Fast GC-PID/FID Analyses using
Resistively Heated Columns for Rapid Analyses in the Field
Oral presentation in Real-Time Detection Systems
Authors:
John N. Driscoll, PID
Analyzers, Sandwich, MA 02653
Stan Stearns, VICI, Houston, TX 77055
Philip Smith, OSHA Labs, Salt Lake City, UT 84081
Objective- The
analysis times for NIOSH ketone and aromatics methods (# 1301, 1501 & 2005)
are between 25-35 minutes. The time consuming operations are the long ramping
and cooling times required. The other difficulty is that if peaks are not
adequately resolved, other components could interfere with the analysis. We
will employ resistively heated columns to reduce the total analysis times by
50-60% to 12-15 minutes and use the PID/FID response ratios to enhance
identification of components of interest. These ratios have been used
previously (1) to identify the molecular structure of hydrocarbons.
Methods- A PID Analyzers
compact GC (<20#) with an external laptop will be used for the analysis that
incorporates new technology developed by
VICI that takes polyimide-coated fused silica (FST) and
removes the polyimide layer. Then the
(FST) is electroplated with nickel. As a
result of the superior heat transfer of the electroplated nickel, we are able
to rapidly and efficiently heat and
achieve excellent resolution for a 30M capillary column. A mini-FID was designed that will easy attach to the outlet of the
PID taking a single detector port and providing improved identification of
components.
Results –For the initial runs with the series of 12 ketones
(NIOSH #1301), we were able to separate 10 of the components by just increasing
the ramp rate from 10o/min to 200 /min. The final time
for analysis was 11 minutes. We do have 8 ramp rates and 4 cooling fan rates so
with an additional ramp, we should be able to separate methyl amyl ketone and
ethyl amyl ketone and use a faster fan rate to reduce the cool down time. For
NIOSH Method #1501, we were able to separate 15 of the 17 compounds in 14
minutes instead of 35 minutes. We were not able to separate nitrobenzene and
naphthalene but there is a such a significant difference in the PID/FID
response ratio that each of the components can be easily identified.
Conclusions
We have shown that the resistively heated columns can be
used to improve both separations & time of analysis. The use of a second
detector (FID) for confirmation of peak identity is more helpful for faster
separations where complete resolution is not attained.
1. Driscoll,
et al., "Gas Chromatographic Detection and Identification of Aromatic and
Aliphatic Hydrocarbons in Complex Mixtures by Coupling Photoionization and
Flame Ionization Detectors," J.
Chrom., 158, 171 (1978).
