Multi-residue analytical method for trace detection of new-generation pesticides in vegetables using gas chromatography-tandem mass spectrometry.

A GC-MS/MS method with low solvent consumption and easy operation was developed to simultaneously determine ten new-generation pesticides, namely fenobucarb, acetochlor, pretilachlor, fipronil, trifloxystrobin, fluazifop-p-butyl, isoprothiolane, tebuconazole, cypermethrin and difenoconazole in leafy vegetables. Influences from ultrasonic sample extraction and the clean-up steps to reduce matrix effects were investigated. Under suitable conditions, good linearity (deviation of back calculated concentration from true concentration lower than 20%) was achieved for all studied pesticides; the method detection limits (MDLs) ranged from 1.4 to 3.6 ng g-1 wet weight. For mustard green and green onion the method yielded good recoveries at two spiking levels (201 and 100 ng g-1) ranging from 80% to 111% (n = 5). The repeatability, expressed as relative standard deviation (RSD), was lower than 11% (n = 5). The method was successfully used to quantify pesticide residues in 207 vegetable samples (green onions, mustard greens, and lettuce) collected in Thua Thien Hue and Quang Binh Provinces, Central Vietnam. The insecticide cypermethrin was found at critical levels in 98% of the vegetable samples. Green onions had high pesticide residues with a significant number of samples containing pesticides at concentrations exceeding the maximum residue levels (MRLs).

Metal speciation in sediment and bioaccumulation in Meretrix lyrata in the Tien Estuary in Vietnam.

The concentrations of seven toxic metals (cadmium (Cd), nickel (Ni), chromium (Cr), arsenic (As), lead (Pb), copper (Cu), and zinc (Zn)) were determined in sediments and the soft tissues of a bivalve species (Meretrix lyrata) collected from the Tien Estuary in Tien Giang Province, South Vietnam. The total metal concentrations in sediments (mg/kg dry weight) increased as Cd (0.06) < Cu (5.0) < Pb (13.9) < As (16.3) < Ni (24) < Cr (50) < Zn (62). Speciation analysis revealed that these metals existed mainly in the residual fraction (43-94%), followed by the Fe-Mn oxide-bound (5-35%) and organic/sulfide-bound (0.6-9.2%) fractions. The metal concentrations in M. lyrata (mg/kg dry weight) were in the ranges of 1.3-1.9 (Cd), 1.5-2.8 (Ni), 1.8-3.4 (Cr), 11-16 (As), 0.3-0.6 (Pb), 6.9-8.7 (Cu), and 95-128 (Zn), which are safe for human consumption. The order of the mean biota-sediment accumulation factor (BSAF) of the metals in the non-residual fractions of the sediment for M. lyrata was Cd > Cu > As > Zn > Cr > Ni > Pb. The Risk Assessment Codes (RACs) suggest that the highest mobility of Cd (with RAC = 37%) poses greater environmental risk to aquatic biota. Correlation analysis results show that M. lyrata can be used as a biomonitor of Cd and Cu pollution in the exchangeable, acid-soluble, and non-residual sediment fractions.

Simultaneous Determination of Hydrochlorothiazide and Losartan Potassium in Pharmaceutical Product by UV-Vis Spectrophotometric Method with Kalman Filter Algorithm.

In this paper, hydrochlorothiazide (HCT) and losartan potassium (LSP) in tablets are simultaneously determined with UV-Vis spectrophotometry and chemometrics without separation. The spectra of standard and sample solutions were recorded in the wavelength from 220 to 300 nm at 1.0 nm intervals. The concentrations of HCT and LSP in the sample solutions were computed with the Kalman filter algorithm written on the Microsoft Excel 2016 and Visual Basic for Applications (VBA) platform. The method validation was determined via the accuracy and repeatability of measurements when analyzing HCT and LSP in the Splozarsin Plus tablet and comparing the mean values of their contents in the sample with those analyzed with HPLC. The proposed method is simple with a low cost compared with the standard HPLC method.

Determination of Chromium in Natural Water by Adsorptive Stripping Voltammetry Using In Situ Bismuth Film Electrode.

Development of adsorptive stripping voltammetry (AdSV) combined with in situ prepared bismuth film electrode (in situ BiFE) on glassy carbon disk surface using diethylenetriamine pentaacetic acid (DTPA) as a complexing agent and NO3 - as a catalyst to determine the trace amount of chromium (VI) is demonstrated. According to this method, in the preconcentration step at E dep = -800 mV, the bismuth film is coated on the surface of glassy carbon electrodes simultaneously with the adsorption of complexes Cr(III)-DTPA. In addition to the influencing factors, the stripping voltammetry performance factors such as deposition potential, deposition time, equilibration time, cleaning potential, cleaning time, and technical parameters of differential pulse and square wave voltammetries have been investigated, and the influence of Cr(III), Co(II), Ni(II), Ca(II), Fe(III), SO4 2-, Cl-, and Triton X has also been investigated. This method gained good repeatability with RSD <4% (n = 9) for the differential pulse adsorptive stripping voltammetry (DP-AdSV) and RSD < 3% (n = 7) for the square wave adsorptive stripping voltammetry (SqW-AdSV), and low limit of detection: LOD = 12.10-9 M ≈ 0.6 ppb (at a deposition potential (E dep) of -800 mV and the deposition time (t dep) of 50 s) and LOD = 2.10-9 M ≈ 0.1 ppb (at E dep = -800 mV and t dep = 160 s) for the DP-AdSV and SqW-AdSV, respectively. This method has been successfully applied to analyze chromium in natural water.

Voltammetry Determination of Pb(II), Cd(II), and Zn(II) at Bismuth Film Electrode Combined with 8-Hydroxyquinoline as a Complexing Agent.

A novel method was developed for the simultaneous determination of Pb(II), Cd(II), and Zn(II) based on the cathodic stripping response at a bismuth film electrode associated with oxine as a chelating agent. The developed method provided a high and sharp electrochemical response compared with the method without oxine. A linear response of peak currents was observed for Pb(II), Cd(II), and Zn(II) concentration in the range from 2 ppb to 110 ppb. The detection limits of Pb(II), Cd(II), and Zn(II) were 0.45, 0.17, and 0.78 ppb, respectively. This method was successfully applied to the determination of Pb(II), Cd(II), and Zn(II) in lake-water and river-water samples. The metals were detected at the ultratrace level, showing the feasibility of the proposed method for environmental applications.