carcinogenic and mutagenic. For those reasons, a reliable and sensitive method was proposed for the determination of neutral nitrogen compounds in fuel samples, such as gasoline and diesel using preconcentration with modified silica gel (Merck 70-230 mesh ASTM) followed by differential pulse voltammetry (DPV) technique on a glassy carbon electrode. The electrochemical behavior of carbazole and indole studied by cyclic voltammetry (CV) suggests that their reduction occurs via a reversible electron transfer followed by an irreversible chemical reaction. Very well resolved diffusion controlled voltammetric peaks were obtained in dimethylformamide (DMF) with tetrabutylammonium tetrafluoroborate (TBAF(4) 0.1molL(-1)) for indole (-2.27V) and carbazole (-2.67V) versus Ag|AgCl|KCl(sat) reference electrode. The proposed DPV method showed a good linear response range from 0.10 to 300mgL(-1) and a limit of detection (L.O.D) of 7.48 and 2.66mugL(-1) for indole and carbazole, respectively. The results showed that simultaneous determination of indole and carbazole presents in spiked gasoline samples were 15.8+/-0.3 and 64.6+/-0.9mgL(-1) and in spiked diesel samples were 9.29+/-1 and 142+/-1mgL(-1), respectively. The recovery was evaluated and the results shown the values of 88.9+/-0.4 and 90.2+/-0.8% for carbazole and indole in fuel determinations. The proposed method was also compared with UV-vis spectrophotometric measures and the results obtained for the two methods were in good agreement according to the F and t Student's tests.

Determination of acetaldehyde in fuel ethanol by high-performance liquid chromatography with electrochemical detection.

The cyclic voltammetric behavior of acetaldehyde and the derivatized product with 2,4-dinitrophenylhydrazine (DNPHi) has been studied at a glassy carbon electrode. This study was used to optimize the best experimental conditions for its determination by high-performance liquid chromatographic (HPLC) separation coupled with electrochemical detection. The acetaldehyde-2,4-dinitrophenylhydrazone (ADNPH) was eluted and separated by a reversed-phase column, C18, under isocratic conditions with the mobile phase containing a binary mixture of methanol/LiCl(aq) at a concentration of 1.0 x 10(-3) M (80:20 v/v) and a flow rate of 1.0 mL min(-1). The optimum condition for the electrochemical detection of ADNPH was +1.0 V vs. Ag/AgCl as a reference electrode. The proposed method was simple, rapid (analysis time 7 min) and sensitive (detection limit 3.80 microg L(-1)) at a signal-to-noise ratio of 3:1. It was also highly selective and reproducible [standard deviation 8.2% +/- 0.36 (n = 5)]. The analytical curve of ADNPH was linear over the range of 3-300 mg L(-1) per injection (20 microL), and the analytical recovery was > 99%.