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A HPLC method with automated column switching and UV-diode array detection is described for the simultaneous determination of Vitamin D(3) and 25-hydroxyvitamin D(3) (25-OH-D(3)) in a sample of human plasma. The system uses a BioTrap precolumn for the on-line sample cleanup. A sample of 1ml of human plasma was treated with 2ml of a mixture of ethanol-acetonitrile (2:1 (v/v)). Following centrifugation, the supernatant was evaporated to dryness under a stream of dry and pure nitrogen. The residue was reconstituted in 250muL of a solution of methanol 5mmoll(-1) phosphate buffer, pH 6.5 (4:1 (v/v)), and a 200mul aliquot of this solution was injected onto the BioTrap precolumn. After washing during 5min with a mobile phase constituted by a solution of 6% acetonitrile in 5mmoll(-1) phosphate buffer, pH 6.5 (extraction mobile phase), the retained analytes were then transferred to the analytical column in the backflush mode. The analytical separation was then performed by reverse-phase chromatography in the gradient elution mode with the solvents A and B (Solvent A: acetonitrile-phosphate buffer 5mmoll(-1), pH 6.5; 20:80 (v/v); solvent B: methanol-acetonitrile-tetrahydrofuran, 65:20:15 (v/v)). The compounds of interest were detected at 265nm. The method was linear in the range 3.0-32.0ngml(-1) with a limit of quantification of 3.0ngml(-1). Quantitative recoveries from spiked plasma samples were between 91.0 and 98.0%. In all cases, the coefficient of variation (CV) of the intra-day and inter-day-assay precision was

In this work, a flow analysis system with hydride generation and Fourier transform infrared (FTIR) spectrometric detection has been developed for the determination of antimony in pharmaceuticals. The method is based on the on-line mineralization/oxidation of the organic antimonials present in the sample and pre-reduction of Sb(V) to Sb(III) with K(2)S(2)O(8) and KI, respectively; prior to the stibine generation. The gaseous SbH(3) is separated from the solution in a gas phase separator, and transported by means of a nitrogen carrier into a short pathway (10 cm) IR gas cell, where the corresponding FTIR spectrum is acquired by accumulating 3 scans in a continuous mode. The 1893 cm(-1) band was used for the quantification of the antimony. The procedure is carried out in a closed system, which reduces sample handling and makes possible the complete automation of the antimony determination. The figures of merit of the proposed method (linear range: 0-600 mg l(-1), limit of detection (3sigma)=0.9 mg l(-1), limit of quantification (10sigma)=3 mg Sb l(-1), precision (R.S.D.) less than 1% and sample frequency=28 h(-1)), are appropriate for the designed application. Furthermore, precise and accurate results were found for the analysis of different antimonial pharmaceutical samples, indicating that the methodology developed represents a valid alternative for the determination of antimony in pharmaceuticals, which could be suitable for the routine control analysis.

This report describes the determination of paraquat (PQ) in human blood plasma samples by a direct-injection reversed-phase ion-pair chromatographic method. Blood plasma filtrate was injected directly into the LiChrospher(R) RP-18 alkyl-diol silica (ADS) precolumn integrated in a column switching system using a mixture of 3% 2-propanol and 10 mM sodium octane sulfonate (SOS) in a 0.05 M phosphate buffer (pH 2.8). After washing with this phase, the ADS precolumn was back-flushed with the analytical mobile phase consisting of 40% of methanol and 10 mM SOS in a 0.05 M phosphate buffer (pH 2.8) at a flow rate of 1.0 ml min(-1), in order to carry the analyte to a conventional reversed-phase analytical column, where the separation of PQ was achieved and finally detected by UV at 258 nm. The recoveries of PQ from human blood plasma samples ranged between 95.0 and 99.5% at nine different concentrations (from 0.05 to 3.00 microg of PQ ml(-1)) with coefficients of variation <2.5% (n=3). The precision expressed as relative standard deviation was below 3.5% for between-day and below 4.3% for within-day measurements (n=5). The detection limit (signal-to-noise ratio, S/N>3) was 0.005 microg ml(-1) with an injection volume of 200 microl. The proposed method is promising for the identification and quantification of PQ at low concentration levels and is suitable for its analysis in human blood plasma samples from intentional or accidental poisonings cases with a sample throughput of 5 samples per hour.

An on-line flow injection (FI) precipitation-dissolution system with microwave-assisted sample digestion has been developed for the electrothermal atomic absorption spectrometry (ETAAS) determination of trace or ultratrace amounts of molybdenum in human blood serum and whole blood samples. After the exposure of the sample to microwave radiation, the on-line precipitation of molybdenum was achieved by the merging-zone of a 0.5-ml plug of sample with a plug of potassium ferrocyanide, which were carried downstream with a solution of 0.5 mol l(-1) of HNO(3). The interfering effects of iron and copper were minimized by the introduction of a flow of a 5% (w/v) sodium potassium tartrate (for iron) and 2% (w/v) of thiourea (for copper and zinc) in a 5% (v/v) ammonia and 2% (v/v) ammonium chloride solution previous to the precipitation reaction. The reddish-brown precipitate of molybdenyl ferrocyanide was collected on the walls of a knotted reactor. The precipitate was dissolved with the introduction of 1 ml of a 3.0 mol l(-1) NaOH solution and the best performance in terms of detection limit and precision was achieved when a sub-sample of 140 mul was collected in a capillary of a sampling arm assembly, to introduce 20 mul volumes into the atomizer by means of positive displacement with air through a time-based injector. A detection limit (3sigma) of 0.1 mug Mo l(-1) using an aqueous standard solution was obtained. The method is quantitative and is applied over the range 0.2-20.0 mug Mo l(-1). The precision of the method evaluated by ten replicate analyses of aqueous standard solutions containing 0.5 and 1.0 mug Mo l(-1) was 2.8 and 3.1% (relative standard deviation, RSD) (for n=5), respectively. Whereas, the precision evaluated by five replicate analysis of a serum and a whole blood sample were 3.3 and 3.8% RSD. An enrichment factor of ca. 3.5 was achieved with the introduction of 0.5 ml aqueous standard solutions at a sample flow rate of 1.0 ml min(-1). Recoveries of spiked molybdenum in blood serum and whole blood were in the ranges 96-102 and 94-98%, respectively. The results obtained for two human whole blood certified reference materials were in good agreement with the indicative values.

In this work total (Si-tot) and 'soluble' or reactive (Si-sol) concentrations of silicon in natural and tap waters were sequentially determined by electrothermal atomic absorption spectrometry (ETAAS). First, samples were on-line diluted based on the merging-zone principle in order to allow the determination of Si-tot within the 300-1000 mugSil(-1) range. After the dilution process, a sub-sample was collected in the capillary of a sampling arm assembly (SAA). Thereafter, samples were subject to a precipitation/dissolution process in order to allow the determination of Si-sol within the 280-850 mugSil(-1). Si-sol was precipitated with ammonium chloride and collected on the walls of a knotted coil. The precipitate was dissolved with ammonium molybdate in an acidic medium (HNO(3)) and a sub-sample was then collected in the SAA. In both cases, 10 mul volumes of the sub-sample were injected into the atomizer with the previous introduction of 20 ng of Eu as chemical modifier (10 mul) by the spectrometer autosampler. The recovery values obtained with natural waters spiked samples were over 46% and the agreement between observed and certified samples values was good. The proportion of Si-sol in comparison with the Si-tot was high (85-95%) in most natural waters. The precision of the method was 2.4-3.5 and 4.5-6.2% (n=10) for the determination of Si-tot and Si-sol, respectively.

In this paper, the on-line coupling of solid-phase extraction, based on a restricted-access support with high-performance reverse phase chromatography for the analysis of carbamazepine (CBZ) and carbamazepine-10,11-epoxide (CBZ-E) in human plasma samples is described. A precolumn packed with 25 mum C(18) alkyl-diol support is used for direct plasma injection. Using column-switching techniques, the analytes were enriched on the precolumn by a 5 mM phosphate buffer (pH 7) with 2% of methanol solution at a flow-rate of 0.8 ml min(-1), while proteins and endogenous hydrophilic substances in plasma were washed off to waste. The enriched analytes were then back-flushed onto the analytical C(18) column, separated by a mixture of 10 mM phosphate buffer (pH 7) acetonitrile (70:30 v/v) solution at a flow-rate of 1.0 ml min(-1) and detected by the ultraviolet absorbance set at 212 and 285 nm and without transfer loss. Linear calibration graphs were obtained for sample injection volumes of 50 (0.2-4.0 of mug of CBZ ml(-1) and 0.1-5.0 mug of CBZ-E ml(-1), respectively), and 20 mul (5.0-20.0 mug of CBZ ml(-1)); in either case the r-value was >0.9963. Recoveries from spiked plasma samples were quantitative for both analytes and the coefficients of variation were below 3.83%. The lowest samples concentrations that can be quantified with acceptable accuracy and precision was 0.2 mug CBZ ml(-1) and 0.1 mug CBZ-E ml(-1) when a sample volume of 50 mul was injected. Concentrations of 0.08 and 0.05 mug ml(-1) of CBZ and CBZ-E were considered the limit of detection for a signal-to-noise ratio of 3. Furthermore, the developed column-switching method was successfully applied to the determination of CBZ and CBZ-E in plasma samples of patients submitted to CBZ therapy.

A new analytical procedure for the speciation of antimony in liver tissues is presented here. For this purpose, a flow injection system has been developed for the treatment of samples and the determination of antimony by hydride generation - atomic absorption spectrometry. The method involves the sequential and the on-line extraction of antimony(III) and antimony(V) from solid lyophilized blood and hamsters liver tissues, with 1.5 mol l(-1) acetic acid and 0.5 mol l(-1) sulfuric acid for Sb(III) and Sb(V), respectively. Reduction of Sb(V) to Sb(III) for stibine generation is effected by the on-line pre-reduction with l-cysteine. The linear ranges were 2.5-20 and 1.0-25 mug l(-1) of Sb(III) and Sb(V), respectively. The detection limits (3sigma) were 1.0 mug l(-1) for Sb(III) and 0.5 mug l(-1) for Sb(V). The relative standard deviation values for fifteen independent measurements were 2.1 and 1.8% for Sb(III) and Sb(V), respectively. The recovery studies performed with samples of cattle liver provided results from 98 to 100% for Sb(III) and from 100 to 103% for Sb(V) for samples spiked with single species. For samples spiked with both Sb(III) and Sb(V), the recovery varied from 97 to 103% for Sb(III) and from 101 to 103% for Sb(V).

In this study a flow injection (FI) system used in conjunction with hydride generation (HG), atomic absorption spectrometry (AAS) and microwave (MW) aided pre-reduction of selenite (Se(IV)) to selenate (Se(IV)) with HCl:HBr has been developed in order to differentiate both inorganic selenium species. As full control of the MW reduction step is possible, the experimental approach allows the use of milder acidic conditions (10% v/v of HCl and HBr) than those conventionally accomplished with hydrochloric acid alone (>/=50% v/v). Experimental parameters were optimized by the univariate optimization method. In either case, the linear range was from 1.0 to 30 mug l(-1). The detection limits based on 3sigma of the blank signal were 0.25 mug l(-1) for Se(IV) and 0.30 mug l(-1) for Se(VI). The reproducibility, about 3% RSD and recoveries of different amounts of Se(VI) and Se(IV) added to water and orange juice samples (97-103%) were good. The main advantage of the proposed method is that the sequential determination of Se(IV) and Se(VI) is performed at a high sampling frequency (ca. 50 samples per h) in a closed system without Se losses, and with a minimum sample waste, operator attention, and sample manipulation.

A flow injection (FI) on-line precipitation-dissolution was developed for electrothermal atomic absorption spectrometry (ETAAS) determination of (ultra)trace amounts of beryllium in water samples. Beryllium was precipitated quantitatively with NH(4)OH+NH(4)Cl and collected in a knotted tube of Tygon without using a filter, while the other matrix components flowed downstream to waste. The precipitate was dissolved with nitric acid and a sub-sample was collected in a capillary of a sampling arm assembly, to introduce 10 mul volumes into the graphite tube by means of positive displacement with air through a time-based injector. This sequence was timed to synchronize with the previous introduction of 6 mug of Lu (in 20 mul) by the spectrometer autosampler. The effect of a number of possible cations on the beryllium precipitation process was studied. While, the addition of Ba(2+), Sr(2+), Ca(2+), Mg(2+), Mn(2+), Zn(2+), Co(2+) and Ni(2+) did not produce any perceptible precipitate on the reaction coil walls, the addition of Al(3+), Cr(3+) and Fe(3+) produced large precipitated particles. However, their tolerance limit was well above the levels at which theses species are commonly found in most natural waters. The detection limit (3sigma) of 25 ng l(-1) in the sample solution was obtained. The precision of the method, evaluated by ten replicate analyses of solutions containing 20 and 200 pg of beryllium were 4.8 and 4.0% (n=5), respectively. Enrichment factors from 7.0 to 10.3 and from 10.5 to 13.8 were obtained for precipitation times from 25 to 38 s and from 43 to 50 s for waste and tap waters, respectively. These results indicate that the enrichment factor was limited by the interference of some matrix metals which could precipitate as hydroxides (or related species) and be retained in the reaction coil. The integrated system permits fully automated operation, avoiding time-consuming manual work and enhancing the reproducibility and precision of the determination of beryllium. The results obtained for the determination of beryllium in certified reference materials (trace elements in water), together with the good recovery of spiked analytes, demonstrate the applicability of the procedure to the analysis of natural waters.

An on-line automated flow injection system with microwave-assisted sample digestion for the electrothermal atomic absorption spectrometric determination of bismuth in biological materials is described. After the exposure of the sample to microwave radiation, the analyte was subject to a precipitation/dissolution process. Bismuth was precipitated with the stannite ion in basic medium and collected on the walls of a knotted coil, while the other matrix components flowed downstream to waste. The precipitate was dissolved with nitric acid and a sub-sample was collected in a capillary of a sampling arm assembly, to introduce 20 mul volumes into the graphite tube by means of positive displacement with air through a time-based injector. The analytical figures of merit were first evaluated by filling the sampling arm with a standard solution of bismuth and thereafter injecting aliquots of this solution into the atomizer. The calibration graph was linear from the detection limit (8 pg) to 1.2 ng of bismuth. The sensitivity was of 26.8 mug l(-1) for 0.2 A-s and the characteristic mass (m(o)) was of 11.8 pg/0.0044 A-s. The precision of the method, evaluated by replicate analyses of solutions containing 20 and 200 pg of bismuth, were 5.5 and 3.0% (n=10), respectively. When solutions were introduced in the flow system here described, the calibration graph was linear in the range 0.04-6.0 mug l(-1), which means that a preconcentration factor of 10 was obtained for bismuth. The precision slightly deteriorated, e.g. the replicate analysis of solutions containing 1 and 10 pg of bismuth were 7.1 and 5.3% (n=10), respectively. However, the recoveries values obtained with urine and whole blood bismuth spiked samples were over 96.5% and the agreement between observed and certified values was good.

An on-line flow injection-hydride generation/atomic absorption spectrometry method was developed for the preconcentration and selective determination of inorganic arsenic [As(III) and As(V)] and its methylated species. The separation of the arsenic species was performed by an automated pH-selective arsines generation technique, using sodium tetrahydroborate(III) as reductant. Each arsine was cryogenically trapped in a PTFE coil, knotted and sealed inside another wider diameter tube, through which liquid nitrogen was suctioned by negative pressure. Then, based on their different boiling points, the arsine species were selectively liberated by using a heating cycle of microwave radiation, followed by atomic absorption detection. A sample solution aliquot mixed with 1% citric acid was used for the determination of As(III) alone, while a second sample aliquot mixed with 2 mol l(-1) nitric acid was used for the quantitative determination of total inorganic arsenic, monomethylarsonic acid and dimethylarsinic acid. Based on 10 ml sample, the detection limits lie within the range 20-60 ng As l(-1), which are sufficiently low to detect the arsines-forming species in natural waters. These values are negatively affected by the reagents purity and background noise due to flame flickering, but the sensitivity can substantially be improved by increasing sample size or running several consecutive reactions.

A literature search on the speciation of arsenic in environmental and biological samples shows an increasing interest of many researchers in the subject. Because of the low level of arsenic species in real samples, many problems related with its speciation remain unresolved: species instability during sampling, storage and sample treatment, incomplete recovery of all species, matrix interferences, lack of appropriate certified reference materials and of sensitive analytical methods, etc. These aspects are underlined in this paper. The continued development of new analytical procedures pretending to solve some of these problems claim for an up-to-date knowledge of the recent publications. Therefore, this paper pretends to review the latest publications on the chemical speciation of arsenic, emphasizing the increasing activity in the development of accurate and precise analytical methods. In most of the cases, separation and preconcentration is necessary, followed by element-specific detection for sensitivity improvement. Hydride generation following separation procedures (e.g., ion-exchange or high performance liquid chromatography) coupled to atomic absorption or atomic emission detectors proved to have sufficient sensitivity to monitor arsenic exposure, although restricts the analysis to hydride-forming species. Modified procedures including some kind of heating in the presence of highly oxidizing agents have proved successful to completely decompose the arsenic containing compounds to arsenate and so to extend the range of compounds which can be determined by these methods. On-line arrangements have the additional advantage of avoiding excessive sample handling, although some of them involve numerous steps and others are too costly to be recommended for routine use. The analytical figures of merits, specially detection limits are given for most of the methods in order to afford comparison and judge possible applicability. These studies, which have been approached in many different ways, would lead to knowledge that are determinant in the understanding of the cycle of this element in environment and of its physiological and toxicological behavior in the living organisms.

The levels of DDT residues were studied in 145 breast milk samples 25 days postpartum from women living in various rural populations where DDT has been used in farming activities and to interrupt malaria transmission. All participants showed quantifiable milk levels of DDT residues in the range from 5.1 to 68.3 micrograms/l and their levels significantly increased (P < 0.05) with maternal age. The determination of DDT residues (as DDE) in human milk was performed after a saponification process by gas chromatography with electron-capture detection. Confirmatory analysis was achieved using high-performance liquid chromatography with a diode array detection.

A simple head-space (HS) flow injection (FI) system with chemiluminescence (CL) detection for the determination of iodide as iodine in urine is presented. The iodide is converted to iodine by potassium dichromate under stirring in the closed HS vial, and the iodine is released from urine by thermostatting and is carried in a nitrogen flow through an iodide trapping solution. The concomitant introduction of aliquots of iodine, luminol and cobalt(II) solutions by means of a time-based injector into an FI system allowed its mixing in a flow-through cell in front of the detector. The emission intensity at 425 nm was recorded as a function of time. The salting-out of the standard solutions affected the gas-liquid distribution coefficient of iodine in the HS vial. The typical analytical working graphs obtained under the optimized experimental conditions were rectilinear from 0 to 5 mg l(-1) iodine, achieving a precision of 2.3 and a relative standard deviation of 1.8 for ten replicate analyses of 50 and 200 microg l(-1) iodine. However, a second-order process becomes significant at higher iodine concentrations (from 10 to 40 mg l(-1)). The detection limit of the method is 10 microg l(-1) (80 ng) iodine when 8 ml samples are taken. Data for the iodide content of 10 urine samples were in good agreement with those obtained by a conventional catalytic method, and recoveries varied between 101 and 103% for urine samples spiked with different amounts of iodide. The analysis of one sample takes less than 20 min. In the present study the iodide levels found for 100 subjects were 86.8 +/- 19.0 (61-125) microg l(-1), which is lower than the WHO's optimal level (150-300 microg per day).

A factorial composite design was employed for the exploration of the response as a function of the flow rate and length of the dispersion coil of a flow injection system employed for on-line dilution and determination of copper by flame-AAS. For this purpose, an empirical response function (RF), which takes into account the peak height and the response time, was employed to evaluate the response. This RF was modified using the coefficient of variation in order to discriminate not only for high absorbance and adequate response time, but also for the best precision.

A single channel flow injection manifold has been employed to carry out the direct determination of toluene in gasolines by FT-IR without any sample pretreatment and by using different strategies. Toluene can be directly determined by measuring the absorbance at 728 cm(-1), using a base line established between 835 and 575 cm(-1); and in this case a limit of detection of 0.01% (v/v) can be obtained with a dynamic range up to 2% (v/v). In some cases it could be convenient to determine toluene by derivative flow-injection FT-IR in order to avoid matrix interferences in the analysis of some types of gasolines. Carrying out the first order derivative FI-FT-IR measurements on the 728 cm(-1) band between the peak at 731 and the valley at 725 cm(-1) toluene can be determined without problems in establishing the base line and with a limit of detection of 0.01% (v/v). On the other hand, the use of the quotient between the first order derivative absorbance values of toluene, at the 728 cm(-1) band, and benzene, at the 675 cm(-1) band, can be applied for the determination of toluene in gasolines in which benzene has been previously analyzed, avoiding problems related to the determination of the base line and making measurements independent of the spacer employed.

A simple and flexible time-based injector is described for the introduction of almost any desirable volume of sample and reagents in flow systems. The feasibility of application is demonstrated by improving the azomethine-H spectrophotometric method for the precise and accurate determination of boron in soil and coffee plant tissues. On-line programmed functions include: sequential injections and zone trapping, with a significant reduction of sample and reagent consumption.

Two experiments are reported here. First, the effect of lithium chloride (1, 2 and 4 mEq/kg IP for 21 days) on body weight was assessed in female and male rats. Food intake was measured in the rats treated with 2 mEq/kg. All the doses tested significantly increased body weight in female rats. A linear relationship between body weight gain and lithium dose was also observed. In contrast, in male rats, the low doses of lithium (1 and 2 mEq/kg) did not affect body weight, whereas the high dose (4 mEq/kg) decreased body weight. These results confirm previous reports on a sex-dependent effect of lithium on body weight in rats. In the second experiment, body weight and food intake were assessed in female rats treated with lithium alone, or in combination with insulin or sulpiride, a D2 dopamine receptor blocker. It was found that the effect of lithium on body weight and feeding was additive to the effects of sulpiride and insulin. These findings are indirect evidence that lithium enhances body weight in rats by a different mechanism than the one described for sulpiride or insulin.

The lead content of soil along the roadside in Mérida City was investigated. Where motor vehicle traffic volume was less than 5000 motor vehicles per day, almost no lead accumulation was observed in the surface soil (0-2 cm), but where the motor vehicle traffic volume was greater than 10,000 motor vehicles per day, levels of lead increased by a factor of up to approximately 18. The soil lead content decreased with distance from the edge of the roadside and with depth of sampling.

Manganese(II) ( 1.5 ng/ml) is determined by measuring either of the two emission peaks given by alkaline oxidation of luminol. Several other metal ions, which enhance both emission peaks, are masked by cyanide ions.

The chemiluminescence emission produced by the oxidation of alkylamines by benzoyl peroxide has been used to determine up to ca. 0.5 mumole/ml of aliphatic secondary and tertiary amines in chloroform or acetone. The emission intensity is decreased with increasing age and water content of the solvent.

Oxidation of p-benzoquinone by hydrogen peroxide in an alkaline medium gives chemiluminescence emission with maximum intensity at 660 and 560 nm. 1,4-Naphthaquinone gives only a single maximum at 660 nm. These emissions can be used for the determination of microg amounts of the quinones. The interference effect of some organic compounds is described.

Sulphide (0.1 ng/ml) is determined by measuring the chemiluminescence given by its oxidation in aqueous solution by hydrogen peroxide, catalysed by peroxidase. The detection limit is 0.05 ng/ml. Several other, rather less sensitive, systems are also described. Sulphite and thiocyanate, which depress the emission, are masked with formaldehyde.

Molecular emission cavity analysis (MECA) is used for the determination of total sulphur in fuel oils. The sulphur is reduced by heating the sample with Devarda's alloy in an HCl medium, with subsequent liberation of H2S and measurement of the chemiluminescent S2 emission intensity in the MECA cavity. The total sulphur recovery from different sulphur-containing compounds and fuel oils is always ca. 100%. The precision and accuracy are good. Applications to certified and commercial fuel oils are discussed.