Chromatography focus on
Biodiesel Sample 1 (Canola) Manual Prep
Free Glycerin Monoglycerides Diglycerides Triglycerides
WorkBench
0.168 0.163 0.291 0.286 0.565 0.554
Repeatability (r)
Run 1 Run 2 r Run 1 Run 2 r Specification 0.000 0.000 0.000 0.000 0.000 0.000 2.58E-04 0.169 0.169 0.282 0.286 0.533 0.536
Total Glycerin 0.984 0.991 0.007 1.023 1.003 0.020 Manual Prep
Free Glycerin Monoglycerides Diglycerides Triglycerides
Biodiesel Sample 2 (soybean) WorkBench
0.141 0.140 0.022 0.021 0.006 0.005
0.083
Chemist 1
Free Glycerin 0.004 Monoglycerides 0.107 Diglycerides
0.032
Triglycerides 0.009 Total Glycerin 0.152
0.004 0.111 0.033 0.009 0.156
0.004 0.109 0.033 0.008 0.154
Run 1 Run 2 Average Run 1 Run 2 Average 0.004 0.114 0.034 0.009 0.161
Chemist 2 0.004
0.118 0.036 0.009 0.166
Chemist 3
Free Glycerin 0.004 Monoglycerides 0.116 Diglycerides
0.033
Run 1 Run 2 r Run 1 Run 2 r Specification 0.008 0.008 0.000 0.008 0.008 0.000 0.138 0.144 0.022 0.023 0.009 0.009
Total Glycerin 0.177 0.184 0.007 0.176 0.174 0.002 0.046 glycerin
Table 7. For two different types of biodiesels, the results obtained using the WorkBench prep and the manual prep were statistically identical. The precision (repeatability) observed for the WorkBench samples were well within ASTM specifications.
150 pA
100 50
Chemist 1 monoglycerides diglycerides triglycerides
Repeatability (r) 0.002
Triglycerides 0.007 Total Glycerin 0.160
0.004 0.115 0.033 0.007 0.159
0.004 0.113 0.032 0.006 0.155
Run 1 Run 2 Average Run 1 Run 2 Average 0.004 0.114 0.033 0.007 0.157
Chemist 4 0.004
0.114 0.033 0.006 0.157
0.004 0.113 0.032 0.006 0.156
0.004 0.113 0.034 0.008 0.160
Reproducibility ASTM R (R)
0.000 0.005
Specification 0.007
0.094
Reproducibility ASTM R (R)
0.000 0.004
Specification 0.007
0.091
Table 8. Each chemist obtained the same results when using the Agilent WorkBench for automated sample preparation. The precision (reproducibility) was well within the ASTM specification for multiple operators.
100 150
B. Comparison of manual sample prep and WorkBench sample prep The biodiesel samples prepared manually and with the WorkBench were analysed according to ASTM method D6584. Figure 4 shows a comparison of biodiesel sample 1 (canola) chromatograms resulting from the manual prep and the WorkBench prep. In the regions where the various glycerins elute, both chromatograms look identical. For all samples, the free and total glycerins were quantified and the results are listed in Table 7.
The WorkBench sample prep yielded results that were identical to those prepared manually. Both samples were prepared and analysed in duplicate to determine the repeatability of the sample preparations. Repeatability (r) is used to measure the precision for a single operator by taking the difference between duplicate analyses of each sample.
As can be seen in Table 7, the samples prepared using the WorkBench exceeded minimum repeatability specification set by ASTM for this analysis. This shows that after a 10-fold reduced scale, samples prepared with Workbench can easily provide the same precise results as manually prepared samples using much larger amounts of chemicals, reagents and solvents.
C. Multiuser precision - reproducibility Figure 5 shows the same soybean biodiesel sample prepared by four different chemists on four different days. The chromatography between each chemist is nearly identical.
The quantitative results obtained by each chemist are shown in Table 8 along with an evaluation of the precision between groups (reproducibility). These results show a very high level of precision when several chemists develop and prepare the same sample with the automated Agilent WorkBench.
References
1. “D6584 Test Method for Determination of Free and Total Glycerine in B-100 Biodiesel Methyl Esters by Gas Chromatography”; ASTM International: 100 Barr Harbor Drive, West Conshohocken, PA, USA, 2010.
2. Agilent 7696A Sample Prep WorkBench, Agilent Technologies, Publication Number 5990-6908EN, January 28, 2011. 3. “Improved Data Quality through Automated Sample Preparation”, Rebecca Veeneman and Dale Synder, Agilent Technologies, Publication Number 5990-6974EN, December 10, 2010.
50
Chemist 2
100 150
50
Chemist 3
100 150
50 2.5 5 7.5 10 12.5 15 17.5 20 22.5 Min.
Figure 5. A comparison of data from a soybean biodiesel sample prepared by for different chemists working on four different days. Each chemists develop a WorkBench sample preparation protocol and then analysed the samples using ASTM method D6584. These results are identical.
Conclusion
This paper demonstrates that a complex, multi-step sample preparation protocol can be automated with the Agilent 7696A WorkBench. Analytical results obtained with WorkBench prepared samples were the same as those obtained using a traditional manual sample preparation. Even after scaling the preparation steps for the 2-mL vials, the quantitative precision was very high with WorkBench prepared samples. Reducing the sample prep scale with the WorkBench also used 10-times less solvents, reagents, and calibration standards. Additionally, there was no need to use disposable glassware and expensive volumetric glassware.
Chemist 4
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