Identification and determination of methylmercury compounds in fish using combination gas chromatograph-mass spectrometer

Mercury determination in blood by gas chromatography-mass spectrometry

A stable isotope dilution gas chromatography-mass spectrometry method using 196Hg as an internal standard is described for determining Hg in blood. In this method, the blood samples are not subjected to any digestion to avoid the loss of Hg. A solution of 0.6M HCl is used to free Hg present in blood from proteins. The pH of the solution is adjusted to 9 using borate buffer and Hg chelated using lithium bis(trifluoroethyl)dithiocarbamate. All isotope ratio measurements are made using an organic mass spectrometer. Overall precision values for the five major Hg isotopes relative to 202Hg are 1.6-2.3% when 10 ng samples of chelated Hg are analyzed. No appreciable memory or carryover effect is observed when two synthetic mixtures differing in 196Hg/202Hg ratios by a factor of 30 are sequentially analyzed. The method is validated by determining Hg in blood samples using isotope dilution GC-MS.

Determination of methylmercury in human blood using capillary gas chromatography and selected-ion monitoring

A capillary gas chromatographic method, using selected-ion monitoring in the electron-impact mode, was developed for the analysis of methylmercury (MeHg) in human blood. The samples, spiked with the internal standard propylmercury bromide (PropHgBr), were, after addition of sodium bromide and cupric sulfate, extracted with toluene. The organic phase was extracted with an ethanol-water solution of sodium thiosulfate. After addition of sodium bromide solution, the ethanol-water phase was extracted with toluene. Methylated derivatives (MeHgCH2Br and PropHgCH2Br) were formed by the addition of a diethyl ether solution of diazomethane. The chromatographic properties of the derivatives were much better than those of the non-methylated compounds. The m/z 215 fragment of MeHgCH2Br and the molecular ion m/z 338 of PropHgCH2Br were monitored. The calibration graphs, with a linear correlation coefficient of 0.992 (n = 12) in the 1-5 micrograms/l concentration range, passed through the origin. The detection limit for MeHg in human blood was ca. 0.5 microgram/l. Analysis of spiked blood samples at concentrations of about 2 and 10 micrograms/l gave a relative standard deviation of 4.2 and 5.5%, respectively (n = 10).

Tissue distribution of (14C) methyl mercury in the lobster, Homarus americanus

[14C] Methyl mercury was administered by three different routes: intravascular (iv) injection, ingestion, and absorption from the ambient water. After iv administration (0.1 mg/kg) [14C] methyl mercury was rapidly removed from the plasma, followed by slow loss from the hepatopancreas and a strikingly persistent increase in the amount of radioactivity in the tail muscle. Most (80-90%) of the radioactivity in the hepatopancreas was shown by TLC methods to be the parent compound, and approximately 10% of this persisted for 6 days after injection. The half-life in this organ was found to be 21 days. One month after iv treatment with methyl mercury, the only organs that contained more than 0.1 ppm of this xenobiotic were egg masses, male gonads, heart, brain, intestine, and tail muscle. The half-lives for disappearance from sexual organs were greater than 1 month. After ingestion of [14C] methyl mercury (0.1 mg/kg) in food the hepatopancreas contained most of the administered dose at 6 days (68%), while the stomach (10%), tail muscle (8%), and carcass (15%) contained less. A unique distribution pattern emerged 6 days after exposure to [14C] methyl mercury-containing ambient water (0.1 ppm). The tail muscle contained most (50%) of the absorbed dose, whereas the hepatopancreas and carcass contained only 23 and 10%, respectively. In view of the small molecular size and high lipid solubility of methyl mercury and the lipophilic properties of the chitin-protein exoskeleton of the lobster, it is likely that significant uptake directly from the water as well as storage of absorbed methyl mercury occurred in the tail region. Residue analysis on untreated lobsters indicated that the egg masses contained the largest amount of methyl mercury (0.1 ppm). The hepatopancreas and carcass (muscle) levels were less than 0.05 ppm.

Recent developments in the analysis of toxic elements

One may conclude that it is impractical to confine oneself to any one analytical method since ever more sensitive instrumentation continues to be produced. However, in certain methods such as anodic stripping voltammetry and flameless atomic absorption it may be background contamination from reagent impurities and surroundings rather than instrument sensitivity which controls the limits of element detection. The problem of contamination from dust or glassware is greatly magnified when the sample size becomes ever smaller. Air entering laboratories near highways may contain trace quantities of lead, cadmium, barium, antimony, and other elements from engine exhaust. Even plastic materials contacting the sample may be suspect as a source of contamination since specific metals may be used as catalysts in the synthesis of the plastic and traces may be retained in it. Certain elements may even be deliberately added to plastics during manufacture for identification purposes. Nondestructive methods such as neutron activation and x-ray techniques thus offer great advantages not only in time but in the elimination of impurities introduced during sample ashing. Future improvements in attainable limits of detection may arise largely from progress in the ultrapurification of reagents and "clean-room" techniques. Finally, the competence of the analyst is also vitally important in the skillful operation of modern complex analytical instrumentation and in the experienced evaluation of data.