Large-volume injections in capillary gas chromatography using a separately heated packed pre-column: application to mercury speciation in natural water

Abstract

Large-volume injection using a system consisting of packed column GC, serially connected to capillary GC, and coupled to a microwave-induced plasma atomic emission spectrometric (MIP-AES) detector is described. The greater sample capacity of the packed column is exploited to allow large-volume injections to be accommodated. Preliminary chromatographic separation of the solvent and mercury species on the packed pre-column permits selective transfer of the analytes to a capillary GC system. There, the mercury species can be focused and further separated on the analytical column, minimizing the risks of extinguishing the plasma due to excess solvent reaching the MIP, and stationary phase or detector fouling, which accompany large-volume injections using alternative methods. Application to the determination of mercury species in natural waters following solid-phase extraction on a dithiocarbamate resin, elution into acidic thiourea, complexometric extraction into hexane and Grignard derivatization is used to illustrate the benefits and limitations of this approach. The relative limit of detection obtained for methylmercury is 8 pg 1-1 utilizing 50 pl injection on to the packed pre-column, compared with 40 pg 1-1 for direct injection of 13 pl into the capillary GC-MIP-AES system. This improved performance has enabled more detailed kinetic studies of the uptake of methylmercury from humic-rich natural waters on the dithiocarbamate resin to be undertaken, and shows that incipient and added analyte behave differently during enrichment, which may have implications for the use of spiking during method development.

Determination of methylmercury in fish tissues by isotope dilution SPME-GC-ICP-MS

“…1. The source of Hg 0 was confirmed to be thermal decomposition of the derivatized Hg species, as indicated by the fact that 198 Hg was the dominant signal (as opposed to a natural abundance pattern if the procedural blank was the major source) at 60 s when using a 500 ng ml 21 enriched MM 198 Hg (96.2%) spike. All Hg species were well separated with little tailing of the peaks under the chosen experimental conditions, as is evident from Fig.…”

“…The plasma was then extinguished and the spray chamber and nebulizer assembly replaced with the transfer line and its adapter. The final optimization of lens voltage, RF power and Ar carrier gas flow for dry plasma conditions was performed by injection of 1 mlo fa5 0n gm l 21 propylated MMHg standard in isooctane. The temperature of the GC injector is critical, since too high a temperature can lead to thermal decomposition of not only the mercury derivatives, but the SPME polymer coating as well.…”

“…At equilibrium, variations in the extraction time will not affect the amount of analyte extracted by the fibre, thereby providing the best measurement precision. 44 Thus, the effect of extraction time in the range of 2-30 min was investigated by using a 100 ng ml 21 MMHg standard solution. It was found that an 8 min extraction time is required to achieve an equilibrium distribution of derivatized MMHg between the matrix and the PDMS fibre, as is shown in Fig.…”

“…Mercury has been introduced into the environment through both geochemical and anthropogenic sources, 1 resulting in a well-known environmental pollutant that exists in three major forms, elemental Hg 0 , a common form in air, inorganic Hg 21 (normally associated with ligands such as sulfur and humic substances) and organic Hg, and in particular, monomethylmercury (MMHg). MMHg is the most toxic form of mercury present in the environment and its bioaccumulation in fish provides the major route of exposure for humans.…”

A geração química de vapor em espectrometria atômica

“…Para a especiação do mercúrio em águas naturais e em águas naturais ricas em ácidos húmicos, foi introduzida uma etapa de pré-concentração com uma resina impregnada com dietilditiocarbamato 225,226 . Uma coluna capilar, colocada em série, permitiu aumentar o volume de amostra introduzida, levando à especiação de mercúrio em águas naturais 227 . Já a amalgamação e a micro-extração em fase sólida foram utilizadas por Frech et al 228 na especiação do mercúrio em amostras ambientais utilizando GC-MIP-OES.…”