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 gasoline1, 

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 analyzed a single control fluid sample, CAAB Control 2003 (identified 

internally as FTAG-12221) and have participated in the ASTM RFG Crosscheck program. Results of these 

analyses are summarized below.

Control Fluid Analysis: For every analytical 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 analysis 

date; the red line indicates the overall mean mass-% olefin.

Figure 1. Control Fluid Results. Mass-% Olefin versus Assay Date
Submitted Samples: During this time period the majority of submitted samples were ASTM RFG 

Crosscheck samples. These samples were analyzed by both D6550 and D13192. The olefin composition 

reported for D1319 is expressed at volume-%, and is corrected for the oxygenate composition of the sample. 

Regression analysis of the olefin values reported by D1319 versus D6550 is shown in Figure 2.

Figure 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 analysis. Samples reported as 0.0 mass-% olefin by D6550 were excluded 

from the analysis because the method requires that assay results below the lowest standard (nominally 1 

mass-%) must be reported as zero.
The regression analysis demonstrates that these two methods are highly correlated, but does not address the 

nature of any method bias. To consider method bias, the difference between the results was calculated (Delta 

= D6550 mass-% - D1319 vol-%) and graphed versus analysis date as well as versus D6550 mass-%. These 

graphs, shown in Figures 3 and 4, demonstrate that the differences in the percent olefin values reported by

these two methods were:

a) random with respect to analysis 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 performed 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 reported percentages 

are comparable (usually 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 gasolines by supercritical-fluid 

chromatography. ASTM D6550.

2. Standard test method for hydrocarbon types in liquid petroleum products by fluorescent indicator 

adsorption. ASTM D1319.