1998 "Rigi" Meeting

On-line sample strategies for LC/MS and GC/MS in environmental research

U. A. Th. Brinkman, Free University, Department of Analytical Chemistry, de Boelelaan 1083, 1081 HV Amsterdam, The Netherlands

The growing concern about the quality of our environment lends additional importance to the development of on-line methods for the trace-level determination of (in)organic compounds in water, soil, food and biological samples. The design of fully integrated analytical procedures is a distinct step forward if large numbers of samples have to be analysed in a routine fashion. The complexity of the problems at hand generally requires the use of highly efficient separation techniques such as column LC and capillary GC. In their turn, these have to be combined with on-line analyte-enrichment procedures such as solid-phase extraction (SFE) to achieve the required sensitivity, and with an NMR, FTIR or MS detector to obtain information concerning analyte identity.

In recent years, distinct progress has been made in the field of LC/MS and LC/MS/MS. However, analyte identification and/or confirmation at the trace level still requires considerable improvement of analyte detectability. In other words, SPE/LC/MS, which is a truly hyphenated technique, has to be utilised. In the lecture, due attention will be given to aspects such as the selection of proper sorbents for the SPE procedure, alternatives to be considered for field studies, and the role played by the type of application. As a special topic, the possibility of simplifying SPE/LC/MS by reducing the SPE/LC part of the system to a single short column (SSC), will be discussed, and the practicality of SSC/MS and SSC/MS/MS for environmental screening studies will be demonstrated.

Finally, it will be shown that on-line SPE procedures for LC/MS can also be used, without any real modification, for GC/MS and GC/MS/MS. Real-life examples will be used to demonstrate the excellent sensitivity and selectivity of the GC-based approaches, especially if they are combined in one setup with GC/AED (atomic emission detection).

LC/MS: From Frustration to Success

Robert D. Voyksner, Research Triangle Institute, P.O. Box 12194, Research Triangle Park, NC 27709, USA

The monitoring of many non-volatile or thermally unstable polar organics relies on the development of sensitive, specific and cost effective LC/MS techniques. Atmospheric pressure ionisation (API) techniques of electrospray and APCI can meet these goals due to the capability for generating molecular ions and fragment ion by collision induced decomposition (CID) from low pg quantities of most biochemical, pharmaceutical or environmentally relevant compounds. Still achieving pg-ng/mL detection limits on target compounds can be a very challenging problem. Matrix suppression, incompatibilities between chromatographic conditions and API-MS operating conditions and the need to develop methods for high throughput analysis are often the reasons for failures in sensitivity and specificity. This presentation will highlight approaches to achieve low detection limits in complex matrices.

To achieve low detection limits requires an understanding of the API process. The importance of solution chemistry and the suppression of the target compound signal by various chromatographic additives or matrix components will be explained. Secondly, achieving low detection limits requires the removal of matrix interferences that can suppress the signal or generate chemical background noise. Removing these interferences often can take several steps involving sample preparation (e.g., liquid-liquid extraction, solid phase extraction, immunoaffinity) chromatography and MS detection (e.g., MS or. tandem MS). The presentation will show some of the interplay between sample preparation, chromatography and MS detection. While tandem MS (MS/MS) can offer great specificity, permitting minimal sample clean-up and high throughput chromatography, ion suppression in the API interface can still occur. On the other hand, specificity in anon-MS/MS analysis is often obtained through sample preparation and chromatography, slower processes when compared to mass selectivity in tandem MS. Example of several analysis ( e.g. antibiotics and vitamin D metabolites) using LC/MS and LC/MS/MS on a ion trap and triple quadrupole will serve to compare the techniques and highlight their capabilities for qualitative and quantitative determinations.

This work was supported by FDA cooperative agreement FD-U-000589 and by Hoffman La Roche.
Robert D. Voyksner is sponsored as invited speakerby Hewlett Packard, Switzerland.

Isotopes in Planetary Sciences

Rainer Wieler, ETH Zürich

Mass spectrometers are among the indispensable tools in modern Earth and Planetary Sciences, where they are mainly used to measure isotopic ratios. Often, precision on the order of 1 part in 10000 is required, in other cases one needs to determine isotopic ratios with a spatial resolution of about 10 micrometers, for example to determine the age difference between core and rim of a single crystal. Mass spectrometers are used to study an incredibly wide spectrum of problems, as diverse as the origin of the chemical elements, the formation of the solar system and the age of the planets, the history of rocks, mixing of oceans and lakes, the climate in the past or the age of a groundwater reservoir etc. The talk will discuss a few examples, emphasising studies on meteorites and lunar samples.

Some meteorites contain tiny grains, whose isotopic composition of many elements varies by up to several orders of magnitude, much more than in any other known natural material. These grains condensed in the envelopes of stars near the end of their life, and have survived for billions of years. The isotopic composition of this "stardust" is an excellent fingerprint of the processes how new elements are synthesised in various types of stellar "cooking pots". Mass spectrometric study of these grains is thus astrophysics in the laboratory. Lunar dust retains noble gases from the "solar wind", implanted at different times in the past several billion years. The lunar surface is therefore our only long term archive of solar history. The absolute age of rocks can be deduced by long-lived radioactive nuclides that are still existent today. In addition, for meteorites and other ancient objects, nuclide pairs where the radioactive parent has completely decayed a long time ago allow us to determine small age differences very precisely. Some of these isotope systems are becoming widely used since precise isotopic ratio measurements are possible with multiple collector ICP mass spectrometers.