Trimethyl Lead Research Articles

Simultaneous enrichment and speciation of lead and mercury by magnetic solid-phase extraction coupled to HPLC-ICP-MS based on magnetic hydrazine-linked covalent organic frameworks

BackgroundTrace levels of organic and inorganic lead and mercury species in the environment, including divalent lead (Pb2+), trimethyllead (TML), divalent mercury (Hg2+), monomethylmercury (MeHg), and ethylmercury (EtHg), are highly toxic to humans and ecology. It is of great importance for speciation of lead and mercury to evaluate the toxicity of lead and mercury and their biogeochemistry in the environment. However, simultaneous multi-elemental enrichment and speciation at trace level remains a challenge. There are few reports of simultaneous magnetic solid-phase extraction (MSPE) of organic and inorganic lead and mercury species at trace level in the real water. ResultsIn this work, a novel core-shell magnetic hydrazine-linked covalent organic frameworks (Fe3O4@COF-TCH) was prepared for the first time by grafting hydrazine-linked COFs on the Fe3O4 nanoparticles. Fe3O4@COF-TCH with abundant thione and imino groups has strong adsorption for lead and mercury species. Based on it, a simple and practical magnetic solid-phase extraction high-performance liquid chromatography-inductively coupled plasma mass spectrometry (MSPE-HPLC-ICP-MS) method was developed for extraction and determination of trace lead and mercury species, including Hg2+, MeHg, EtHg, Pb2+ and TML. The limits of detection (3δ) of the developed method were 0.08, 0.81, 0.90, 0.56 and 0.88 ng L−1 with the enrichment factors (EFs) of 384, 376, 379, 389 and 360-fold for Pb2+, TML, Hg2+, MeHg and EtHg, respectively. The high accuracy and reproducibility have been proved by the spiked recoveries (94.4–103 %) in real samples. SignificanceThe proposed method with simple operation and high sensitivity has been successfully applied to simultaneous speciation of lead and mercury at trace levels in the water samples with complicated matrices, including underground water, surface water, sea water. Meanwhile, it has the advantages of cost-saving, labor-saving and time-saving and is suitable for the investigation and risk assessment in water. The development of MSPE-HPLC-ICP-MS method provides ideas and guidance for the simultaneous multi-elemental enrichment and speciation.

Synthesis of a novel magnetic nanomaterial for the development of a multielemental speciation method of lead, mercury, and vanadium via HPLC-ICP MS

A new magnetic functionalized material based on graphene oxide magnetic nanoparticles named by us, M@GO-TS, was designed and characterized in order to develop a magnetic solid-phase extraction method (MSPE) to enrich inorganic and organic species of lead, mercury, and vanadium. A flow injection (FI) system was used to preconcentrate the metallic and organometallic species simultaneously, while the ultra-trace separation and determination of the selected species were achieved by high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP MS). Therefore, preconcentration and separation/determination processes were automated and conducted separately. To the best of our knowledge, this is the first method combining an online MSPE and HPLC-ICP MS for multielemental speciation. Under the optimized conditions, the enrichment factor obtained for PbII, trimethyllead (TML), HgII, methylmercury (MetHg), and VV was 27. The calculated LOD for all studied species were as follows: 5 ng L−1, 20 ng L−1, 2 ng L−1, 10 ng L−1, and 0.4 ng L−1, respectively. The RSD values calculated with a solution containing 0.5 μg L−1 of all species were between 2.5 and 4.5%. The developed method was validated by analyzing Certified Reference Materials TMDA 64.3 for total concentration and also by recovery analysis of the species in human urine from volunteers and a seawater sample collected in Málaga. The t statistical test showed no significant differences between the certified and found values for TMDA 64.3. All the recoveries obtained from spiked human urine and seawater samples were close to 100%. All samples were analyzed using external calibration. The developed method is sensitive and promising for routine monitoring of the selected species in environmental waters and biological samples.Graphical abstract

Comparison of two extraction methods for the determination of organolead compounds using sodium tetrapropylborate as derivatization reagent

Two extraction methods of accelerate solvent extraction (ASE) and supercritical fluid extraction (SFE) were used to the extraction of trimethyl lead (TML) and triethyl lead (TEL), which were detected by gas chromatographer coupled with mass spectrometry. Sodium tetrapropylborate, as the derivatization reagent, was applied for the detection of gas chromatography. The recovery rate of ASE were about 88.2% (TML) and 86.4% (TEL) with 15 min consuming. The recovery rate of SFE were about 93.7% (TML) and 94.1% (TEL) with 40 min consuming. Two extraction methods of ASE and SFE were optimized, which were also analyzed in recovery, repeatability, accuracy, limit of detection (LOD) and other aspect. Both ASE and SFE exhibited rational recovery efficiency. The established methods were also applied to the real soil samples. SFE had better extraction effect according to time consumption, recovery rate, LOD and accuracy. However, ASE had more advantages in automated extraction, which could be applied to the pretreatment of large amounts of samples. • Trimethyl lead and triethyl lead of soil environment are extracted and measured. • ASE / SFE - GC system is established for the assessment of trimethyl lead and triethyl lead. • Experimental parameters of ASE and SFE are evaluated and optimized. • Difference and efficiency of ASE and SFE are analyzed for practical application.

Simultaneous enrichment of inorganic and organic species of lead and mercury in pg L−1 levels by solid phase extraction online combined with high performance liquid chromatography and inductively coupled plasma mass spectrometry

Quantification of ultra-trace inorganic and organic species of lead and mercury in unpolluted environmental water is crucial to estimate the mobility, toxicity and bioavailability and interactions. Simultaneous pre-concentration of Pb and Hg species in pg L−1 levels followed by multi-elemental speciation analysis makes great sense to a large set of unstable samples because of time advantages. Herein simultaneous enrichment and speciation analysis of ultra-trace lead and mercury in water was developed by online solid-phase extraction coupled with high performance liquid chromatography and inductively coupled plasma mass spectrometry (SPE-HPLC-ICP-MS) for this aim. Pb(II), trimethyl lead (TML), triethyl lead (TEL), Hg(II), methylmercury (MeHg) and ethylmercury (EtHg) were baseline separated in 11 min under gradient elution using 5 mM l-cysteine (Cys) at pH 2.5 in the 0–1 and 4–15 min and 5 mM Cys + 0.5 mM tetrabutyl ammonium hydroxide solution at pH 2.5 in the 1–4 min. Lead and mercury species in 10 mL intact water samples were adsorbed on a 1 cm C18 enrichment column pre-conditioned with 10 mL of 1 mM 2-mercaptoethanol at 10 mL min−1, and then directly desorbed by the mobile phases. High enrichment factors (459 for Pb(II), 1248 for TML, 1627 for TEL, 2485 for Hg(II), 1984 for MeHg and 1866 for EtHg) were obtained with good relative standard deviations (<5%), leading to low LODs (0.001–0.011 ng L−1) and LOQs (0.004–0.036 ng L−1). Good accuracy of this method was validated by two certified reference materials of total lead in water (GBW08601) and total mercury in water (GBW08603) along with spiked recoveries (89–93%). The method was applied to analyze trace lead and mercury species in river, lake, tap and rain water, and purified and mineral water. Inorganic lead of 13–68 ng L−1 and inorganic mercury of 21–49 ng L−1 were measured in the nine water samples whereas TML, TEL and MeHg were not detected with 2–5 ng L−1 EtHg presented only in one river water and tap water.

Structural and Biochemical Characterization of Organotin and Organolead Compounds Binding to the Organomercurial Lyase MerB Provide New Insights into Its Mechanism of Carbon-Metal Bond Cleavage.

The organomercurial lyase MerB has the unique ability to cleave carbon-Hg bonds, and structural studies indicate that three residues in the active site (C96, D99, and C159 in E. coli MerB) play important roles in the carbon-Hg bond cleavage. However, the role of each residue in carbon-metal bond cleavage has not been well-defined. To do so, we have structurally and biophysically characterized the interaction of MerB with a series of organotin and organolead compounds. Studies with two known inhibitors of MerB, dimethyltin (DMT) and triethyltin (TET), reveal that they inhibit by different mechanisms. In both cases the initial binding is to D99, but DMT subsequently binds to C96, which induces a conformation change in the active site. In contrast, diethyltin (DET) is a substrate for MerB and the SnIV product remains bound in the active site in a coordination similar to that of HgII following cleavage of organomercurial compounds. The results with analogous organolead compounds are similar in that trimethyllead (TML) is not cleaved and binds only to D99, whereas diethyllead (DEL) is a substrate and the PbIV product remains bound in the active site. Binding and cleavage is an exothermic reaction, while binding to D99 has negligible net heat flow. These results show that initial binding of organometallic compounds to MerB occurs at D99 followed, in some cases, by cleavage and loss of the organic moieties and binding of the metal ion product to C96, D99, and C159. The N-terminus of MerA is able to extract the bound PbVI but not the bound SnIV. These results suggest that MerB could be utilized for bioremediation applications, but certain organolead and organotin compounds may present an obstacle by inhibiting the enzyme.

Determination of Lead Species in Algae by Capillary Electrophoresis-Inductively Coupled Plasma-Mass Spectrometry

A method of capillary electrophoresis (CE) coupled with inductively coupled plasma-mass spectrometry (ICP-MS) was established to determine lead ion [Pb(II)], trimethyl lead (TML), and triethyl lead (TEL). An extraction technology for lead with different species in algae was proposed and optimized for qualitative and quantitative analyses. Experimental results showed that these three lead compounds could be effectively separated within 20 min by CE-ICP-MS in a buffer solution of 70 mM H3BO3 and 17.5 M Na2B4O7 (pH 8.9). This method had good reproducibility for migration time (relative standard deviation (RSD) < 4%) and peak area (RSD < 5%). On the basis of this, the three lead compounds were detected in the linearity range of 10–200 μg L−1 with the correlation coefficient over 0.90. The detection limits for Pb(II), TML and TEL (S/N = 3, Pb) were 0.091, 0.023 and 0.030 μg L−1, respectively. The fractional extraction rate of Pb exceeded 80%, and the recoveries of Pb(II), TML, and TEL in algae samples were 103.6%, 95.7% and 90.6%, respectively. The detection results of lead content in laver and kelp samples showed that Pb in algae mainly existed in the form of Pb(II). Given its simplicity, high efficiency, and low sample consumption, the method could provide technical support for the quality control of marine algae and other marine products.

Species characteristics of lead in sea foods collected from coastal water of Fujian, Southeastern of China.

Various sea foods including fish, shellfish and shrimp were collected from different coastal areas of Fujian in China, and their Pb species characteristics were investigated in detail. The results indicated that there are two different species characteristics of Pb existing in sea food samples. About half of samples were detected to have only Pb2+, and another half of samples were detected to have both Pb2+ and trimethyl lead (TML). The results also revealed that Pb species characteristics in the sea foods rather depend on the species of sea food than the sampling area. In comparison with shellfish/shrimp samples, fish samples have higher concentrations of TML and Pb2+. Especially, the average concentration of TML in the TML-detected fish samples is about 3 times of that in the TML-detected shellfish/shrimp samples, indicating that fish has stronger ability to uptake and accumulate TML. The concentrations of total lead in all samples are lower than the maximum allowable limit of national standard, suggesting that the sea foods collected from Fujian are safe for consumption. By considering that TAL has more toxicity than Pb2+, the effect of TML in sea foods on the human health should be paid more attention in the future.

Speciation analysis of lead in marine animals by using capillary electrophoresis couple online with inductively coupled plasma mass spectrometry

We herein reported a environment-friendly microwave-assisted extraction used to extract trace lead compounds from marine animals and a ultrasensitive method for the analysis of Pb²⁺, trimethyl lead chloride (TML) and triethyl lead chloride (TEL) by using CE-ICP-MS. The extraction method is simple and has a high extracting efficiency. It can be used to completely extract both inorganic lead and organolead in marine animal samples without altering its species. The analytical method has a detection limit as low as 0.012-0.084 ng Pb/mL for Pb²⁺, TML, and TEL, and can be used to determine ultratrace Pb²⁺, TML, and TEL in marine animals directly without any preconcentration. With the help of above methods, we have successfully determined Pb²⁺, TML, and TEL in clam and oyster tissue within 20 min with a RSD (n = 6) < 5% and a recovery of 91-104%. Our results showed that Pb²⁺ was the main species of lead in clam and oyster, and organolead (TML) was only found in oyster. The proposed method provides a realistic approach for the accurate evaluation of lead pollution in seafood.

Mechanistic Details of Glutathione Biosynthesis Revealed by Crystal Structures of Saccharomyces cerevisiae Glutamate Cysteine Ligase

Glutathione is a thiol-disulfide exchange peptide critical for buffering oxidative or chemical stress, and an essential cofactor in several biosynthesis and detoxification pathways. The rate-limiting step in its de novo biosynthesis is catalyzed by glutamate cysteine ligase, a broadly expressed enzyme for which limited structural information is available in higher eukaryotic species. Structural data are critical to the understanding of clinical glutathione deficiency, as well as rational design of enzyme modulators that could impact human disease progression. Here, we have determined the structures of Saccharomyces cerevisiae glutamate cysteine ligase (ScGCL) in the presence of glutamate and MgCl(2) (2.1 A; R = 18.2%, R(free) = 21.9%), and in complex with glutamate, MgCl(2), and ADP (2.7 A; R = 19.0%, R(free) = 24.2%). Inspection of these structures reveals an unusual binding pocket for the alpha-carboxylate of the glutamate substrate and an ATP-independent Mg(2+) coordination site, clarifying the Mg(2+) dependence of the enzymatic reaction. The ScGCL structures were further used to generate a credible homology model of the catalytic subunit of human glutamate cysteine ligase (hGCLC). Examination of the hGCLC model suggests that post-translational modifications of cysteine residues may be involved in the regulation of enzymatic activity, and elucidates the molecular basis of glutathione deficiency associated with patient hGCLC mutations.

Development of a methodology for the simultaneous determination of inorganic and organolead compounds using supercritical fluid extraction followed by gas chromatography–mass spectrometry and its application to environmental matrices

A method for the extraction of triethyl lead (TEL +), trimethyl lead (TML +), and Pb 2+ from sand was developed using supercritical modified CO 2–CH 3OH extraction and in situ complexation with sodium diethyldithiocarbamate (NaDDTC) using a 2 5 factorial exploratory design is described. The screened variables were (i) pressure (69–193 bar), (ii) temperature (40–150 °C), (iii) ligand amount (0–100 mg), (iv) methanol volume (0.0–0.5 mL) and (v) static time (0–45 min). The optimum extraction conditions found were as follow: pressure, 193 bar; temperature, 40 °C; amount of NaDDTC, 100 mg; methanol volume, 0.5 mL; static time 45 min; and CO 2 flow rate, 1 mL min −1. Under these conditions the following recoveries were obtained (TML + 97 ± 2%, TEL + 70 ± 5%, and Pb 2+ 100 ± 4%). The presence of NaDDTC is not necessary for the extraction of TML + and TEL +, but it is a very significative parameter for Pb 2+. A second experimental design 2 2 + star for temperature and pressure was realized, but the results were not better than those of the first model. SFE extract derivatization was achieved with pentylmagnesium bromide, and target analyte determination was carried out by gas chromatography–mass spectrometry. Detection limits in the full-scan mode were 4, 10, and 39 pg as lead for TMPeL, TEPeL and PbPe 4, respectively. The method was validated with urban dust containing TML + (CRM 605. Pb 7.9 ±1.2 μg kg −1) and river sediment containing inorganic lead (GBW08301. Pb 79.0 ± 12.0 mg kg −1) as reference materials. The proposed method was applied to lead analysis in sand collected from an oil-polluted beach in Chile.

Simultaneous Determination of Trimethyl- and Triethyllead in Urban Dust by Species-specific Isotope Dilution/Gas Chromatography-Inductively Coupled Plasma Mass Spectrometry

Both (206)Pb-labeled trimethyllead (TML) and triethyllead (TEL) were synthesized from (206)Pb-enriched metallic Pb certified reference material (NIST SRM 983) and iodomethane or iodoethane through a one-process reaction in a closed system using centrifuge tubes, respectively. Organolead compounds in an urban dust reference material (BCR CRM 605) were extracted with an acetic acid/methanol (1:1) solution, which was mechanically shaken for 24 h. After adjusting the pH of the extracted solution to pH 5, the extracted organolead compounds were derivatized by tetrabutylammonium tetrabutylborate (TATB) and measured with GC-ICPMS. The analytical results of TML and TEL for BCR CRM 605 were 8.22 +/- 0.04 microg kg(-1) (mean +/- standard deviation, n = 3) and 1.12 +/- 0.06 microg kg(-1), respectively. The analytical results of TML agreed well with the certified value (7.9 +/- 1.2 microg kg(-1)).

Speciation analysis of mercury and lead in fish samples using liquid chromatography–inductively coupled plasma mass spectrometry

A liquid chromatography–inductively coupled plasma mass spectrometric (LC–ICP-MS) method for lead and mercury speciation analysis was described. Sample containing ionic lead and mercury compounds was subjected to liquid chromatographic separation before injection into the direct injection high efficiency nebulizer (DIHEN, 170-AA). The species studied include inorganic lead (Pb(II)), trimethyl lead (trimethyl-Pb), triethyl lead (triethyl-Pb), inorganic mercury (Hg(II)), methyl mercury (methyl-Hg) and ethyl mercury (ethyl-Hg), which were well separated by reversed-phase liquid chromatography with a C18 column as the stationary phase and a pH 2.8 solution of 0.2% (v/v) 2-mercaptoethanol, 1 mg L −1 ETDA, 174.2 mg L −1 sodium 1-pentanesulfonate and 12% (v/v) methanol as the mobile phase. The lead and mercury species in biological tissues were quantitatively extracted, into 10 g L −1 EDTA and 0.2% (v/v) 2-mercaptoethanol solution taken in a closed centrifuge tube and kept on water bath, using microwaves at 65 °C for 2 min. The spike recovery of individual lead and mercury species determined by spiking the samples with suitable concentration of lead and mercury mixture standard were between 93% and 99%. The detection limits of the species studied were in the range 0.1–0.3 μg Pb L −1 and 0.2–0.3 μg Hg L −1. The procedure has been applied for the speciation analysis of two reference samples namely NRCC DOLT-3 Dogfish Liver and DORM-2 Dogfish Muscle and a swordfish sample obtained locally. The sum of the concentrations of individual species has been compared with the certified values for total lead and mercury to verify the accuracy of the method. The precision between sample replicates was better than 10% with LC–DIHEN-ICP-MS method.

Speciation of lead compounds in fish by capillary electrophoresis-inductively coupled plasma mass spectrometry

A capillary electrophoresis-inductively coupled plasma mass spectrometric (CE-ICP-MS) method for lead speciation application is described. Sample containing ionic lead compounds were subjected to electrophoretic separation before injection into the micro-concentric nebulizer (CEI-100). The species studied include inorganic lead (PbII), trimethyl lead (TML) and triethyl lead (TEL). The separation has been achieved on a 70 cm length × 75 μm id fused silica capillary. The electrophoretic buffer used is 15 mmol l−1 Tris (pH 8.25) containing 10 mmol l−1 SDS (sodium dodecyl sulfate), 0.2 mmol l−1 EDTA and 2% v/v methanol, while the applied voltage is set at +26 kV. The lead species in biological tissues are extracted into 1% m/v EDTA solution taken in a closed centrifuge tube and kept on a water bath, using microwaves at 70 °C for 10 min. The extraction efficiencies of individual lead species added to the sample at 2 μg Pb g−1 level are between 97% and 102%. The detection limits of the species studied are in the range 0.2–0.6 ng Pb ml−1. The procedure has been applied for the speciation analysis of two reference materials namely dogfish liver tissue (NRCC DOLT-3) and oyster tissue (NIST SRM 1566a) and two real-world samples.

Biogeochemistry of trimethyllead and lead in a forested ecosystem in Germany

Lead compounds, especially ionic organolead compounds (OLC), are highly toxic and mobile pollutants strongly affecting many ecosystems. Soil pools and fluxes with precipitation, litterfall and runoff of trimethyllead (TML), one of the dominant ionic OLC in the environment, and Pbtotal were investigated in a forested ecosystem in NE-Bavaria, Germany. In addition, ad/desorption of TML to soils was studied in batch experiments and its degradation in soils was investigated using long term incubations. Total soil storage in the catchment was 11.56 mg Pb ha−1 for TML and 222 kg Pb ha−1 for Pbtotal. More than 90% of the soil storage of TML was found in the wetland soils of the catchment representing only 30% of the area. Most Pbtotal (>90%) was found in the upland soils. In upland soils, TML was only detectable in the forest floor. The annual total deposition from the atmosphere, estimated as throughfall + litterfall fluxes, amounted to 3.7 mg Pb ha−1 year−1 for TML and 52 g Pb ha−1 year−1 for Pbtotal. The contribution of litterfall was 1.5 and 32%, respectively. The concentrations of TML and Pbtotal in wet precipitation were: fog > throughfall > bulk precipitation. The annual fluxes with runoff from the catchment was 0.5 mg Pb ha−1 year−1 for TML and 2.8 g Pb ha−1 year−1 for Pbtotal. TML degraded rapidly in the forest floor (Oa horizon) with a half-life (t1/2) of 33.5 days. The degradation of TML in Fen (t1/2 = 421 days) and in the mineral soil (Bw-C horizon, t1/2 = 612 days) was much slower. Emission of tetramethyllead from wetland soils was not observed during the 1 year incubation. The adsorption affinity of TML to different soils was Fen > Oa > A ≥ Bw-C. The ratio of total soil storages to the present annual input were 3.6 years for TML. TML and Pbtotal are still deposited in remote areas even after the use of tetraalkyllead as additives has been terminated for years. The rates of deposition are, however, much lower than in the past. Forest soils act as a sink for deposited TML and Pbtotal. TML is accumulated mostly in wetland soils and seems to be stable under anoxic conditions for a long time. In upland soils, TML decomposes rapidly. Only small amounts of TML are transferred from soils into runoff.

Simultaneous multi-elemental speciation analysis of organometallic compounds by solid-phase microextraction and multicapillary gas chromatography hyphenated to inductively coupled plasma-time-of-flight-mass spectrometry

A simple, rapid and accurate method on the basis of solid phase microextraction (SPME) in combination with multicapillary gas chromatography (MCGC) hyphenated to inductively coupled plasma-time-of-flight mass spectrometry (ICP-TOFMS) was developed for simultaneous speciation analysis of 10 organometallic compounds of mercury (including inorganic mercury), tin and lead. Headspace SPME was used for extraction/preconcentration of the species from the sample after derivatization with sodium tetraethylborate and subsequent volatilization. Seven SPME fibers were compared in terms of extraction efficiency. A 65 µm polydimethylsiloxane/divinylbenzene fiber offered the best overall extraction efficiency. Using MCGC separation, a total chromatographic run time below 200 s was obtained. With ICP-TOFMS detection peak widths at half height (FWHM) down to 0.3 s were measured without spectral skew thanks to the simultaneous character of the mass spectrometer. Detection limits well below pg g−1 levels were obtained for trimethyllead (TML), dimethyllead (DML), trimethyltin (TMT), dimethyltin (DMT), monomethyltin (MMT), monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT). Somewhat higher detection limits were obtained for methylmercury (MeHg, 1.3 pg g−1) and inorganic mercury (Hg2+, 2.0 pg g−1). For extraction/preconcentration of MeHg and Hg2+ the 75 µm carboxen/polydimethylsiloxane (CAR/PDMS) fiber is a better choice. The analytical precision (RSD, %) for 10 successive injections of a standard mixture containing 100 pg of each species was generally below 5%. Propylmercury (PrHg) was used as the internal standard for MeHg and Hg2+ as well as for lead species determination. The method was validated by the analysis of biological and road dust certified reference materials (CRMs).

Crystallization and preliminary X-ray analysis of the selenate reductase from Thauera selenatis.

Selenate reductase from Thauera selenatis was crystallized using ammonium sulfate as a precipitant. Crystals of selenate reductase belong to the space group C2, with unit-cell parameters a = 116.9, b = 67.5, c = 186.7 A, beta = 90 degrees. Native data to 2.1 A resolution have been collected and a heavy-atom derivative has been identified following soaking of the crystals in a solution of trimethyl lead acetate.

Crystallization and preliminary X-ray analysis of maltose O-acetyltransferase.

Maltose O-acetyltransferase (Mac) is a member of the hexapeptide-repeat family of enzymes, which contains proteins with left-handed parallel beta-helix architecture forming homotrimers. Diffraction data for four well diffracting crystal forms were collected. Crystal form I diffracted beyond 1.53 A resolution but was perfectly merohedrally twinned with an apparent space group P622. Crystal forms II and III (space groups R3 and C2, respectively) could be obtained under very similar conditions by adjusting the buffer pH differently. Crystal forms II and III had several monomers in the asymmetric unit and were difficult to derivatize. However, during soaking with trimethyl lead acetate, the form III crystals dissolved and crystals with a different habit and space group grew in their place (form IV). In three of the crystal forms, a ladder of peaks was visible in the native Patterson maps along the c axis. These peaks were interpreted as corresponding to the vectors between the beta-strands in the turns of the beta-helix. Crystal form IV is suitable for structure determination of Mac exploiting the anomalous scattering of lead.

Solid phase microextraction gas chromatography-glow discharge-optical emission detection for tin and lead speciation

A modified interface between a gas chromatograph (GC) and a hollow cathode (HC) radiofrequency (rf) glow discharge (GD) with detection by optical emission spectrometry (OES) has been investigated for elemental speciation studies. Solid phase microextraction (SPME), used for extraction and preconcentration of organic compounds, is here used for the introduction of the metal species under investigation into the injector of the GC, after preconcentration of metal species ethylated “in situ” with sodium tetraethylborate. Tin [monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT)] and lead species [trimethyllead (TML) and triethyllead (TEL)] were used as models and separated using a capillary column. Detection by rf-(HC)GD-OES was accomplished at 283.9 nm for tin and 283.3 nm for lead. After optimization of the parameters affecting the rf-(HC)GD signals (pressure, radiofrequency power and He flow rate used as plasma gas) and also the parameters affecting the SPME technique (adsorption time, desorption time, injector temperature and position of the fiber into the injector of the GC), the analytical characteristics were calculated. Good detection limits for the tin and lead species under study (0.021 µg L−1 for MBT, 0.026 µg L−1 for DBT, 0.075 µg L−1 for TBT, 0.03 µg L−1 for TEL and 0.15 µg L−1 for TML) were achieved. Finally, the accuracy of the proposed speciation methodology was tested by analysing a certified reference material (sediment PACS-2) from the National Research Council of Canada.

Determination of the speciation of organolead compounds in airborne particulate matter by gas chromatography–inductively coupled plasma mass spectrometry

The speciation of organolead compounds in airborne particulate matter was determined by gas chromatography–inductively coupled plasma mass spectrometry. The analytes were extracted from the sample using 0.5 M acetic acid in methanol. The ionic organolead compounds were extracted into hexane using diethydithiocarbamate at pH 9 in the presence of EDTA to complex inorganic Pb. Derivatisation of the organolead species was performed with butylmagnesium chloride. Separation and detection of the butylated trimethyllead (TML), dimethyllead (DML), triethyllead (TEL) and diethyllead (DEL) was achieved. Detection limits, as Pb, were 3.2 fg for TML, 2.4 fg for DML, 1.8 fg for TEL and 9 fg for DEL for a 1 μl sample injection. Typical precision of repetitive injections was 1.5–4% using tetraethyllead (TrEL) as internal standard. The method proposed was validated by the determination of TML in the reference material CRM 605 and was applied to the analysis of airborne particulate matter in the atmosphere of the city of Oviedo. DML, DEL and methylethyllead (MEL) were detected at pg m −3 levels.

Electrospray mass spectrometry of trimethyllead and triethyllead with in-tube solid phase microextraction sample introduction

A study of positive ionization electrospray mass spectrometry (ES-MS) was performed on trimethyllead (TML) and triethyllead (TEL). The system consisted of in-tube solid phase microextraction (SPME) coupled directly to an electrospray mass spectrometer. Fragmentation patterns of compounds were observed by applying different fragmentation voltages. High voltages produced sufficient fragmentation to elucidate the dissociation of the trialkyllead compounds. Electrospray mass spectrometry has been shown to be a suitable detection system for organolead speciation. Applying fragmentation energy programming, it might be possible to obtain in parallel the molecular and atomic signals of lead compounds. Copyright 1999 John Wiley & Sons, Ltd.