Aging of biological matrices and its effect on bioanalytical method performance

Apart from the well-known matrix effects that can occur in ESI LC–MS, biological matrices may have other effects influencing the quantitative reliability of bioanalytical methods. In this paper, six case studies are presented that show the effect that aging, that is the change in properties and composition of biological matrices over time, can have on the performance of bioanalytical methods. It is shown that selectivity can be affected due to the formation or disappearance of endogenous compounds. Stability can be influenced because of the decrease (or increase) of enzyme activities and recovery can be impacted if the extractability from binding sites in the matrix is enhanced or decreased. A general discussion on the importance of these matrix effects is provided as well as a perspective on how to properly address them in the method-development and validation stages of regulated bioanalysis.

Development and validation of a comprehensive two-dimensional gas chromatography-mass spectrometry method for the analysis of phytosterol oxidation products in human plasma

Phytosterol oxidation products (POPs) have been suggested to exert adverse biological effects similar to, although less severe than, their cholesterol counterparts. For that reason, their analysis in human plasma is highly relevant. Comprehensive two-dimensional gas chromatography (GC×GC) coupled with time-of-flight mass spectrometry (TOF-MS) has been proven to be an extremely powerful separation technique for the analysis of very low levels of target compounds in complex mixtures including human plasma. Thus, a GC×GC/TOF-MS method was developed and successfully validated for the simultaneous quantification of ten POPs in human plasma. The calibration curves for each compound showed correlation coefficients (R(2)) better than 0.99. The detection limits were below 0.1 ng mL(-1). The recovery data were between 71.0% and 98.6% (RSDs <10% for all compounds validated). Good results were obtained for within- and between-day repeatability, with most values being below 10%. In addition, non-targeted sterol metabolites were also identified with the method. The concentrations of POPs found in human plasma in the current study are between 0.3 and 4.5 ng mL(-1), i.e., 10-100 times lower than the typical values found for cholesterol oxidation products.

Stability of Cholesterol, 7-Ketocholesterol and β-Sitosterol during Saponification: Ramifications for Artifact Monitoring of Sterol Oxide Products

Cholesterol has been used to monitor artifact generation. Stability differences among cholesterol oxide products (COPs) and cholesterol in thermal and alkaline conditions are theorized. Thus, use of cholesterol may be unsuitable for detection of artifacts generated from COPs. Stability of cholesterol was compared to that of 7-ketocholesterol (7-keto) and β-sitosterol (βS) under various thermal and alkaline saponification conditions: 1 M methanolic KOH for 18 h at 24 °C (1 M18hr24°C, Control), 18 h at 37 °C (1M18hr37°C), 3 h at 45 °C (1M3hr45°C), and 3.6 M methanolic KOH for 3 h at 24 °C (3.6M3hr24°C). Trends indicated that cholesterol in solution was more stable than 7-keto under all conditions. Compared to βS, cholesterol was more stable under all conditions except for 1M18hr37°C for which stabilities were similar. Compounds were more labile in heat than alkalinity. Poor recoveries of 7-keto during cold saponification with high alkalinity were attributed to alkaline instability. 7-Keto, less stable than cholesterol, should be used to monitor artifact generation during screening of various methods that include thermal and alkaline conditions. In a preliminary analysis of turkey meat, more 3,5-7-one was generated from spiking with cholesterol than with 7-keto.

Lack of effect of oral supplementation with antioxidants on cholesterol oxidation product concentration of human plasma, as revealed by an improved gas chromatography method

A gas chromatographic method was successfully applied to determine cholesterol oxidation products (COPs) in human plasma. The linearity, precision, recovery and sensitivity of the method were determined. Oral supplementation with a combination of vitamin E (800 IU), C (1 g) and beta-carotene (24 mg), given for 21 days to 21 patients, did not significantly decrease plasma COP content. No correlations (n = 26) were found between initial plasma COP content and the following parameters: age, body mass index, plasma content of alpha-tocopherol, cholesterol, high-density lipoprotein cholesterol and triglycerides, and fat, natural antioxidant and oxidized lipid intake. Differences in plasma COP content between type 2 diabetic (n = 6) and nondiabetic (n = 20) patients were not statistically significant. The results from this study lead us to hypothesize that the nonenzymatic oxidation of cholesterol in plasma is negligible compared to COPs originating from the diet. This article also includes a comprehensive review of the drawbacks of the analytical methods of COP determination in plasma and serum.

Separation of phytosterol oxidation products by combination of different polarity gas chromatography capillary columns

The number of characterized phytosterol oxidation products (POPs) from both ring- and side-chain structures has increased during recent decades, resulting in difficulties in the separation of POPs on different gas chromatography (GC) capillary columns. The main objective of this study was to separate a mixture of 29 purified and characterized oxidation products from sito-, campe- and stigmasterol using GC capillary columns with different polarity. For the first time in the area of POPs analysis, the separation efficiency of the combination of two capillary GC columns with different polarities was investigated. A non-polar 5% phenyl coated (DB5-MS) and a mid-polar 35% phenyl coated (DB35-MS) column was combined with a pressfit connector. The main improvement was enhanced base line separation for many of the analyzed POPs, compared with the separations achieved using the individual columns. However, three pairs of POPs co-eluted: 24-hydroxysitosterol/campesterol-5beta,6beta-epoxide, stigmasterol-5beta,6beta-epoxide/campesterol-5alpha,6alpha-epoxide and stigmasterol-5alpha,6alpha-epoxide/campestanetriol.