On line pre-concentration for simultaneous determination of low molecular weight organic acids and inorganic anions in Amazonian river water samples employing ion chromatography with conductivity detection

An ion chromatography procedure, employing an IonPac AC15 concentrator column was used to investigate on line preconcentration for the simultaneous determination of inorganic anions and organic acids in river water. Twelve organic acids and nine inorganic anions were separated without any interference from other compounds and carry-over problems between samples. The injection loop was replaced by a Dionex AC15 concentrator column. The proposed procedure employed an auto-sampler that injected 1.5 ml of sample into a KOH mobile phase, generated by an Eluent Generator, at 1.5 mL min-1, which carried the sample to the chromatographic columns (one guard column, model AG-15, and one analytical column, model AS15, with 250 x 4mm i.d.). The gradient elution concentrations consisted of a 10.0 mmol l-1 KOH solution from 0 to 6.5 min, gradually increased to 45.0 mmol l-1 KOH at 21 min., and immediatelly returned and maintained at the initial concentrations until 24 min. of total run. The compounds were eluted and transported to an electro-conductivity detection cell that was attached to an electrochemical detector. The advantage of using concentrator column was the capability of performing routine simultaneous determinations for ions from 0.01 to 1.0 mg l-1 organic acids (acetate, propionic acid, formic acid, butyric acid, glycolic acid, pyruvate, tartaric acid, phthalic acid, methanesulfonic acid, valeric acid, maleic acid, oxalic acid, chlorate and citric acid) and 0.01 to 5.0 mg l-1 inorganic anions (fluoride, chloride, nitrite, nitrate, bromide, sulfate and phosphate), without extensive sample pretreatment and with an analysis time of only 24 minutes.

Direct simultaneous determination of Pb(II) and Cu(II) in biodiesel by anodic stripping voltammetry at a mercury-film electrode using microemulsions

A mercury film electrode was used to determine direct and simultaneously Pb(II) (at -410 mV) and Cu(II) (at -100 mV) in biodiesel by anodic stripping voltammetry. A linear response was obtained for Pb(II) and Cu(II) in the 2.00 × 10-8-1.00 × 10-7 mol L-1 concentration range and detection limits were 2.91 × 10-9 mol L-1 and 4.69 × 10-9 mol L-1 for Pb(II) and Cu(II), respectively, with recovery around of 100.0%. © 2012 Elsevier Ltd. All rights reserved.

Aplicação de métodos de calibração multivariada para a determinação simultânea de riboflavina (VB2), tiamina (VB1), piridoxina (VB6) e nicotinamida (VPP)

In this work, the artificial neural networks (ANN) and partial least squares (PLS) regression were applied to UV spectral data for quantitative determination of thiamin hydrochloride (VB1), riboflavin phosphate (VB2), pyridoxine hydrochloride (VB6) and nicotinamide (VPP) in pharmaceutical samples. For calibration purposes, commercial samples in 0.2 mol L-1 acetate buffer (pH 4.0) were employed as standards. The concentration ranges used in the calibration step were: 0.1 - 7.5 mg L-1 for VB1, 0.1 - 3.0 mg L-1 for VB2, 0.1 - 3.0 mg L-1 for VB6 and 0.4 - 30.0 mg L-1 for VPP. From the results it is possible to verify that both methods can be successfully applied for these determinations. The similar error values were obtained by using neural network or PLS methods. The proposed methodology is simple, rapid and can be easily used in quality control laboratories.

Determinação de As, Cd e Pb em amêndoas e mesocarpo de babaçu, sapucaia, xixá e castanha-do-pará por espectrometria de absorção atômica

This work describes methods for the simultaneous determination of Cd and Pb by graphite furnace atomic absorption spectrometry and As by hydride generation atomic absorption spectrometry in Brazilian nuts. The samples (~ 0.300 g) were digested to clear solutions in a closed vessel microwave oven. The pyrolysis and atomization temperatures for simultaneous determinations of Cd and Pb were 1100 and 2100 °C, respectively, using 0.5% (w v-1) NH4H2PO4 + 0.03% (w v-1) Mg(NO3)2 as chemical modifier. The limits of detection (3Δ) were 3.8 μg kg-1 for As, 0.86 μg kg-1 for Cd and 13 μg kg-1 for Pb. The reliability of the entire procedures was confirmed by peach leaves (No. 1547 - NIST) certified reference material analysis and addition and recovery tests. The found concentrations presented no statistical differences at the 95% confidence level.

Sequential injections as an alternative to gradient exploitation for implementing differential kinetic analysis in a flow injection system

A novel flow-based strategy for implementing simultaneous determinations of different chemical species reacting with the same reagent(s) at different rates is proposed and applied to the spectrophotometric catalytic determination of iron and vanadium in Fe-V alloys. The method relies on the influence of Fe(II) and V(IV) on the rate of the iodide oxidation by Cr(VI) under acidic conditions, the Jones reducing agent is then needed Three different plugs of the sample are sequentially inserted into an acidic KI reagent carrier stream, and a confluent Cr(VI) solution is added downstream Overlap between the inserted plugs leads to a complex sample zone with several regions of maximal and minimal absorbance values. Measurements performed on these regions reveal the different degrees of reaction development and tend to be more precise Data are treated by multivariate calibration involving the PLS algorithm The proposed system is very simple and rugged Two latent variables carried out ca 95% of the analytical information and the results are in agreement with ICP-OES. (C) 2010 Elsevier B V. All rights reserved.

Estrategias en el desarrollo de métodos analíticos para la determinación simultánea de compuestos orgánicos por espectrofotometría derivada

In this work is proposed, a simple experiment for the simultaneous determination of losartan (L) and hydrochlorothiazide (H) in synthetic and real samples by derivative spectrophotometry technique. For the students it is relevant to know this technique for simultaneous determinations of drugs, allowing that the students recognize that this technique is simple, rapid and applicable to quality control. This experimental work, it is proposed in order to being applied to undergraduates into laboratories of analytical chemistry. Furthermore, it is given the integration of the theoretical knowledge with the experimental work; this correlation is of interest for the students.

Determinação de As, Cd e Pb em amêndoas e mesocarpo de babaçu, sapucaia, xixá e castanha-do-pará por espectrometria de absorção atômica

This work describes methods for the simultaneous determination of Cd and Pb by graphite furnace atomic absorption spectrometry and As by hydride generation atomic absorption spectrometry in Brazilian nuts. The samples (~ 0.300 g) were digested to clear solutions in a closed vessel microwave oven. The pyrolysis and atomization temperatures for simultaneous determinations of Cd and Pb were 1100 and 2100 °C, respectively, using 0.5% (w v-1) NH4H2PO4 + 0.03% (w v-1) Mg(NO3)2 as chemical modifier. The limits of detection (3Δ) were 3.8 μg kg-1 for As, 0.86 μg kg-1 for Cd and 13 μg kg-1 for Pb. The reliability of the entire procedures was confirmed by peach leaves (No. 1547 - NIST) certified reference material analysis and addition and recovery tests. The found concentrations presented no statistical differences at the 95% confidence level.

Improving the Detectability of Sequential Injection Chromatography (SIC): Determination of Triazines by Exploiting Liquid Core Waveguide (LCW) Detection

Coupling a liquid core waveguide cell to a sequential injection chromatograph improved the detection limits for determination of triazine herbicides without compromising peak resolution. Separation of simazine, atrazine, and propazine was achieved in water samples by a 25mm long C18 monolithic column. Detection was made at 238nm using a type II LCW (silica capillary coated with Teflon (R) AF2400) cell with 100cm of optical path length. Detection limits for simazine, atrazine, and propazine were 2.3, 1.9, and 4.5 mu g L-1, respectively. Reduced analysis time and low solvent consumption are other remarkable features of the proposed method.

Método multiresiduo para determinar pesticidas en frutas por extracción con fluido supercrítico

A rapid and reliable method for the determination of 25 compounds selected from four classes of pesticides in samples of fresh apples, grapes, pears, and strawberries purchased at a local supermarket, is presented. The study describes two different methods of extraction: solid-liquid extraction with acetone and supercritical fluid extraction. Clean-up was based on aminopropyl cartridge extraction followed by gas chromatography with an electron capture detector for simultaneous determinations. Confirmatory analysis was carried out by gas chromatography with mass spectrometry in the selected-ion monitoring (SIM) mode. Extraction efficiencies were directly compared and the methods were applied to the analysis of real samples. Recoveries for a majority of pesticides from standard samples at enrichment levels of 0.04-0.10 mg/ kg ranged from 77 to 96 % for both methods. The supercritical fluid extraction method showed good limits of detection (less than 0.01 mg/kg, depending on the pesticide and matrix) as well as minimizing environmental concerns, time, and laboratory effort. © 2006 Centro de Información Tecnológica.

The relationship between extravascular lung water and oxygenation in three patients with influenza A (H1N1)-induced respiratory failure

This case series reports the correlation between extravascular lung water (EVLW) and the partial arterial oxygen pressure/fractional inspiratory oxygen (PaO(2)/FiO(2)) ratio in three patients with severe influenza A (H1N1)-induced respiratory failure. All patients suffered from grave hypoxia (PaO(2), 26-42 mmHg) and were mechanically ventilated using biphasic airway pressure (PEEP, 12-15 mmHg; FiO(2), 0.8-1) in combination with prone positioning at 12 hourly intervals. All patients were monitored using the PICCO system for 8-11 days. During mechanical ventilation, a total of 62 simultaneous determinations of the PaO(2)/FiO(2) ratio and EVLW were performed. A significant correlation between EVLW and the PaO(2)/FiO(2) ratio (Spearman-rho correlation coefficient, -0.852; p < 0.001) was observed. In all patients, a decrease in EVLW was accompanied by an improvement in oxygenation. Serum lactate dehydrogenase levels were elevated in all patients and significantly correlated with EVLW during the intensive care unit stay (Spearman-rho correlation coefficient, 0.786; p < 0.001). In conclusion, EVLW seems increased in patients with severe H1N1-induced respiratory failure and appears to be closely correlated with impairments of oxygenatory function.

Compilation of measurements from two interdisciplinary STAR-shaped surveys in the North Sea: The ZISCH - Dataset

The measurements were obtained during two North Sea wide STAR-shaped cruises during summer 1986 and winter 1987, which were performed to investigate the circulation induced transport and biologically induced pollutant transfer within the interdisciplinary research in the project "ZISCH - Zirkulation und Schadstoffumsatz in der Nordsee / Circulation and Contaminant Fluxes in the North Sea (1984-1989)". The inventory presents parameters measured on hydrodynamics, nutrient dynamics, ecosystem dynamics and pollutant dynamics in the pelagic and benthic realm. The research program had the objective of quantifying fluxes of major budgets, especially contaminants in the North Sea. In spring 1986, following the phytoplankton spring bloom, and in late winter 1987, at minimum primary production activity, the North Sea ecosystem was investigated on a station net covering the whole North Sea. The station net was shaped like a star. Sampling started in the centre, followed by the northwest section and moving counter clockwise around the North Sea following the residual currents. By this strategy, a time series was measured in the central North Sea and more synoptic data sets were obtained in the individual sections. Generally advection processes have to be considered when comparing the data from different stations. The entire sampling period lasted for more than six weeks in each cruise. Thus, a time-lag should be considered especially when comparing the data from the eastern and the western part of the central and northern North Sea, where samples were taken at the beginning and at the end of the campaign. The ZISCH investigations represented a qualitatively and quantitatively new approach to North Sea research in several respects. (1) The first simultaneous blanket coverage of all important biological, chemical and physical parameters in the entire North Sea ecosystem; (2) the first simultaneous measurements of major contaminants (metals and organohaline compounds) in the different ecosystem compartments; (3) simultaneous determinations of atmospheric inputs of momentum, energy and matter as important ecosystem boundary conditions; (4) performance of the complex measurement program during two seasons, namely the spring plankton bloom and the subsequent winter period of minimal biological activity; and (5) support of data analysis and interpretation by oceanographic and meteorological numerical models on the same scales.

(Table 1) Primary production and chlorophyll a concentration in the Northeastern Tropical Atlantic

Results of simultaneous determinations of chlorophyll "a" concentrations and primary production in the northeastern part of the Tropical Atlantic in spring 1977 are discussed. Primary production was low (250-350 mg C/m**2/day in the open parts of the ocean and high (600-1500 mg C/m**2/day) mainly in zones of current divergences and coastal region of the West Africa. Chlorophyll "a" concentration throughout the euphotic zone varied from 6 to 36 mg/m**3 and in the surface layer from 0.05 to 0.60 mg/m**3. Uneven distribution of primary production is due to physiological condition of phytoplankton.

(Table 1) Microplankton biomass determined from ATP and by microscopy

Simultaneous determinations of the microplankton biomass by direct microscopy and by measuring concentration of adenosine triphosphate (ATP) in samples from different depths of the Eastern Pacific revealed considerable differences between values obtained. With the exception of 3 of 62 determinations, the biomass determined from ATP exceeded that measured by microscopy; the latter averaged about 10% of the former for the region as a whole. This sharp difference is largely due to underestimation of ultramicroscopic cells by direct microscopy and to substantial variations in the factor used to convert ATP concentrations to cell biomass.

Simultaneous determination of antidementia drugs by HPLC-MS: validation data of the method and plasma level determinations in 300 patients

Aims: A rapid and simple HPLC-MS method was developed for the simultaneousdetermination of antidementia drugs, including donepezil, galantamine, rivastigmineand its major metabolite NAP 226 - 90, and memantine, for TherapeuticDrug Monitoring (TDM). In the elderly population treated with antidementiadrugs, the presence of several comorbidities, drug interactions resulting frompolypharmacy, and variations in drug metabolism and elimination, are possiblefactors leading to the observed high interindividual variability in plasma levels.Although evidence for the benefit of TDM for antidementia drugs still remains tobe demonstrated, an individually adapted dosage through TDM might contributeto minimize the risk of adverse reactions and to increase the probability of efficienttherapeutic response. Methods: A solid-phase extraction procedure with amixed-mode cation exchange sorbent was used to isolate the drugs from 0.5 mL ofplasma. The compounds were analyzed on a reverse-phase column with a gradientelution consisting of an ammonium acetate buffer at pH 9.3 and acetonitrile anddetected by mass spectrometry in the single ion monitoring mode. Isotope-labeledinternal standards were used for quantification where possible. The validatedmethod was used to measure the plasma levels of antidementia drugs in 300patients treated with these drugs. Results: The method was validated accordingto international standards of validation, including the assessment of the trueness(-8 - 11 %), the imprecision (repeatability: 1-5%, intermediate imprecision:2 - 9 %), selectivity and matrix effects variability (less than 6 %). Furthermore,short and long-term stability of the analytes in plasma was ascertained. Themethod proved to be robust in the calibrated ranges of 1 - 300 ng/mL for rivastigmineand memantine and 2 - 300 mg/mL for donepezil, galantamine and NAP226 - 90. We recently published a full description of the method (1). We found ahigh interindividual variability in plasma levels of these drugs in a study populationof 300 patients. The plasma level measurements, with some preliminaryclinical and pharmacogenetic results, will be presented. Conclusion: A simpleLC-MS method was developed for plasma level determination of antidementiadrugs which was successfully used in a clinical study with 300 patients.

Effect of modifiers for As, Cu and Pb determinations in sugar-cane spirits by GF AAS

Palladium plus magnesium nitrates with and without Ir, Ru and W were evaluated for the simultaneous determination of As, Cu and Pb in cachaca by graphite furnace atomic absorption spectrometry. For 20 mu L sample, 5 mu L Pd(NO(3))(2) and 3 mu L Mg(NO(3))(2) dispensed together onto the Ir-coated platform of the THGA, analytical curves in the 0-30.0 mu g L(-1) As, 0-1.50 mg L(-1) Cu and 0-60.0 mu g L(-1) Pb were built up and typical linear correlation coefficients were always better than 0.999. The limit of detection was 1.30 mu g L(-1) As, 140 mu g L(-1) Cu and 0.90 mu g L(-1) Pb. As, Cu and Pb contents in 10 cachaca samples agreed with those obtained by ICP-MS. Recoveries of spiked samples varied from 96% to 106% (As), 97% to 112% (Cu) and 92% to 108% (Pb). The relative standard deviation (n = 12) was typically 2.7%, 3.3% and 1.9%. (C) 2008 Elsevier Ltd. All rights reserved.