United States
Environmental Protection
Agency
Office of
Solid Waste and
Emergency Response
Publication 9380.5-14FS
PB94-963509
EPA 540/F94/056
September 1994
Indoor Air Analysis of Volatile
Organic Compounds
Using Capillary Column
Gas Chromatography/Mass Spectrometry
Office of Emergency and Remedial Response
Emergency Response Division
Environmental Response Branch MS-101
Quick Reference Fact Sheet
Introduction
The quality of indoor air and the resulting health risk asso-
ciated with some potential exposure to volatile organic
compounds (VOCs) from indoor air have become major
concerns to building occupants, especially office workers.
To effectively address these concerns, indoor air monitor-
ing programs are needed which can produce data of
known quality. The ensuing analytical method developed
by the United States Environmental Protection
Agency/Environmental Response Team (U.S. EPA/ERT),
in conjunction with the Response Engineering and Ana-
lytical Contract (REAC), provides rapid turnaround of
sample results while incorporating rigorous quality assur-
ance/quality control (QA/QC) procedures to ensure reli-
ability of the analytical data.
The gas chromatography/mass spectrometry (GC/MS)
method was developed to provide support for the U.S.
EPA/ERT indoor air quality program. The GC/MS method
was designed to identify and quantify 45 target VOCs
(i.e., aliphatic, aromatic, and chlorinated hydrocarbons) as
well as identify non-target VOCs related to indoor air en-
vironments.
The Analytical Method
Multi-residue trace organic analyses for air samples are
greatly dependent upon MS for unambiguous identifica-
tion and confirmation of volatile and semi-volatile com-
pounds. It is the preferred detection method because of
limitations in selectivity of alternative micro-analytical
techniques. The proposed indoor air method uses a full
scan GC/MS and a fused silica capillary column for ana-
lyzing ambient air samples collected on charcoal tubes.
The method was evaluated on charcoal tubes spiked with
known quantities of 45 target VOCs and indoor air sam-
ples collected from office and home environments. It was
also evaluated by determining desorption efficiencies, re-
covery studies, linearity range, method detection limits
(MDLs), accuracy, and reproducibility. Identification and
quantification of compounds tested were made by compar-
ing retention times and mass spectral data of unknown
compounds with known compounds from calibration
standards.
Materials - Stock standard solutions of 45 target VOCs
were prepared by accurately weighing 500 ±0.1 mg of
each neat compound into a 25 mL volumetric flask and di-
luting to mark with benzene free carbon disulfide (CSa).
Working and daily standards were prepared by serial dilu-
tion of the 20 mg/mL standard mixture with CS2. Standard
stock solutions of decafluorotriphenylphosphine (DFTPP)
and isotopically labeled (cyclohexane-di2, toluene-ds, 1,4-
dichlorobenzene-d4, and naphthalene-ds) internal stand-
ards (IS) were prepared at 10,000 |J.g/mL each by
weighing 100 ± 0.1 mg of DFTPP and IS into two separate
10 mL volumetric flasks and diluting to mark with dichlo-
romethane and CSa, respectively. Secondary solution
standards at 1000 ng/mL were prepared from the stock so-
lution by serial dilutions. The stock and secondary solu-
tions were stored at -10°C to -20°C in Teflon®-lined
crimp-top amber bottles.
Sample Collection - Air samples from home and office
areas were collected on 600-mg two-stage charcoal tubes
(400-mg front- and 200-mg back-activated charcoal sepa-
rated with a foam plug) with Gillian monitoring pumps. A
flow rate of 2 L/min (for a total of 1,200 L samples) was
used throughout the study in order to achieve lower detec-
tion limits. The charcoal tubes were desorbed with 2 mL
CSa spiking 1 mL of the sample extract with IS and ana-
lyzed by a capillary column GC/MS.
GC/MS System - The analytical system consisted of a
HP5995A GC/MS equipped with an HP7673A autosam-
pler and controlled by an HP-1000 RTE-6/VM computer
data system equipped with the National Institute of Stand-
ards and Technology PBM Mass Spectral Library. A 30 m
x 0.32 mm ID, Rtx-5 (Restek Corp.), fused silica capillary
column with a 0.50 |J.m film thickness was used to sepa-
rate the compounds tested. The analytical design was a to-
tally automated system for sample injection, analysis, data
reduction, and reporting.
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Method with Acceptance Criteria
The QA/QC procedures are integral to analytical methods
which produce data of known quality. The following
guidelines were used prior to initiating on-going data col-
lection, i.e., blanks, calibrating standards, or samples:
Tuning and Calibration - The GC/MS system was tuned
daily or every 12 hours with 50 ng DFTPP. The results
were then checked to verify that the U.S. EPA tuning and
mass spectral ion abundance criteria were met. The system
was initially calibrated with a standard VOC mixture in
the concentration range of 1 jig/mL to 100 ug/mL (1,5,
10, 25, 50, and 100 ug/mL) using the internal standard
method; and was routinely checked by analyzing a con-
tinuing calibration standard (VOC mixture at 25 |ig/mL
with IS at 50 (ig/mL) to ensure that the initial instrument
sensitivity and linearity did not change significantly.
Acceptance Criteria - The data from the initial and con-
tinuing calibrations were used to calculate average relative
response factors (RRFj) and continuing relative response
factors (RRFC), respectively. For the calibration to be
valid, a criteria of maximum percent relative standard de-
viation (%RSD < 30) and a minimum RRFj > 0.2 was
adopted for all target compounds in the initial calibration.
For the continuing calibration check, measured RRFC must
be within ± 20% (i.e., %D < 20) of the mean values calcu-
lated during initial calibration. In addition, all target com-
pounds must have a minimum RRFC > 0.2.
Desorption Efficiency (BE) - Desorption efficiency cor-
rections were applied for each compound detected from
samples analyzed. The DEs were determined for the
method Target Compound List (TCL) at 2, 10, 50, and
200 [Ag levels and were established for every new lot of
carbon for each compound before samples were analyzed.
Detection Limits, Accuracy, and Precision - The MDLs
for the compounds tested were determined to be better
than 0.2 parts-per-billion-by-volume (ppbv) at the 99 per-
cent confidence level. The linearity of the GC/MS system
(1 to 100 |ig/uL) was demonstrated by the initial six point
calibration data for the target compounds. The accuracy
and reproducibility (precision) of the method, determined
by analyzing a set of four replicate spikes at 50 ug level,
was found to be better than 80 percent and 10 percent, re-
spectively.
Applications
The indoor air method has been used for over five years to
analyze ambient air samples from indoor (homes and of-
fices) and outdoor (tire fires) environments. The results
from an indoor air study in a northern New Jersey urban
office and site were compared with a VOC-INDO data
base [a national data base comprised of 320 VOCs (with
66 VOCs measured indoors and 321 measured outdoors)
from a distribution of volatile organic chemicals in indoor
and outdoor air]. Nearly 90 percent of the indoor air data
was from California and New Jersey. The outdoor air data
was predominately from California, New Jersey, and
Texas.
The range of results for individual compounds varied from
not detected [ = 0.1 ppbv] to less than 1.0 ppbv
(indoor air) and 36.0 ppbv (outdoor air). The compounds
normally detected are either in the background outdoor/ur-
ban air (1,1,1-trichloroethane, carbon tetrachloride,
trichloroethene, etc.) or from automobile exhaust (ben-
zene, toluene, and xylene).
The MDLs for the compounds tested were determined to
be better than 0.2 ppbv at the 99 percent confidence level.
The accuracy and reproducibility (precision) were better
than 80 percent and 10 percent, respectively. The QA/QC
procedures were found to be essential criteria for obtaining
reliable analytical data. Based on over five years of experi-
ence using the proposed indoor air method with full scan
GC/MS and fused silica capillary column, the following
conclusions have been reached:
° The analytical results obtained are usually close to the
method detection limit values.
° The method provided quality VOC data for indoor
and outdoor air environments with quick turnaround
(one day) for emergency response samples.
o The results indicate that 1, 1, 2, 2-tetrachloroethane
may undergo in-situ degradation or reaction on char-
coal tubes.
o The advantage of GC/MS over GC/FID detection is
that a broad spectrum of target compounds can be un-
ambiguously identified and quantified and non-target
compounds identified as tentatively identified com-
pounds (TICs).
Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
For more information, contact:
Raj Singhvi, Phone (908) 321-6761
(908) 321-6660 (24-hour hotline)
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