Analytes In Aqueous Solution Research Articles

Evaluation of selected filters for collection and subsequent supercritical fluid extraction of suspended solids for trace organic analysis

This study evaluated selected filters in order to find an appropriate filter that can be used to separate suspended solids (SS) from the aqueous phase with minimal sorption of the dissolved organic constituents in the aqueous phase, and that is compatible with subsequent supercritical fluid extraction (SFE) of hydrophobic organic compounds (HOCs) from the SS collected onto them. The sorption study for the filters was limited to the use of analytes in aqueous solution with no SS. Membrane filters and a glass-fiber filter with binder showed considerable sorption behaviour during filtration of aqueous solutions consisting of six polynuclear aromatic hydrocarbons (PAHs) as analytes. The extent of sorption of the analytes by the filters increased with the more hydrophobic compounds. A glass-fiber filter with no binder (MSI TCLP) was found to be non-sorbing towards the PAH analytes, and was further shown to be an appropriate filter for a series of 56 base/neutral/acid extractable organic compounds. SFE of the filter as received showed extractable compounds detectable by GC-MS. Thus, pre-cleaning of the filter is required for the removal of SFE-extractable background compounds prior to its use in the collection of SS for subsequent SFE.

Determination of the fungicides folpet, captan and captafol by cloud-point preconcentration and high-performance liquid chromatography with electrochemical detection

A method is described for the determination of residues of the fungicides Folpet, Captan and Captafol in river water using an isocratic high-performance liquid chromatographic system. Electrochemical detection with single and dual glassy-carbon electrodes was evaluated for possible amperometric detection of these fungicides; the reductive-oxidative detection mode with a dual electrode in the series configuration proved to be more appropriate than direct reductive detection with a single working electrode. To concentrate the fungicide residues, a cloud-point preconcentration step employing the non-ionic surfactant Triton X-114 was applied. Furthermore, the presence of the surfactant contributes to the stability of these analytes in aqueous solution, avoiding their hydrolysis. The method described shows good recoveries and good precision, with relative standard deviations of less than 10%. Detection limits of about 4 μg/1 were achieved for all three fungicides studied for 15 ml of preconcentrated sample.

Recovery of plutonium from phosphate containing aqueous analytical waste solutions using macroporous anion exchange resin

Distribution ratios of Pu(IV) between 7.5M HNO3+0.75M H3PO4+0.3M H2SO4 media and a macroporous anion-exchange resin Amberlyst A-26 (MP) increased from 40 to 250 when 1M aluminium nitrate was added to the aqueous medium. When 1M ferric nitrate was used in place of aluminium nitrate the distribution ratio further increased to 850. The 10% Pu(IV) breakthrough capacities with a 5 ml bed resin column, using synthetic feed solutions containing 1M aluminium nitrate, were 1.4 g l−1, 3.2 g l−1 at flow rates of 30 ml per hour and 10 ml per hour, respectively. The corresponding 10% Pu(IV) breakthrough capacities in the presence of 1M ferric nitrate were 8.5 g l−1 and 12.8 g l−1. More than 97% of plutonium could be recovered from actual analytical phosphate waste solutions.

Determination of 6-amino-2,2-dimethyl-1,3-dioxepan-5-ol by postcolumn derivatization witho-phthalaldehyde/2-mercapto-ethanol after ion-pair chromatography

A high-performance liquid chromatographic method is discribed for the determination of 6-amino-2,2-dimethyl-1,3-dioxepan-5-ol using Spherisorb ODS II stationary phase and mobile phase 30:70 (v/v) methanol: aqueous 1-octane sulfonic acid. Detection was fluorimetric following postcolumn derivatization with o-phthaladehyde/2-mercaptoethanol. The procedure was applied to the analysis of aqueous solutions and microcrystalline suspensions in liquid paraffin, prepared for investigation of the toxicological profile. The method was validated for selectivity, linearity of detector response, repeatability, limit of detection and quantitation. The HPLC method was selective. The instrumental limit of detection was 0.5 ng per injection (0.05 μg mL−1). The method detection limits were 0.5 μg mL−1 aqueous solution and 5 μg mL−1 liquid paraffin suspension, the quantitation limit 0.05 mg mL−1 aqueous solution and 1.0 mg mL−1 liquid paraffin. Linearity was within 0.94–47.1 μg mL−1. Intra-assay accuracy accounted for 99–100% in the range 0.05–226 mg mL−1 aqueous solution, intra-assay precision for 2% (C.V.). For microcrystalline liquid paraffin suspensions with 1 and 250 mg mL−1 99 and 109% was found for intra-assay accuracy. Intra-assay precision was 5% (C.V.). Reliable results over a wide concentration range can be obtained. The procedure is considered valid for determination of the analyte in aqueous solution or microcrystalline paraffin oil suspensions.

Carbon-enhanced inductively coupled plasma mass spectrometric detection of arsenic and selenium and its application to arsenic speciation

Addition of carbon as methanol or ammonium carbonate to the aqueous analyte solutions in combination with increased plasma power input enhanced the inductively coupled plasma mass spectrometry (ICP-MS) signal intensities of arsenic and selenium. In the presence of the optimum 3% v/v methanol concentration the signal intensities achieved were about 4500–5000 counts s–1 per ng ml–1 of arsenic and about 700–1100 counts s–1 per ng ml–1 of selenium (82Se), corresponding to enhancement factors of 3.5–4.5 compared with aqueous solution for the two elements. Differences in sensitivity (calculated on the basis of analyte atom) were observed between the individual arsenic species and between the selenium species in aqueous as well as in carbon-added solutions. The presence of 3% v/v methanol in the analyte solutions doubled the level of the background signal for arsenic and selenium, but its fluctuation (noise) was not increased. Therefore, the observed increase in analyte sensitivity led to a similar increase in signal-to-noise ratio. The addition of carbon as ammonium carbonate enhanced the arsenic signal by a similar factor but caused severe contamination of the ICP-MS instrument by carbon. In the 3% v/v methanol solutions of arsenic and selenium the signal intensity from antimony (internal standard) was enhanced by a factor of 1.5, which indicates that the enhancement effect of the arsenic and selenium signals by methanol is only to a limited extent caused by improved sample transport/nebulization efficiency. It is proposed that an increased population of carbon ions or carbon-containing ions in the plasma facilitates a more complete ionization of analytes lower in ionization energy than carbon itself. The enhanced detection power for arsenic was applied to arsenic speciation by high-performance liquid chromatography (HPLC)–ICP-MS, and made possible the detection of the arsenocholine ion (AsC) in extracts of shrimp at the 5–10 ng g–1 concentration level. The limit of detection was improved by a factor of 3.4 after addition of methanol and was 4.7 ng g–1 as the AsC ion.

Determination of Sb, Ni and V in slurry from airborne particulate material collected on filter by graphite furnace atomic absorption spectrometry

A microdigestion procedure performed directly in the autosampler cup is proposed. Small quartz filter pieces loaded with the particulate material are transferred to the cup. The sample is digested by a mixture of nitric, sulfuric and hydrofluoric acid (1:1:1) under sonication. After the addition of a boric acid solution the elements are determined by graphite furnace atomic absorption spectrometry using the autosampler to deliver the slurry into the furnace. A mixture of palladium and magnesium nitrates was used as a modifier for Sb. Spiking studies showed recoveries close to 100% using aqueous analytical curves for Ni and Sb. For V, an analytical curve in the blank slurry, obtained by submitting an unloaded filter to the same procedure, was used. The method was applied to two standard reference materials, Coal Fly Ash (NIST 1633a) and Urban Particulate (NIST 1648) and the concentrations showed good agreement with the certified or recommended values using aqueous analytical solutions.

Bilayer lipid membranes for electrochemical sensing

AbstractBilayer lipid membranes (BLMs) are described as selective and sensitive electrochemical transducers for inorganic ions and organic species. The electrostatic properties of BLMs, which are significant in controlling ion permeation processes, and the possible mechanisms for signal generation are presented herein. Operation of a BLM‐based transducer hinges on a selective interaction between analyte in aqueous solution and membrane‐embedded receptors; as a result, the electrostatic fields and/or the physical phase structure of the membrane alters, leading to an analytical signal (most commonly conductivity changes) which can be related to the analyte concentration. Examples of electrochemical sensors based on this principle and efforts to stabilize these bilayer membranes are presented in this review article.

Determination of iodine-129 in vegetable samples by inductively coupled plasma mass spectrometry

Work has been carried out at the Harwell Laboratory to develop an inductively coupled plasma mass spectrometry (ICP-MS) method capable of measuring 129I at contaminated environmental levels in vegetable samples. The inherent sensitivity of ICP-MS using conventional pneumatic nebulization is insufficient for this task, so that preconcentration and/or improved efficiency of sample introduction are required. The development of a method for introducing 129I into the ICP mass spectrometer in the form of I2 is described. The volatility of this species is used to overcome the low transport efficiency of pneumatic nebulization for the introduction of analytes in aqueous solution. Sample preparation and results for spiked vegetable material are discussed. Based on field blanks, a limit of detection of 0.2 ng, equivalent to approximately 1.4 ng kg–1(0.009 Bq kg–1) fresh mass of vegetable, is reported. A method precision of 12% relative standard deviation at 2.7 ng cm–3 has been achieved.

Determination of Ce, Pr, Nd and Sm in High Purity La2O3by Inductively Coupled Plasma Atomic Emission Spectrometry

Abstract High purity lanthanum oxide was analysed to determine traces of Ce, Pr, Nd, and Sm by employing inductively coupled plasma atomic emission spectrometry (ICP-AES). Lanthanum oxide was dissolved in nitric acid and the solution was nebulized into the plasma generated by a RF generator (56 MHz; 1.5kW). Analytical lines of Ce, Pr, Nd, and Sm, which were free of interference from the spectral lines of both La and the other rare earths, were scanned on a Jobin-Yvon, Model JY-38 THR-1000 1m-Czerny-Turner monochromator. Standards containing the four analytes (Ce, Pr, Nd, and Sm) in the concentration range 0.01–0.2 μg/ml and La at 2 mg/ml were used for calibration. Detection limits ranged between 6 and 16 ng/ml for the four analytes in aqueous solution.

Automatic determination of diltiazem and desacetyldiltiazem in human plasma using liquid— solid extraction on disposable cartridges coupled to HPLC — Part II: Optimization of liquid—solid extraction

An automatic liquid-solid extraction (LSE) procedure to be coupled to HPLC for the determination of diltiazem and desacetyldiltiazem in plasma has been developed. The LSE operations are performed on disposable extraction cartridges (DECs) by means of a sample processor equipped with a robotic arm holding a needle through which the different liquids are dispensed. The operating parameters of LSE have been optimized with respect to recovery, detectability and reproducibility by using, whenever possible, aqueous solutions of the analytes. Different kinds of DECs have been tested. For the compounds studied, DECs filled with 50 mg of cyanopropyl silica have been selected. The influence of the pH of the buffer used in the washing step has been studied, leading finally to the selection of the same phosphate buffer (pH 7.4) as in the HPLC mobile phase. The minimum volume of methanol which still gives a nearly complete elution of the analytes from the extraction cartridges has been determined. Under these conditions, a high sensitivity can be obtained without an evaporation step. Moreover, the volume of buffer to be added to the methanolic eluate before injection into the HPLC system has been optimized in such a way that a focusing effect is obtained at the top of the analytical column while the dilution of the extract is minimized.

Use of photothermal deflection spectrometry (PDS) for studies of analytes in aqueous solutions

A crossed-beam photothermal deflection spectrophotometer (PDS) instrument was built, evaluated and applied to the determination of lanthanide neodymium. A dye laser filled with rhodamine 6 G and pumped by an argon ion laser at 514 nm was operated with outputs between 4 and 500 mW at the cuvette position and chopped at 2 Hz. The deflection of a He-Ne probe laser beam, crossing the exciting dye laser, was measured by a two-dimensional position sensitive device and two lock-in amplifiers. The setup was evaluated with a solid carbon sample and the liquids toluene and Nd3+/HClO4.

Improving the Infrared Detection of Analytes in Aqueous Solution Using Polymer Coated Atr Elements

Abstract Preliminary results of ATR/FTIR experiments indicate that thinly coating the ATR elements with suitable polymers improves the ability to detect test analytes in aqueous solutions. Experiments were performed using the test analyte, nitrobenzene, in aqueous solutions containing a range of methanol concentrations. the time dependence and effect of methanol concentration on the nitrobenzene IR absorbance was investigated.

Fluorescence behaviour of an alkyl lysophospholipid in the presence of 1,6-dipheylhexatriene

The alkyl lysophospholipid (ALP), 1- O-octadecyl-2- O-methyl- dl-glycero-3-phosphorylchlorine (Et-18-OMe), which shows anticancer and antimetastatic properties, causes a very large increase in the fluorescence intensity of the known fluorescent probe, 1,6-diphenyl-1,3,5-hexatriene (DPH), when DPH enters the hydrophobic region of the ALP bilayer. This phenomenon is used to determine 2–166 μg ml −1 Et-18-OMe by adding a dilute solution of DPH in tetrahydrofuran to an aqueous analyte solution. Parameters that affect the fluorescence intensity are studied.

A rapid and sensitive HPLC procedure for the determination of atrazine residues in soil-water extracts.

An automated procedure is described for the rapid determination of the residual herbicide atrazine at ppb levels in soil-water extracts. The system consists of an autosampler connected to a C18 precolumn linked via a switching valve to a C18 analytical column and spectrophotometer. Peak height is superior to peak area for quantifying results with coefficients of variation of 0.48% and 0.89%, respectively, for 7.5 ng standard injections. Precolumn concentration eliminates the need for sample cleanup and achieves up to a 37% increase in peak height compared to an isocratic system. In a black earth soil, atrazine is identified as the principal phytotoxic constituent. The minimum detectable level is one-tenth the critical no-effect threshold for wheat. The method is well suited for predicting possible atrazine injury to susceptible crops and the measurement of other nonpolar analytes in aqueous solution.

The lipid membrane as a selective chemical transducer

The bilayer lipid membrane is described as a selective electrochemically based transducer for organic species and inorganic ions. The possible mechanisms which can be employed for signal generation are summarized. Operation hinges on a selective interaction between analyte in aqueous solution and membrane embedded receptors. Complexation of these latter species results in physical perturbation of the membrane structure and/or electrostatic fields, leading to the evolution of an analytical signal based on ion current modulation through the membrane.