Double Spike Isotope Dilution GC-ICP-MS for Evaluation of Mercury Species Transformation in Real Fish Samples Using Ultrasound-Assisted Extraction

Abstract

Sample preparation continues being a key factor to obtain fast and reliable quantification of Hg species. Assisted procedures enhance the efficiency and reduce the extraction time; however, collateral species transformations have been observed. Moreover, differential interconversions have been observed even between similar matrixes, which introduce an important uncertainty for real sample analysis. Trying to minimize Hg species transformations, we have tested a soft ultrasound-assisted extraction procedure. Species quantification and transformations have been evaluated using double spike isotope dilution analysis (IDA) together with gas chromatography inductively coupled plasma mass spectrometry (GC-ICP-MS) for a CRM material (Tort-2) and shark and swordfish muscle samples. Optimum extraction solution and sonication time led to quantitative extraction and accurate determination of MeHg and IHg in a short time, although different behaviors regarding species preservation were observed depending on the sample. Negligible species transformations were observed in the analysis of the CRM, while a small but significant demethylation factor was observed in the case of real samples. In comparison with other extraction procedures, species transformations became smaller, and fewer differences between fish species were found. Similar results were obtained for fresh and lyophilized samples of both fish samples, which permit one to analyze the fresh sample directly and save time in the sample preparation step. The high grade of species preservation and the affordability of the extraction procedure allow one to obtain accurate determinations even for routine laboratories using quantification techniques, which do not estimate species transformations.

Atomic spectrometry update. Elemental speciation review

“…Three different extraction methods were used: (a) heating at 85 C for two hours, (b) MAE at 60 W for three minutes and (c) standing at room temperature for 24 hours, with TMAH employed as the extractant in each case. The spike isotopes used were 199 Hg for inorganic Hg and 201 Hg for MeHg. Mercury species were simultaneously derivatised and extracted in situ, with 1% sodium tetrapropyl borate (NaPr 4 B) in a sodium acetate/acetic acid buffer at pH 4 into isooctane, prior to GC separation and isotope ratio measurements by ICP-MS. A MXT-1 column (length 30 m, i.d.…”

“…It was reported that signicant mercury species transformation was only observed for one oyster sample resulting in 18% demethylation of inorganic Hg. In a separate paper, 201 double spiking IDA was also described in the investigation of UAE of Hg species in sh samples. Four different extraction solutions, (5 mol L À1 HCl, 60 mmol L À1 HCL in saturated NaCl, 3.0 mol L À1 KOH in MeOH and 25% TMAH in H 2 O), were evaluated in this work.…”

“…Four different extraction solutions, (5 mol L À1 HCl, 60 mmol L À1 HCL in saturated NaCl, 3.0 mol L À1 KOH in MeOH and 25% TMAH in H 2 O), were evaluated in this work. About 100 mg of TORT-2 CRM, lobster hepatopancreas, was suspended in 4 mL of extractant and the enriched Me 201 Hg and 199 Hg spikes added. The sample and spike were equilibrated by shaking for 15 minutes, followed by UAE for 30 minutes at a constant temperature of 50 C. Aer the UAE procedure, samples were centrifuged and a 1 mL aliquot removed for Hg species derivatisation with 0.4 mL NaPr 4 B (2% in 0.2 mol L À1 NaOH), 4 mL 1.1 mol L À1 sodium acetate adjusted to pH 5 and 1 mL of hexane with gentle shaking for 10 minutes.…”

“…Mercury species in the SPM and sediment samples were extracted, aer spiking and a 15 minutes equilibration period, using a focussed MAE procedure at 75 C for four minutes. The species present in the samples were quantied by ID-GC-ICP-MS aer spiking with 199 Hg enriched (91%) iHg and 201 Hg enriched (96.5%) MeHg. The propylation procedure for Hg species and GC-ICP-MS separation was the same as that described above in ref.…”

A broad-applicability method for mercury speciation in various seafoods using microwave-assisted extraction and ion chromatography-inductively coupled plasma mass spectrometry

“…(2) The development of a robust method for the accurate and sensitive determination of each mercury species in various seafood samples is necessary. In reality, the most practical analytical methods for mercury speciation are inductively coupled plasma mass spectrometry (ICP-MS)-based hyphenated techniques such as high performance liquid chromatography (HPLC) hyphenated with ICP-MS (HPLC-ICP-MS), 10,11,[14][15][16][17][18][19][20][21][22] ion chromatography hyphenated with inductively coupled plasma mass spectrometry (IC-ICP-MS), 8,9,23 gas chromatography (GC) hyphenated with ICP-MS (GC-ICP-MS) and capillary electrophoresis (CE) hyphenated with ICP-MS (CE-ICP-MS), 6,[24][25][26] although several sensing methods including colorimetric and uorescence methods have been developed for the rapid and specic determination of CH 3 Hg + and/or C 2 H 5 Hg + in recent years. [27][28][29] Among all ICP-MS-based techniques, CE-ICP-MS has lower sensitivity and poorer repeatability due to the low sample injection volume, 6,26 whereas most HPLC-ICP-MS methods previously reported employed an expensive reverse-phase C18 or C8 column as the separation column and thus involved higher analysis cost.…”