Focus on Sulphur Analysis - Analytical Instrumentation 23 Figure 2a: Sulphur Calibration Curve
Using the same modified EPA method, described above, the chlorine repeatability data was analysed for LOD, LOQ and MDL at the 95% confidence level. These estimates are shown in Table 1b. It should be noted the elevated signal to noise (S/N) ratio of 84.4 indicates that a much lower concentration can be analysed and that detection limits are likely to be lower than indicated.
STDEV LOD
MSDL, 95% S/N Ratio
Table 1b: Chlorine Limit of Detection
Operators can calibrate the MESA-6000 with their own standards to generate and store up to 50 different calibration curves.
The same high quality calibration curve can be obtained on the MESA-6000 for chlorine as can be seen in figure 2b. The chlorine in mineral oil range of concentration standards used is - 0, 5, 25, 50, 150, 500, 300 and 500 mg/kg chlorine.
Figure 2b: Typical Chlorine Calibration Curve Equivalency
In order to determine how the MESA-6000 methodology performance might compare to established sulphur measurement technologies, a similar set of calibration standards and sample sets were prepared and measured by the following technologies:
• Energy Dispersive X-Ray Fluorescence Instrumentation (EDXRF) MESA-6000 • Combustion UV Fluorescence analyser Method ASTM D-5453 • Energy Dispersive X-Ray Fluorescence Method ASTM D-4294
Following instrument calibration with sulphur in mineral oil standards, 11 samples were analysed. Analysis demonstrates that for the 9 lower concentration materials the MESA-6000 and D5453 results readily compare. For the 2 higher concentration samples, which are outside the scope of D5453, the MESA-6000 and D4294 results are found to be equivalent to each other.
Sample Type Gasoline Diesel
Precision and Estimation of Level of Detection
To determine precision, an 11mg/kg sulphur in diesel sample was used. The data was derived from the average of two consecutive 180 second analyses of 5ml of the diesel run consecutively 14 times. This data is illustrated in Figure 3a.
Figure 3a: Sulphur Precision Data
Kerosene E85 RFG
Jet A ULSD
Transformer Oil B100
Sample Type Crude Sweet * Crude Sour*
ASTM D5453 39.2 7.3
226 6.4
33.1 437 7.97 38
1.5
ASTM D2494 3600
1.03% Table 2: ASTM D-5453 and ASTM D-4294 to MESA-6000
Case Study: Sulphur in Automotive and Transportation Fluids
The repeatability data was then analysed using a modified EPA method detection limit (MDL) technique to estimate level of detection (LOD) and level of quantification (LOQ) and MDL at the 95 percent confidence level. These estimates are shown in Table 1a. It should be noted that the elevated signal to noise (S/N) ratio of 24.8 indicates that a lower concentration can be analysed and that detection limits are likely to be lower than indicated here.
STDEV LOD
MSDL, 95% S/N Ratio
Table 1a: Sulfur Limit of Detection
As with previous testing, a-certified 40 mg/kg Chlorine performance check sample was used to determine the precision for chlorine. The data was derived from the average of two consecutive 180 second analyses of 5 ml of transformer oil run consecutively 21 times. This data is illustrated in Figure 3a.
Figure 3b: Chlorine Precision Data
MESA-6000 Sulphur 0.42 mg/kg 1.25 mg/kg 0.72 mg/kg 24.8
Five laboratories participated in a modified round robin ruggedness study. The MESA-6000 instruments utilised were all calibrated in the 0-50 mg/kg sulphur in mineral oil and 50-1000 mg/Kg sulphur in mineral oil calibration ranges.
All lab sites measured the sulphur content, in 11
various petroleum products. Each days result was derived from the average of two consecutive 180 second analyses of 5 ml of sample in the same sample analysis cup. The day one and day two results were then
averaged to yield a final result for each sample from all five labs. The test was designed to permit evaluation of between instrument agreement and short term calibration stability. The results are displayed in Table 3 below.
Sample Typre Diesel Low S B- 11 (Diesel) Gasoline E10 Diesel Low S B20 (Diesel)
Transformer Oil Kersosene Jet A HFO
Jet B5 Hydraulic Fluid
Lab 1 5 9
35 3 5
34
234 446 941 433 508
Lab 2 6
10 35 4 7
33
233 441 938 429 508
Table 3: Results of Automotive and Transportation Fluids
Case Study: Chlorine recovery in the presence of high Sulphur in Crude Oil
Seven mineral oil samples were analysed in the laboratory for simultaneous determination of low chlorine and sulphur. These samples contained 50ppm chlorine and varying values of sulphur 0ppm – 1.5wt%. High levels of sulphur will have an adverse effect on the ability to accurately measure
Lab 3 6 8
35 3 6
32
236 440 936 429 500
Lab 4 6 8
36 3 6
31
237 435 921 425 498
Lab 5 6
12 37 5 9
34
240 449 953 437 510
MESA-6000 35
8.8
231 5.0 34
437 8.0 35
2.2
MESA-6000 3603
1.23%
MESA-6000 Chlorine 0.48 mg/kg 1.44 mg/kg 0.88 mg/kg 84.4
February / March 2011 •
www.petro-online.com
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