From: FJSchwende

To: EPA Docket Number EPA - HQ - OAR - 2008 - 0558 Cc: FBertram, BKolowich , JSopata Date: April 7 , 2010 Subject: D6550

– data summary and recommendation. The ASTM Method, D6550, an SFC based method for the determination of the olefin content of gasoline 1 , has been performed in the NVFEL Testing Services Group for approximately 3 years. A single instrument has been utilized for this method, a Selerity Technologies Inc, Series 3100 SFC. Over that period of time we have anal yz ed a single control fluid sample, CAAB Control 2003 (ident ified internally as FTAG - 12221) and have participated in the ASTM RFG Crosscheck program. Results of these anal ys es are summarized below. Control Fluid Analysis: For every anal yt ical run, three replicates of the Control Fluid were run before and after the submitted samples. All six replicates were reported to the database unless a verifiable reason was observed to exclude a value (for instance, depletion of the injected sample, resulting in an erroneously low value). For the 144 values reported to the database, the mean mass - % olefin content was 9.9, with a standard deviation of 0.42 (relative standard deviation of 4%). Figure 1 shows a plot of these values versus anal ys is date; the red line indicates the overall m ean mass - % olefin. Figure 1 . Control Fluid Results. Mass - % Olefin versus Assay DateSubmitted Samples: During this time period the majority of submitted samples were ASTM RFG Crosscheck samples. These samples were anal yz ed by both D6550 and D1319 2 . The olefin composition reported for D1319 is expressed at volume - %, and is corrected for the oxygenate composition of the sample. Regression anal ys is of the olefin values reported by D1319 versus D6550 is shown in Figure 2. F igure 2 . Regression of D1319 versus D6550.

In this figure, six points with uncorrected D1319 values were included in the graph (red squares) but were not included in the regression analy sis. Samples reported as 0.0 mass - % ol efin by D6550 were excluded from the anal ys is because the method requires that assay results below the lowest standard (nominally 1 mass - %) must be reported as zero.The regression anal ys is demonstrates that these two methods are highl y correlated, but do es not address the

nature of an y method bias. To consider method bias, the difference between the results was calculated (Delta = D6550 mass - % - D1319 vol - %) and graphed versus analy sis date as well as versus D6550 mass - %. These graphs, shown in Figures 3 and 4, demonstrate that the di fferences in the percent olefin values reported by these two methods were : a) random with respect to analy sis date; b) biased positive for olefin compositions below approximately 5 mass - %; c) less than +/ - 2.4 for all samples over this time period. Figure 3 . Delta versus Date.Figure 4 . Delta versus D6550

Recommendation: Control Fluid results indicate that D6550 is able to provide consistent mass - % olefin values when performe d according to the requirements of the standard test method. Even though the basis for the reported olefin composition is different from D1319 (mass - % versus volume - %) the repo rted percentages are comparable (usuall y within 1 percentage point of each other and never more than 2.5 percentage points different). Based on these findings, I recommend the use of ASTM D6550 as an alternative test method for the determination of olefins in gasoline. 1. Standard test method for determination of olefin content of ga solines by supercritical - fluid chromatograph y. ASTM D6550. 2. Standard test method for hydrocarbon typ es in liquid petroleum products by fluorescent indicator adsorption. ASTM D1319.