Chromatographic Methods for Environmental Analysis - Fundamentals of Environmental Sampling and Analysis - page 276

Table 10.7 Comparison of major liquid chromatography detectors

Mass LOD Approximate

(State of the art) a linear range b Detector Applications

10 4

UV-VIS absorption Specific for UV-VIS light- 1 pg

absorbing compounds

10 5 Fluorescence Specific for compounds 10 fg

able to fluoresce

10 3 Refractive index Universal detector; 10 ng

No gradient flow can
be used

10 5

Conductivity Specific for ionic species 500 pg

10 5 Mass spectrometry Universal detector 1 pg

Adapted from a Skoog et al. (1998) and b Rubinson and Rubinson (2000). 1gram¼ 10 9 nanogram¼
10 12 picogram¼10 15 femtogram. Mass limit of detection (LOD) is calculated from injected mass
that yields a signal equal to five times the s noise. The linear range for mass spectrometry was
based on a sector instrument, and other mass detectors such as quadrupole and ion-trap instruments
are narrower.

chromatographic instruments are the key player. In the environmental area, early
usages started with the residual analysis of pesticides in the 1960-70s.
Chromatographic techniques have since become the routine for many environmental
professionals who are involved in research, as well as monitoring for regulatory and
compliance purposes.

10.4.1 Gases, Volatile, and Semivolatile
Organics with GC

GC has gained its popularity largely because of its speed, high resolution, ease of
use, and affordability. The compounds can be analyzed directly by GC, however,
they are limited to gases, volatile organic compounds (VOCs), and semivolatile
compounds (SVOCs). We have defined what constitutes VOCs and SVOCs in
previous chapters on the basis of boiling points and Henry's law constant (Section
2.1.2 and 7.3.1).
GC has been at the center of the US EPA's strategy for monitoring organic
compounds in the environment since the early to mid-1970s. There are three major
categories of GC-based US EPA methods (Table 10.8; for details of these methods,
one should review Chapter 5 for their sources). The first group is the US
EPA methods for the determination of toxic organic compounds in air, collectively
called the TO series. The volatile air toxins are generally sampled by adsorbent trap
made of Tenax, molecular sieve, activated charcoal, XAD-2 resin, or graphited
carbon. Desorption is then accomplished by thermal or solvent using CS 2 . VOCs are
then analyzed by GC-FID (general detection), GC-ECD (halogenated species), or
GC-MS.