Handbook of Solvents - George Wypych - ChemTech - Ventech!

1086 Myrto Petreas
and legal repercussions associated with the results. Portable devices have been developed
for field use with on-site analysis of alcohol. 34-36 These portable devices could be adapted
for use with other organic solvents of interest in industrial hygiene and occupational health.
Gas chromatographs (GCs) equipped with suitable detectors allow analysis of more
than one solvent vapor at a time. The subject exhales through a valve system and the exhaled
volume of air, or a fraction of it, is drawn into the GC. 21,26,37-39 Depending on the detector
used, one or more cylinders containing appropriate gases under pressure are required to operate
the instrument, limiting its field use. An Electron Capture Detector (ECD), which is
the most sensitive for polyhalogenated solvents, requires helium and/or nitrogen. A Flame
Ionization Detector (FID), which is a universal detector for aliphatic and aromatic hydrocarbons,
requires nitrogen, air and hydrogen. The advent of the Photoionization Detector
(PID) offered a compromise, in that it can detect all the above classes of organic solvents
(with varying sensitivity) requiring only one gas (nitrogen, air or helium) for its operation.
A simple system employed a portable GC/PID modified to sample 1 mL of air from a
Haldane-Priestley tube into which the subject would exhale. 25,40 The latter assured collection
of end-exhaled air and this device was successfully used to assess exposures to
styrene 26 and PERC. 40
Mass spectrometry (MS) offers the advantages of high sensitivity and specificity at the
cost of portability and the need of highly trained operators. Direct exhalation into the MS is
not possible because the ion source of the detector operates under high vacuum. Two approaches
have been taken to overcome this limitation. In the first, an inlet system was designed
where the high pressure breath sample was directed over a methyl silicone
membrane, permeable to organic molecules but not to air, that served as the entry port to the
ion source operating under high vacuum. 41 With the second approach, the inlet system was
attached to the source of an Atmospheric Pressure Ionization mass spectrometer (API/MS),
that operates under atmospheric pressure. 42,43
In summary, the basic advantage of the direct reading/analyzing instruments is that
there is no sample collection, transportation, storage, handling and analysis where the sample
integrity may be compromised. The disadvantages are the need for expensive, specialized
equipment, usually requiring highly trained operators and the difficulty, or some times
impossibility, of field use.
The other category of breath sampling methodology involves sample collection in the
field with subsequent analysis in the laboratory. There are two groups of devices in this category:
1. Sample containers that hold the total volume or part of the exhalation in a gaseous
form.
2. Sample adsorbents that trap the chemicals of interest from the exhaled breath.
In the first group belong rigid containers such as stainless steel, aluminum, or glass vials
of various sizes, open at both ends. The subject exhales into the vial and then the two
openings are closed, either with caps or with stopcocks. Vials of this kind have been used
extensively in experimental studies involving exposures to industrial chemicals.
24,28,29,44-47,53-55,61,64
The advantages of these containers are inertness of the walls, low cost, reusability and
simplicity of the technique. The disadvantages are the potential for contamination,
photodegradation, or dilution of the collected breath sample with atmospheric air, sorption
and/or reaction of the vapor with surfaces and breakage during transportation or storage.
The problem of condensation of water vapor has been addressed by heating the tubes, 28,29,47
but this approach increases the complexity and counters the main advantages. Another limitation
is that only a small volume of sample can be withdrawn for analysis from a rigid container,
with ensuing restrictions on the analytical sensitivity.