Handbook of Solvents - George Wypych - ChemTech - Ventech!

15.2.1 Use of breath monitoring 1087
The last limitation is overcome when collapsible bags are used for sample collection.
The bags are commonly made of Tedlar (clear) or Mylar (aluminized) material. The subject
exhales directly into the bag through a valve and when an appropriate volume has been collected,
the valve is closed. The bag is transported to the laboratory where an aliquot is withdrawn
for analysis through a septum. The collapsibility of the bag allows any volume to be
withdrawn without air infiltration. Disadvantages, however, include losses because of permeation
through the walls, sorption and/or reaction of the vapor with the wall surfaces and
photodegradation. The latter concern is eliminated with the aluminized Mylar bags, which
also minimize sorption and permeation through the walls.
The second group of field sampling devices with subsequent analysis involves the use
of adsorbents. Extensively used in personal monitoring in industrial hygiene surveys, these
devices were naturally considered for exhaled breath sampling. Commercially available
glass tubes containing granular adsorbent material such as activated charcoal, Tenax, molecular
sieve, etc. could be used with selected organic vapors. However, because of the high
pressure drop during exhalation through the adsorbent bed, and the condensation of water
vapor, these materials have not been used much for direct sampling of exhaled breath. One
device 48 is, basically, a respirator mask with two commercial charcoal inhalation canisters
and an exhalation port fitted with a wafer of charcoal cloth. A Wright respirometer connected
to the exhalation port records the volume of exhaled air. Another hand-held device
employed a custom-made glass tube containing charcoal to collect organic vapors in exhaled
air, while the volume collected was measured with a Wright respirometer and adjusted
for back-pressure measured with an attached pressure gauge. 25,40
Commercial tubes or specially made cartridges containing the appropriate adsorbent
have been used in conjunction with bag sampling for exhaled breath monitoring. 49 The subject
exhales into the bag, the contents of which are subsequently pumped through the tube or
canister containing the adsorbent. This combination offers the advantages of bag sampling
(low cost, low resistance), while eliminating the disadvantages (losses, bulkiness). The organic
vapors can be thermally desorbed from the adsorbent material and the concentrations
measured with polymer-coated surface-acoustic-wave detector, 50 GC or GC/MS analysis.
31,49 Alternatively, solvent vapors can be extracted from the adsorbent with an appropriate
solvent prior to conventional analysis.
15.2.1.6 When is breath monitoring appropriate?
Breath monitoring may be used to assess exposures to solvents either qualitatively or quantitatively.
Qualitative information may be useful when exposure to a number of solvents is
suspected. For qualitative purposes, either mixed-exhaled or end-exhaled air samples may
be used. Provided that the sample collection and the analytical techniques are appropriate, a
list of solvents may be thus identified and quantitative measurements planned.
Quantitative information is needed for regulatory enforcement situations, where appropriately
collected breath samples are compared to BEIs to assess whether exposure limits
have been exceeded. BEIs have been developed after thorough studies of
pharmacokinetics for a limited number of occupational contaminants. Exhaled air is used as
a surrogate for blood when the relationships between exhaled air, alveolar air and (arterial
or mixed venous) blood have been established.
Besides regulatory purposes, breath monitoring can provide valid information on solvent
exposures when:
• The pharmacokinetics (absorption, distribution, metabolism, elimination) of the
solvent are well established.
• The solvent is not soluble in the conducting portion of the lung (anatomical dead
space).