Petru Jitaru

The fate of mercury species in a sub-arctic snowpack during snowmelt

An extensive mercury study was conducted in April 2002 prior to and during the annual melting of a snowpack in a sub-arctic site along the Hudson Bay (Canada). Gas-phase measurements show that the snowmelt coincides with an elemental mercury (Hg°) pulse in the snowpack air far above ambient levels. Additional measurements of inorganic mercury (Hg2+) and methylmercury (MeHg+) in snow pits, in surface snow and in a meltwater sample clearly reveal that most of Hg is removed from the snow during the first days of snowmelt. We estimate that gas-phase exchanges contribute poorly to remove Hg from the snowpack; consequently during a snowmelt day more than 90% of Hg present in the snow surface is likely released with the meltwater. In arctic areas, where Hg accumulates at an accelerated rate in the snow surfaces [Lu et al., 2001] during mercury depletion events (MDE), the discharge of this toxic and bio-accumulating pollutant in water systems could be a threat to ecosystems and local indigenous populations.

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).

A systematic approach to the accurate quantification of selenium in serum selenoalbumin by HPLC–ICP-MS

In this paper, two different methods are for the first time systematically compared for the determination of selenium in human serum selenoalbumin (SeAlb). Firstly, SeAlb was enzymatically hydrolyzed and the resulting selenomethionine (SeMet) was quantified using species-specific isotope dilution (SSID) with reversed phase-HPLC (RP-HPLC) hyphenated to (collision/reaction cell) inductively coupled plasma-quadrupole mass spectrometry (CRC ICP-QMS). In order to assess the enzymatic hydrolysis yield, SeAlb was determined as an intact protein by affinity-HPLC (AF-HPLC) coupled to CRC ICP-QMS. Using this approach, glutathione peroxidase (GPx) and selenoprotein P (SelP) (the two selenoproteins present in serum) were also determined within the same chromatographic run. The levels of selenium associated with SeAlb in three serum materials, namely BCR-637, Seronorm level 1 and Seronorm level 2, obtained using both methods were in a good agreement. Verification of the absence of free SeMet, which interferes with the SeAlb determination (down to the amino acid level), in such materials was addressed by analyzing the fraction of GPx, partially purified by AF-HPLC, using RP-HPLC (GPx only) and size exclusion-HPLC (SE-HPLC) coupled to CRC ICP-QMS. The latter methodology was also used for the investigation of the presence of selenium species other than the selenoproteins in the (AF-HPLC) SelP and SeAlb fractions; the same selenium peaks were detected in both control and BCR-637 serum with a difference in age of ca. 12 years. It is also for the first time that the concentrations of selenium associated with SeAlb, GPx and SelP species in such commercially available serums (only certified or having indicative levels of total selenium content) are reported. Such indicative values can be used for reference purposes in future validation of speciation methods for selenium in human serum and/or inter-laboratory comparisons.

Speciation analysis of selenoproteins in human serum by solid-phase extraction and affinity HPLC hyphenated to ICP-quadrupole MS

Anion exchange-solid-phase extraction carried out prior to double column affinity-high performance liquid chromatography (AF-HPLC) coupled on-line with conventional inductively coupled plasma-(quadrupole) mass spectrometry is proposed for simultaneous speciation analysis of selenoprotein P (SelP), glutathione peroxidase (GPx) and selenoalbumin (SeAlb) in human serum. Efficient interference-free AF-HPLC separation of GPx, SelP and SeAlb is obtained within a total chromatographic run time less than 15 min. The repeatability in terms of relative standard deviation (R.S.D., %, n = 10) is 7% for GPx and SelP and 4% for SeAlb. The detection limits are 0.1 ng mL−1 for GPx, 1.0 ng mL−1 for SelP and 1.3 ng mL−1 for SeAlb. The method was validated by the analysis of two human serum reference materials certified for total Se content.

Towards an improved qualitative and quantitative determination of glutathione peroxidase, selenoprotein P and selenoalbumin in human serum by HPLC coupled to ICP-MS

This paper deals primarily with the validation of a clean-up procedure based on anion exchange solid-phase extraction for the accurate determination of glutathione peroxidase (GPx), selenoprotein P (SelP) and selenoalbumin (SeAlb) in human serum by affinity HPLC (AF-HPLC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS). In addition, the identification and the purity assessment of the GPx, SelP and SeAlb peak fractions separated by AF-HPLC is addressed by their analysis using matrix assisted laser desorption ionization-time of flight mass spectrometry.