Mass spectrometers, isotopic analyses quadrupole

Today there are a number of mass spectrometer companies producing a wide variety of different types of quadrupole-based, sector field and ToF instruments for quite different applications in the trace, ultratrace, isotope and surface analysis of inorganic materials and for the structural analysis of organic and bioorganic compounds. Mass spectrometry for the structural analysis of organic compounds including large biomolecules is described elsewhere. 

However, nowadays some other different mass spectrometers are used for ICP-MS time-of-flight (TOP) systems for multielemental analysis of transient signals, ion trap analysers for ion storage, multicollector instruments for precise isotope ratio measurements and double-focusing sector field mass spectrometers for high mass resolution, but still the majority of instruments are equipped with quadrupole filters, which are simpler and cheaper. 

Most isotope ratio measurements have been performed using sector mass spectrometers. Some work has been reported, notably by Heumann [35], in which a quadrupole-based system was used. Instruments used for measurement of isotope ratios are most often dedicated to that purpose. In most instances only a relatively small mass range needs to be monitored, just enough to encompass the isotopes of the analyte element. Without the ability to scan the entire elemental mass range [usually from mlz = 6 (Li) through mfc = 238 (U) for elemental analysis], mass spectrometers designed to measure isotope ratios cannot readily be adapted for other purposes. See Chapter 2 for a discussion of instrumentation required for elemental analysis of solid materials and Chapter 3 for a treatment of the in-strumenation needed for elemental analysis of solutions. 

Modem mass spectrometers are usually one of four types magnetic sector, quadrupole, time-of-flight, or ion trap. A brief introduction to each is provided. Classical applications are discussed to illustrate how these devices have shaped the landscape of elemental and isotopic chemical analysis. 

Despite these difficulties the use of the silica gel technique for the solid probe/quadrupole mass spectrometer system holds promise for the analysis of some nutritionally important metals Both zinc and copper have been extracted successfully from serurn and zinc has also been extracted from urine and feces by using an anion exchange purification Biorad A61X8 (100-200 mesh) chloride form) anion exchange resin has been used to separate copper and zinc from acidic solutions (6) We have adapted this method to the separation of these two metals from acidic solutions of AAS standards urine serum and deproteinated fecal homogenate by elution with sucessively dilute acid solutions Recovery of an isotopic spike ai subsequent mass spectral analysis has been demonstrated with a Zn spike added to 1ml aliquots of a Fisher Certified AA Standard (zinc concentration Img/ml) Results of this experiment are shown in Table III ... 

Although quantitative analysis of endogenous plant hormones by traditional GC has serious limitations, isotopic dilution analysis by GC-SIM using a single internal standard labelled with a stable isotope, such as H, C or N, is a completely different proposition [3-6]. Because the cost of a simple, computer-controlled, quadrupole-mass spectrometer has fallen substantially, and many highly enriched, isotopically-labelled compounds suitable for use as internal standards in quantitative analysis, can be either synthesized (1) or purchased from commercial sources (see Table 1), capillary GC-SIM is now the quantitative assay of choice in the vast majority of laboratories in which endogenous plant hormones are analysed on a routine basis. 

At the heart of the TIMS ion source are one or more hot filaments that serve to vaporize and ionize atoms or molecules of interest. Once generated, the ions are accelerated, focused, and directed into the mass analyzer for measurement. The classic TIMS instrument consists of an ion source, a single magnetic sector mass separator, and an ion detector. Such an instrument is capable of measuring isotope ratios as small as 1 x 10 6, sufficient for the isotopic analysis of most elements. For radionuclide analysis, smaller isotope ratios are often encountered. Specialized mass spectrometers include multiple magnetic and electric sectors and sector instruments with retarding quadrupole lenses (Smith, 2000) to measure down to the 10-9 range. 

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