Application of chitosan functionalized with 3,4-dihydroxy benzoic acid moiety for on-line preconcentration and determination of trace elements in water samples

Chitosan resin functionalized with 3,4-dihydroxy benzoic acid (CCTS-DHBA resin) was used as a packing material for flow injection (FI) on-line mini-column preconcentration in combination with inductively coupled plasma-atomic emission spectrometry (ICP-AES) for the determination of trace elements such as silver, bismuth, copper, gallium, indium, molybdenum, nickel, uranium, and vanadium in environmental waters. A 5-mL aliquot of sample (pH 5.5) was introduced to the minicolumn for the adsorption/preconcentration of the metal ions, and the collected analytes on the mini-column were eluted with 2 M HNO₃, and the eluates was subsequently transported via direct injection to the nebulizer of ICP-AES for quantification. The parameters affecting on the sensitivity, such as sample pH, sample flow rate, eluent concentration, and eluent flow rate, were carefully examined. Alkali and alkaline earth metal ions commonly existing in river water and seawater did not affect the analysis of metals. Under the optimum conditions, the method allowed the determination of metal ions with detection limits of 0.08 ng mL⁻¹ (Ag), 0.9 ng mL⁻¹ (Bi), 0.07 ng mL⁻¹ (Cu), 0.9 ng mL⁻¹ (Ga), 0.9 ng mL⁻¹ (In), 0.08 ng mL⁻¹ (Mo), 0.09 ng mL⁻¹ (Ni), 0.9 ng mL⁻¹ (U), and 0.08 ng mL⁻¹ (V). By using 5 mL of sample solution, the enrichment factor and collection efficiency were 8–12 fold and 96–102%, respectively, whereas the sample throughput was 7 samples/hour. The method was validated by determining metal ions in certified reference material of river water (SLRS-4) and nearshore seawater (CASS-4), and its applicability was further demonstrated to river water and seawater samples.     

Solid-phase extraction and spectrophotometric determination of trace amounts of copper in water samples

A simple method for rapid and selective extraction, preconcentration and determination of copper as it's neocuproine complex by using octadecylsilica membrane disks and spectrophotometry is presented. Extraction efficiency and the influence of flow rates of sample solution and eluent, pH, amount of neocuproine and hydroxylamine hydrochloride, type and least amount of eluent for elution of copper complex from disks, break through volume and limit of detection were evaluated. Also the effects of various cationic interferences on percent recovery of copper were studied. Extraction efficiencies >99% were obtained by elution of the disks with minimal amount of solvent. The limit of detection of the proposed method is 0.12 ppb. The method was applied to the recovery and determination of copper in different water samples.     

DNA Quantification in Nanoliter Volumes

A novel method for the determination of proteins at nanogram levels was proposed based on the decrease of resonance light scattering (RLS) signal resulting from the interaction of dibromo-o-nitrophenylfluorone (DBONPF)-sodium lauroyl glutamate (SLG) with proteins. At pH 2.97, the decrease RLS intensity was proportional to the concentration of proteins in the range of nanogram levels with 3σ detection limits being 3.4 ng mL⁻¹ for bovine serum albumin (BSA), 1.7 ng mL⁻¹ for human serum albumin (HSA), 4.1 ng mL⁻¹ for γ-globulin (γ-IgG), 4.4 ng mL⁻¹ for egg albumin, 6.2 ng mL⁻¹ for pepsin (Pep) and 3.7 ng mL⁻¹ for α-chymotrypsin (Chy). The method is no protein-to-protein variability, simple, rapid, practical and relatively free from interference from coexisting substance, as well as much more sensitive than most of the reported methods. The proposed method was successfully applied to determine total protein in human serum samples.     

Simultaneous determination of disulfiram and bupropion in human plasma of alcohol and nicotine abusers

An isocratic high-performance liquid-chromatographic method has been developed for the simultaneous determination of disulfiram and bupropion in human plasma samples. Analyses were carried out on a C₈ reversed-phase column using a mobile phase composed of 50% acetonitrile and 50% aqueous phosphate buffer, containing triethylamine. Diode-array detection was used, operating at a wavelength of 250 nm. For the clean-up of plasma samples, a solid phase extraction procedure, based on C₂ cartridges, was implemented. Extraction yields of the analytes were satisfactory, being always higher than 84%. The calibration curve was linear over the 5–500 ng mL^-1 plasma concentration range for both disulfiram and bupropion. The method showed a high sensitivity (limit of detection of 1.5 ng mL^-1) and satisfactory precision, selectivity and accuracy. The application to human plasma samples obtained from some alcohol and nicotine abusers also gave good results.     

Ammonium pyrrolidinedithiocarbamate-modified activated carbon micro-column extraction for the determination of As(III) in water by graphite furnace atomic absorption spectrometry

A simple and selective method using ammonium pyrrolidinedithiocarbamate modified activated carbon (APDC-AC) as solid phase extractant has been developed for speciation of As(III) in water samples. At pH 1.8–3.0, As(III) could be adsorbed quantitatively by APDC-AC, and then eluted completely with 2.0 mL of 0.1 mol L⁻¹ HNO₃, while As(V) could almost not be retained at pH 1–7. Effects of acidity, sample flow rate, concentration of elution solution and interfering ions on the recovery of As(III) have been systematically investigated. Under the optimal conditions, the adsorption capacity of APDC-AC for As(III) is 7.3 mg g⁻¹. The detection limit (3σ) of As(III) is 0.05 ng mL⁻¹ for graphite furnace atomic absorption spectrometry (GFAAS) with enrichment factor of 50, and the relative standard deviation (RSD) is 4.1% (n = 9, C = 5 ng mL⁻¹). The method has been applied to the determination of trace As(III) in water, and the recoveries of As(III) are 100 ± 10%. Correspondence: Yiwei Wu, Department of Chemistry and Environmental Engineering, Hubei Normal University, Huangshi 435002, P.R. China     

Development of a colloidal gold-based lateral-flow immunoassay for the rapid simultaneous detection of clenbuterol and ractopamine in swine urine

A multianalyte lateral-flow immunochromatographic technique using colloidal gold-labeled polyclonal antibodies was developed for the rapid simultaneous detection of clenbuterol and ractopamine. The assay procedure could be accomplished within 5 min, and the results of this qualitative one-step assay were evaluated visually according to whether test lines appeared or not. When applied to the swine urines, the detection limit and the half maximal inhibitory concentration (IC₅₀) of the test strip under an optical density scanner were calculated to be 0.1 ± 0.01 ng mL⁻¹ and 0.1 ± 0.01 ng mL⁻¹, 0.56 ± 0.08 ng mL⁻¹, and 0.71 ± 0.06 ng mL⁻¹, respectively, the cut-off levels with the naked eye of 1 ng mL⁻¹ and 1 ng mL⁻¹ for clenbuterol and ractopamine were observed. Parallel analysis of swine urine samples with clenbuterol and ractopamine showed comparable results obtained from the multianalyte lateral-flow test strip and GC-MS. Therefore, the described multianalyte lateral-flow test strip can be used as a reliable, rapid, and cost-effective on-site screening technique for the simultaneous determination of clenbuterol and ractopamine residues in swine urine.      

Determination of trace rhodium by supramolecular catalytic kinetic spectrofluorimetry of β-CD-rhodium-KBrO3-vanillin salicylhydrazone

A sensitive catalytic kinetic spectrofluorimetric approach for determining ng mL⁻¹ levels of rhodium is presented, and the possible mechanism of the catalytic reaction was investigated. The determination is based on the catalytic property of rhodium to enhance the reaction of o-vanillin salicylhydrazone (OVSH) with potassium bromate in a water-ethanol medium at pH 4.80 and 45 °C. The presence of β-cyclodextrin (β-CD) obviously sensitized the assay due to its high inclusion ability towards OVSH. Under optimized experimental conditions, fluorescence measurements of the β-CD-rhodium-KBrO₃-OVSH catalytic kinetic reaction system were carried out in its fluorescent band centered at λ_ex = 333 nm and λ_em = 476 nm, respectively. The calibration graph was linear over the concentration range of 0.47–100 ng mL⁻¹ with a detection limit of 0.14 ng mL⁻¹. The effect of interferences was discussed, and the results show that the extraction method can be used to separate rhodium from interference species such as iridium. The proposed method, applied to several synthetic mixtures containing rhodium mixed with varying amounts of metal salts, produced satisfactory results.     

On-Line Solid Phase Extraction and Simultaneous Determination of Hafnium and Zirconium by ICP–Atomic Emission Spectroscopy

A new simple flow injection analysis (FIA) system is described for on-line preconcentration by solid phase extraction and simultaneous determination of Hf and Zr in different samples using inductively coupled plasma atomic emission spectroscopy with a charge coupling detector (CCD). Quinalizarin (QA) was loaded on an octadecyl silica-polyethylene mini-column for the retention of Hf and Zr ions in complexed form. A 0.3 M ammonium acetate was used as buffer for providing suitable conditions for complexation and increasing reproducibility. Retained ions on the solid phase were then eluted by a solution containing 3.0 M HCl and 0.5 M HNO₃. In this work, for reducing bandwidths of eluted ions, elution of minicolumn was carried out from opposite direction. The same solution was used as both carrier and eluent, in order to increase the reproducibility. The eluted ions were introduced into the conventional nebulizer of ICP–AES instrument. Effects of different parameters, including instrumental parameters of ICP and FIA were optimized. An enrichment factor of 330 for each analyte ion was obtained at a concentration level of 80 ppb. The detection limits of the proposed method for Hf and Zr were 0.16 ng mL⁻¹ and 0.04 ng mL⁻¹ respectively. The ability of the method for the recovery of Hf and Zr ions was tested in the presence of several diverse metal ions in a synthetic mixture and some real matrices. It was also applied to the determination of Zr and Hf ions in a standard soil and in a standard alloy as real samples.     

Development of a cloud point extraction and preconcentration method for silver prior to flame atomic absorption spectrometry

The possibility was investigated of using 2-mercaptobenzothiazole (MBT) for Ag(I) concentration by micellar extraction at cloud point (CP) temperature and subsequent determination by flame atomic absorption spectrometry (FAAS). The method is based on the complexation of Ag(I) with 2-mercaptobenzothiazole (MBT) in the presence of non-ionic micelles of Triton X-114. The effect of experimental conditions such as pH, concentration of chelating agent and surfactant, equilibration temperature and time on cloud point extraction was studied. Under the optimum conditions, the preconcentration of 10 mL of water sample in the presence of 0.1% Triton X-114 and 2 × 10⁻⁴ mol L⁻¹ 2-mercaptobenzothiazole permitted the detection of 2.2 ng mL⁻¹ silver. The calibration graph was linear in the range of 10–200 ng mL⁻¹, and the recovery of more than 99% was achieved. The proposed method was used in FAAS determination of Ag(I) in water samples.     

Determination of marker pteridines in urine by HPLC with fluorimetric detection and second-order multivariate calibration using MCR-ALS

A liquid chromatographic method has been developed, in combination with the multivariate curve resolution-alternating least squares algorithm (MCR-ALS), for the simultaneous determination of marker pteridines in urine samples. A central composite design has been applied to optimize the factors influencing the separation (buffer concentration, buffer pH, flow rate, oven temperature, mobile-phase composition). A set of 15 calibration samples were randomly prepared, in a concentration range of 0.5–10.5 ng mL⁻¹ for neopterin, biopterin, and pterin; 4.0–8.0 ng mL⁻¹ for xanthopterin; and 0.5–4.5 ng mL⁻¹ for isoxanthopterin. The validation was carried out with fortified urine samples from healthy adults. The optimized conditions were a mobile-phase composition of 10 mM citric buffer at pH 5.44 and acetonitrile (94.5/5.5, v/v), a flow rate of 1.0 mL min⁻¹, and an oven temperature of 25 °C. The detection system consisted of a fast-scanning spectrofluorimeter, which allows obtaining of second-order data matrices containing the fluorescence intensity as a function of retention time and emission wavelength. In this work, MCR-ALS was used to cope with coeluting interferences, on account of the second-order advantage inherent to this algorithm which, in addition, is able to handle data sets deviating from trilinearity, like the high-performance liquid chromatography data analyzed in the present report. The developed approach enabled us to determine five pteridines, some of them with overlapped profiles, reducing the experimental time and reagent consumption. Ratio values for pteridines/creatinine in urine, for infected children with different pathologies, are reported in this work.     

Rapid Fluorometric Screening of Antibiotics in Seafood

Simple and rapid fluorometric screening methods have been developed based on the competitive binding between the target and an intercalating fluorophore dye to double-stranded-DNA (dsDNA). In this study, the long-wavelength fluorescente dye TOTO-3 was employed as the indicator. Compounds that interact with dsDNA will affect the binding of TOTO-3 to the nucleic acid thereby changing the fluorescence intensity. The analyte concentration is indirectly determined by the decrease in fluorescence intensity. A fiber optic fluorescence screening system was developed for rapid and convenient sample processing. Lambda DNA (48.5 kb) was chosen as a suitable sensing nucleic acid material. Detection of sulfathiazole and chloramphenicol in shrimps using this method was studied in the range of 0.5–25 ng mL⁻¹ of sulfathiazole and of 1–50 ng mL⁻¹ of chloramphenicol. Detection limits of 0.5 ng mL⁻¹ of sulfathiazole and 1 ng mL⁻¹ of chloramphenicol were achieved. This approach is useful as a routine test in the monitoring of antibiotics in the environment or aquaculture products. The easy operation and the rapid and sensitive detection make this a potential high-throughput screening method.     

Selective solid-phase extraction of trace Fe(III) from biological and natural water samples using nanometer SiO2 modified with acetylsalicylic acid

A new method using acetylsalicylic acid (aspirin) modified SiO₂ nanoparticles (nanometer SiO₂-aspirin) as a solid-phase extractant (SPE) has been developed for the preconcentration of trace amounts of Fe(III) prior to their determination by inductively coupled plasma optical emission spectrometry. The preconcentration conditions of analytes were investigated, including the pH value, the shaking time, the mass of sorbent, the sample flow rate and volume, the elution condition and the interfering ions. At pH 4, the sorption capacity of nanometer SiO₂-aspirin was found to be 1.28 mmol g⁻¹. The preconcentration factor is 50. The detection limit (3σ) for Fe(III) was 0.49 ng mL⁻¹. The method was validated by analyzing two certified reference materials (GBW 08301, river sediment and GBW 08303, polluted farming soil), and the results obtained are in good agreement with standard values. The method was also applied to the determination of trace Fe(III) in biological and water samples with satisfactory results. Correspondence: Xiangbing Zhu, Department of Chemistry, Lanzhou University, Lanzhou 730000, P.R. China     

Extraction and determination of chloramphenicol in feed water,milk, and honey samples using an ionic liquid/sodium citrate aqueous two-phase system coupled with high-performance liquid chromatography

A green, simple, non-toxic, and sensitive sample pretreatment procedure coupled with high-performance liquid chromatography (HPLC) was developed for the analysis of chloramphenicol (CAP) that exploits an aqueous two-phase system based on imidazolium ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, [Bmim]BF₄) and organic salt (Na₃C₆H₅O₇) using a liquid–liquid extraction technique. The influence factors on partition behaviors of CAP were studied, including the type and amount of salts, the pH value, the volume of [Bmim]BF₄, and the extraction temperature. Extraction efficiency of the CAP was found to increase with increasing temperature and the volume of [Bmim]BF₄. Thermodynamic studies indicated that hydrophobic interactions were the main driving force, although electrostatic interactions and salting-out effects were also important for the transfer of the CAP. Under the optimal conditions, 90.1% of the CAP could be extracted into the ionic liquid-rich phase in a single-step extraction. This method was practical when applied to the analysis of CAP in feed water, milk, and honey samples with a linear range of 2~1,000 ng mL⁻¹. The method yielded a limit of detection of 0.3 ng mL⁻¹ and a limit of quantification of 1.0 ng mL⁻¹. The recovery of CAP was 90.4–102.7% from aqueous samples of real feed water, milk, and honey samples by the proposed method. This novel process is much simpler and more environmentally friendly and is suggested to have important applications for the separation of antibiotics.     

Development of a liquid chromatography-mass spectrometry method for the determination of ursolic acid in rat plasma and tissue: application to the pharmacokinetic and tissue distribution study

A fast and sensitive liquid chromatography–mass spectrometry method was developed for the determination of ursolic acid (UA) in rat plasma and tissues. Glycyrrhetinic acid was used as the internal standard (IS). Chromatographic separation was performed on a 3.5 μm Zorbax SB-C18 column (30 mm × 2.1 mm) with a mobile phase consisting of methanol and aqueous 10 mM ammonium acetate using gradient elution. Quantification was performed by selected ion monitoring with (m/z)⁻ 455 for UA and (m/z)⁻ 469 for the IS. The method was validated in the concentration range of 2.5 − 1470 ng mL⁻¹ for plasma samples and 20 − 11760 ng g⁻¹ for tissue homogenates. The intra- and inter-day assay of precision in plasma and tissues ranged from 1.6% to 7.1% and 3.7% to 9.0%, respectively, and the intra- and inter-day assay accuracy was 84.2 − 106.9% and 82.1 − 108.1%, respectively. Recoveries in plasma and tissues ranged from 83.2% to 106.2%. The limits of detections were 0.5 ng mL⁻¹ or 4.0 ng g⁻¹. The recoveries for all samples were >90%, except for liver, which indicated that ursolic acid may metabolize in liver. The main pharmacokinetic parameters obtained were T _max = 0.42 ± 0.11 h, C _max = 1.10 ± 0.31 μg mL⁻¹, AUC = 1.45 ± 0.21 μg h mL⁻¹ and K _a = 5.64 ± 1.89 h⁻¹. The concentrations of UA in rat lung, spleen, liver, heart, and cerebellum were studied for the first time. This method is validated and could be applicable to the investigation of the pharmacokinetics and tissue distribution of UA in rats.     

Nanometer-sized zirconium dioxide microcolumn separation/preconcentration of trace metals and their determination by ICP-OES in environmental and biological samples

A new method is proposed using a microcolumn (20 mm × 2.0 mm) packed with nanometer-sized zirconia as solid-phase extractor for the separation/preconcentration of Mn, Cu, Cr, Zn, Ni and Co prior to their determination by inductively coupled plasma optical emission spectrometer (ICP-OES) in environmental samples. The factors affecting the separation and preconcentration of analytes such as pH, sample flow rate and volume, eluent concentration and volume were determined, interfering ions were studied, and the optimal experimental conditions were established. The adsorption capacity of nanometer-sized ZrO₂ for Mn, Cu, Cr, Zn, Ni and Co was found to be 1.3, 1.3, 1.7, 2.0, 3.9 and 1.5 mg g⁻¹, respectively. The detection limits of the method were 12, 58, 24, 2, 7 and 36 ng L⁻¹, respectively, with a preconcentration factor of 25. The precision of this method was 1.7% (Mn), 2.9% (Cu), 5.9% (Mn), 3.8% (Mn), 6.2% (Mn) and 4.3% (Mn) with 9 determinations of 10 ng mL⁻¹ of target analytes, respectively. The method was successfully applied to the determination of trace metals in lake water, dried fish samples, certified reference materials of human hair and milk, and provided satisfactory results.     

DABTZ as a new reagent for solid phase extraction and spectrophotometric determination of trace amount of Hg(II) in water sample

A novel sensitive and simple method for rapid and selective extraction, preconcentration and determination of mercury as its 2,2' diamino-4,4' bithiazole (DABTZ) complex by using octadecylsilica cartridges and spectrophotometry is presented. Extraction efficiency and the influence of flow rates of sample solution and eluent, pH, amount of DABTZ, type and least amount of eluent for elution of mercury complex from cartridges, break through volume and limit of detection were evaluated. Also the effects of various cationic and anionic interferences on percent recovery of mercury were studied. Average extraction efficiency > 90% was obtained by elution of the cartridge with minimal amount of solvent in the presence of interferences. A preconcentration factor of 152 and a detection limit of 10.92 ng mL(-1) were obtained. The method was applied to the recovery and determination of mercury in different water samples.     

Determination of vanadium(V) with CdTe quantum dots as fluorescent probes

CdTe quantum dots (QDs) were modified with thioglycolic acid (TGA) and synthesized in aqueous medium. The optimum fluorescence intensity was found to be at pH 6.24 with a CdTe QDs concentration of 4.96 × 10⁻⁷ mol L⁻¹. The quenched fluorescence intensity of CdTe QDs is linearly proportional to V(V) concentration from 10 to 200 ng mL⁻¹ with correlation coefficient R = 0.9985. The limit of detection for V(V) was 2.07 ng mL⁻¹. The proposed method was successfully applied to the analysis of trace amounts of V(V) in water samples with recovery of 96.5–101.8%, and the results were in good agreement with those of electrothermal atomic absorption spectrometry.     

Determination of trace Cd and Pb in natural waters by direct single drop microextraction combined with electrothermal atomic absorption spectrometry

A new method of direct single-drop microextraction combined with electrothermal atomic absorption spectrometry (ETAAS) is presented for the determination of trace Cd and Pb with dithizone (H₂DZ) as chelating reagent. Factors influencing the microextraction efficiency and determination, such as pH, microdrop volume, stirring rate, extraction time were evaluated. Under the optimized experimental conditions, the detection limits of the method are 2 and 90 pg mL⁻¹ for Cd and Pb, and the relative standards deviations for 0.5 ng mL⁻¹ Cd and 10 ng mL⁻¹ Pb are 11 and 12.8%. After 10 min of extraction, the enrichment factors for Cd and Pb are 118 and 90, respectively. The results for the determination of Cd and Pb in tap water, spring water, river water, pond water, lake water and spiked water samples demonstrate the accuracy, recovery and applicability of the method. An environmental water certified reference material (GSBZ 50009-88) was analyzed, and the determined values are in a good agreement with the certified values. Correspondence: Bin Hu, Department of Chemistry, Wuhan University, Wuhan 430072, P.R. China     

Chemiluminescence of Peracetic Acid in Alkaline Medium and its Application to Dihydralazine Sulfate Determination

The chemiluminescence (CL) of peracetic acid (PAA) in alkaline medium is very weak but is strongly enhanced after the addition of dihydralazine sulfate (DHZS). Based on this phenomenon, a simple, rapid and highly sensitive flow-injection CL method for the determination of DHZS was developed. The CL emission was linearly related to the DHZS concentration in the range of 20–4000 ng mL⁻¹ with a detection limit (3σ) of 1.2 ng mL⁻¹. As a preliminary application, the proposed method was successfully applied to the determination of DHZS in pharmaceutical preparations; the recovery of DHZS in human urine was between 96.5% and 102.2%. A detailed CL mechanism was proposed and singlet molecular oxygen (¹O₂) was suggested to be produced in the CL reaction process.     

Simple and sensitive assay for nucleic acids by use of the resonance light-scattering technique with the anionic dye methyl blue in the presence of cetyltrimethylammonium bromide

This is the first report on the determination of nucleic acids based on the enhancement of resonance light scattering (RLS) of the anionic dye methyl blue (MB) in the presence of cetyltrimethylammonium bromide (CTMAB). In tris(hydroxymethyl) aminomethane buffer of pH 9.0, MB and nucleic acids react with CTMAB to form large particles of complex, which results in strong enhanced RLS signals characterized by three peaks at 334 nm, 393.5 nm and 548 nm. Mechanistic studies show that the enhanced RLS stems from the aggregation of MB on nucleic acids through the bridged and synergistic effect of CTMAB. With the enhanced RLS signals at the best wavelength at 334 nm, the enhanced RLS intensity is proportional to the concentration of nucleic acids in a wide range. The lowest limit of determination was 2.1 ng mL⁻¹, three synthetic samples were analyzed satisfactorily.