Environmental Engineering Reference
In-Depth Information
houses in the 1980s. Requests for problem home investigations for potential
formaldehyde-related health problems have decreased significantly over the
past decade. Such investigations are now made only occasionally. Formalde-
hyde measurements are often made in problem building investigations,
because HCHO is one of the contaminants included in routine screening.
Historically, the NIOSH bubbler/chromotropic acid method (NIOSH
method 3500) has been the most widely used HCHO sampling/analytical
technique. In this procedure, a sampling pump draws air through 15 to 20 ml
of a 1% sodium bisulfite solution. Formaldehyde is collected by forming
sodium formaldehyde bisulfite, an addition product. A sampling rate of 1
L/min is typically used, with a sampling duration of 1 to several hours.
Samples are analyzed colorimetrically. The sampling/analytical accuracy is
reported to be 92 to 95%. The method has a long history of use and is
considered to be very reliable.
The DNPH-HPLC method has recently become a relatively popular
technique for measuring indoor air concentrations of HCHO. The method
can be used to collect HCHO, other aldehydes, and ketones on 2,4-dinitro-
phenyl hydrazone (DNPH)-coated substrates including glass fiber filters,
silica gel, and C
cartridges. Collected aldehydes and ketones are converted
to stable hydrazones which are analyzed by high-performance liquid chro-
matography (HPLC). The DNPH-HPLC method has several major advan-
tages. These include specificity for different aldehydes, including HCHO,
and high sensitivity (it can detect a concentration of 9 ppbv in a 20 L sample).
Though DNPH sampling is highly accurate in laboratory environments, it
is subject to significant negative interference in the presence of O
18
.
Both chromotropic acid and DNPH analytical methods are employed
with passive sampling devices. Passive samplers are commercially available
that allow quantification of HCHO after exposure for 8 hr, 24 hr, and 7 days.
Passive samplers employing a 7-day sampling duration have been widely
used for sampling residences and in research studies. Results are integrated
and provide no indication of peak values which may be responsible for acute
symptoms. They are generally not suitable for problem building investiga-
tions. Sampling devices based on the chromotropic acid and DNPH-HPLC
methods are both relatively specific for HCHO and have low LODs based
on conditions of use. A passive sampler based on the MBTH method is used
for HCHO measurements. It, however, measures total aldehydes, and
because of its lack of specificity has limited usefulness in IAQ investigations.
It does have the advantage of high sensitivity with a sampling time of 2 to
3 hours. Passive samplers are relatively attractive as HCHO sampling
devices because vendors provide both samplers and analyses at relatively
low cost ($40 to 60 per sample).
Formaldehyde can also be measured by automated devices that provide
quasi-real-time results. These are based on HCHO absorption in solution
and colorimetric analysis using the pararosaniline method. This method is
specific and highly sensitive, with an LOD significantly lower than the
3
