Page 25 - Shimadzu Journal vol.8 Issue2

Hydrocarbon Processing Industry

For ISO 8754, repeatability was assessed by performing two
sets of 20 analyses (40 total analyses) of the same sample on the
same instrument in the same laboratory by the same operator.
Equation 3: Repeatability (r) in weight percent (wt. %) according to ISO 8754
for sulfur in concentration range of 0.03 to 0.05 wt. % (a) and greater than Reproducibility was assessed in the same manner as that for ASTM
0.05 wt. % (b). The target concentration is represented as S. D4294. The results were then compared to the calculated, statisti-
cal limit as per the method specifications, calculated based on equa-
tions 3 and 4. The analytical chamber was operated under ambient
atmospheric conditions for all analyses.

Equation 4: Reproducibility (R) in weight percent (wt. %) according to ISO The lower limit of detection (LLD) was calculated using equation 5.
8754 for sulfur in concentration range of 0.03 to 0.05 wt. % (a) and greater
than 0.05 wt. % (b). The target concentration is represented as S.

Results for Standard Test Method
Compliance
Equation 5: Equation to calculate the Lower Limit of Detection (LLD). C is
the concentration of S in ppm, NET is the fluorescent X-ray intensity of S A summary of results of this study are presented in Tables 3 and 4
(cps/µA), BG is the background intensity of S (cps/µA), T is the integration
time (sec), and A is the current (µA). for ASTM D4294 and Tables 5 and 6 for ISO 8754.

Table 3. Results for repeatability (r) testing based on ASTM D4294 criteria.
Count Time Method Result in Air Result in He
Test Sample Conc. % RSD % RSD
(sec) Criterion (ppm) (ppm) (ppm)
Repeatability Base Oil 50 ppm 300 5.4 - - 5.0 2.89
Repeatability Base Oil 100 ppm 200 8.5 - - 7.1 2.08
Repeatability Base Oil 500 ppm 200 24 16 0.89 12 0.71
Repeatability Base Oil 0.5 wt. % 100 105 64 0.29 44 0.26
Repeatability Base Oil 4.0 wt. % 100 405 257 0.17 159 0.12
Repeatability Diesel 100 ppm 200 7.6 - - 5.2 1.29
Repeatability Base Oil 500 ppm 100* 24 23 1.26 13.5 0.72
Repeatability Base Oil 0.5 wt. % 50* 105 80 0.35 41 0.22
Repeatability Base Oil 4.0 wt. % 50* 402 220 0.19 91 0.12
*Analysis performed more rapidly than specified in method for given concentration.
Note: Samples represented by dashes (-) are more amenable to analysis with helium atmosphere.

Table 4. Results for reproducibility (R) testing based on ASTM D4294 criteria.
Count Time Method Result in Air Result in He
Test Sample Conc. % RSD % RSD
(sec) Criterion (ppm) (ppm) (ppm)
Repeatability Base Oil 50 ppm 300 24 - - 5.4 2.44

Repeatability Base Oil 500 ppm 200 105 31 1.00 12 0.43
Repeatability Base Oil 4.0 wt. % 200 1776 388 0.25 667 0.09
Repeatability Diesel 100 ppm 200 41 - - 17 1.85
Note: Samples represented by dashes (-) are more amenable to analysis with helium atmosphere.

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Shimadzu Journal vol.8 Issue2 67