On-line Preconcentration Research Articles

Field-amplified sample injection combined with capillary electrophoresis for the simultaneous determination of five chlorophenols in water samples.

A sensitive method of CZE-ultraviolet (UV) detection based on the on-line preconcentration strategy of field-amplified sample injection (FASI) was developed for the simultaneous determination of five kinds of chlorophenols (CPs) namely 4-chlorophenol (4-CP), 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), and 2,6-dichlorophenol (2,6-DCP) in water samples. Several parameters affecting CZE and FASI conditions were systematically investigated. Under the optimal conditions, sensitivity enhancement factors for 4-CP, 2-CP, 2,4-DCP, 2,4,6-TCP, and 2,6-DCP were 9, 27, 35, 43, and 43 folds, respectively, compared with the direct CZE, and the baseline separation was achieved within 5min. Then, the developed FASI-CZE-UV method was applied to tap and lake water samples for the five CPs determination. The LODs (S/N=3) were 0.0018-0.019µg/mL and 0.0089-0.029µg/mL in tap water and lake water, respectively. The values of LOQs in tap water (0.006-0.0074µg/mL) were much lower than the maximum permissible concentrations of 2,4,6-TCP, 2,4-DCP, and 2-CP in drinking water stipulated by World Health Organization (WHO) namely 0.3, 0.04, and 0.01µg/mL, respectively, and thereby the method was suitable to detect the CPs according to WHO guidelines. Furthermore, the method attained high recoveries in the range of 83.0-119.0% at three spiking levels of five CPs in the two types of water samples, with relative standard deviations of 0.37-8.58%. The developed method was proved to be a simple, sensitive, highly automated, and efficient alternative to CPs determination in real water samples.

Evaluation of polypropylene and polyethylene as sorbent packing materials in on-line preconcentration columns for trace Pb(II) and Cd(II) determination by FAAS

A novel flow injection solid phase extraction system coupled with flame atomic absorption spectrometer for automatic trace metal determination has been developed. The efficiency of two commercially available low-cost polymers (high-density polyethylene and polypropylene) as packing materials in on-line preconcentration columns for metal extraction was evaluated. Sodium diethyl dithiocarbamate was used as chelating reagent to form the desirable metal complexes while methyl isobutyl ketone was adopted to elute and deliver them into the flame atomizer for measurement and quantification. A comparable study between the two sorbents regarding the analytical performance characteristics was performed and revealed that polypropylene was more suitable than high-density polyethylene regarding the metal complex retention. All main parameters affecting the sensitivity of the proposed method were thoroughly optimized. By adopting polypropylene sorbent and a preconcentration time of 90 s the sampling frequency was 30 h−1, the enhancement factor was 180 and 44, the detection limit (3s) 1.5 and 0.30 μg L−1 while the precision was 2.8% (at 50.0 μg L−1) and 2.9% (at 20.0 μg L−1), for Pb(II) and Cd(II), respectively. The accuracy of the developed method was assessed by the analysis of a certified reference material and spiked environmental water samples.

Antibody-free detection of amyloid beta peptides biomarkers in cerebrospinal fluid using capillary isotachophoresis coupled with mass spectrometry

This study reports a capillary isotachophoresis (ITP) – electrospray ionization mass spectrometry (ESI-MS) method for the determination of several amyloid β (Aβ) peptides, which are biomarkers of Alzheimer’s disease (AD) in cerebrospinal fluids (CSF). For the first time, these peptides have been detected directly from CSF by MS without recourse to an immunocapture-based sample pre-treatment. The antibody-free approach is based on the marriage between capillary ITP, a powerful on-line electrokinetic preconcentration technique, and MS for simultaneous detection of different Aβ peptides. To ensure a good performance, the ITP process of fluorescently labelled Aβ peptides was for the first time implemented and verified with laser induced fluorescent detection, prior to methodology transfer to MS detection. Better detection sensitivity was achieved with labelled Aβ peptides for both detection modes. Using hydroxyl ions as the terminating and acetate as the leading ions, our method allows efficient ITP preconcentration under alkaline conditions of the slowly migrating Aβ peptides to reach quantifiable concentration down to 50 pM. The developed ITP-MS approach allows reliable quantification of different fluorescently derivatized Aβ peptides, i.e. Aβ 1–42, Aβ 1–40 and Aβ 1–38 down to sub nM ranges in CSF samples from AD and non-demented (healthy control) patients. Good agreement (<20% deviation) for the determination of Aβ 1–42/Aβ 1–40 ratio in CSF was achieved between results obtained with this new ITP-MS and our recently developed method based on large volume sample stacking coupled to CE. Discrimination of one AD patient from two healthy controls was successfully made with the Aβ 1–42/Aβ 1–40 ratio obtained by the developed ITP-MS method for the tested cerebrospinal fluid samples.

Performance of restricted access copper-imprinted poly(allylthiourea) in an on-line preconcentration and sample clean-up FIA-FAAS system for copper determination in milk samples

A new on-line solid phase preconcentration method using an ion-imprinted polymer with restrict access material based on copper-imprinted poly(allylthiourea) modified with 2-hydroxyethyl methacrylate and bovine serum (IIP-HEMA-BSA) to preconcentrate Cu2+ ions and exclude protein from milk samples via FIA-FAAS was developed. The samples were on-line preconcentrated at pH 4.5 through a mini-column packed with 50.0 mg of IIP-HEMA-BSA at a flow rate of 7.6 mL min−1 followed by a counter-current elution with 1.00 mol L−1 HCl towards the FAAS detector. The interference of ions commonly found in milk samples and the presence of BSA were investigated in the Cu2+ ions preconcentration. The method provided an analytical curve ranging from 3.6 to 100.0 μg L−1, preconcentration factor of 24-fold, limit of detection of 1.1 μg L−1 and sample throughput of 20 h−1. The accuracy of the method was attested by Cu2+ ions addition/recovery tests as well as by using GFAAS of samples microwave-assisted digested. The proposed method was successfully applied to the copper determination in milk samples, requiring only pH adjustment followed by preconcentration step as sample pretreatment. Copper content in bovine milk sample was 0.635 ± 0.042 mg kg−1, while to soybean milk samples were between 0.048 ± 0.008 and 0.094 ± 0.005 mg kg−1. To the best of our knowledge, the potential of IIP-HEMA-BSA for Cu2+ ions extraction from biological samples and simultaneous removal of macromolecules employing minimal sample pretreatment was demonstrated for the first time. The proposed extraction method stands out by being simple, fast and a low-cost analytical strategy when compared to the conventional microwave-assisted acid digestion.

Amplification of lysozyme signal detected in capillary electrophoresis using mixed polymer brushes coating with switchable properties

In this work, a mixed polymer brushes based on poly(2-methyl-2-oxazoline) (PMOXA) and poly(acrylic acid) (PAA) coated capillary with switchable protein adsorption/desorption properties was developed and applied for on-line extraction and preconcentration of lysozyme. The study of electroosmotic flow (EOF) and fluorescence microscope showed that the inner surface charge of PMOXA/PAA mixed brush coated capillary displayed the switchable behavior toward the change of pH value and ionic strength (I), and PMOXA/PAA mixed brushes coated capillary could adsorb high amounts of lysozyme at pH 7 (I = 10−5 M), and the most of adsorbed lysozyme could then be desorbed at pH 3 (I = 10−1 M). Subsequently, this coated capillary with switchable lysozyme adsorption/desorption ability was applied for on-line extraction and preconcentration of lysozyme during capillary electrophoresis (CE) performance. Under the process of on-line preconcentration, the detection signal (peak area) of lysozyme obtained in PMOXA/PAA coated capillary was 26 times that obtained in bare capillary under normal CE while the contour chain length of PAA was 1.56 times that of PMOXA. Moreover, the value of low detection limit (LOD) of lysozyme using above coated capillary under on-line preconcentration method reached to 4.5 × 10−9 mg/mL, and 1 × 105-fold sensitivity enhancement was realized for lysozyme as compared with the bare capillary under normal CE.

Graphene oxide as an efficient adsorbent of solid-phase extraction for online preconcentration of inorganic and organic mercurials in freshwater followed by HPLC-ICP-MS determination

For the past several decades, lots of adsorbent nanomaterials have been adopted for the enrichment of mercuric compounds. In this paper, graphene oxide bounded silica particles were employed as the absorbent for online preconcentration of Hg(II), methylmercury (MeHg) and ethylmercury (EtHg) by solid phase extraction. The adsorbent offered satisfactory adsorption capacities of 40.7 for Hg(II), 91.4 for MeHg and 103.8 mg g−1 for EtHg. Enrichment conditions such as type, concentration and volume of conditioning and eluting reagents were optimized. The pH, volume and flow rate of sample were also optimized. High enrichment factors (1963, 1881 and 1794 for Hg(II), MeHg and EtHg, respectively) were obtained with 10 mL sample (adjusted to pH 4–7) at 10 mL min−1 flow rate, 5 μL of 10 mM benzoic acid for elution and 4 mL of 1 mM 4-phenyl-3-aminothiourea for preconditioning. The detection limits obtained were downscaled to be 0.005 for Hg(II), 0.006 for MeHg and 0.009 ng L−1 for EtHg with relative standard deviations of all the analytes below 5%. Standard reference material and spiked water samples were analyzed for validating the method with satisfactory recoveries of 89–106%. The present method was successfully applied to determine mercury compounds in drinking water, and river and tap water, in which Hg(II), MeHg and EtHg were presented below the China's drinking standard limit of 1 μg L−1.

Simultaneous detection of Tripterygium wilfordii sesquiterpene alkaloids by microemulsion electrokinetic chromatography coupled with large volume sample stacking

A new simple, rapid and sensitive method using microemulsion electrokinetic chromatography (MEEKC) coupled with large volume sample stacking (LVSS) for the detection of five Tripterygium wilfordii sesquiterpene alkaloids (peritassine A, wilforgine, wilfordine, triptonine B and wilforine) was developed in this paper. For the separation of five Tripterygium wilfordii sesquiterpene alkaloids, a running buffer composed of 0.5% (w/v, 17 mmol/L) sodium dodecyl sulfate, 3.0% (v/v) n-butanol, 0.5% (v/v) n-hexane, 3.0% (v/v) ethanol, 7.0% (v/v) acetonitrile and 86.5% (v/v) 5 mmol/L Na2B4O7–10 mmol/L NaH2PO4 buffer (pH 8.5) was used. In order to improve the sensitivity, MEEKC combined with on-line preconcentration of large volume sample stacking was applied. The detection limits (defined as S/N = 3) in the range of 0.003–0.009 μg/mL were feasible. The proposed LVSS-MEKC was successfully applied to the detection of four analytes in Tripterygium wilfordii root bark with the average recoveries ranged from 103.2% to 107.2%.

Selective drug metabolite trace analysis by very high-volume injections and heartcut two-dimensional (2D)-ultrahigh performance liquid chromatography (UHPLC)

The application of two-dimensional liquid chromatography (2D-LC) is gradually growing also in the area of metabolite profiling and identification. The current contribution describes a heartcut 2D-UHPLC configuration that is applied in support of drug metabolism studies in development. The setup applies four LC columns: two analytical UHPLC columns to perform the first and second dimension separations, which are both preceded by a short HPLC column operated as trapping column. The first HPLC column allows a significant online preconcentration by large volume injection. The second short HPLC column is placed between the first and second dimension columns and enables the selection of orthogonal conditions in the second dimension independent of the first dimension making the heartcutting 2D approach more generic.The value of the setup was demonstrated with selective ultraviolet chromatograms obtained for the two major hydroxylated metabolites of atorvastatin separating them from a very high biological background, originating from an injection of 4 mL feces extract, by heartcut 2D-LC. In a second application, the main metabolite of imipramine was baseline separated from some minor metabolites that were co-eluting in the first dimension, allowing accurate and sensitive quantification. A quantification limit in the attogram/mL range was achieved thanks to the injection of 200 mL diluted urine, corresponding to 100 mL urine on column.

An On-Line Flow-Injection Sorbent Extraction System Coupled with Flame Atomic Absorption Spectrometry for Thallium Determination Using a PTFE Turning-Packed Column

A novel time-based flow-injection–solid-phase extraction system (FI–SPE) coupled with flame atomic absorption spectrometry (FAAS) for automatic on-line preconcentration and determination of thallium was developed. The efficiency of poly-tetrafluoroethylene (PTFE) turnings packed into a column as sorbent material was investigated for thallium extraction. Total thallium was determined by oxidizing thallium(I) to thallium(III), adding bromine in acidic solution. The formed [TlBr4]− anionic bromo complex was retained onto the PTFE turnings by on-line mixing with sodium diethyl dithiocarbamate (DDTC). The preconcentrated Tl(III)-DDTC complex was then effectively eluted with methyl isobutyl ketone (MIBK) and introduced into the flame atomizer for measurement and quantification. The column proved to be effective, stable, and reproducible, with a long lifetime. The enrichment factor was 105 for 60 s preconcentration time, and the sampling frequency 40 h−1. The detection limit was 1.93 μg L−1, and the relative standard deviation (RSD) was 3.2% at 50.0 μg L−1 concentration. The accuracy of the proposed method was estimated by analyzing certified reference materials and environmental and biological samples.

Determination of picomolar concentrations of thiol compounds in natural waters and biological samples by tandem mass spectrometry with online preconcentration and isotope-labeling derivatization

We present a sensitive, selective and robust method for the determination of 14 thiol compounds in aqueous samples. Thiols were derivatized with ω-bromoacetonylquinolinium bromide (BQB) and its deuterium labeled equivalent D7-ω-bromoacetonylquinolinium bromide (D7). Derivatized thiols were preconcentrated by online solid-phase extraction (SPE) followed by liquid chromatography separation and electrospray ionization tandem mass spectrometry determination (SPE/LC-ESI-MS/MS). The robustness of the method was validated for wide ranges in pH, salinity, and concentrations of sulfide and dissolved organic carbon (DOC) to cover contrasting natural water types. The limits of detection (LODs) for the thiols were 3.1–66 pM. Between 6 and 14 of the thiols were detected in different natural sample types at variable concentrations: boreal wetland porewater (0.7–51 nM), estuarine sediment porewater (50 pM–11 nM), coastal sea water (60 pM–16 nM), and sulfate reducing bacterium cultures (80 pM–4 nM). MS/MS fragmentation of the compounds produces two pairs of common product ions, m/z 130.2/137.1 and 218.1/225.1, which enables scanning for unknown thiols in precursor ion scan mode. Using this approach, we identified cysteine, mercaptoacetic acid, N-acetyl-L-cysteine and sulfurothioic S-acid in boreal wetland porewater. The performance of the developed method sets a new state of the art for the determination of thiol compounds in environmental and biological samples.

On-line preconcentration of sodium dodecyl sulfate-protein complexes using electrokinetic supercharging method with a prefilled water plug in capillary sieving electrophoresis.

An electrokinetic supercharging (EKS) method with a prefilled water plug at the head column of capillary was developed for on-line preconcentration of sodium dodecyl sulfate (SDS)-protein complexes in capillary sieving electrophoresis (CSE). Conventional EKS is a combination of electrokinetic injection with transient isotachophoresis (tr-ITP). The capillary is first filled with background electrolyte, then an appropriate amount of a leading electrolyte is filled and electro-injection is carried out for certain duration. After that, terminating electrolyte is filled, and tr-ITP is subsequently initiated, followed by capillary electrophoresis (CE) separation. In this work, the performance of EKS was evaluated by integrating multiple sub-methods step by step, and a water plug containing polymer was introduced before electrokinetic injection in order to further improve the concentration effect. The positive effects of the sub-methods were verified, including molecular sieving effect of polymer, field enhanced sample injection (FESI) with and without a water plug, and transient isotachophoretic electrophoresis-based FESI. It was observed that analyte discrimination usually encountered in conventional electrokinetic injection was eliminated due to the similar charge to mass ratios of SDS-protein complexes. Based on these results, a hybrid on-line preconcentration method, EKS with injecting a water plug containing polymer before sample electrokinetic injection, was proposed and used to indiscriminately preconcentrate SDS-protein complexes, which provided a sensitivity enhancement factor of more than 1000. It was very suitable for the analysis of low-abundance proteins, providing the information of their molecular mass.

Data trend shifts induced by method of concentration for trace metals in seawater: Automated online preconcentration vs. borohydride reductive coprecipitation of nearshore seawater samples for analysis of Ni, Cu, Zn, Cd, and Pb via ICP‐MS

AbstractThis research compares performance, reproducibility, and detection limits of ambient seawater analysis for trace metals using both borohydride reductive coprecipitation and an automated chelation column (seaFAST™ 2) preconcentration for matrix interferent elimination on total and dissolved grab samples in nearshore to marine waters, over a broad concentration range, prior to inductively coupled plasma mass spectrometry (ICP‐MS) injection. A move to an online preconcentration method both minimizes sample preparation, and eliminates correction errors when accounting for trace impurities in precipitated samples, induced via reagents. The reproducability of the online preconcentration method described, coupled with low blanks and method detection limits (MDLs), demonstrates the effectiveness of the automated procedure using ethylenediaminetriacetic and iminodiacetate acid chelation exchange resin and multianalyte determination by ICP‐MS for total and dissolved Ni, Cu, Zn, Cd, and Pb in marine water samples. Average CASS‐5 recoveries using the online preconcentration method (n = 9) were 109% ± 7%, 104% ± 5%, 103% ± 7%, 101% ± 3%, and 86% ± 8%, respectively. The MDLs obtained from the automated method for Ni, Cu, Zn, Cd, and Pb were 3.3, 1.8, 13.5, 4, and 10 times lower, respectively, than for the Borohydride method. There were statistically significant differences between the methods for CASS‐5 recoveries of Ni, Cu, Zn (p &lt; 0.0001), and Pb (p = 0.0024). Comparison of methods gave high concordance (rC ≥ 0.90) between methods for total and dissolved Ni, Cu, Zn, and Pb, and total Cd.

Sensitive Photochemically Induced Fluorescence Sensor for the Determination of Nitenpyram and Pyraclostrobin in Grapes and Wines

The primary aim of this study is to report a new approach for pesticide determination, based on the use of automated luminescent sensors for the analysis of specific analytes. In this regard, we have selected two widely used pesticides—nitenpyram and pyraclostrobin—as target compounds. The proposed system makes use of multicommutated flow injection analysis by employing photochemically induced fluorescence as detection technique. Strong fluorescent photodegradation products were obtained on-line by UV-irradiation of the analytes. Then, the on-line separation and pre-concentration of the analytes were carried out on the surface of C18 silica gel beads placed inside the flow cell, where the analytical signal was recorded. The proposed analytical method presents a detection limit of 0.2 mg kg−1 for both analytes. After an appropriate sample treatment, the method complies with the current maximum residue limits in table grapes and wine grapes. We carried out recovery experiments in grapes and wines, obtaining recoveries between 96 and 107% in all cases. The simplicity, low-cost, and high sensitivity of the proposed method make it an attractive approach for the analysis of these two pesticides in food commodities.

Novel sequential separation and determination of a quaternary mixture of fungicides by using an automatic fluorimetric optosensor

ABSTRACTA versatile flow-through multi-optosensor is proposed for the separation and spectrofluorimetric determination of mixtures of four widely used pesticides: carbendazim, thiabendazole, carbaryl and o-phenylphenol at µg g−1 levels in fruits. The flow system is based on the online pre-concentration and separation of the pesticides on a solid sensing microzone, followed by the sequential measurement of their native fluorescence. The separation of the pesticides takes place on a solid support located in the same flow cell, on which analytes are temporarily immobilized and separated from the matrix due to their different retention/desorption kinetics when they interact with the C18 silica gel microbeads. Suitable analytical parameters were obtained for the selected analytes, with method detection and quantification limits ranging between 0.1–0.5 and 0.2–1.6 µg g−1, respectively. These values comply with the maximum residue limits (MRLs) established by the Codex Alimentarius for these commodities; in addition, carbendazim, thiabendazole and ortho-phenylphenol comply with the MRLs of The European Union. The developed method was applied to the analysis of citrus fruits by performing recovery studies. Recoveries between 85% and 115% were obtained in all cases, and the results were confirmed by a liquid chromatography–mass spectrometry reference method.

Development of an online-coupled MARGA upgrade for the 2 h interval quantification of low-molecular-weight organic acids in the gas and particle phases

Abstract. A method is presented to quantify the low-molecular-weight organic acids such as formic, acetic, propionic, butyric, pyruvic, glycolic, oxalic, malonic, succinic, malic, glutaric, and methanesulfonic acid in the atmospheric gas and particle phases, based on a combination of the Monitor for AeRosols and Gases in ambient Air (MARGA) and an additional ion chromatography (Compact IC) instrument. Therefore, every second hourly integrated MARGA gas and particle samples were collected and analyzed by the Compact IC, resulting in 12 values per day for each phase. A proper separation of the organic target acids was initially tackled by a laboratory IC optimization study, testing different separation columns, eluent compositions and eluent flow rates for both isocratic and gradient elution. Satisfactory resolution of all compounds was achieved using a gradient system with two coupled anion-exchange separation columns. Online pre-concentration with an enrichment factor of approximately 400 was achieved by solid-phase extraction consisting of a methacrylate-polymer-based sorbent with quaternary ammonium groups. The limits of detection of the method range between 0.5 ng m−3 for malonate and 17.4 ng m−3 for glutarate. Precisions are below 1.0 %, except for glycolate (2.9 %) and succinate (1.0 %). Comparisons of inorganic anions measured at the TROPOS research site in Melpitz, Germany, by the original MARGA and the additional Compact IC are in agreement with each other (R2 = 0.95–0.99). Organic acid concentrations from May 2017 as an example period are presented. Monocarboxylic acids were dominant in the gas phase with mean concentrations of 306 ng m−3 for acetic acid, followed by formic (199 ng m−3), propionic (83 ng m−3), pyruvic (76 ng m−3), butyric (34 ng m−3) and glycolic acid (32 ng m−3). Particulate glycolate, oxalate and methanesulfonate were quantified with mean concentrations of 26, 31 and 30 ng m−3, respectively. Elevated concentrations of gas-phase formic acid and particulate oxalate in the late afternoon indicate photochemical formation as a source.

Characterization of Selected Pharmaceutical Micropollutants in River Water Using In-Situ Suspended Aggregate Microextraction and Field Enhancement Sample Injection-Capillary Electrophoresis

A new sample preconcentration technique known as in-situ suspended aggregate microextraction (iSAME) was used for the extraction of acetaminophen, ibuprofen, indomethacine, ciprofloxacin and diclofenac in river waters. The iSAME has been optimized in terms of surfactants selection and concentration, sample volume and extraction time. A combined surfactant of hexadecyltrimethyl ammonium bromide (CTAB) with 5-sulfosalicylic acid dihydrate (SSA) was studied to attain better extraction recoveries for the targeted pharmaceuticals. The separation of analytes was performed using capillary electrophoresis (CE) with online preconcentration by field enhancement sample injection (FESI) mode. The linearity, detection limits and recoveries were recorded and the sensitivity increased with enhancement factor of 11-140 folds. The developed method was successfully applied for the detection of selected pharmaceuticals in river water samples.

Sample Preconcentration Protocols in Microfluidic Electrophoresis.

Electrophoretic on-line sample preconcentration techniques in microfluidic channels improve the sensitivity prior to the separation. Among various techniques, the most important field-amplified sample stacking and sweeping on cross-channel microchips are demonstrated. As a novel microfluidic preconcentration approach, a large-volume sample stacking with electroosmotic flow pump (LVSEP) on straight-channel chips is also presented, which can omit a complicated voltage program for sample injection processes. In this chapter, we describe how to prepare and how to run these on-line sample preconcentration methods in microchip electrophoresis.

On-line preconcentration and determination of iron by flow injection analysis in nuclear fuels

Determination of trace level of iron in metallic uranium is of great importance. The developed procedure involves online pre-concentration and separation of iron and its determination using flow injection analysis system. The analyte forms complex with mandelic acid and retained in the micro column packed with cation exchanger and matrix goes to waste. The eluted iron was determined and the detection limit of the method is 5 ppb with a precision (RSD) at 100 ppb level of 6.2%.

Solid-Phase Extraction and Large-Volume Sample Stacking-Capillary Electrophoresis for Determination of Artificial Sweeteners in Water Samples

A sensitive and rapid method for the simultaneous analysis of artificial sweeteners, aspartame, acesulfame, cyclamate, saccharine, and phenylalanine in water samples using solid-phase and large-volume sample stacking-capillary electrophoresis (SPE-LVSS-CE) has been developed. Under optimal conditions, the proposed method had a linear range of 0.08 to 2.0 mg L−1, with limits of detection ranging from 0.03 to 0.18 mg L−1 with inter- and intraday repeatabilities < 10% (as a relative standard deviation) in all cases. The enrichment factor obtained was in a range from 20 to 89 times for each artificial sweetener compared with a conventional capillary zone electrophoresis (CZE). The method is adequate to analyze artificial sweeteners in water samples with different ionic strengths. The proposed method was employed in the analysis of 20 samples including drinking water such as mineral water, distilled water, spring water, and tap water. Nine of the tested samples were positive for the presence of aspartame, saccharine, and acesulfame with concentrations between 0.19 and 0.75 mg L−1, 0.08 mg L−1, and 0.08 mg L−1, respectively. The SPE-LVSS-CE is a robust, easy, fast, and efficient strategy for online preconcentration of artificial sweeteners in complex matrices.

Determination of ultratrace tellurium in water by hydride generation atomic absorption spectrometry using online separation and pre-concentration with nano-TiO2 microcolumn

Silica gel loaded with nano-TiO2 was used as solid phase extraction materials to prepare a microcolumn for the online enrichment of trace tellurium in water and then determined by hydride generation atomic absorption spectrometry (HG-AAS). The effect of pH and the flow rate of sample on the extraction efficiency, NaOH concentration on the elution efficiency and other factors influencing hydride generation efficiency of tellurium were carefully investigated. Under the optimized experimental conditions, the sensitivity and the limit of detection (LOD) of this method were 0.009 L/μg and 0.04 μg L−1, respectively, which were 1000 and 850 times better than those obtained by the traditional flame atomic absorption spectrometry (FAAS); and the LOD for tellurium was improved by 45 times in this work, when compared with that by hydride generation-atomic absorption spectrometry (HG-AAS) without any separation and pre-concentration. This method was found to be interference-free of transitional metal ions, probably because of the surface of the nano-TiO2 was positively charged under acidic conditions, and it does not adsorb their cations. This method was successfully applied to the determination of tellurium in water samples.