On-line Trace Enrichment Research Articles

Imprinted polymer grafted from silica particles for on-line trace enrichment and ICP OES determination of uranyl ion

Analytical performance of an ion imprinted polymer (IIP)-coated silica packed micro-column in combination with inductively coupled plasma optical emission spectrometry (ICP OES) has been evaluated for on-line trace enrichment and determination of uranyl ion. The influences of the column and radial viewing ICP OES parameters such as flow rate of eluent, RF power, nebulizer gas pressure, and viewing zone of plasma on the transient signal-to-noise ratio were investigated at wavelength of 385.958nm. The breakthrough capacity of the column and signal enhancement factor of the method were evaluated as 1.7×10−3mmolg−1 and 230, respectively. The limit of detection (LOD) for the proposed method was obtained as 0.09μgL−1. A dynamic linear range was observed in the concentration window from 0.3 to 250μgL−1 (r2=0.996). Robustness of the method was evaluated by Dong's criterion. The accuracy of the method was investigated by determining uranyl ion in spiked samples of spring, well, and tap water and also by comparing the results with those obtained using inductively coupled plasma mass spectrometry (ICP MS).

Quantification and confirmation of priority organic micropollutants in water by LC-tandem mass spectrometry

Liquid chromatography coupled to tandem mass spectrometry with a triple quadrupole analyser was used to determine selected (medium) polar organic pollutants—isoproturon, diuron and pentachlorophenol, as the herbicides simazine, atrazine, terbuthilazine, alachlor, and metolachlor—in treated water from urban solid-waste leachates. Two millilitres of water was preconcentrated by on-line trace enrichment (solid-phase extraction liquid chromatography) which allowed rapid analysis, but still with a satisfactory sensitivity, as the limits of quantification were 0.05 µg L−1, while the limits of detection were in the range of 0.001–0.01 µg L−1. Confirmation of the identity of compounds was ensured by the use of two tandem mass spectrometry transitions. Moreover, a study of matrix effects was thoroughly investigated by applying the developed procedure to different ground and surface waters. A simple dilution of the water sample with high-performance-liquid-chromatography-grade water was sufficient to minimize and/or remove this undesirable effect in all water samples tested, this approach being feasible due to the excellent sensitivity of the method.

Online trace enrichment to determine pyrethroids in river water by HPLC with column switching and photochemical induced fluorescence detection

The potential of online trace enrichment on a highly apolar short column in LC was evaluated for the determination of pyrethroids in river water. Twelve millilitres of water samples, modified with 8 mL ACN (ACN/water 40:60, v/v), were passed through 50 x 4.6 mm ID first separation column packed with 5 microm Hypersil Elite C18. Pesticides were preconcentrated in this column while the matrix background was eluted to waste. Separation of pesticides was performed on a 3.5 microm symmetric C18 column (250 x 4.6 mm ID) with an ACN step gradient as mobile phase and fluorescence detection was used after postcolumn derivatization by using UV light. The use of photochemically induced fluorescence for detection improved sensitivity and selectivity. Quantification limits ranged from 0.05 to 0.1 microg/L and pesticide recoveries at two concentration levels (0.1 and 0.5 microg/L) were between 93.1 and 118.6%, with RSD between 2.5 and 7.5% (n = 3) in river water samples. No matrix effect was detected.

Strategies for quantification and confirmation of multi-class polar pesticides and transformation products in water by LC–MS 2 using triple quadrupole and hybrid quadrupole time-of-flight analyzers

Liquid chromatography–tandem mass spectrometry (LC–MS 2) is an excellent technique for the determination of polar pesticides and transformation products in water. On-line trace enrichment by solid-phase extraction (SPE)-LC in combination with MS 2 satisfies most analytical demands of modern laboratories for pesticide-residue analysis, with respect to sensitivity (limits of detection and limits of quantification at sub-μg/L levels), selectivity, reliability and rapidity, and all with very little sample manipulation. However, several obstacles have to be overcome when developing SPE-LC–MS 2 multi-residue and confirmative methods. The different physicochemical characteristics and wide polarity range of pesticides and their transformation products make their simultaneous preconcentration, chromatographic separation and determination difficult. Also, for the correct confirmation of the identity of compounds, it is necessary to increase the number of monitored MS transitions, which normally leads to a loss in sensitivity. This may hamper confirmation at low concentrations in a single chromatographic run (i.e., when a second analysis is not performed). In this article, we discuss different strategies for developing sensitive multi-residue methods for pesticides in water, able to correctly quantify and confirm compounds detected in samples. We discuss the use of different analyzers, triple quadrupole and hybrid quadrupole time-of-flight and compare their performances for screening purposes, and for the quantification and confirmation of positive samples. We present several practical cases of water samples, including some positive findings that would result in false positives if no criteria were applied for unequivocal confirmation of the identity of detected compounds.

On-line trace enrichment of phenolic compounds from water using a pyrrole-based polymer as the solid-phase extraction sorbent coupled with high-performance liquid chromatography

A pyrrole-based conductive polymer was prepared and applied as new sorbent for on-line solid-phase extraction (SPE) of phenol and chlorophenols from water samples. Polypyrrole (PPy) was synthesized by chemical oxidation of the monomer in non-aqueous solution. The efficiency of this polymer for extraction of phenol and chlorophenols was evaluated using 35 mg of PPy as the sorbent in an on-line SPE system coupled to reversed-phase liquid chromatography with UV detection. The mobile phase were mixture of phosphate buffer–acetonitrile and compounds were eluted by the mobile phase using a six-port switching valve. High volumes of water, up to 160 ml, could be preconcentrated without the loss of phenols, except for the more polar ones. The R.S.D. for a river water sample spiked with phenol and chlorophenols at sub-ppb level was lower than 7% ( n =5) and detection limits of 15–100 and 35–150 ng l −1 for tap and river water were obtained, respectively.

Trace enrichment and determination of silver by immobilized DDTC microcolumn and flow injection atomic absorption spectrometry

Flow injection (FI) system incorporating a microcolumn of immobilized diethyldithiocarbamate (DDTC) on surfactant-coated alumina was combined with atomic absorption spectrometry for on-line trace enrichment and determination of silver in different matrices. Silver was deposited on the microcolumn by processing a standard or solution of analyte at pH 3–4 on the column. Injection of 250μl of ethanol then served to elute the retained species to atomic absorption spectrometry (AAS). A sample volume of 20ml resulted in a pre-concentration factor of 125, and precision at the 20μgl−1 was 4% (R.S.D.). The procedure was applied to tap water, well water, rain water, sea water, radiology film, and lead concentrate samples. The accuracy was assessed through recovery experiments, independent analysis by furnace-AAS, and analysis of certified reference material.

Trace enrichment and determination of silver by immobilized DDTC microcolumn and flow injection atomic absorption spectrometry

Flow injection (FI) system incorporating a microcolumn of immobilized diethyldithiocarbamate (DDTC) on surfactant-coated alumina was combined with atomic absorption spectrometry for on-line trace enrichment and determination of silver in different matrices. Silver was deposited on the microcolumn by processing a standard or solution of analyte at pH 3–4 on the column. Injection of 250 μl of ethanol then served to elute the retained species to atomic absorption spectrometry (AAS). A sample volume of 20 ml resulted in a pre-concentration factor of 125, and precision at the 20 μg l −1 was 4% (R.S.D.). The procedure was applied to tap water, well water, rain water, sea water, radiology film, and lead concentrate samples. The accuracy was assessed through recovery experiments, independent analysis by furnace-AAS, and analysis of certified reference material.

On-line trace enrichment of phenolic compounds from water using a pyrrole-based polymer as the solid-phase extraction sorbent coupled with high-performance liquid chromatography

A pyrrole-based conductive polymer was prepared and applied as new sorbent for on-line solid-phase extraction (SPE) of phenol and chlorophenols from water samples. Polypyrrole (PPy) was synthesized by chemical oxidation of the monomer in non-aqueous solution. The efficiency of this polymer for extraction of phenol and chlorophenols was evaluated using 35 mg of PPy as the sorbent in an on-line SPE system coupled to reversed-phase liquid chromatography with UV detection. The mobile phase were mixture of phosphate buffer–acetonitrile and compounds were eluted by the mobile phase using a six-port switching valve. High volumes of water, up to 160 ml, could be preconcentrated without the loss of phenols, except for the more polar ones. The R.S.D. for a river water sample spiked with phenol and chlorophenols at sub-ppb level was lower than 7% ( n=5) and detection limits of 15–100 and 35–150 ng l −1 for tap and river water were obtained, respectively.

Liquid chromatography and tandem mass spectrometry: a powerful approach for the sensitive and rapid multiclass determination of pesticides and transformation products in water.

In this paper we will show the results of our research on the direct simultaneous determination of multi-class pesticides and transformation products with different polarities and acid-base properties by applying an on-line trace enrichment coupled to the chromatographic system supplied with electrospray interface (SPE-LC-MS/MS method). The specific chromatographic separation allows the correct determination of almost fifty compounds (37 pesticides and 10 transformation products) using very low sample volume and very little sample handling. Recoveries between 70-120% were obtained for all compounds in drinking and groundwater, meanwhile in surface water 44 compounds were correctly quantified. Relative standard deviations lower than 15% were obtained for all compounds. Even at the lowest concentration level tested (25 ng L(-1)) 40 compounds presented satisfactory recoveries and repeatability. The use of methanol as organic modifier and the increase of injection volume are also studied. The applicability of the developed method to a monitoring programme is demonstrated by applying it to the analysis of hundreds of samples.

Immobilized 1,5-diphenylcarbazone as a complexing agent for on-line trace enrichment and determination of copper by flow injection-atomic absorption spectroscopy

A rapid on-line preconcentration technique for the determination of copper in different samples by FI-AAS has been devised. Preconcentration is based on the deposition of analyte on a micro-column of 1,5-diphenylcarbazone immobilized on surfactant coated alumina and subsequent elution by injection of a small volume of hydrobromic acid (500 µl of 0.75 mol l−1acid). A sample volume of 30 ml resulted in a preconcentration factor of 100, and precisions at the 100 and 10 µg l−1 levels were 3.2 and 3.5% RSD, respectively. The procedure was applied to spring water, well water, sea-water, stainless steel and a multivitamin tablet and the accuracy was assessed through recovery experiments, independent analysis by furnace-AAS, and the analysis of a certified reference material.

Rapid Target Analysis for Pesticides in Water by Online Coated Capillary Microextraction Combined with Liquid Chromatography and Tandem Mass Spectrometry

The applicability of online trace enrichment with custom-made coated capillaries combined with tandem mass spectrometry was demonstrated for the target analysis of selected pesticides (mainly herbicides, e.g., triazines, phenylureas, and acetanilides) in water. The developed method allows rapid determination of several widely used plant protectants within a total analysis time of 11 min. Good linearity (r > or = 0.995) was obtained for the selected pesticides in the range of 0.050-50 microg/L. The relative standard deviations (RSDs) of the peak areas were < or = 3.8% for spiked Milli-Q water (5 microg/L). The RSDs obtained in analyses of spiked (1 microg/L) water samples (brook water, river water, sewage plant effluent) ranged from 2.9 to 6.8%, indicating low influence of the matrix on enrichment and detection. The detection limits, which ranged from 10 to 90 ng/L, fulfilled the requirements of the European regulations for drinking water. The polyacrylate coating of the extraction capillary showed good stability in the presence of water and acetonitrile and allowed > or = 100 extractions with 1 capillary.

Online Trace Enrichment and Determination of Cobalt Ion as an Anionic Complex by Flow Injection Atomic Absorption Spectrometry

A flow injection system incorporating a microcolumn of activated alumina was combined with atomic absorption spectrometry for on-line trace enrichment and determination of cobalt in waters and vitamin B12. Deposition of cobalt as its cyano complex was effected with the use of an acidic alumina microcolumn, and injection of ammonia solution (500 μl, 2 M) served to elute species retained on the atomic absorption spectrometer. A sample volume of 15 ml resulted in a preconcentration factor of 120, and precision at the 500 and 50 μg liter−1 levels was ±3.1 and ±3.3% (RSD), respectively. The procedure was applied to mineral water, spring water, river water, and vitamin B12 and accuracy was assessed through a recovery experiment.

Large-volume liquid chromatographic trace-enrichment system for environmental analysis

The fully automated on-line trace enrichment of 27 (polar) pollutants, using volumes of up to 1,000 mL, on a polymeric precolumn followed by liquid chromatography —diode-array detection has been studied. Various parameters influencing the reproducibility of these large volume injections like breakthrough volume, precolumn capacity, matrix effects, and enrichment flow rate are discussed. The relative standard deviation of the recoveries after enrichment of 25–500 mL of sample is 1–20%. Enrichment flow rates up to 15 mL min−1 can be used with an optimum at 10 mL min−1. A pore size of 300 A provides the best results using the polymeric PLRP-S material. The breakthrough volumes show significant dependence upon the concentration of the analytes in the sample.

On-line trace enrichment for the simultaneous determination of microcystins in aqueous samples using high-performance liquid chromatography with diode-array detection

The need for a rapid, sensitive and reliable analytical method for cyanobacterial toxins, microcystins, has been emphasized by the awareness of toxic cyanobacteria as a human-health risk through drinking water. A new high-performance liquid chromatographic method with column switching was developed for the determination of microcystin-LR, -RR and -YR from water samples without pre-purification. The filtered water sample was passed through a Zorbax CN precolumn at a flow-rate of 3 ml/min for on-line trace enrichment. After valve switching, concentrated analytes were eluted in back-flush mode and separated on a Luna C 18 column with a gradient of acetonitrile –20 m M phosphate buffer (pH 2.5). The method showed excellent precision, accuracy and speed with detection limits of 0.02 μg/ml from 100 ml of surface water. The total analysis time per sample was about 90 min. This method improves reliability, sensitivity and sample throughput, and shortens the analysis time compared to analysis methods using off-line solid-phase extraction.

Automated determination of phenylcarbamate herbicides in environmental waters by on-line trace enrichment and reversed-phase liquid chromatography–diode array detection

A fully automated liquid chromatographic method using on-line trace-enrichment, gradient elution and diode array detection is described for the trace-level determination of several phenylcarbamate herbicides, such as carbetamide, propham, desmedipham, phenmedipham, chlorbufam and chlorpropham, in environmental water samples. In this work, two different enrichment pre-columns have been assayed, a 5.8×4.6 mm I.D., 10 μm ODS Prelute cartridge and a 10×2 mm I.D. cartridge filled with 10 μm PRP-1 polymer, both coupled to a 150×4.6 mm I.D. analytical column filled with 5 μm ODS. Using the C 18 pre-column, up to 50 ml of water sample could be percolated without peak broadening of any compound. However, a lack of reproducibility was observed in the case of carbetamide, the most polar analyte, after performing recovery experiments by percolating drinking and surface water samples spiked at several levels (0.5 and 4 μg l −1). On the other hand, the PRP-1 pre-column allowed the enrichment up to 100 ml of water sample with satisfactory results for every compound, including carbetamide. The procedure was validated by recovery experiments in environmental water samples spiked at 0.2 and 1 μg l −1 yielding average recoveries between 84–108% with relative standard deviations in the range 2–12%. Detection limits as low as 0.04 μg l −1 were achieved. It was observed that desmedipham and phenmedipham degraded rapidly in the environmental water samples as showed the degradation studies performed along 24 h in drinking and surface waters spiked at 4 μg l −1. Although the standard mixture, prepared in HPLC water, was stable for around one week, in the environmental water matrices more than 95% of each herbicide degraded after 6 h, and new chromatographic peaks corresponding to the degradation products were detected.

High-performance liquid chromatographic analysis of biogenic amines in cells and in culture media using on-line dialysis and trace enrichment

A highly sensitive method is presented for the automatic quantitative detection of DOPA metabolites in low concentrations in cells derived from the neural crest using reversed-phase HPLC in combination with fluorescence and electrochemical detection. The HPLC system was combined with on-line dialysis and on-line trace enrichment for the detection of small quantities of DOPA metabolites in culture media. Parameters like detector settings, pH, dialysis time and flow-rates are evaluated and optimized. Static–continuous dialysis can be performed at a low flow-rate concomitant with a high dialysis efficiency (up to >65%) depending on the type of DOPA metabolite. Counterflow dialysis can be used to analyse, with low efficiencies (17–29%), samples consisting of large volumes. Samples containing up to at least 7% (w/v) protein can be analysed in the low flow-rate static–continuous mode. In this last mode of dialysis, limits of detection for dopamine, norepinephrine, epinephrine and n-methyldopamine in DMEM/HAMF12 medium samples are 100 fmol or even lower. Serotonin is detectable at 10 fmol at a signal/noise ratio of 3. Biogenic amines were detectable at a concentration of 10 fmol/μl in a volume of 100 μl medium with an intra- and inter-assay imprecision <6.4%. This method is applied to study the differentiation level of tumour cells in culture and slices of a tumour derived from the neural crest. With this system, we also detected the excretion of DOPA metabolites from PC-12 cells after treatment with prenylamine.

On-line trace enrichment in hyphenated liquid chromatography–nuclear magnetic resonance spectroscopy

The potential of on-line trace enrichment combined with column liquid chromatography–nuclear magnetic resonance detection (LC–NMR) is demonstrated for the identification of hop bitter acids in hop extracts. By performing on-line solid-phase extraction on 1–5 ml of hop extract (which contains the six major hop bitter acids) the detection/analysis time in the stopped-flow detection mode could be reduced 4-fold, from 60 min to 15 min per individual peak. The applicability of combined trace enrichment and separation using a single short (12.5 mm×4.6 mm I.D.) high-pressure-packed column combined on-line with NMR was also studied. Sample enrichment of 5 ml of a solution spiked with three drugs at 5 μg/ml was sufficient for the acquisition of high-quality spectra both in the stopped-flow and even in the continuous-flow detection mode. The examples demonstrate that analyte detectability can be significantly improved by performing on-line sample enrichment prior to LC–NMR analysis.

Quantitative analysis of HBY 097 and its metabolites in human serum and urine by HPLC

Two HPLC methods were developed: one for the quantitation of HBY 097 reverse transcriptase inhibitor and its metabolites M2 and M3 in human serum, and one for the quantitation of metabolite M5 in urine. The HPLC procedure for the quantitation of HBY 097 and its metabolites M2 and M3 in human serum involved protein precipitation with acetonitrile followed by automated on-line trace enrichment. The HPLC procedure for the analysis of metabolite M5 in urine involved enzymatic hydrolysis of urine with β-glucuronidase to convert metabolite M5 (glucuronide of M3) to M3. Reverse phase chromatographic separation with gradient elution, UV detection at 335 nm, and internal standard were used to quantitate analytes in both procedures. The lower quantitation limits were 25 ng ml −1 for HBY 097 and metabolites M2 and M3 in serum, and 0.5 μg ml −1 for the metabolite M5 in urine measured as metabolite M3 after hydrolysis. The HBY 097 and metabolite M3 concentrations were specific but metabolite M2 was semi-specific because the two diastereomers of M2 were not resolved by the present chromatographic procedure. Both procedures were applied to the quantitation of HBY 097 and its metabolites in serum and urine of HIV positive patients who were enrolled in a clinical study of drug safety and pharmacokinetics.

Baker's yeast biomass (Saccharomyces cerevisae) for selective on-line trace enrichment and liquid chromatography of polar pesticides in water.

Baker's yeast cells (Saccharomices cerevisae) were successfully immobilized onto silica gel and used in the on-line isolation and trace enrichment of desisopropylatrazine, desethylatrazine, hydroxyatrazine, simazine, cyanazine, atrazine, carbaryl, propanil, linuron, and fenamiphos. Since humic and fulvic acids were not coextracted, no cleanup was necessary. The pesticides were spiked at 0.1-1 microgram L-1 in tap water, groundwater, and seawater and were preconcentrated using on-line solid-phase extraction into a yeast immobilized on silica gel precolumn followed by liquid chromatography with diode array detection. All the variables that affect the enrichment step, such as amount of yeast immobilized, dimensions of the precolumn, sample pH, and preconcentration flow rate, were optimized. The degree of selectivity was evaluated by comparing the chromatograms obtained after on-line sample preconcentration on the yeast precolumn with those obtained by on-line solid-phase extraction using a precolumn filled with C18 material. The relative standard deviation for the whole procedure in the determination of the selected pesticides at the 0.3 microgram L-1 concentration level ranged from 1 to 9%, depending on the pesticide and the type of water. Detection limits within the range 0.01-0.5 microgram L-1 were obtained by percolating only 25 mL of water sample without any additional cleanup step.

Improvements in environmental trace analysis by GC-IR and LC-IR

Research has been carried out to enlarge the potential of infrared (IR) spectrometry as a detector in gas and liquid chromatography (GC and LC). The study has been directed to applications in environmental analysis. Examples of recently obtained results are presented. The analyte detectability of GC-IR has been improved by incorporation of an on-column interface for the introduction of large sample volumes. The feasibility of the technique is demonstrated by the identification of pesticides in water at a level of 0.5 μg 1 −1 using on-line desorption of pre-sampled solid-phase extracted cartridges. The detectability of LC-IR, based on solvent elimination interfacing, has been enhanced by on-line trace enrichment. The applicability has been extended to buffered aqueous mobile phases by on-line post-column liquid-liquid extraction into a volatile solvent, and to gradient separations by reduction of the analytical flow using capillary LC combined with post-column addition of a make-up liquid. With both techniques, herbicides have been identified in water samples in the low μg 1 −1 range.