Mass spectrometry inlet systems

To examine a sample by inductively coupled plasma mass spectrometry (ICP/MS) or inductively coupled plasma atomic-emission spectroscopy (ICP/AES) the sample must be transported into the flame of a plasma torch. Once in the flame, sample molecules are literally ripped apart to form ions of their constituent elements. These fragmentation and ionization processes are described in Chapters 6 and 14. To introduce samples into the center of the (plasma) flame, they must be transported there as gases, as finely dispersed droplets of a solution, or as fine particulate matter. The various methods of sample introduction are described here in three parts — A, B, and C Chapters 15, 16, and 17 — to cover gases, solutions (liquids), and solids. Some types of sample inlets are multipurpose and can be used with gases and liquids or with liquids and solids, but others have been designed specifically for only one kind of analysis. However, the principles governing the operation of inlet systems fall into a small number of categories. This chapter discusses specifically substances that are normally liquids at ambient temperatures. This sort of inlet is the commonest in analytical work. 

Few of the naturally occurring elements have significant amounts of radioactive isotopes, but there are many artificially produced radioactive species. Mass spectrometry can measure both radioactive and nonradioactive isotope ratios, but there are health and safety issues for the radioactive ones. However, modem isotope instmments are becoming so sensitive that only very small amounts of sample are needed. Where radioactive isotopes are a serious issue, the radioactive hazards can be minimized by using special inlet systems and ion pumps in place of rotary pumps for maintaining a vacuum. For example, mass spectrometry is now used in the analysis of Pu/ Pu ratios. 

Mass Spectrometry. The mass spectra were obtained on a CEC 21-llOB mass spectrometer with the batch inlet system maintained at 250°C to assure complete vaporization of the samples. Sensitivity factors for quantitative analysis were obtained from standards of di-, tetra-, hexa-, and octa-chlorodibenzo-p-dioxin. The factors for the intermediate chlorinated species were estimated by interpolation. The analyses were based... 

The mass spectra of mixtures are often too complex to be interpreted unambiguously, thus favouring the separation of the components of mixtures before examination by mass spectrometry. Nevertheless, direct polymer/additive mixture analysis has been reported [22,23], which is greatly aided by tandem MS. Coupling of mass spectrometry and a flowing liquid stream involves vaporisation and solvent stripping before introduction of the solute into an ion source for gas-phase ionisation (Section 1.33.2). Widespread LC-MS interfaces are thermospray (TSP), continuous-flow fast atom bombardment (CF-FAB), electrospray (ESP), etc. Also, supercritical fluids have been linked to mass spectrometry (SFE-MS, SFC-MS). A mass spectrometer may have more than one inlet (total inlet systems). 

Quite often a normal electron ionization mass spectrum appears insufficient for reliable analyte identification. In this case additional mass spectral possibilities may be engaged. For example, the absence of the molecular ion peak in the electron ionization spectrum may require recording another type of mass spectrum of this analyte by means of soft ionization (chemical ionization, field ionization). The problem of impurities interfering with the spectra recorded via a direct inlet system may be resolved using GC/MS techniques. The value of high resolution mass spectrometry is obvious as the information on the elemental composition of the molecular and fragment ions is of primary importance. 

The purpose of this paper was to briefly describe fundamentals of isotope ratio mass spectrometry (IRMS), review the analytical systems currently available both for traditional dual-inlet (DI-IRMS) and the newer continuous-flow (CF-IRMS) and describe the specialized instruments that are in general use for isotopic measurements. 

Caldecourt, V.J. Heated Sample Inlet System for Mass Spectrometry. Anal. Chem. 1955, 27, 1670. 

Mass spectrometry is a sensitive analytical technique which is able to quantify known analytes and to identify unknown molecules at the picomoles or femto-moles level. A fundamental requirement is that atoms or molecules are ionized and analyzed as gas phase ions which are characterized by their mass (m) and charge (z). A mass spectrometer is an instrument which measures precisely the abundance of molecules which have been converted to ions. In a mass spectrum m/z is used as the dimensionless quantity that is an independent variable. There is still some ambiguity how the x-axis of the mass spectrum should be defined. Mass to charge ratio should not lo longer be used because the quantity measured is not the quotient of the ion s mass to its electric charge. Also, the use of the Thomson unit (Th) is considered obsolete [15, 16]. Typically, a mass spectrometer is formed by the following components (i) a sample introduction device (direct probe inlet, liquid interface), (ii) a source to produce ions, (iii) one or several mass analyzers, (iv) a detector to measure the abundance of ions, (v) a computerized system for data treatment (Fig. 1.1). 

Kristensen GH, Klausen MM, Hansen VA, Lauritsen FR (2010) On-line monitoring of the dynamics of trihalomethane concentrations in a warm public swimming pool using an unsupervised membrane inlet mass spectrometry system with off-site real-time surveillance. Rapid Commun Mass Spectrom 24(l) 30-34... 

Mass spectrometry. Reaction of OH to form an ion, HS04, which can be measured by mass spectrometry was first demonstrated by Eisele and Tanner (1991). Figure 11.45 is a schematic diagram of this approach (Tanner et al., 1997). Air is sampled through an inlet system described in detail by Eisele et al. (1997) and mixed with isotopically labeled 34SOz, forming H24S04 via reactions discussed in Chapter 8.C.2 ... 

Figure 4 Schematic diagram of high-pressure liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) system with dual-inlet system for isotope dilution analyses. (From Ref. 32.)...

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