Agilent Measurement Journal - Issue 3 - 2007 - (Page 65)

detector performance. To address this issue we tested a “selective sample introduction” device that can be used to perform the in situ reaction. This device can be operated in such a manner as to reduce or remove the high boiling compounds and residual derivatizing agents. We believe such an approach can create new possibilities for reducing the amount of sample pretreatment necessary prior to GC/MS analysis, resulting in improved lab productivity, instrument reliability and analysis reproducibility. Figure 12 shows an Agilent 6890/5975C GC/MS system ﬁtted with a ProSep precolumn separation device (Apex Technologies) that was developed to divert the low-boiling derviatizing agent and the bulk of the high-boiling compounds through the vent port. This also enabled the selection of components for introduction onto the two GC columns joined by a purged tee. The purged tee permitted back-ﬂushing of the ﬁrst column to eliminate the very close eluting high boilers while the analysis continued on the second analytical column. This was demonstrated in an experiment using C24-FAME (fatty acid methyl esters) standards and cholesterol esters. Fatty acids are an important class of lipid metabolites and can be identiﬁed by their retention on deﬁned chromatographic systems and by mass spectrometry. We added fatty acid standards to cholesterol esters to provide a high-boiling cutoff marker. Other late-eluting components (such as trigylcerides) would also be eliminated as they elute near or after the cholesterols. Silica B Si Si Si OH OH OH Silica C Si Si Si Si Si Si H H H Figure 10. A new deactivated silica Type-C material with a high surface area and 4.0 µm particle size was developed for LC separation of polar metabolites. Type-B silica was converted to Type-C material having a silica hydride (Si-H) surface. x102 1.0 0.9 0.8 + EIC(120.00000-120.20000) Scan Mix4_Gradient09A_Temp25_02.d Amino acid L-Tryptophan L-Leucine L-Phenylalanine L-Isoleucine L-Tyrosine L-Methionine L-Valine L-Aspartic acid L-Glutamic acid L-Alanine 0.7 0.6 0.5 Trp 0.4 0.3 0.2 0.1 Phe Retention time 11.07 11.22 11.25 11.31 11.33 11.55 11.61 11.83 11.83 12.05 Amino acid L-Threonine L-Glycine L-Serine L-Proline L-Asparagine L-Glutamine L-Arginine L-Histidine L-Lysine Retention time 12.29 12.32 12.52 12.94 13.20 13.35 16.63 16.67 17.01 Leu Ile Pro Gln Tyr Met Val Arg Glu Ala Thr Gly Ser 11 11.5 Asp 12 12.5 13 13.5 14 14.5 15 Counts (%) vs. Acquisition Time (min) Asn 15.5 16 16.5 10.5 17 Figure 11. This EIC shows the separation of mixture containing 19 amino acids. Lys His Agilent Measurement Journal 65

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 3 - 2007

Applying Ingenuity to the Measurement of Emerging Technologies Contents Emerging Innovations Department Delivering Bigger Benefits by Optimizing Customer Workflows Measuring Material Properties at the Nanoscale Utilizing In Situ Atomic Force Microscopy in Life Science, Pharmaceutical and other Bio-Related Applications WiMAX™: Plotting a New Path to Global Mobility Addressing the Triple Complexity of Triple-Play Networks What Next for Mobile Telephony? Exploring the Inner Workings of Tire-Pressure Monitoring Systems Developing, Assessing and Applying a High-Resolution Thin-Film Magnetic Probe Making Accurate Settling-Time Measurements Using a Vector Network Analyzer Applying Metabolomics Methods to the Study of Bacterial Leaf Blight in Rice Plants Measuring Stream Dynamics with Fiber Optics survey

Agilent Measurement Journal - Issue 3 - 2007

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