ABSTRACT:A hydride generation-inductively coupled plasma optical emission spectrometry (ICP-OES) technique was developed to determine inorganic As, including total As, As(III), and As(V), in drinking water samples in optimized conditions as follows: wavelength of 193.7 nm, integration time of 5-10 s, RF power of 1.3 kW, and the flow rates of plasma gas and auxiliary gas of 15 and 0.2 l/min for ICP-OES, the sample flow rates of 1.2 ml/min, reductant, and acid 0.4 ml/min and carrier gas 0.3 l/min, 0.4% (w/v) NaBH 4 with 40% (w/v) KI within 10 min as a reductant for total As, 0.4% (w/v) NaBH 4 for As(III) and 2 mol/l HCl for hydride generation. As(V) was obtained from the difference between total As and As(III). The linear dynamic range was 1-100 µg/l with a correlation coefficient of 0.9998. The limit of detection of total As, As(III), and As(V) was 0.38, 0.07, and 0.37 µg/l, respectively. The limit of quantification of total As, As(III), and As(V) was 1.28, 0.24, and 1.17 µg/l, respectively. 94.9-99.1% recovery for each As species was achieved. This fast and easy method was applied to determine arsenic in drinking water samples with satisfactory recovery (79-112%).
Flow injection-hydride generation-atomic absorption spectrophotometry (FI-HG-AAS) and square wave cathodic stripping voltammetry (SWCSV) were compared to detect inorganic arsenic species in lemongrass and turmeric. Two species, arsenite (As III ) and arsenate (As V ), were considered as they are known to occur in most terrestrial plants. As III and total water-soluble inorganic arsenic (TAs inorg ) were determined under different conditions.As III was selectively determined by using a soft generation condition, i.e., low HCl concentration, whereas TAs inorg was determined after pre-reduction of As V to As III with a KI/ascorbic acid mixture. The As V content was estimated as the difference between both measurements. Under optimal conditions, the limits of detection (LOD) by FI-HG-AAS were 0.02 and 0.03 µg/l for As III and TAs inorg , respectively. Relative standard deviations (n = 9) of less than 4% were obtained for both inorganic arsenic species. The accuracy was also verified by analysing spiked samples and certified reference material: CTA-VTL-2 (Virginia Tobacco leaves). The recoveries of both species were found to be between 90 and 115%. The determination of inorganic arsenic species by SWCSV in the samples is based on the formation of a copper-arsenic intermetallic compound at the hanging mercury drop electrode (HDME) during the preconcentration step. Only As III was deposited on the Hg electrode when Cu was present in the HCl medium. TAs inorg can be determined by reducing As V to As III with sodium thiosulphate. As V is quantified as the difference. At optimum conditions, the LOD for As III and As V were 0.5 and 0.4 µg/l, respectively. Relative standard deviations (n = 10) of less than 5% were obtained and the method was validated by analysing the spiked samples and certified reference material. FI-HG-AAS showed better LOD than SWCSV for both inorganic arsenic species. There was, however, a strong agreement between TAs values obtained by using FI-HG-AAS and SWCSV technique in lemongrass, turmeric, and the certified reference material (CTA-VTL-2). As V was the main inorganic arsenic species found in lemongrass and turmeric. The results confirm that the As content of both samples do not exceed the food safety limits for Thailand and several countries.
A sensitive and rapid method to analyse Pb(II) in canned fish samples was developed using square-wave adsorptive cathodic stripping voltammetry based on the adsorptive accumulation of 8-hydroxyquinoline complexes of Pb(II) onto a hanging mercury drop electrode, followed by reduction of adsorbed species by voltammetric scan with square wave pulse modulation. The optimum conditions were found to be 0.1 M CH 3 COONH 4 as a supporting electrolyte, pH 7.5, 8-hydroxyquinoline concentration of 15 µM, accumulation potential −0.70 V (versus Ag/AgCl), accumulation time 120 s, scan rate 0.3 V/s, and pulse amplitude 20 mV. Under the optimum conditions a linear calibration graph was obtained in the concentration range of 0.5-90.0 µg/l with correlation coefficient 0.9973, a limit of detection of 0.108 µg/l, and a limit of quantification of 0.360 µg/l. The recovery values were obtained in the range 93.7-95.1%. The relative standard deviations (n = 10) at lead concentration 5.0 µg/l was 2%. The method was successfully applied to the determination of lead content in canned fish samples. The concentration of Pb(II) in canned fish samples (wet weight) was found to be in the range of 0.121-0.285 µg/g, which is lower than the limit (1.00 µg/g) issued by the Ministry of Public Health of Thailand.
ABSTRACT:A sample preparation method has been developed to detect cadmium and lead in commercial frozen seafood samples. After being digested with concentrated HNO 3 in a closed polypropylene vessel, the clear sample solution was separated and preconcentrated by solid phase extraction using octadecyl silica membrane discs modified with 8-hydroxyquinoline prior to determination by graphite furnace atomic absorption spectrometry (GFAAS). The preconcentration conditions including pH, ligand quantity, eluent concentration, and volume were found to be effective with 10.0 mg of 8-hydroxyquinoline in 2.0 ml ethanol and pH 6.0. The retained cadmium and lead were efficiently eluted with 5.0 ml of 1.0 M HNO 3 and determined by GFAAS. The detection limits for cadmium and lead were 0.073 µg/l and 0.332 µg/l, respectively. The proposed method was tested with the certified reference material, DORM-2 (Dogfish muscle), with good agreement. The recoveries were found to be 100-103% (n = 4) for Cd and 92-108% (n = 5) for Pb with relative standard deviation (n = 5) of 3% for Cd and 4% for Pb. The extraction was found to be unaffected by coexisting ions. The method was applied satisfactorily to the seafood samples and trace levels of cadmium and lead were found.
A simple method for determination of copper contents in natural rubber (NR) latex based on the complex formation between Cu(II) and zinc diethyldithiocarbamate (Zn(II)-DDTC) and extraction with dichloromethane followed by visible spectrophotometry at 435 nm was developed. A low-cost wet digestion system for NR latex was adopted by digesting a sample in a Pyrex tube with the a mixture of concentrated H 2 SO 4 and concentrated HNO 3 at 180°C. Under the optimum conditions, the linear range of 0.1-4.0 mg/l (R 2 > 0.99), the limit of detection and the limit of quantification were 0.0356 and 0.1188 mg/l, respectively, the intra-day (n = 10) and inter-day (n = 6) relative standard deviations were 0.4-3.2 and 0.8-3.4%, respectively, and recoveries of 92-101% were obtained. Fe(III), Mn(II), and Zn(II) did not interfere with the tolerance limit of 9.0, 9.0, and more than 500 mg/l, respectively, which are higher than their usual concentrations in latex. The method was applied to copper determination in a concentrated latex sample prepared from field latex samples by centrifugation. The copper content was found to be 6.8-7.0 mg/kg (on total solids content) and copper content in the field NR latex sample was 16.6-23.8 mg/kg (on total solids content). No difference was observed between the proposed method and ICP-OES as well as between the proposed digestion and Kjeldahl digestion.
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