Nohora P. Vela

Chromium speciation by anion-exchange high-performance liquid chromatography with both inductively coupled plasma atomic emission spectroscopic and inductively coupled plasma mass spectrometric detection

Development of a new method for the determination of Cr(III) and Cr(VI) is described. Anion-exchange high-performance liquid chromatography (HPLC) was used to separate Cr(III) and Cr(VI) with on-line detection by inductively coupled plasma atomic emission spectroscopy (ICP-AES) at 2766 A in preliminary studies, and inductively coupled plasma mass spectrometry (ICP-MS) with single-ion monitoring at m/z 52 and m/z 53 for final work. A mobile phase consisting of ammonium sulfate and ammonium hydroxide was used, and a simple chelation procedure with EDTA was followed to stabilize the Cr(III) species in standard solutions. ICP-MS results indicated the feasibility of using chromium isotope m/z 53 instead of the more abundant m/z 52 isotope due to a high mobile-phase background most significantly from the SO+ polyatomic interference. The absolute detection limits based on peak-height calculations were 40 pg for Cr(III) and 100 pg for Cr(VI) in aqueous media by HPLC-ICP-MS. The linear dynamic range extended from 5 ppb (ng/ml) to 1 ppm (micrograms/ml) for both species. By HPLC-ICP-AES, detection limits were 100 ng for Cr(III) and 200 ng for Cr(VI). Cr(III) was detected in NIST-SRM 1643c (National Institute of Standards and Technology-Standard Reference Material, Trace Elements in Water) by HPLC-ICP-MS at the 20 ppb level.

Lead speciation by gradient high-performance liquid chromatography with inductively coupled plasma mass spectrometric detection

Speciation of inorganic lead (PbII), triethyllead chloride (TEL), triphenyllead chloride (TPhL) and tetraethyllead (TTEL) was investigated using gradient high-performance liquid chromatography (HPLC) with detection by inductively coupled plasma mass spectrometry (ICP-MS). Ion-pair reversed-phase chromatography was used. The detection limits were 0.37, 0.14, 0.17 and 3.9 ng of Pb for PbII, TEL, TPhL and TTEL, respectively. The reproducibility of peak height measurements ranged from 3.1 to 4.2%(relative standard deviation). The method was evaluated by analysing National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 2715 Lead in Reference Fuel for tetraethyllead and a water Quality Control Sample from the Environmental Protection Agency for inorganic lead. Both the direct solution nebulization and HPLC–ICP-MS results compare favourably with reference values. The applicability of the method to other alkyllead compounds is discussed.

Potential of liquid chromatography–inductively coupled plasma mass spectrometry for trace metal speciation. Invited lecture

Liquid chromatography (LC) and supercritical fluid chromatography (SFC) coupled with plasma mass spectrometry for ultra-trace level detection of metal-containing compounds are discussed. The compatibility of liquid and supercritical fluid flow rates with the plasma allows real-time chromatograms to be obtained. Different LC modes including reversed phase, ion exchange and size exclusion have been used in the separation of metal-containing species and some of these applications are discussed in this paper. Studies to date have developed potential methods for arsenic, mercury, lead, tin and chromium speciation. Sub-ng to pg detection is available with LC sample introduction into the plasma. Chromatographic methods which introduce samples as gases, such as SFC provide the best levels of detection, usually in the pg to sub-pg range.

Supercritical fluid extraction of organotins from biological samples and speciation by liquid chromatography and inductively coupled plasma mass spectrometry

Supercritical fluid extraction is used to extract tributyltin and triphenyltin from biological samples. The extraction conditions with carbon dioxide as supercritical fluid (methanol modifier used) are optimized for the organotins from fish tissue certified reference material. The total extraction time is found to be approximately 15 min. The recovery studies at the optimal conditions shows a recovery of 44% for tributyltin and 23% for triphenyltin. The reproducibilities for both the compounds extracted are within 2% R.S.D. The optimum conditions obtained are also used to extract tributyltin and triphenyltin from tuna fish obtained from a local grocery store.

Determination of tri- and tetra-organotin compounds by supercritical fluid chromatography with inductively coupled plasma mass spectrometric detection

Supercritical fluid chromatography (SFC) coupled with inductively coupled plasma mass spectrometry (ICP-MS) is used for the separation and detection of tetra- and tri-organotin compound mixtures. The carbon dioxide effluent from the SFC system, using a capillary column (SB-biphenyl-30), does not require a modification in the standard ICP-MS operating conditions. Several parameters such as interface temperature, oven temperature, carbon dioxide pressure programme, mobile phase composition and column length are evaluated in order to optimize the separation conditions of several organotins. Detection limits of 0.26, 0.80, 0.57 and 0.20 pg are found for tetrabutyl tin, tributyltin chloride, triphenyltin chloride and tetraphenyltin, respectively. The relative standard deviation for five 0.05 mm3 injections containing 0.5 ng of Sn ranged from 1.3 to 3.4%.

Comparison of flame ionization and inductively coupled plasma mass spectrometry for the detection of organometallics separated by capillary supercritical fluid chromatography

Organotin compounds are separated by capillary supercritical fluid chromatography (SFC) and a comparison of the detection by flame ionization (FID) and inductively coupled plasma mass spectrometry (ICP-MS) is presented. Resolution, detection limits, linear dynamic range and reproducibility are the parameters compared between SFC-FID and SFC-ICP-MS, for the detection of tri- and tetraorganotin compounds. The resolution obtained in the SFC-FID system is not always observed in SFC-ICP-MS. Degradation in resolution is due to fluctuations in transfer line temperature. Baseline resolution for the organotins considered is achieved in both systems by using a longer column. Detection limits (DLs) are calculated as 3 sigma/S, where sigma is the standard deviation of the blank signal and S is the slope of the calibration curve. Detection limits of 10.3, 12.5, 12.0 and 9.0 pg are obtained for tetrabutyltin, tributyltin chloride, triphenyltin chloride and tetraphenyltin, respectively, using SFC-FID. An improvement in detection limits of one order of magnitude is achieved by SFC-ICP-MS for the same organotins (0.26, 0.80, 0.57 and 0.20 pg, respectively). The relative standard deviations using SFC-FID for five 50-nl injections, containing 0.5 ng Sn, ranged from 3.2 to 6.4%. Using SFC-ICP-MS, five replicate injections of 0.05 ng Sn give R.S.D.s from 1.3 to 3.4%.

Trace metal speciation via supercritical fluid extraction–liquid chromatography–inductively coupled plasma mass spectrometry

Supercritical fluid CO2 was used for the extraction of organotin compounds present in fish. A sample of tuna fish was spiked with trimethyltin chloride, tributylin chloride and triphenyltin chloride. Parameters such as cartridge size, type of modifier, and type and temperature of the restrictor were evaluated for the spiked sample. Extraction conditions were optimized by measuring total metal content using ICP-MS detection. The extracts were also analysed by LC–ICP-MS. Optimized extraction conditions were applied to a fish tissue CRM that contained tributyltin and triphenyltin. LC–ICP-MS analysis indicated that the extracted species varied with the modifier used. Extraction efficiencies for the CRM were lower when compared with the results obtained for the spiked samples using the same extraction conditions. However, extraction efficiencies were up to 80% for trimethyltin and 40% for triphenyltin with the fish tissue CRM when 1% water was added as a modifier and diethyldithiocarbamic acid ammonium salt or pyrrolidinecarbothioic acid ammonium salt were added as complexing agents.

Distribution and accumulation of a mixture of arsenic, cadmium, chromium, nickel, and vanadium in mouse small intestine, kidneys, pancreas, and femur following oral administration in water or feed.

Manufactured gas plant (MGP) sites are contaminated with coal tar and may contain metals such as arsenic (As), cadmium (Cd), chromium (Cr), nickel (Ni), and vanadium (V). These metals are known to cause cancer or other adverse health conditions in humans, and the extent and cost of remediating MGP sites may be influenced by the presence of these metals. Studies assessed the distribution of these metals in female B6C3F1 mice ingesting (1) a metal mixture in water or (2) an MGP mixture in NIH-31 feed. The highest metal levels were measured in the small intestine and kidneys of mice receiving the metal mixture in water. For mice receiving the metal mixture in water, levels of As, Cd, and Cr, in the small intestine, levels of As, Cd, Cr, and V in the kidneys, levels of As and Cd in the pancreas, and levels of Cr and V in the femur were significantly greater than controls at 4, 8, 12, 16, and 24 wk. Except for Ni levels in the small intestine and femur and Cr levels in the kidneys, levels of metals were much lower in mice administered the MGP mixture in feed. The highest concentrations of metals in mice ingesting the MGP mixture in feed were found in the small intestine and kidneys, but few were significantly greater than controls. Levels of As in the small intestine at 6 and 18 wk and levels of Cr in the kidneys at 12, 18, and 24 wk were significantly greater than in controls. The data suggest that tissue burdens in small intestine, kidneys, pancreas, and femur of arsenic, cadmium, chromium, and vanadium are less when metals are present as an MGP mixture in feed than as a mixture in water. The reduced distribution and accumulation of metals in the organs of mice ingesting the MGP mixture in feed compared to the levels in organs of mice ingesting the metal mixture in water suggests that metals may be less likely to accumulate in humans ingesting MGP mixtures, thereby presenting a lower overall human health risk. The data presented indicate that the matrix in which metals are present will affect the uptake of individual metals and the organ specificity.

Hydride generation, electrothermal vaporization and liquid chromatography as sample introduction techniques for inductively coupled plasma mass spectrometry☆

Although the most common method of sample introduction for inductively coupled plasma-mass spectrometry (ICP-MS) used is pneumatic nebulization, it suffers from limitations particularly with respect to the transport efficiency. In an effort to improve the analyte transport to the plasma, many alternative techniques have been studied, including electrothermal vaporization (ETV) and hydride generation, among others. Flow injection and liquid chromatography, although they employ pneumatic nebulization, have also been studied as sample introduction techniques due to the ability to analyze small volume samples and obtain speciation information. Here, some advances in sample introduction for ICP-MS will be discussed including hydride generation and ETV techniques. In addition, recent studies in HPLC-ICP-MS will also be described. Advantages and disadvantages of each method will be reviewed together with the application to some representative samples.

Multi-element detection for supercritical fluid chromatography by inductively coupled plasma mass spectrometry

The feasibility of multi-element detection using supercritical fluid chromatography (SFC) with inductively coupled plasma mass spectrometry (ICP-MS) has been investigated for organomercury and organolead compounds. Since a quadrupole mass spectrometer is a sequential instrument, multi-element detection of transient signals presents difficulties; therefore, detection is usually performed in a single-ion monitoring mode. The applicability of utilizing time-resolved acquisition (TRA) software for quantitative determinations using SFC was investigated and compared with results obtained for single-ion monitoring modes. Detection limits were found to be approximately 5–10 pg for diethylmercury (DIEM) using TRA detection and 3 pg using single-ion monitoring detection. The detection limits of tetrabutyllead (TTBL) and tributyllead (TRBL) acetate were found to be 0.7–3 and 50–100 pg, respectively, for the TRA acquisitions, and 0.5 and 10 pg for single-ion monitoring measurements. The calibration graphs were linear over three decades for DIEM and TTBL, and two decades for the TRBL. The precision of the technique was between 1 and 5% relative standard deviation for 5 ng injections of the compounds of interest. The accuracy of the SFC–ICP-MS single-ion monitoring technique was demonstrated by analysis of a National Institute of Standards and Technology (NIST) standard reference material (SRM) 2715 Lead in Reference Fuel, giving a concentration of 785 ± 9.71 ppm of tetraethyllead, with the SFC–ICP-MS system, compared with the certified value of 784 ± 4.00 ppm at the 95% confidence level.