Flow injection on-line displacement/solid phase extraction system coupled with flame atomic absorption spectrometry for selective trace silver determination in water samples

A novel flow injection (FI) on-line displacement solid phase extraction preconcentration and/or separation method coupled with FAAS in order to minimize interference from other metals was developed for trace silver determination. The proposed method involved the on-line formation and subsequently pre-sorption of lead diethyldithiocarbamate (Pb-DDTC) into a column packed with PTFE-turnings. The preconcentration and/or separation of the Ag(I) took place through a displacement reaction between Ag(I) and Pb(II) of the pre-sorbed Pb-DDTC. Finally, the retained analyte was eluted with isobutyl methyl ketone (IBMK) and delivered directly to nebulizer for measuring. Interference from co-existing ions with lower DDTC complex stability in comparison with Pb-DDTC, was eliminated without need for any masking reagent. With 120 s of preconcentration time at a sample flow rate of 7.6 mL min−1, an enhancement factor of 110 and a detection limit (3 s) of 0.2 μg L−1 were obtained. The precision (RSD, n = 10) was 3.1% at the 10 μg L−1 level. The developed method was successfully applied to trace silver determination in a variety of environmental water samples and certified reference material.     

Using on-line solid phase extraction for flow-injection spectrophotometric determination of salbutamol

In the proposed procedure, the determination of salbutamol with Folin-Ciocalteau reagent (FC) using a flow injection analysis technique (FIA) with spectrophotometric detection at 750 nm is described. The lab-made FIA system consisted of a peristaltic pump Gilson Minipulse 3 equipped with Tygon tubes, double 6-port external Vici Valco sample injector and S 2000/SAD500 fiber optic spectrophotometer. It was controlled by a PC with use of originally compiled LabVIEW^®—supported software containing the mathematical library with various statistical functions for off-line data evaluation. Concentration, volume of reagents and flow rate were optimised by a simplex method. The proposed system was used for the direct determination of salbutamol sulphate in the tablets and the human urine without preliminary pre-treatment of the sample. The negative effect of interfering substances (excipients of the tablets and matrix of the urine) is overcome by a solid phase extraction (SPE), when salbutamol is adsorbed on the solid phase in the microcolumn, which is integrated directly into the flow system. Pre-treatment of the sample takes place directly in the flowing stream. The sample throughput without carryover of on-line SPE was 60-80 samples per hour. With the SPE column (Baker—carboxylic acid), salbutamol was determined in the linear range from 1 to 15 μg ml⁻¹ (R.S.D.=1.2%), with detection limit (3σ) 0.1 μg ml⁻¹ and a frequency of 40-60 samples per hour in the water solutions. The salbutamol was determined in the linear range from 2 to 20 μg ml⁻¹ (R.S.D.=1.7%), with detection limit (3σ) 1 μg ml⁻¹ and a frequency of 30 samples per hour in the samples of the human urine.     

In-field determination of nanomolar nitrite in seawater using a sequential injection technique combined with solid phase enrichment and colorimetric detection

A novel sequential injection method for the determination of nitrite at nanomolar level in seawater samples has been developed. The pink azo compound was formed based on the Griess reaction and quantitatively adsorbed onto a Sep-Pak C18 cartridge. The enriched azo compound was rinsed with water and ethanol (28%, v/v) in turn, and then eluted with an eluent containing 26.6% (v/v) ethanol and 0.108 mol L⁻¹ H₂SO₄. Finally the azo compound was measured using a spectrophotometer at 543 nm. Under the optimized conditions, the linear calibration ranges were 0.71–42.9 nmol L⁻¹ for a 150-mL sample and 35.7–429 nmol L⁻¹ for a 15-mL sample. The relative standard deviation of 8 measurements was 1.44% for 14.3 nmol L⁻¹ nitrite. For the 150 mL sample, the detection limit was estimated to be 0.1 nmol L⁻¹. The throughput of the method was about 4 samples per hour. The proposed method has been successfully applied to the in-field determination of nanomolar concentrations of nitrite in seawater.     

Determination of pesticides in water samples by solid phase extraction and gas chromatography tandem mass spectrometry

A multiresidue method for the determination of more than 80 pesticides in water has been developed and validated. The proposed method is based on SPE followed by GC coupled to MS/MS. Different variables affecting SPE procedure, such as cartridges, sample volume and solvents were studied, and mass spectrometric conditions were optimised in order to increase selectivity and sensitivity. Calibration curves were linear over the range of 0.03-0.5 microg/L. Recoveries were in the range of 70-110% and repeatability was below 20% for the lowest calibration point. LODs ranged from 0.001 to 0.025 microg/L and LOQs from 0.003 to 0.076 microg/L. Finally, the method was successfully applied to the analysis of water samples from southeast of Spain.     

A general screening method for doping agents in human urine by solid phase extraction and liquid chromatography/time-of-flight mass spectrometry

A general screening method based on solid phase extraction (SPE) and liquid chromatography/time-of-flight mass spectrometry (LC/TOFMS) was developed and investigated with 124 different doping agents, including stimulants, -blockers, narcotics, -adrenergic agonists, agents with anti-estrogenic activity, diuretics and cannabinoids. Mixed mode cation exchange/C8 cartridges were applied to SPE, and chromatography was based on gradient elution on a C18 column. Ionization of the analytes was achieved with electrospray ionization in the positive mode. Identification by LC/TOFMS was based on retention time, accurate mass and isotopic pattern. Validation of the method consisted of analysis of specificity, analytical recovery, limit of detection and repeatability. The minimum required performance limit (MRPL), established by World Anti-Doping Agency (WADA), was attained to 97 doping agents. The extraction recoveries varied between 33 and 98% and the median was 58%. Mass accuracy was always better than 5 ppm, corresponding to a maximum mass error of 0.7 mDa. The repeatability of the method for spiked urine samples, expressed as median of relative standard deviations (RSD%) at concentrations of MRPL and 10 times MRPL, were 14% and 9%, respectively. The suitability of the LC/TOFMS method for doping control was demonstrated with authentic urine samples.     

Unknown residual solvents identification in drug products by headspace solid phase microextraction gas chromatography-mass spectrometry

Summary A sensitive headspace SPME method for the extraction of residual solvents from pharmaceutical products has been developed and optimized. It was found that minimizing sample and headspace volume has a beneficial effect on extraction efficiency. At the same time the method reproducibility was seriously affected by reducing sample and headspace volume. The added air volume was not found to have any significant influence on method sensitivity. The method showed reproducibilities of less than 10% and detection limits as low as 1 ppb for benzene and dichloromethane. The headspace SPME method is around 1000 times more sensitive than static headspace. The optimized parameters were headspace volume 1.5 mL, sample volume 10 μL, and extraction time 30 min. The method was successfully applied to the identification of unknown residual solvents in three different proprietary active drug substances and was successfully applied to the confirmation of the presence of benzene in a proprietary drug substance. Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001     

Exploiting the bead injection LOV approach to carry out spectrophotometric assays in wine: application to the determination of iron

A sequential injection lab-on-valve (SI-LOV) system was used to develop a new methodology for the determination of iron in wine samples exploiting the bead injection (BI) concept for solid phase extraction and spectrophotometric measurement. Nitrilotriacetic Acid (NTA) Superflow resin was used to build the bead column of the flow through sensor. The iron (III) ions were retained by the bead column and react with SCN⁻ producing an intense red colour. The change in absorbance was monitored spectrophotometrically on the optosensor at 480 nm. It was possible to achieve a linear range of 0.09-5.0 mg L⁻¹ of iron, with low sample and reagent consumption; 500 μL of sample, 15 μmol of SCN⁻, and 9 μmol of H₂O₂, per assay. The proposed method was successfully applied to the determination of iron in wine, with no previous treatment other than dilution, and to other food samples.     

Determination of alkyl, chloro and mononitrophenols in water by sample-acetylation and automatic on-line solid phase extraction-gas chromatography-mass spectrometry

Summary On-line solid phase extraction-gas chromatographymass spectrometry has been used for trace analysis of phenols in water samples at the low ng L⁻¹ level. Phenols have been derivatized by in-sample acetylation prior to an automatic SPE-GC-MS procedure. The method was validated with 26 alkyl, chloro and mononitrophenols including 4-nonylphenol and 17-ethinylestradiol. Target analysis was performed by time-scheduled, selected ion monitoring. The on-line SPE-GC approach resulted in low sample volume (typically 10 mL), good reproducibility, sensitivity and considerable saving of reagents, material and manual work.     

Micro solid phase spectrophotometry in a sequential injection lab-on-valve platform for cadmium,zinc, and copper determination in freshwaters

This work describes the development of a solid phase spectrophotometry method in a μSI-LOV system for cadmium, zinc, and copper determination in freshwaters. NTA (Nitrilotriacetic acid) beads with 60–160 μm diameter were packed in the flow cell of the LOV for a μSPE column of 1 cm length. The spectrophotometric determination is based on the colourimetric reaction between dithizone and the target metals, previously retained on NTA resin. The absorbance of the coloured product formed is measured, at 550 nm, on the surface of the NTA resin beads in a solid phase spectrophotometry approach.     

Determination of herbicides by solid phase extraction gas chromatography-mass spectrometry in drinking waters

A solid phase extraction (SPE) method has been optimized for the gas chromatography-mass spectrometry (GC-MS) simultaneous determination of herbicides belonging to the following different families: carbamate (molinate), atrazines (atrazine, propazine, simazine, ametryne, cyanazine, terbutylazine, deethylterbutylazine, deethylatrazine), dinitroaniline (trifluralin, pendimethalin), chloroacetamide (alachlor, metolachlor). Different solid substrates have been compared (C18, cyano, styrene-divinylbenzene, phenyl, graphitic carbon). The type of conditioning and elution solvent, its volume, and the sample flow rate have been considered as variables affecting the recovery yields of the herbicides.The optimized experimental conditions are C18 phase conditioned with 3 mL acetone, loaded with 1 L water sample at 5 mL min⁻¹, and eluted with 3 mL acetone. Good recoveries (included between 79% and 99%) and R.S.D. (included between 2% and 12%) have been obtained for all analytes, except for deethylatrazine whose recovery was 46 ± 7%. The recovery of deethylatrazine increases up to 94 ± 17% if a non-porous graphitic carbon is coupled to the C18 phase, keeping the other parameters constant as optimized. The optimized method has been successfully checked for the identification and quantitation of the selected herbicides in raw and drinking water samples, with quantitation limits as low as 0.01 μg L⁻¹, fully in agreement with the current legislation. The method is easily routinable. After development, the method is currently routinely applied for the analysis of herbicides in waters and, up today, more than one thousand samples have been analysed at the “Laboratorio della Società Metropolitana Acque di Torino” (Laboratory of the Municipal Waterworks of Turin) in charge of the control of drinking water quality in Torino.     

Gas chromatography-mass spectrometry determination of 3-mercaptohexan-1-ol and 3-mercaptohexyl acetate in wine: a comparison of headspace solid phase microextraction and solid phase extraction methods

A gas chromatography-mass spectrometry method was established using headspace solid phase microextraction (HS-SPME) as the sampling procedure to analyse 3-mercaptohexan-1-ol (3-MH) and 3-mercaptohexyl acetate (3-MHA), two molecules with a tropical fruit aroma, in wine at trace level. This method offers important advantages, as it neither requires time-consuming sample preparation nor uses dangerous organic compounds, thus making control of wine aroma easier and suitable for routine analysis. As a comparison, a solid phase extraction (SPE) method, already described elsewhere for aroma analysis, was applied to quantify these analytes, extending this exhaustive enrichment to two important thiols. Detection limits for both the approaches were close to the sensory threshold value, resulting lower for the HS-SPME procedure and suitable for requirements in the oenological field. The application of the two proposed methods to 52 wines of different varieties gave similar results.     

Automated capillary electrophoresis with on-line preconcentration by solid phase extraction using a sequential injection manifold and contactless conductivity detection

An extension of a capillary electrophoresis instrument coupled to a sequential injection analysis manifold was developed for automated measurements with on-line solid-phase extraction preconcentration. An in-house built capacitively coupled contactless conductivity detector was employed for sensitive detection with narrow capillaries of 25 μm internal diameter. The system was assembled into standardized 19 in. frames and racks for easy transport and mobile deployment. The system can be left running unattendedly without manual intervention with good operation stability. To demonstrate the application of the system, a method for the determination of four drugs, namely ibuprofen, diclofenac, naproxen and bezafibrate, was developed with enrichment factors of up to several hundreds. Detection of the drug residues down to the nM-scale was found possible and the method was found suitable for the detection of ibuprofen in the waste water of a hospital in Hanoi.     

Post column derivatization with a lead dioxide solid phase reactor as part of a continuous chromatographic detection system: Speciation measurements of chromium

Summary A post chromatographic chemical reaction detector is described for the determination of Cr (III) and Cr (VI) in the range of 100ng/ml to 10μg/ml. All chromium species which exist in a lower oxidation state than the sixvalent form are oxidized to chromate in a lead dioxide solid phase reactor. The detection is performed by complexation of the chromate with 1,5-diphenylcarbazide, which forms a red-violet complex detectable at 540 nm. The conditions which are necessary for a fast oxidation inside the solid phase reactor are discussed. The system which can also be run in the flow injection mode is applied to measurements of synthetic waste waters and to samples from a steel work. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Ultratraces analysis of organochlorine pesticides in drinking water by solid phase extraction coupled with large volume injection/gas chromatography/mass spectrometry

This study describes an SPE coupled with large volume injection (LVI) analytical method for the analysis of organochlorine pesticides, BHC (alpha, beta, delta), aldrin, endosulfan (alpha, beta), endrin, dieldrin, and DDT, from aqueous samples. Determination was carried out by GC with MS. The LODs of organochlorine pesticides were determined at 10 ng/L concentration levels, and the results show that SPE-LVI-GC/MS has the potential to accurately determine organochlorine pesticides in water, as it avoids analyte classes in the various steps of a typical extraction procedure.     

Coupling of solid phase microextraction with electrospray ionization ion mobility spectrometry and direct analysis of venlafaxine in human urine and plasma

The capability of electrospray ionization-conventional ion mobility spectrometry (ESI–IMS) for direct analysis of the samples extracted by solid phase microextraction (SPME) was investigated and evaluated for the first time. To that end, an appropriate new desorption chamber was designed and constructed, resulting in the possibility of direct exposure of the SPME fiber to the electrospray solvent flow. Two different elution methods in dynamic and static modes were exhaustively investigated. The results indicated that the interface could help us to have an accurate and sensitive analysis without disturbing the electrospray process, in static elution method. Venlafaxine as a test compound was extracted from human urine and plasma by a convenient headspace SPME method. The positive ion mobility spectrum of the extracted drug was obtained and the analyte responses were calculated. The coupled method of SPME–ESI–IMS was comprehensively validated in terms of sensitivity, dynamic range, and recovery percentage. Finally, various real samples of human urine and plasma were analyzed, all verifying the feasibility and success of the proposed method for the easy routine analysis.     

Determination of arsenic and selenium by hydride generation and headspace solid phase microextraction coupled with optical emission spectrometry

A hydride generation headspace solid phase microextraction technique has been developed in combination with optical emission spectrometry for determination of total arsenic and selenium. Hydrides were generated in a 10 mL volume septum-sealed vial and subsequently collected onto a polydimethylsiloxane/Carboxen solid phase microextraction fiber from the headspace of sample solution. After completion of the sorption, the fiber was transferred into a thermal desorption unit and the analytes were vaporized and directly introduced into argon inductively coupled plasma or helium microwave induced plasma radiation source. Experimental conditions of hydride formation reaction as well as sorption and desorption of analytes have been optimized showing the significant effect of the type of the solid phase microextraction fiber coating, the sorption time and hydrochloric acid concentration of the sample solution on analytical characteristics of the method developed. The limits of detection of arsenic and selenium were 0.1 and 0.8 ng mL^− 1, respectively. The limit of detection of selenium could be improved further using biosorption with baker's yeast Saccharomyces cerevisiae for analyte preconcentration. The technique was applied for the determination of total As and Se in real samples.     

Speciation of selenium(IV) and selenium(VI) in environmental samples by the combination of graphite furnace atomic absorption spectrometric determination and solid phase extraction on Diaion HP-2MG

A simple solid phase extraction procedure for speciation of selenium(IV) and selenium(VI) in environmental samples has been proposed prior to graphite furnace atomic absorption spectrometry. The method is based on the solid phase extraction of the selenium(IV)-ammonium pyrrolidine dithiocarbamate (APDC) chelate on the Diaion HP-2MG. After reduction of Se(VI) by heating the samples in the microwave oven with 4 mol l⁻¹ HCl, the system was applied to the total selenium. Se(VI) was calculated as the difference between the total selenium content and Se(IV) content. The experimental parameters, pH, amounts of reagents, eluent type and sample volume were optimized. The recoveries of analytes were found greater than 95%. No appreciable matrix effects were observed. The adsorption capacity of sorbent was 5.20 mg g⁻¹ Se (IV). The detection limit of Se (IV) (3sigma, n = 11) is 0.010 μg l⁻¹. The preconcentration factor for the presented system was 100. The proposed method was applied to the speciation of selenium(IV), selenium(VI) and determination of total selenium in natural waters and microwave digested soil, garlic, onion, rice, wheat and hazelnut samples harvested various locations in Turkey with satisfactory results. In order to verify the accuracy of the method, certified reference materials (NIST SRM 2711 Montana Soil, NIST SRM 1568a Rice Flour and NIST SRM 8418 Wheat Gluten) were analyzed and the results obtained were in good agreement with the certified values. The relative errors and relative standard deviations were below 6 and 10%, respectively.     

Preconcentration and determination of boron in milk,infant formula,and honey samples by solid phase extraction-electrothermal atomic absorption spectrometry

This work presents alternative procedures for the electrothermal atomic absorption spectrometric determination of boron in milk, infant formulas, and honey samples. Honey samples (10% m/v) were diluted in a medium containing 1% v/v HNO₃ and 50% v/v H₂O₂ and introduced in the atomizer. A mixture of 20 µg Pd and 0.5 µg Mg was used for chemical modification. Calibration was carried out using aqueous solutions prepared in the same medium, in the presence of 10% m/v sucrose. The detection limit was 2 µg g^− 1, equivalent to three times the standard error of the estimate (s_y/x) of the regression line. For both infant formulas and milk samples, due to their very low boron content, we used a procedure based on preconcentration by solid phase extraction (Amberlite IRA 743), followed by elution with 2 mol L^− 1 hydrochloric acid. Detection limits were 0.03 µg g^− 1 for 4% m/v honey, 0.04 µg g^− 1 for 5% m/v infant formula and 0.08 µg mL^− 1 for 15% v/v cow milk. We confirmed the accuracy of the procedure by comparing the obtained results with those found via a comparable independent procedure, as well by the analysis of four certified reference materials.     

Dynamic solid phase microextraction for sampling of airborne sarin with gas chromatography-mass spectrometry for rapid field detection and quantification

A portable dynamic air sampler and solid phase microextraction were used to simultaneously detect, identify, and quantify airborne sarin with immediate analysis of samples using a field portable gas chromatography-mass spectrometry system. A mathematical model was used with knowledge of the mass of sarin trapped, linear air velocity past the exposed sampling fiber, and sample duration allowing calculation of concentration estimates. For organizations with suitable field portable instrumentation, these methods are potentially useful for rapid onsite detection and quantification of high concern analytes, either through direct environmental sampling or through sampling of air collected in bags.     

Solid phase micro-extraction coupled with ion mobility spectrometry for the analysis of ephedrine in urine

Quantitative solid phase micro-extraction (SPME) coupled with ion mobility spectrometry is demonstrated using the analysis of ephedrine in urine. Since its inception in the 1970's ion mobility spectrometry (IMS) has evolved into a useful technique for laboratories to detect explosives, chemical warfare agents, environment pollutants and, increasingly, for detecting drugs of abuse. Ephedrine is extracted directly from urine samples using SPME and the analyte on the fiber is heated by the IMS desorber unit and vaporized into the drift tube. The analytical procedure was optimized for fiber coating selection, extraction temperature, extraction time, sample pH, and analyte desorption temperature. The carryover effects, ion fragmentation characteristics, peak shapes, and drift times of ephedrine were also evaluated based on the direct interfacing of SPME to IMS. A limit of detection of 50 ng/mL of ephedrine in urine and a linear range of 3 orders of magnitude were obtained, showing that SPME-IMS compares well to other techniques for ephedrine and drug analysis presented in the literature.