Challenges in mass spectrometry based targeted metabolomics.

The gap of the post-genomic era is increasingly being filled by the metabolomics approach, comprising a technology for analyzing small molecule endogenous metabolites (<1500 Dalton) in complex biological samples. This new analytical science has progressed within the last years particularly with regard to improvements in mass spectrometry based detection, now allowing highly robust, reproducible, selective and sensitive qualitative or quantitative analysis of endogenous metabolites. The precise and accurate quantitation of these metabolites via targeted metabolomics, now critically contributes to the quantitative analysis of endogenous compounds in biomarker discovery and validation thus to future personalized therapy. The analytical methods of choice in (MS-based) targeted metabolomics primarily are HPLC-API-MS/MS, FIA-APIMS/MS and GC-MS. In the parent paper, we provide an introduction and brief survey on the technological basis of targeted metabolomics in biomarker research, discuss various relevant analytical aspects in mass spectrometry including comparison to non-targeted approaches, effects of sample preparation, impact of sample stability, carryover- and matrix effects, need for standardization and for proficiency tests, standardization of analytical methods as well as the requirement for method validation.

Intraabdominal tissue concentration of ertapenem.

OBJECTIVES: Ertapenem, a class I carbapenem, is approved for the treatment of mild to severe intraabdominal infections, but its in vivo concentrations in intraabdominal tissues are unknown. The purpose of this study was to determine the concentration of ertapenem in intraabdominal tissue. PATIENTS AND METHODS: After informed consent 48 patients, 23 female and 25 male with a median age of 58 years (34-81), requiring surgical intervention at intraabdominal organs were enrolled. Patients received 1 g of ertapenem intravenously for perioperative prophylaxis. Tissue samples were taken after resection of parts of the organs. Plasma samples were taken when tissue samples were taken. Drug concentrations were determined by liquid chromatography/mass spectrometry. An ANCOVA test (analysis of covariance) was performed to assess organ-specific differences in ertapenem concentration and penetration ratios. RESULTS: Mean+/-SD ertapenem tissue concentration (mg/kg) was 16.0+/-8.8 in the gall bladder, 12.1+/-5.3 in the colon, 7.0+/-5.7 in the small bowel, 4.5+/-2.3 in the liver and 3.4+/-2.9 in the pancreas. The mean tissue/plasma ratio was 0.19 (colon), 0.17 (small bowel), 0.17 (gall bladder), 0.088 (liver) and 0.095 (pancreas). The ANCOVA test revealed statistically significant organ-specific differences in ertapenem tissue concentration in the gall bladder versus liver/pancreas and in tissue penetration for the colon versus liver/pancreas. CONCLUSIONS: These pharmacokinetic results support the assumption that ertapenem is suitable for the treatment of intraabdominal infections.

On the signal response of various pesticides in electrospray and atmospheric pressure chemical ionization depending on the flow-rate of eluent applied in liquid chromatography-tandem mass spectrometry.

The API-MS signal response of several pesticides (atrazine, simazine, isoproturon, diuron, chlorfenvinphos, chlorpyrifos, alachlor, trifluralin) depending on the flow-rate of eluent entering the MS interface was investigated. The investigations were based on API-MS-MS analyses of standard pesticide mixtures in the flow injection mode (FIA) at systematically varied eluent flow-rates using both an ESI interface (Turboionspray) and a heated nebulizer type APCI source. In the result, the individual compounds included in this study showed significant differences in their signal response behaviour depending on the flow-rate of eluent applied. The most hydrophobic compounds among the investigated pesticides (chlorpyrifos and trifluralin) showed drastic losses of sensitivity with increasing eluent flow-rate in both ESI and APCI, while more hydrophilic compounds like atrazine, simazine and isoproturon showed the expected signal response (concentration-sensitive in ESI, mass-flow-sensitive in APCI) at least within a certain range of flow-rates (200-600 microl/min in ESI, 200-2000 microl/min in APCI). These findings lead to the conclusion that application of a programmed HPLC eluent flow-rate may be advantageous to achieve maximum sensitivity of API-MS detection for all pesticides of interest. This is exemplified by the implementation of a flow gradient into an online SPE-HPLC-APCI-MS/MS method for improved analysis of pesticides in drinking water.