Central California Ozone Study (CCOS) - Desert Research Institute

Methyl t-butyl ether should be quantified from canister samples, using the method of
analysis for C 3 -C 12 hydrocarbons. The individual response factor should be determined for MTBE
and its concentration reported in ppbC.
A.7.2 Carbonyl Compounds
Formaldehyde and other volatile carbonyl compounds are to be collected, utilizing solid
adsorbent cartridges coated with 2,4-dinitrophenylhydrazine (DNPH) reagents, by the method
consistent with the EPA document "Technical Assistance Document for Sampling and Analysis of
Ozone Precursors" (October 1991, EPA/600-8-91/215). The method is based on the specific
reaction of organic carbonyl compounds with DNPH deposited on silica gel or C 18 bonded SepPak
cartridges in the presence of an acid to form stable derivatives, hydrazones, which are
subsequently analyzed by high performance liquid chromatography (HPLC).
A carbonyl sampling system consists of a diaphragm pump capable of maintaining air flow
through the cartridges of 500 - 1500 ml/min, flowmeter, six-port solenoid manifold allowing
unattended collection of up to six carbonyl samples, needle valves for flow rate regulation, and
check valves to protect cartridges from outside air when air is not being sampled through a given
cartridge. For automatic operation, the timer starts and stops the pump at the appropriate time.
The timer also opens the six-port solenoid valve when the pump starts and closes it when the pump
stops. A charcoal filter is attached to the pump outlet in order to remove traces of acetonitrile
from DNPH cartridges.
Carbonyl compounds collected in the cartridges (as hydrazones) are eluted with HPLC
grade acetonitrile and analyzed by HPLC with UV detection at 360 nm. A reverse phase HPLC
column is used. Identifications are made based on matching the HPLC retention times with those of
authentic standards. A three-level calibration curve (plus blank) is constructed for each quantified
hydrazone. C1-C7 carbonyl compounds are recommended for quantification as follows:
formaldehyde, acetaldehyde, acetone, acrolein, propionaldehyde, crotonaldehyde, methyl ethyl
ketone, methacrolein, butyraldehyde, benzaldehyde, valeraldehyde, tolualdehyde, and
hexanaldehyde.
A.7.3 C8-C20 Hydrocarbons by Tenax Sampling and Analysis by GC/FID or GC/MS
Volatile hydrocarbons in the range of C 8 -C 20 , are usually collected using Tenax solid
adsorbent. The Tenax sampling unit draws two parallel streams of air allowing for the collection
of duplicate samples, with the pump downstream of the Tenax. The flow rates are controlled by a
flow controller or are measured before and after each run using a calibrated mass flow meter and
the mean value is used to calculate volumes of air sampled. Prior to use, the Tenax solid
adsorbent is cleaned by Soxhlet extraction with hexane/acetone mixture, packed into Pyrex glass
tubes and thermally conditioned for four hours by heating at 300 °C under nitrogen purge.
Approximately 10% of the precleaned Tenax cartridges are tested by GC/FID for purity prior to
sampling. After sampling, the Tenax cartridges are capped tightly using clean Swagelok caps
(brass) with graphite/vespel ferrules, and placed in metal containers with activated charcoal on
the bottom.
C-14