Determination of cholesterol in milk fat by supercritical fluid chromatography

Supercritical fluid chromatography for lipid analysis in foodstuffs

The task of lipid analysis has always challenged separation scientists, and new techniques in chromatography were often developed for the separation of lipids; however, no single technique or methodology is yet capable of affording a comprehensive screening of all lipid species and classes. This review acquaints the role of supercritical fluid chromatography within the field of lipid analysis, from the early developed capillary separations based on pure CO₂ , to the most recent techniques employing packed columns under subcritical conditions, including the niche multidimensional techniques using supercritical fluids in at least one of the separation dimensions. A short history of supercritical fluid chromatography will be introduced first, from its early popularity in the late 1980s, to the sudden fall and oblivion until the last decade, experiencing a regain of interest within the chromatographic community. Afterwards, the subject of lipid nomenclature and classification will be briefly dealt with, before discussing the main applications of supercritical fluid chromatography for food analysis, according to the specific class of lipids.

Improved quantification of prostaglandins in biological samples by optimizing simultaneously the relationship eicosanoid/internal standard and using liquid chromatography tandem mass spectrometry

Although a wide variety of articles on quantification of eicosanoids by using internal standards are published every year, little has been done on how much internal standard should be added. This article demonstrates that the application of experimental design enables estimating the interaction eicosanoid/internal standard and to select confidently an optimal amount of internal standard and a response factor (RF) for the analysis of eicosanoids in a high number of samples, where the amount of sample is limited and the unknown levels of eicosanoids are spanned in a wide range of concentrations. The results revealed that the interaction eicosanoid/internal standard is an important factor that affects the validity of the RF and subsequently the accuracy of the analysis.

Statistical power and analytical quantification

It is suggested that power analysis should be formally incorporated into quantification experiment reports in order to substantiate the conclusions derived from experimental data more effectively. The article addressed the issues of power analysis calculation, sample size estimation and appropriate data reporting in quantitative analytical comparisons. Illustrative examples from the literature are used to show how the described power analysis theory could be applied in practice.

Experimental design considerations in quantification experiments by using the internal standard technique: Cholesterol determination by gas chromatography as a case study

An overview on experimental design in quantification experiments using the internal standard technique is described. Particular emphasis is given to the modelling of the relationship analyte/internal standard and the estimation of the optimal amount of internal standard to be used throughout the analytical concentration range by using a uniform shell design with a minimum number of seven experiments. The described approach is demonstrated in the analysis of cholesterol in various reference materials by gas chromatography (GC), using alpha-5 cholestan as internal standard. The outlined approaches can be applied in the determination of any kind of analyte.

The composition of bovine milk lipids: January 1995 to December 2000

Data from recent publications on bovine milk lipids are presented and discussed. This includes extraction of lipids, triacylglycerols, phospholipids, other complex lipids, sterols, isoflavones, and fatty acids. Improved gas-liquid and high performance liquid chromatography were used. Data on the trans and cis isomers of fatty acid and of conjugated linoleic acids are given, and the analyses are described. Papers about the lipids in milks and dairy products from the United States are few; where with the exception of trans-fatty acid isomers and conjugated linoleic acids, almost no research has been reported.

Analysis of non-saponifiable lipids by super-/subcritical-fluid chromatography

Because of the particular properties of carbon dioxide or carbon dioxide/modifier mobile phases, super- or subcritical-fluid chromatography (SFC) can be an alternative to more classical chromatographic methods such as gas chromatography (GC) or high-performance liquid chromatography (HPLC) for the separation of unsaponifiable lipids. These fluids can also be helpful in the extraction and/or the concentration steps of sterols, tocopherols or carotenoids from complex samples. Supercritical extraction, off-line prefractionation or semi-preparative supercritical fluid chromatography, carried out before the analysis are described. The effects on separation of analytical parameters such as pressure, nature of and modifier percentage or stationary phase nature are also reported. The performance of capillary, packed or capillary packed columns is discussed, as well as the consequences of their use (choice of stationary phases, type of coupled detector). Numerous examples of fine separations are reported.