Analytical Methods, Hyphenated Instruments

In 1990, Chemical Abstracts Service listed over 10 million substances in their Registry. Moreover, the growth of new compounds is exponential, leading to a doubling of known chemicals every eleven years. Thus there is an ever-increasing need to efficiently identify substances and quantitate material with a high degree of confidence. Hyphenated instruments, combinations of accepted instrumental techniques where the sample is passed from one instrument directly into another, were developed to aid in solving this problem. Hyphenated analytical methods provide more complementary information in a shorter time period leading to faster and more reliable results, than data obtained from traditional instrumental methods. The number of types of analytical instruments that can be joined is very large. Combinations include separation-separation, separation-identification, and identification-identification techniques. The combination of gas chromatography and mass spectrometry offers several advantages over the use of these techniques individually. Capillary gas chromatography provides very high separation efficiency. The mass spectrometer adds to this separation capability the unique ability to provide molecular structural information. Thus the gc/ms is a significant labor- and time-saving device, accomplishing separation, component transfer, identification, and quantitation all in a single instrument. Gc/ms has been particularly valuable in the environmental field, where laboratories responsible for the monitoring of hazardous compounds depend heavily on gc/ms to separate components present in an environmental sample, and to identify and quantitate each. A related technique is that of inductively coupled plasma/mass spectrometry (icp/ms), where the plasma serves as a good interface and ion source for the quadrupole mass spectrometer. Gas chromatography/fourier transform infrared spectroscopy (gc/ftir) is especially powerful when combined with mass spectrometry. One of the factors involved in making the ternary gc/ir/ms system viable was the development of faster, more powerful computers to acquire, analyze, and report large quantities of data. One area where ir information particularly complements ms data is in the differentiation of isomeric compounds. Another analysis handled effectively by gc/ir/ms is essential oil characterization. The confidence level in the identification capability for gc/ir/ms is enhanced by the ability to search large spectral databases. The replacement of a gas chromatograph with a liquid chromatograph (lc) substantially enhances the separation of compounds which might decompose or which are not readily volatilized. However, removing the large quantities of lc solvent presents a challenge. Tandem mass spectrometry or ms/ms has been used for structure elucidation of unknowns and has the ability to provide sensitive and selective analysis of complex mixtures. Ms/ms is based on the characterization of selected ions in the mass spectrum of a sample through further fragmentation and analysis, and has found application in trace analysis of biological tissue, complex hazardous waste site samples, and human blood serum, and in drug testing. Keywords: Gas chromatography; Infrared spectroscopy; Mass spectrometry; Liquid chromatography; Instrumental interfaces