Simultaneous Determination Of Trace Levels Research Articles

Simultaneous Determination of Trace Amounts of Cobalt and Nickel in Water and Food Samples Using a Combination of Partial Least Squares Method and Dispersive Liquid–Liquid Microextraction Based on Ionic Liquid

A new, sensitive, and simple combined method including ionic liquid (IL)-based dispersive liquid–liquid microextraction and partial least squares method (PLS) was developed for simultaneous preconcentration and determination of cobalt and nickel in water and food samples. In this work, a small amount of an IL 1-hexyl-3-methylimmidazolium bis (trifluormethylsulfonyl)imid ([Hmim][Tf2N]) as an extraction solvent was dissolved in ethanol as a disperser solvent and then the binary solution was rapidly injected by a syringe into the water sample containing Co2+ and Ni2+, which were complexed by 1-(2-pyridylazo)-2-naphthol. After preconcentration, the absorbance of the extracted ions was measured in the wavelength range of 200–700 nm. The partial least squares method was then applied for simultaneous determination of each individual ion. The parameters controlling the behavior of the system were investigated and optimum conditions were selected. Eleven binary mixtures of cobalt and nickel were selected as the calibration set. The calibration models were validated with four synthetic mixtures containing the metal ions in different proportions, which were randomly designed. The best calibration model was obtained by using PLS-1 regression. Calibration graphs were linear in the range of 2.0–20.0 and 2.0–15.0 ng mL−1 with a limit of detection of 0.65 and 0.32 ng mL−1 for cobalt and nickel, respectively. The root mean square errors of prediction for cobalt and nickel were 0.4032 and 0.2980, respectively. Satisfactory results were reported for simultaneous determination of trace levels of cobalt and nickel in water, food, and geological certified reference material samples.

Development of analytical procedures for the simultaneous determination of tri- to heptabrominated diphenyl ethers and hexabrominated biphenyl (BB 153) in sediment samples

A simple analytical procedure was developed for simultaneous determination of trace levels of tri- to hepta-BDEs as well as 2,2Œ,4,4Œ,5,5Œ-hexabromobiphenyl (BB 153). The mechanical shaking extraction technique for the isolation of target analytes was optimised. Different extraction solvent combinations were tested under different extraction time periods of 3, 6, 12 and 16 h. The n-hexane:acetone (2:1, v/v) combination gave the best recovery at the optimum extraction of 12 h. Target analytes were quantified using a high capillary gas chromatograph (GC) equipped with an electron capture detector. Under the optimum GC conditions, the resolution of the co-eluting BDE 154 and BB 153 was achieved. The overall recoveries of target analytes in the matrix spike experiment conducted ranged between 84.4 and 110% for BDE 183 and BDE 28, respectively. The method was applied to 19 field sediment samples collected from a control site and from 3 sampling locations (upstream, point of discharge and downstream) of the Black River, which receives effluent from a wastewater treatment plant (WWTP). The sum of the mean concentrations of all of the 7 PBDE congeners was 4.63, 0.35, enot detectablef and 4.43 ng/g, for the control site, upstream, point of discharge and downstream samples, respectively. The concentrations of BB 153 were generally low in these samples and ranged between ND and 0.89 ng/g. The developed method allows for the simultaneous determination of PBDE congeners and BB 153. It is efficient, moderately rapid and cost-effective.

Application of Soluble Membrane Filter in Simultaneous Determination of Trace Levels of Cadmium, Copper, Lead and Zinc in Food Additives by Inductively Coupled Plasma Atomic Emission Spectrometry

A method for simultaneous determination of trace levels of Cd(II), Cu(II), Pb(II) and Zn(II) in food additives by inductively coupled plasma atomic emission spectrometry ( ICP–AES ) after soluble membrane filter pre-concentration was developed. Based on collection of the chelates of metal ions(II) with 2-(5-bromo-2-pyridylazo)-5- diethylaminophenol ( 5-Br-PADAP ) on soluble membrane filter, the analyte ions were pre-concentrated and separated from sample matrix solutions. Multi-channel membrane filter device and soluble mixed cellulose ester membrane were selected. Analytical parameters such as pH, amount of 5-Br-PADAP, sample volume, etc. were optimized. Under the matrix of Na+, K+ and Mg2+, the limits of detection were 0.02 – 0.03, 0.14 – 0.23, 0.31 – 0.53, 0.10 – 0.15 μg L-1 for Cd(II), Cu(II), Pb(II) and Zn(II) respectively. The developed method was successfully applied to sodium benzoate, potassium sorbate and basic magnesium carbonate with spiked recoveries of 94% – 115%. Some sample analysis results were checked by inductively coupled plasma mass spectrometry ( ICP–MS ) directly.

Simultaneous determination of pesticides at trace levels in water using multiwalled carbon nanotubes as solid-phase extractant and multivariate calibration

The application of solid-phase extraction with multivariate calibration for simultaneous determination of three toxic pesticides in tap and reservoir waters was presented. The proposed analytical method was used for the determination of atrazine, methidathion, and propoxur in complex water samples without the need for chromatographic separation. Among the applied multivariate calibration methods, partial least squares (PLS-1) method was found the most effective for pesticides quantification. Multiwalled carbon nanotubes (MWCNTs) adsorbent showed a perfect extraction/preconcentration of pesticides present at trace levels. The experimental factors that affect pesticides extraction by MWCNTs adsorbent such as sample volume, eluent volume, solution pH, and extraction flow rate were studied and optimized. The figures of merit of the proposed method were: limits of detection 3, 2, and 3 μg l −1 and linear ranges 5–30, 3–60, and 5–40 μg l −1 for atrazine, methidathion, and propoxur, respectively. A good precision was reported for the method, R.S.D. values were always less than 5.0%. Satisfactory results were reported for simultaneous determination of trace levels of pesticides in complex matrices. In tap water, the percent recoveries for pesticides were extended from 95 to 104% and R.S.D. from 1 to 3%, while lower recoveries were observed in reservoir water: 84–93% (R.S.D.: 1–3). Although the pesticides can be accurately quantified by SPE and liquid chromatography, SPE–PLS-1 method was found simpler and operated at lower running costs.

Simultaneous determination of chromium(III) and cadmium(II) by differential pulse anodic stripping voltammetry on a stannum film electrode

A stannum film electrode has been developed for the simultaneous determination of trace levels of chromium(III) and cadmium(II) by differential pulse anodic stripping voltammetry (DPASV). The stannum film electrode was generated in situ by depositing simultaneously the stannum film and the metals obtained by reduction of Cd(II) and Cr(III) at −1.4 V on a glassy carbon electrode. Then, the reduced products were oxidized by scanning the potential of the electrode from −1.4 to −0.4 V using DPASV. The electrode exhibited well-defined and separated stripping signals for both metals accompanied with a low background contribution. The possible mechanism of this design was proposed. Under the optimized working conditions, the detection limit was 2.0 and 1.1 μg l −1 for Cr(III) and Cd(II) at a deposition time of 3 min. Finally, the stannum film electrode was successfully applied to the determination of Cd(II) in tap water with satisfactory results.

Simultaneous determination of trace levels of ethylmercury and methylmercury in biological samples and vaccines using sodium tetra(n-propyl)borate as derivatizing agent

Because of increasing awareness of the potential neurotoxicity of even low levels of organomercury compounds, analytical techniques are required for determination of low concentrations of ethylmercury (EtHg) and methylmercury (MeHg) in biological samples. An accurate and sensitive method has been developed for simultaneous determination of methylmercury and ethylmercury in vaccines and biological samples. MeHg and EtHg were isolated by acid leaching (H2SO4-KBr-CuSO4), extraction of MeHg and EtHg bromides into an organic solvent (CH2Cl2), then back-extraction into Milli-Q water. MeHg and EtHg bromides were derivatized with sodium tetrapropylborate (NaBPr4), collected at room temperature on Tenax, separated by isothermal gas chromatography (GC), pyrolysed, and detected by cold-vapour atomic fluorescence spectrometry (CV AFS). The repeatability of results from the method was approximately 5-10% for EtHg and 5-15% for MeHg. Detection limits achieved were 0.01 ng g-1 for EtHg and MeHg in blood, saliva, and vaccines and 5 ng g-1 for EtHg and MeHg in hair. The method presented has been shown to be suitable for determination of background levels of these contaminants in biological samples and can be used in studies related to the health effects of mercury and its species in man. This work illustrates the possibility of using hair and blood as potential biomarkers of exposure to thiomersal.

Ion Chromatography Determination of Heavy Metals in Airborne Particulate with Preconcentration and Large Volume Direct Injection

A flow injection analysis system with on-line enrichment was developed for simultaneous determination of trace levels of Cu2+, Ni2+, Zn2+, Co2+, Mn2+, Cd2+, Pb2+ and Fe3+, by high-performance ion chromatography (HPIC) with spectrophotometric detection. It is a highly sensitive and low cost alternative methodology. Ion Pac CS5A was used as the analytical column with eluent composition of sodium nitrate 160 mM and oxalic acid 36 mM. Quantification after post-column reaction with PAR allows detection limits between 0.5 and 5.0 ppb to be attained. The total analysis time is less than 30 min. The proposed procedure was compared with a large volume direct injection method using loop volumes up to 5 mL. Both procedures were applied to the analysis of heavy metals in the PM10 fraction of atmospheric particulate samples. Airborne pollutants such as nickel and cobalt can be quantified in 24 h samples of particulate matter at concentrations of a few ng m−3.

Determination of Imidacloprid and metabolites by liquid chromatography with an electrochemical detector and post column photochemical reactor

A procedure for the determination of Imidacloprid and its main metabolites was set up by means of liquid chromatography with an electrochemical detector and post-column photochemical reactor (LC- hν-ED). Sample clean-up was developed for bees, filter paper and maize leaves. Chromatographic conditions were based on a reversed-phase C-18 column operated by phosphate buffer 50 mM/CH 3CN (80/20, v/v) at pH 2.9. Detection of Imidacloprid and its metabolites was performed at a potential of 800 mV after photoactivation at 254 nm. Compared to conventional techniques such as gas chromatography/mass spectrometry (GC/MS) or LC coupled to other detectors, the present method allows simultaneous trace-level determination of both Imidacloprid (0.6 ng ml −1) and its main metabolites (2.4 ng ml −1).

Simultaneous determination of cadmium (II) and lead (II) with clay nanoparticles and anthraquinone complexly modified glassy carbon electrode

An anthraquinone (AQ) improved Na-montmorillonite nanoparticles (nano-SWy-2) chemically modified electrode (CME) has been developed for the simultaneous determination of trace levels of cadmium (II) and lead (II) by differential pulse anodic stripping voltammetry (DPASV). This method is based on a non-electrolytic preconcentration via ion exchange model, followed by an accumulation period via the complex formation in the reduction stage at −1.2 V, and then by an anodic stripping process. The mechanism of this design was proposed and the analytical performance was evaluated with several variables. Under the optimized working conditions, the detection limit was 3 and 1 nM for Cd 2+ and Pb 2+, respectively. The calibration graphs were linear in the concentration ranges of 8×10 −9 to 1×10 −6 mol L −1 (Cd 2+) and of 2×10 −9 to 1×10 −6 mol L −1 (Pb 2+). Many inorganic species did not interfere with the assay significantly; the high sensitivity, selectivity, and stability of this nano-SWy-2-AQ CME were demonstrated. The applications for the detection of trace levels of Cd 2+ and Pb 2+ in milk powder and lake water samples indicate that it is an economical and potent method.

Validated procedure for simultaneous trace level determination of the anti-cancer agent gemcitabine and its metabolite in human urine by high-performance liquid chromatography with tandem mass spectrometry.

A sensitive, accurate and reproducible procedure has been developed for the quantitative determination of gemcitabine (2',2'-difluorodeoxycytidine, dFdC) and its metabolite 2',2'-difluorodeoxyuridine (2dFdU) in human urine. The samples (2 mL) were extracted by solid-phase extraction (SPE) and analyzed by reversed-phase high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC/MS/MS), operating in multiple reaction monitoring (MRM mode). This procedure was validated using 2'-deoxycytidine as internal standard (IS). The urine assay was linear over the range 0-50 microg/L, with a limit of quantification (LLOQ) of 0.2 microg/L for gemcitabine and 1.0 microg/L for the metabolite. The respective limits of detection (LODs) for dFdC and 2dFdU were 0.05 and 0.3 microg/L. The precision and accuracy of the assay were determined on three different days. The within-series precision was found to be always less than 8.5 and 12.7% for gemcitabine and 2dFdU, respectively. The overall precision expressed as relative standard deviation (CVr) was always less than 7.1% for both analytes. The recovery of gemcitabine was always greater than 90% with a CVr <6.3%. The measurement uncertainty determined from the validation data assessed the possibility of determining this drug and its metabolite at trace levels in urine, considering that the combined uncertainty of the whole procedure was always less than 30%.

Application of adsorptive cathodic differential pulse stripping method for simultaneous determination of copper and molybdenum using pyrogallol red

A reliable and sensitive procedure for the simultaneous determination of trace levels of copper and molybdenum is proposed. The complexing of copper(II) and molybdenum(VI) with pyrogallol red (PGR) is analyzed by cathodic stripping differential pulse voltammetry based on the adsorption collection of the complexes onto a hanging mercury drop electrode (HMDE). The effect of chemical and instrumental parameters on the sensitivity and selectivity were studied. Copper and molybdenum peaks potential were observed at about +0.13 and −0.22 V versus Ag/AgCl electrode, respectively. A standard addition method was utilized for the analysis of voltammogram data, under the optimum conditions and with accumulation time of 90 s. The measured peak current at about +0.14 and −0.22 V is proportional to the concentration of Cu(II) and Mo(VI) over the range of 2–70 and 0.8–80 ng ml −1, respectively. The limit of detection are 0.3 and 0.1 ng ml −1 for Cu(II) and Mo(VI), respectively. The capability of the method for the analysis of real samples was evaluated by determination of copper and molybdenum in river water, tap water and alloy. Atomic absorption spectrometry was applied as a reference method for determination of copper and molybdenum in water samples.

Mercury-free simultaneous determination of cadmium and lead at a glassy carbon electrode modified with multi-wall carbon nanotubes

A multi-wall carbon nanotube (MWNT) modified glassy carbon electrode (GCE) was described for the simultaneous determination of trace levels of cadmium and lead by anodic stripping voltammetry (ASV). In pH 4.5 NaAc–HAc buffer containing 0.02 mol/l KI, Cd 2+ and Pb 2+ first adsorb onto the surface of a MWNT film coated GCE and then reduce at −1.20 V. During the positive potential sweep, reduced cadmium and lead were oxidized, and two well-defined stripping peaks appeared at −0.88 and −0.62 V. Compared with a bare GCE, a MWNT film coated GCE greatly improves the sensitivity of determining cadmium and lead. Low concentration of I − significantly enhances the stripping peak currents since it induces Cd 2+ and Pb 2+ to adsorb at the electrode surface. The striping peak currents change linearly with the concentration of Cd 2+ from 2.5×10 −8 to 1×10 −5 mol/l and with that of Pb 2+ from 2×10 −8 to 1×10 −5 mol/l. The lowest detectable concentrations of Cd 2+ and Pb 2+ are estimated to be 6×10 −9 and 4×10 −9 mol/l, respectively. The high sensitivity, selectivity, and stability of this MWNT film coated electrode demonstrated its practical application for a simple, rapid and economical determination of trace levels of Cd 2+ and Pb 2+ in water samples.

Selective Separation and Simultaneous Determination of Trace Levels of Five Types of Fluorinated Quinolone Drugs by Thin-Layer Chromatography/Fluorescence Densitometry

This paper reports the determination of trace levels of 5 types of fluorinated quinolone drugs, i.e., ciprofloxacin, norfloxacin, enoxacin, pefloxacin, and ofloxacin, by thin-layer chromatography (TLC)/fluorescence densitometry. The new analytical method uses 2-step TLC development, selective separation, and simultaneous determination of the 5 drugs. The method was also applied to the determination of recoveries of standards of the 5 drugs in plasma and urine samples. The results show that the method has a wide linear range, high repeatability, and good stability.

Simultaneous determination of trace-levels of alloying zinc and copper by semi-mercury-free potentiometric stripping analysis with chemometric data treatment

Assays of copper and zinc in brass samples were performed by semi-mercury free potentiometric stripping analysis (S-MF PSA) using a thin-film mercury covered glassy-carbon working electrode and dissolved oxygen as oxidizing agent during the stripping step. The stripping peak transients were resolved by chemometrics, which enabled simultaneous determination of both the copper and the zinc concentrations, thereby eliminating the conventional necessary pretreatment of the sample solution, such as initial addition of Ga(III) or solvent extraction of copper. The brass samples were diluted by factors in the range 2 · 104– 5 · 105 which resulted in quantification of the copper and of zinc contents comparable to the specified values within 10%. On the basis of the chemometric treatment, an empirical expression is deduced relating the stripping time to the recorded potential.

Microbore liquid chromatographic-mass spectrometric determination of atrazine and its major hydroxylated degradate in water at parts-per-trillion levels using electrospray

A liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) method was developed to determine atrazine (ATR) and hydroxyatrazine (HA) in water at parts-per-trillion (ppt) levels. In addition to protonaed molecular ions, sodiated molecular and dimer ions were observed in full-scan electrospray mass spectra of the analytes, providing additional information for the identification of ATR and HA. The quantification is based on the use of isotopically labeled internal standards that were added to water samples prior to the sample extraction using a carbon black cartridge. The relative response factor for each of the native compounds relative to its corresponding internal standard was measured and used to minimize the analytical error. The precision and accuracy data were obtained from the analysis of standard water samples containing 50 ppt ATR and 100 ppt HA. Relative standard deviation and relative error are less than 15% ( n=6) for both ATR and HA determinations. The method has been successfully used to analyze agricultural run-off samples for ATR and HA levels. Analytical results compared well with those obtained by using GC-high-resolution and fast atom bombardment high-resolution MS methods developed in this laboratory. Preliminary results for analysis of a standard containing a mixture of ATR, HA, deethylatrazine and deisopropylatrazine suggest that the LC-ESI-MS method can be applied to simultaneous trace-level determination of the major products of atrazine degradation in the environment.

Trace-Level Determination Of Hydroxyatrazine And Dealkylated Degradation Products Of Atrazine In Waters

Abstract Dealkylated degradation products of atrazine, dealkyl- and deisopropyl-atrazine have been now detected in environmental waters, but determination of hydroxyatrazine has not been reported just because this product is not amenable to GC-MS. An analytical procedure has been developed for the simultaneous trace-level determination of some widely used chorotriazines and of three main degradation products, deisopropyl-, deethyl- and hydroxyatrazine, using a selective solid-phase-extraction coupled on-line to liquid chromatography. The preconcentration has been carried out with two precolumns in series. The first one, packed with the PRP-1 sorbent allowed the preconcentration of hydroxyatrazine and other metabolites. Analytes of interest were then desorbed from the PRP-1 precolumn in their ionic form and transferred to a second precolumn packed with a cation exchanger, which was afterwards coupled on-line to an analytical C18 column. The use of the selective cation-exchanger sorbent for the preconcentra...

Neutron activation analysis for osmium and ruthenium in platinum

A sensitive procedure for the simultaneous determination of trace levels of osmium and ruthenium in platinum, by thermal neutron activation analysis utilizing γ-ray spectrometry, was developed. The radiochemical separation method utilized perchloric acid for a selective oxidation of osmium and ruthenium to the volatile tetroxides. The distillation of the tetroxides greatly reduced the radiation hazard presented by the bulk of the activities in the matrix. Activities of 15-day191Os and 40-day104Ru were measured by accumulation of pulses from a 3″ diameter NaI(Tl) crystal detector. Analyses of γ-ray spectra were achieved using digital computer techniques. The procedure provided analyses for a high purity platinum stock of 0.032±0.007 ppm Os and 0.044±0.005 ppm Ru.

Neutron activation analysis for iridium, palladium and silver in platinum

A sensitive procedure for the simultaneous determination of trace levels of iridium, palladium and silver in a platinum stock, by thermal-neutron activation analysis utilizing gamma-ray spectrometry, was developed. The radiochemical-separation scheme involved an elution of the chloro complexes of iridium and silver, and subsequently palladium, through a strongly-basic anion-exchange resin, followed by further chemical-separation methods. The ion-exchange method served to greatly reduce the hazard from radiations emitted by the bulk of the activities in the matrix. Activities of 13.5-hr109Pd, 74.2-d192Ir and 255-d110m Ag were monitored by accumulation of pulses from a 3-in diam. NaI(T1) crystal detector. Further discrimination was attained by resolution of decay curves. The procedure provided analyses for a platinum stock of 0.015±0.0021 ppm Ir; 0.028±0.0043 ppm Pd and 2.4±0.27 ppm Ag.