Mass spectrometry memory

Infrared Spectrophotometry. The isotope effect on the vibrational spectmm of D2O makes infrared spectrophotometry the method of choice for deuterium analysis. It is as rapid as mass spectrometry, does not suffer from memory effects, and requites less expensive laboratory equipment. Measurement at either the O—H fundamental vibration at 2.94 p.m (O—H) or 3.82 p.m (O—D) can be used. This method is equally appticable to low concentrations of D2O in H2O, or the reverse (86,87). Absorption in the near infrared can also be used (88,89) and this procedure is particularly useful (see Infrared and raman spectroscopy Spectroscopy). The D/H ratio in the nonexchangeable positions in organic compounds can be determined by a combination of exchange and spectrophotometric methods (90). 

Tor reference. Positive identification can be made only by collecting the compound or transierring it as it elutes directly into another apparatus for analysis by other means, such as infrared or ultraviolet spectroscopy, mass spectrometry, or nuclear magnetic resonance. Commercially available apparatus is available which combines in a single unit both a gas chromatograph and an infrared, ultraviolet, or mass spectrometer for routine separation and identilicalion. The ancillary system may also be microprocessor-based, with an extensive memory for storing libraries of known infrared spectra or fragmentation patterns (in the case of mass spectrometers). Such systems allow microprocessor-controlled comparison and identilicalion of detected compounds. 

Another procedure for sulfur isotope measurements has been developed where samples are converted to solid arsenic sulfide, AS0S3 (s), and measured by thermal ionization mass spectrometry (TIMS) (22). This technique offers several advantages over the gaseous methods in that both memory and isotope effects are eliminated, and the chemical procedure is simpler. A precision of 1 0/00, and the capability of making measurements on small samples, makes the TIMS technique competitive with gas phase MS techniques. 

The use of membrane introduction mass spectrometry (MIMS) was first reported in 1963 by Hoch and Kok for measuring oxygen and carbon dioxide in the kinetic studies of photosynthesis [46], The membrane module used in this work was a flat membrane fitted on the tip of a probe and was operated in the MIS mode. The permeated anaytes were drawn by the vacuum in the MS through a long transfer line. Similar devices were later used for the analysis of organic compounds in blood [47], Memory effects and poor reproducibility plagued these earlier systems. In 1974, the use of hollow-fiber membranes in MIMS was reported, which was also operated in the MIS mode [48], Lower detection limits were achieved thanks to the larger surface area provided by hollow fibers. However, memory effects caused by analyte condensation on the wall of the vacuum transfer line remained a problem. 

Mass spectrometry concerns the dynamics of unimolecular ionic reactions. Given that an ion has no memory of its mode of formation, the method of ionization is incidental and the ion s reactivity depends upon its own energy state. Experimental conditions are such as to minimise the occurrence of ion—molecule reactions [497] and their effects can usually be neglected. Mass spectrometry is a molecular beam experiment in the sense that each ion is an isolated system. The assembly of ions is not at a temperature, although in limited circumstances it may be possible to speak of their rotational temperature, translational temperature and perhaps even vibrational temperature. The familiar mass spectrum identifies the reaction products, but provides little other information about the reaction dynamics. This purist s view of mass spectrometry colours this article. 

Since the pioneering work by Gray (1975), mass spectrometry of elements ionized in an inductively coupled gas plasma at atmospheric pressure (ICP-MS) has gained a steadily increasing application for trace-element analysis. The determination of mercury by this technique seems to be quite free from interfering polyatomic mass fragments formed by constituents of the plasma and sample matrices, which may disturb the determination of elements with lower mass units (Houk, 1986 Delves, 1988 Lyon et al., 1988 Templeton et al., 1989 Olesik, 1991). However, especially in the case of mercury, several users of ICP-MS have experienced severe memory effects from samples with high mercury levels. 

GC-MS of trace metals was initially explored using acetylacetone and the fluorinated analogs as a means of chelating metals for GC analysis. When this methodology was extended to mass spectrometry, it was discovered that there could be a significant memory effect that would cause... 

If gas chromatography-mass spectrometry (GC-MS) equipment is available, you can also analyze the steam distillate using this method (Experiment 54B). GC-MS is a sensitive method for determining the components in a volatile mixture. This technique is capable not only of separating the components of a mixture but also of identifying each component of the mixture. By comparing the mass spectrum of each substance eluting from the column with mass spectra from the computer-based library of spectra in the instrument s memory, you can completely identify each component of fhe mixture. 

The use of gas chromatography-mass spectrometry (GC-MS) as an analytical technique is growing in importance. GC-MS is a powerful technique in which a gas chromatograph is coupled to a mass spectrometer that functions as the detector. If a sample is sufficiently volatile to be injected into a gas chromatograph, the mass spectrometer can detect each component in the sample and display its mass spectrum. The user can identify the substance by comparing its mass spectrum with the mass spectrum of a known substance. The instrument can also make this comparison internally by comparing the spectrum with spectra stored in its computer memory. 

Al-Ammar,A., Gupta, R. K., and Barnes, R. M. (1999). Elimination of boron memory effect in inductively coupled plasma-mass spectrometry by addition of ammonia. Spectrochim. 

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