Biomedical subjects

J Shiowatana

Publications and source records attributed to J Shiowatana.

5 recordsLinked to original sources

PubMed2005

Assessment of lead availability in contaminated soil using isotope dilution techniques.

Isotope dilution methods using a stable isotope tracer ((207)Pb) were developed for the determination of Pb availability in contaminated soils. The methods included determination of E values (isotopically exchangeable pool), L values (plant labile pool) and isotopic exchange kinetics (IEK). Isotopically exchangeable Pb was monitored at different exchange times based on measurement of the (207)Pb/(208)Pb ratio in soil solution following addition of the tracer. The rate of decrease in the (207)Pb/(208)Pb ratio in solution could be described by using the same IEK equation as used previously with radioisotope tracers. The amounts of isotopically exchangeable Pb in Pb-contaminated soils estimated from long-term IEK parameters were in good agreement with directly determined E values up to 15 days. However, values of some of the fitted IEK parameters cast doubts on the validity of using the IEK approach with (207)Pb, most probably as a result of irreversible fixation of some of the spike by reactive surfaces in the soils. Estimation of isotopically exchangeable Pb using short-term kinetics data was unsuccessful, substantially underestimating E values. Results for the control (uncontaminated) soil were highly variable, most probably as a result of fixation of tracer by the soil and poor analytical precision due to low solution Pb concentrations. A compartmental analysis of the variation in E values with time indicates a good potential for estimating bioavailable Pb in contaminated soils. The amounts of available Pb obtained from summation of the E(1)(min) and E(1 min-24 h) pools (E((available))), accounting for an average of 57.62% of total soil Pb, were significantly correlated with both the L values and with Pb extracted from soil with EDTA.

Chelating Agents↗

PubMed2001

A flow system for the determination of metal speciation in soil by sequential extraction.

A flow extraction system with on-line and off-line flame atomic absorption spectrometric (FAAS) detection was developed to speed up, facilitate, and improve the accuracy of sequential extraction for metal speciation in solid materials. A flow extraction system with off-line detection was more advantageous than the on-line detection. In the proposed system, extraction was performed in a closed extraction chamber where extractants were flowing through sequentially. The extract from each extraction was collected in 4-10 fractions to obtain a total of approximately 180 ml for subsequent FAAS determination. The system is simple, easy to construct and operate. It has less risk of contamination and human error. A widely used three-step sequential extraction scheme was used to evaluate the novel system by analyzing Ca, Fe, Mn, Cu, and Zn in a certified reference material. The extraction time for three-step sequential extraction of soil sample was 4 h. The analytical results for Ca, Fe, Mn, Cu, and Zn of a soil certified reference material using the proposed system were compared with those of the conventional batch extraction.

Environmental Monitoring↗

PubMed2001

Continuous and stopped flow injection for catalytic determination of total iodine in urine.

This paper describes the use of flow injection (FI) techniques for the determination of iodine in urine, based on the catalytic effect of iodide in the redox reaction between Ce(IV) and As(III). The proposed procedures minimize errors in the conventional batch method arising from the reading of absorbance at a fixed time after addition of Ce(IV) reagent. Two FI systems, for the continuous and stopped modes of operation were assembled. In the continuous-FI system, a thermostated bath was used to increase the sensitivity. However this is not necessary for the stopped-FI system. The two systems are comparable in terms of sensitivity, sample throughput and detection limit. The continuous-FI and the stopped-FI exhibited detection limits (3 sigma) of 2.3 and 3 micrograms I l-1 respectively. Both systems have equal sample throughputs of 35 samples h-1. Calibration plots for both techniques are linear. The FI procedures provide very short analysis times compared to the batch procedure. Using the linear regression test, there is no significant difference between the results from the four methods, i.e., continuous-FI, stopped-FI, conventional method and ICP-MS. The proposed methods are readily applicable for automation and can be an alternative to the conventional procedure for the survey of the iodine deficiency disorder. A condition for sample digestion is also proposed to reduce the amount of chloric acid required for complete digestion. Kinetic information of the reaction can also be obtained from the stopped flow mode.

Flow Injection Analysis↗

PubMedDate not supplied

Fractionation of arsenic in soil by a continuous-flow sequential extraction method.

Batch sequential extraction techniques for fractionating metals or metalloids in soils are time consuming and subject to several potential errors. The development of a continuous-flow sequential extraction method for soil As is described and assessed, having the benefits of simplicity, rapidity, less risk of contamination, and less vulnerability to changes in extraction conditions compared with traditional batch methods. The validated method was used to fractionate soil As using water, NaHCO3, NaOH, and HCl, followed by digestion of the residue with HNO3 and HF acids. The extracts and digests were analyzed for As by graphite furnace atomic absorption spectrometry. Good recoveries of total soil As (97-115%) were obtained and fractionation data generally comparable with those obtained using conventional batch techniques. Soils from a tin-mining area in Thailand and soils from As-contaminated cattle (Bos taurus) dip sites in Australia were used to test the applicability of the method, and to demonstrate the usefulness of the extractogram obtained. The ability to produce detailed extractograms for As and other elements (Al, Fe, and Ca) enabled an examination of elemental associations in individual fractions. With the exception of As extracted with HCl, the extractograms generally support previous suggestions of the likely forms or associations of As present in the different soil fractions.

Animals↗

PubMedDate not supplied

A novel continuous-flow sequential extraction procedure for metal speciation in solids.

A continuous-flow extraction system was developed to speed up, facilitate, and improve the accuracy of the chemical fractionation of metals in solid materials. A three-step sequential extraction scheme was used to evaluate the novel system by analyzing calcium (Ca), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in a soil certified reference material (National Institute of Standards and Technology [NIST] SRM 2710). In the proposed system, extraction occurred in a closed chamber through which extractants were passed sequentially. The extracts were collected in a number of subfractions for subsequent name atomic absorption analysis. Apart from the advantages of simplicity, speed, and less risk of the contamination that flow analysis systems usually possess, the continuous-flow system can improve the accuracy of chemical fractionation of metals by sequential extraction. The system ensures that extraction is performed at designated pH values without any need of adjustment. Variation of sample weight to chamber volume ratios from 1:12 to 1:40 had no effect on the extractability of the metals studied. In the extraction of the acid soluble fraction, concentrations of acetic acid in the range 0.11 to 0.5 mol L(-1) had no significant effect on the amounts of metals extracted, except Fe. Increasing the concentration of hydroxylamine in the reducible fraction step from 0.04 to 0.5 mol L(-1) affected the extraction efficiency for Fe, Mn, and Zn. The extraction profile, rather than a single value of extracted concentration, of each element offers additional information about the kinetics of leaching processes and chemical associations between elements in the solid materials.

Environmental Monitoring↗