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ANALYTICAL APPROACH analysis. The detection limit was about 0.03 ppm C (signal-to-noise ratio of 3). Quantitative determinations of hydrocarbon concentrations above 0.05 ppm C were reproducible to better than 20% RSD. Under the t e s t i n g conditions used in t h e AQIRP, a concentration of 0.05 ppm C is equivalent to an emission rate of approximately 1.0 mg/mi. S p e c i a t i o n of a l d e h y d e s , k e t o n e s , a n d a l c o h o l s . Oxygenated hydrocarbons, such as aldehydes, ketones, and alcohols, require different sampling and analysis procedures than the aliphatic and aromatic hydrocarbons. Cj-Cg aldehydes and ketone species were sampled in impingers containing an acetonitrile solution of 2,4-dinitrophenylhydrazine (DNPH) derivatizing reagent, and the 2,4-dinitrophenylhydrazone derivatives were determined using HPLC. Methanol and ethanol were collected in impingers containing distilled water and determined by GCFID on a DB-WAX 30-m megabore capillary column. The 0.03-ppm detection limit was similar to that for the C j - C 1 2 hydrocarbons. C h a r a c t e r i z a t i o n of f u e l s . As mentioned earlier, detailed speciation of the fuels and fuel feedstocks was necessary for development of the GC library data file. Once the testing program was under way, the fully blended fuels were characterized in detail by t h e Ford Research and Exxon Research and E n g i n e e r i n g laboratories using GC and GC/MS. The composition data, which was in good agreement between the two laboratories, was averaged to provide the final fuel speciation data set. In
Analytical instruments (gas or liquid chromatographs)
Test/ environmental data (vehicle I.D., fuel, temperature)
Emissions analyzers (HC, CO, NO x ,C0 2 )
addition, a n u m b e r of other fuel properties, including total aromatics, total olefins, total saturated hydrocarbons, bromine number, Reid vapor p r e s s u r e , sulfur content, carbon/ hydrogen ratio, density, and the temperature at which a certain percentage of fuel is volatilized (T 90 ), were measured (17). Quality assurance
Several quality assurance procedures were developed to ensure the highest possible reliability of the emissions measurements (see Table I). The GC retention time scale was calibrated daily by analysis of a 21-component gas reference material consisting of C 1 - C 1 2 rc-alkanes, ethylene, acetylene, 2-methylbutene, 1,3-butadiene, benzene, isooctane, toluene, />-xylene and o-xylene. Although the concentration of each gas reference species was known within 2 - 4 % (95% confidence limits), this mixture was not used as a quantitative reference material. Instead, methane and propane (2% accuracy) were used as quantitative standards. The response factor for all hydrocarbons, except methane, was assumed to be directly proportional to the number of carbons, as verified in previous studies (7). Peak areas were used for quantitation of the hydrocarbons, and the FID response was nearly linear for the C j C, 2 hydrocarbons within the concentration range expected for this study. Recovery studies. One of the best tests for assessing the validity of an analytical technique is to "spike" a sample with the analytes of interest, carry out the analytical procedure, and determine the recovery of the "spiked" analytes. Various standards
Instrument computers
Site host computers (Ford, GM)
Instrument computers
Data collation (EDS)
Development of working data set (SAI)
Data distribution and data analysis
Figure 3. Computer protocols for the transmission, collection, and processing of emissions data.
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1154 A • ANALYTICAL CHEMISTRY, VOL. 63, NO. 23, DECEMBER 1, 1991
