Determination of mercury species in natural waters at picogram level with on-line RP C18 preconcentration and HPLC-UV-PCO-CVAAS

Detection of proteins by hyphenated techniques with endogenous metal tags and metal chemical labelling

The absolute and relative quantitation of proteins plays a fundamental role in modern proteomics, as it is the key to understand still unresolved biological questions in medical and pharmaceutical applications.

High-performance liquid chromatographic/ion-trap mass spectrometric speciation of aquatic mercury as its pyrrolidinedithiocarbamate complexes

Mercury-pyrrolidinedithiocarbamate complexes are first time used for speciation of aquatic mercury with high-performance liquid chromatographic/ion trap-mass spectrometric method utilizing atmospheric pressure chemical ionization (APCI). The separation of the four mercury species was achieved in less than 5 min with a linear gradient profile of aqueous methanol from 70 up to 100% (v/v) in 4th min, isocratic elution at 100% up to 5th min and followed by a negative gradient to 70% in 6th min. The best separation was achieved on a reverse phase Zorbax Eclipse XDB C18 column (50 mm x 2.1 mm i.d., 1.8 microm particle size). The on-column limits of detection (injection volume 1 microL) were 370 pg for methylmercury (MeHg+), 280 pg for ethylmercury (EtHg+), 250 pg for phenylmercury (PhHg+) and 90 pg for inorganic mercury (Hg2+) when the data were collected in selective ion monitoring (SIM) mode. A method of isolation and preconcentration of the mercury species using a "home-made" C18 solid phase extraction (SPE) microcolumns was developed to enhance sensitivity of the method. The preconcentration factor as much as 2500 was achieved with on-column complex formation of mercury-pyrrolidinedithiocarbamate. Methanol (100%) was chosen for elution of preconcentrated mercury species. The method was applied for the determination of mercury species in river water samples.

Reversed-phase high-performance liquid chromatographic separation of inorganic mercury and methylmercury driven by their different coordination chemistry towards thiols

Since mercuric mercury (Hg(2+)) and methylmercury (CH(3)Hg(+)) display different toxicological properties in mammals, methods for their quantification in dietary items must be available. Employing Hg-specific detection, we have developed a rapid, isocratic, and affordable RP-HPLC separation of these mercurials using thiol-containing mobile phases. Optimal separation was achieved with a 50mM phosphate-buffer containing 10mM L-cysteine at pH 7.5. The separation is driven by the on-column formation of complexes between each mercurial and L-cysteine, which are then separated according to their different hydrophobicities. The developed method is compatible with inductively coupled plasma atomic emission spectrometry and was applied to analyze spiked human urine.

Thiourea catalysis of MeHg ligand exchange between natural dissolved organic matter and a thiol-functionalized resin: a novel method of matrix removal and MeHg preconcentration for ultratrace Hg speciation analysis in freshwaters

Ultratrace analysis of dissolved MeHg in freshwaters requires both dissociation of MeHg from strong ligands in the sample matrix and preconcentration for detection. Existing solid phase extraction methods generally do not efficiently adsorb MeHg from samples containing high concentrations of natural dissolved organic matter. We demonstrate here that the addition of 10-60 mM thiourea (TU) quantitatively releases MeHg from the dissolved matrix of freshwater samples by forming a more labile complex (MeHgTU+) that quantitatively exchanges MeHg with thiol-functionalized resins at pH approximately 3.5 during column loading. The contents of these columns were efficiently eluted with acidified TU and MeHg was analyzed by Hg-TU complex ion chromatography with cold-vapor atomic fluorescence spectrometry detection. Routinely more than 90% of MeHg was recovered with good precision (average relative standard deviation of 6%) from natural waters-obtained from pools and saturated sediments of wetlands and from rivers-containing up to 68.7 mg C L-1 dissolved organic matter. With the preconcentration step, the method detection limit of 0.29 pg absolute or 0.007 ng L-1 in 40-mL samples is equivalent to that of the current state-of-the- art as practiced by skilled analysts. MeHg in 20-50-mL samples was completely trapped. On the basis of our knowledge of the chemistry of the process, breakthrough volume should depend on the concentrations of TU and H+. At a TU concentration of 12 mM breakthrough occurred between 50 and 100 mL, but overall adsorption efficiency was still 85% at 100 mL. Formation of artifactual MeHg is minimal; only about 0.7% of ambient MeHg is artifactual as estimated from samples spiked with 4 microg L-1 HgII.

Cloud point extraction preconcentration prior to high-performance liquid chromatography coupled with cold vapor generation atomic fluorescence spectrometry for speciation analysis of mercury in fish samples

A cloud point extraction methodology was developed for simultaneous preconcentration of Hg(II), methylmercury (MeHg), ethylmercury (EtHg), and phenylmercury (PhHg) prior to reversed-phase high-performance liquid chromatography (HPLC) on-line coupled with cold vapor atomic fluorescence spectrometry for speciation analysis of mercury in fish. The four mercury species were taken into complexes with ammonium pyrrolidine dithiocarbamate (APDC) in aqueous nonionic surfactant Triton X-114 medium and concentrated in the surfactant-rich phase by bringing the solution to the temperature of 40 degrees C. Baseline separation of the enriched complexes was achieved on an RP-C(18) column with a mixture of methanol, acetonitrile, and water (65:15:20, v/v) containing 200 mmol L(-1) HAc (pH 3.5) as the mobile phase. An on-line postcolumn oxidation of the effluent from HPLC, in the presence of K2S2O8 in HCl, was applied in the system followed by an optimal cold vapor generation of mercury species. The variables affecting the complexation and extraction steps were examined. The preconcentration of 10 mL of solution with 0.08% w/v Triton X-114 and 0.04% w/v APDC at pH 3.5 gave enrichment factors of 29, 43, 80, and 98 for MeHg, EtHg, PhHg, and Hg(II), respectively. Low detection limits (S/N = 3) were obtained, ranging from 2 to 9 ng L(-1) (as Hg) for all species. The developed method was successfully applied to the speciation of mercury in real fish samples.

Speciation of Organometallic Compounds in Environmetal Samples by Gas Chromatography after Flow Preconcentration on Fullerenes and Nanotubes

The development of a simple speciation method for the determination of lead (trimethyllead(I), dimethyllead(II), triethyllead(I), and diethyllead(II)), mercury (methylmercury(I), ethylmercury(I), mercury(II)), and tin (n-butyltin(III), di-n-butyltin(II), tri-n-butyltin(I), tin(IV)) compounds in environmental samples was described. The potential of C70 fullerenes and multiwalled carbon nanotubes (MWNTs) as sorbents was investigated for the first time; this study revealed that there are no significant differences between them in terms of sensitivity, selectivity, precision, and reusability. Comparative studies showed that MWNTs and C60 and C70 fullerenes were superior to graphitized carbon black and RP-C18 for the extraction of the 11 compounds studied. The accuracy of the MWNT method was evaluated from recovery values with two standard reference coastal sediments, and good concordance in the results were obtained. Detection limits of 0.5-2 pg/mL were obtained when using a sorbent column containing 160 mg of MWNTs (sample breakthrough, 50 mL of water). The method was successfully applied to the determination of lead, mercury, and tin compounds in water and coastal sediment samples with satisfactory results.

Chelating sorbents based on silica gel and their application in atomic spectrometry

This mini-review covers chelating sorbents anchored to silica gel and their analytical applications for the preconcentration, separation and determination of trace metal ions, focussing mainly on the last 20 years. The article summarizes also the experience gathered by our research group in the synthesis and characterization of new modified silica gels "via silanization", and their affinity toward selective extraction and separation of trace elements. The introduction of 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-gel) and methylthiosalicylate silica gel (TS-gel) chelating sorbents in trace and ultratrace analysis provide vital breakthroughs in preconcentration methods. These home-made materials allow certain analytes to be selectively extracted from complex matrices without matrix interference and good detection limits. The advantages of these new chelating sorbents in comparison with 8-hydroxyquinoline chelating sorbent immobilized on silica gel are discussed.

Solid-phase extraction–gas chromatography–mass spectrometry using a fullerene sorbent for the determination of inorganic mercury(II), methylmercury(I) and ethylmercury(I) in surface waters at sub-ng/ml levels

A novel, straightforward solid-phase extraction system for the determination of inorganic mercury and organomercury compounds in water is proposed. The analytes, in a buffer medium at pH 4.5, are sorbed as diethyldithiocarbamate complexes on a C60 fullerene column an subsequently eluted and derivatized with sodium tetra-n-propylborate in ethyl acetate. Following elution, 1 microl of extract is injected into a gas chromatograph-mass spectrometer system. The proposed gas chromatography-mass spectrometry speciation method exhibits a linear range of 4-1 ng/ml, and a detection limit of 1.5 ng/l (sample volume, 50 ml). Its repeatibility, as relative standard deviation (RSD) (from 11 standards containing 50 ng/l for each analyte), is ca. 7%. No interferences from metals ions, such as Zn2+, Fe3+, Sb3+, As3+, Pb2+, Ni2+, Cu2+, Sn2+, Co2+, Mn2+ and Cd2+ were encountered at concentrations 1000 times higher than those of the mercury compounds. The method was used for the speciation of inorganic mercury, methylmercury and ethylmercury in various types of water including sea and waste water.

Synthesis, Characterization of Silica Gel Phases-Chemically Immobilized-4-Aminoantipyrene and Applications in the Solid Phase Extraction, Preconcentration and Potentiometric Studies

Two new 4-aminoantipyrene chemically-immobilized silica gel phases: ii (N,N-donor) and iii (N,O-donor), were synthesized and characterized by IR and surface coverage determination. The latter was accomplished by thermal desorption and metal probe methods, giving 0.300 and 0.312 mmol g(-1) for ii and 0.220 and 0.250 mmol g(-1) for iii. Moreover, potentiometric titration provided a surface coverage of 0.323 mmol g(-1) for ii. The metal capacity values in mmol g(-1) of ii, iii and the active silica gel phase i for a series of di- and trivalent metal ions were determined at pH 1.0 - 6.7. Phase i showed the lowest values, while ii and iii reflected higher affinity toward most of the metal ions. The highest values were 0.300 for Hg(II)-ii and 0.220 mmol g(-1) for Cd(II)-iii. Distribution coefficients (log Kd) were in the range of 3.57 - 4.76 for ii and 2.32 - 3.46 for iii, thus confirming certain selectivity characters of the solid extractors. The application of the phases as solid extractors and preconcentrators for some heavy metal ions is presented. Good percentage extraction and removal of 94 - 98 +/- 4 - 6% of the spiked 1.000 microg ml(-1) of Hg(II), Cd(II), Pb(II), Cu(II) and Zn(II) and good percentage recovery of 94 - 99 +/- 3 - 6% of 50 ng ml(-1) of these ions from tap water samples were obtained. Stability constants of H(I) and Cu(II) with ii for the two-phase mixture at 25 degrees C and I = 0.1 (KCI) were determined potentiometrically. The pKa of ii are 5.6 and 8.4, while the log K values for CuHL and CuL (L = ii) are 6.3 and 5.8, respectively, leading to the determination of several analytical data for Cu(II)-ii.

Application of chromatographic and electrophoretic methodology to the speciation of organomercury compounds in food analysis

Trace metals such as mercury, especially its organic compounds, are an important risk to the environment and to man due to their accumulation in the food chain. For this reason, the routine determination of the very toxic methylmercury, and of other organic and inorganic mercury compounds in marine and land animals, vegetables, fruits and fresh water is of increasing importance in health and environmental control programmes throughout the world. The majority of speciation methods for organomercurials involve a series of fundamental steps for the identification and quantification of samples of biological origin: extraction or isolation from the matrix; derivatisation and concentration; detection; separation of different species of interest and of interference. Each of these steps, as part of the chromatographic analysis of MeHg and of other organomercurials is revised in this study using food samples.

Simultaneous analysis of lead, mercury and selenium species by capillary electrophoresis with combined ethylenediaminetetraacetic acid complexation and field-amplified stacking injection

In this study, speciation analysis was carried out for multispecies of lead, mercury and selenium by capillary electrophoresis (CE) with combined complexation and field-amplified stacking injection (FASI). Ethylenediaminetetraacetic acid (EDTA) was added to the sample mixture to form UV-absorbing complexes with the analytes, thus enabling direct UV detection. It was also used in the running electrolyte to improve resolution. Under optimal conditions, ten analytes were baseline-separated within 20 min. The influence of operational conditions (pH, EDTA concentration, sodium dodecyl sulfate concentration) on the electrophoretic behavior of the species was studied. The analyte-related parameters were calculated based on the migration equation. Enhancement of detection, up to 1700-fold, was achieved for the charged complexes with FASI, and sub-ng/mL detection limits were obtained. The performance of this method was compared with high-performance liquid chromatography, gas chromatography and other CE procedures.

Chemical modification of analytes in speciation analysis by capillary electrophoresis, liquid chromatography and gas chromatography

Chemical modification of target analytes is widely used in modern analytical methods. This review focuses on the application of chemical modification techniques is the simultaneous analysis of metallic species by capillary electrophoresis, liquid chromatography and gas chromatography. Emphasis is placed on the procedures relating to analyses carried out by capillary electrophoresis. The development of this topic in the past five years is evaluated for liquid chromatography and gas chromatography. The advantages, performance and application in real samples are compared for the three techniques.