Parallel sample introduction techniques

ESI and APCI techniques are limited by the rate of sample introduction into the ion source. Autosampler technology is the primary rate-determining factor but in addition to this, fluid transfer rates and chromatographic separation can also be bottlenecks in the process. TWo approaches, generally categorized as parallel sample introduction and fast serial sample introduction, have been taken to increase the throughput. 

Tt may be safe to say that the interest of environmental scientists in airborne metals closely parallels our ability to measure these components. Before the advent of atomic absorption spectroscopy, the metal content of environmental samples was analyzed predominantly by wet or classical chemical methods and by optical emission spectroscopy in the larger analytical laboratories. Since the introduction of atomic absorption techniques in the late 1950s and the increased application of x-ray fluorescence analysis, airborne metals have been more easily and more accurately characterized at trace levels than previously possible by the older techniques. These analytical methods along with other modem techniques such as spark source mass spectrometry and activation analysis... 

Parallel to this progress, new ionization methods have been developed that are based on the direct desorpHon of ions from polymer surfaces. With the introduction of "desorption/ionization" techniques, it has become possible to eject large molecules into the gas phase directly from the sample surface, and thereby mass spectra of intact polymer molecules have been produced. Much progress to date has been made using matrix-assisted laser desorp-tion/ionization (MALDl-MS), which is capable of generating quasimolecular ions in the range of 10 Daltons (Da) and beyond. 

The field of fatty acid separation was revolutionized by the development of GC, which allowed nearly complete separation of the common fatty acids. Later workers developed methods for GC separation of steroids, and of the steryl and glyceryl esters by high-temperature GC. The introduction of the flame ionization detector (FID) transformed GC from a method of qualitative separation into a method of quantification, which has remained unsurpassed to the present day. In parallel, TLC was developed as both a preparative and analytical technique for the resolution of the nonvolatile lipids. Because of the nearly universal applicability to all lipid analyses and the use of inexpensive apparatus, TLC made lipid separations accessible to all laboratories and it has remained unsurpassed as a method of sample preparation for modern analytical methods of lipid analyses. 

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