5.8 Summary
In this chapter we illustrated the utility of combining chromatography and MS systems. A variety of possible components provide for interesting instruments that can be used to analyze a broad range of analytes. Hard and soft ionizations techniques provide for the determination of the molecular weight of the analyte, as well as unique fragmentation patterns for confirmational identification of an unknown chemical structure. More inexpensive instruments, such as quadrupole and time of flight mass spectrometers, allow only unit resolution of ions while double focusing instruments yield the determination of differences with resolution of four decimal points in masses. Mass spectrometry, like NMR, is one of the most powerful techniques available to chemists and it is becoming more and more important. While most of the instruments presented in the chapter have detection limits in the sub parts per million range, extremely lower detection limits (10-15 moles) have been obtained in research-grade instruments.
A summary of mass filters and their characteristics is given below in Table 5.2.
Table 4.2 Summary of Mass Filter Features. Source: Company Literature and Personal Communiqué David Koppenaal, Thermal Scientific & EMSL, Pacific National Laboratory.
| Type of Mass Filter | Resolution |
Detection Limit |
Approximate Instrument Price |
|---|---|---|---|
Single Quadrupole |
250-500 |
low ppb – high ppt |
$80 000 - $100 000 |
| Ion Trap | 1 000 – 10 000 |
ppb |
$250 000 - $300 000 |
| Time of Flight | 3000 – 10 000 |
high ppt |
$300 000 - $400 000 |
| Ion Mobility | 500 - 2000 |
ppb |
$100 000 |
| Double Focusing | 10 000 – 20 000 |
mid to high ppt |
$750 000 - $1 000 000 |
| Fourier Transform Ion Cyclotron | 200 000 – 1 000 000 |
ppb |
$1 000 000 + |
Magnetic Sector / Multi-collector with the Mattauch-Herzog Geometry |
~500 |
high ppb |
$350 000 - $400 000 |
| Proton Transfer Reaction Ionization Chamber | Depends on type of mass filter |
ppt |
$120 000 |
| Orbital Trap (Electrostatic Ion Trap) | 150 000 – 200 000 |
ppb |
$600 000 |
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©Dunnivant & Ginsbach, 2008