Reference materials lipids

Most used methods are spectrophotometry and immunochemistry, in dedicated laboratories ultracentrifugation. A handbook on this material has been written by Rifai et al. (1997). Certified reference materials for the determination of lipids in serum are provided by NIST. 

A critical aspect is the different solubility of specific lipid molecules in the solvents, which may result in a different distribution of lipids in the solution with respect to the residue. The analytical procedures thus need to be validated with suitable reference materials. 

Evaluating the P/S ratio requires particular care first, because of the presence of mixtures of more than one binder, such as egg and oil in tempera grassa secondly, due to the presence of waxes, and in particular beeswax, which has been widely used as a coating and restoration material and thirdly, due to the contribution of FAs from other sources such as fouling or micro-organisms, which can considerably alter the P/S values from those expected for reference materials. For instance, because the ratio for walnut oil falls between the value of linseed oil, poppy oil and egg lipids, using the P/S ratio it is not possible to differentiate between pure walnut oil, and mixtures of linseed and poppy oil or egg. 

Gel permeation chromatography (GPC)/normal-phase HPLC was used by Brown-Thomas et al. (35) to determine fat-soluble vitamins in standard reference material (SRM) samples of a fortified coconut oil (SRM 1563) and a cod liver oil (SRM 1588). The on-line GPC/normal-phase procedure eliminated the long and laborious extraction procedure of isolating vitamins from the oil matrix. In fact, the GPC step permits the elimination of the lipid materials prior to the HPLC analysis. The HPLC columns used for the vitamin determinations were a 10 im polystyrene/divinylbenzene gel column and a semipreparative aminocyano column, with hexane, methylene chloride and methyl te/t-butyl ether being employed as solvent. 

Precht, D., Molkentin, J. and de Froidmont-Goertz, I. (1998) Anhydrous butterfat reference material CRM 519 certification of triglyceride composition and cholesterol content including homogeneity and stability tests. Fett. Lipid., 100, 546-554. 

Supported lipid membranes and membrane arrays functionalized with TMPs have been fabricated by numerous research groups (see for example [5,37,127-135] and references therein). Lipid polymerization could be a useful strategy to enhance the operating lifetime of these materials when incorporated into biosensing and drug screening devices. A key issue that must be addressed is the potentially adverse effects that lipid polymerization may have on TMP structure and activity, which can be separated into two major subtopics ... 

PLE is used in many food and feed applications for the analysis of a great variety of POPs. One reason for this is the acceptance of this technique by the US EPA in Method 3545 (50). A classic PLE approach involves extraction of the contaminants together with the lipid fraction, which is removed by external clean-up. Already in 1997, Schantz and co-workers (51) evaluated this technique for the extraction of OCPs and PCBs in certified reference materials (CRMs)... 

Buchgraber, M., Ulberth, E, and Bowadt, S. 2001. The certification of the trans fatty acid content in three edible oil-based reference materials, 24th World Congr. Exhibition Int. Society for Fat Research Lipids, Fats and Oils Reality and Public Perception, Berlin, September, Abstracts, 6. 

As with DHS, the IHSS open-ocean standard may be used. If a reference material typical for the area under investigation is desired, it may be prepared following standard techniques (see Section 25.5.4). However, for PHC a considerable amount of particulate material is necessary, i.e., at least several grams. Several protocols can be followed, e.g., with or without removal of lipid material. The one given by Kononova (1966) is outlined in Section 25.5.4 with some modifications. 

The D-camphor bisketal derivative (32) of natural mammalian lipid bis(monoacylglycero)phosphate (BMP) has been synthesised to identify the stereochemical configuration of its diglycerophosphate (DGP) backbone by NMR spectroscopy. As reference materials the sn-1,1 (33), sn-3,3 (34), and sn-3,1 (35) DGP analogues have also been prepered. ... 

Research in physiology carried out in the 1930s established that the lipid fraction of semen contains small amounts of substances that exert powerful effects on smooth mus cle Sheep prostate glands proved to be a convenient source of this material and yielded a mixture of structurally related substances referred to collectively as prostaglandins We now know that prostaglandins are present m almost all animal tissues where they carry out a variety of regulatory functions... 

Matrix Components The term matrix component refers to the constituents in the material aside from those being determined, which are denoted as analyte. Clearly, what is a matrix component to one analyst may be an analyte to another. Thus, in one hand for the case of analyses for elemental content, components such as dietary fibre, ash, protein, fat, and carbohydrate are classified as matrix components and are used to define the nature of the material. On the other hand, reference values are required to monitor the quality of determinations of these nutritionally significant matrix components. Hence, there is a challenging immediate need for certified values for dietary fibre, ash, protein, fat, and carbohydrate. Concomitantly, these values must be accompanied by scientifically sound definitions (e.g. total soluble dietary fibre, total sulpha-ted ash, total unsaturated fat, polyunsaturated fat, individual lipids, simple sugars, and complex carbohydrates). 

Since poly(hydroxybutyrate), a naturally abundant poly(hydroxyalkanoate) (PHA, Fig. 1), was first isolated and characterized by Lemoigne in 1925, PHAs have been studied extensively by biochemists who referred to them as lipids [1, 2]. Further research on PHAs however, made it clear that these materials are in fact water-insoluble polyesters, which are synthesized and accumulated intra-cellularly as storage compounds by many different bacteria. Using various types of substrates, an almost infinite variety of PHAs can be synthesized [3-9]. 

In the present chapter, we first provide some general information concerning the chemistry of waxes and lipids currently encountered in various items from our cultural heritage and we detail the main protocols based on direct mass spectrometry that have been developed so far. We then discuss the mass spectra obtained by EI-MS on a range of reference substances and materials sampled from museum and archaeological artefacts. We then focus on the recent possibilities supplied by electrospray ionisation for the elucidation of the structure of biomarkers of beeswax and animal fats. 

Immunocytochemical methods have been widely applied to visualize proteins, carbohydrates, or lipids in sectioned material. The advantage of using immunocytochemistry is to be able to localize the molecules of interest within the tissue. Several procedures have been described. Basically, these procedures can be split into four main steps that are described in subheadings (1) tissue preparation, (2) the primary antibodies, (3) the visualization of the target, and (4) enhancement of signals with antibody complexes. In addition, a protocol for alkaline phosphatase will be presented in detail in Subheading 5. The terms primary and secondary antibodies refer to the order in which they are applied to the target. The immunocytochemical procedures are not limited to sectioned... 

In the mucosal environment, effects of salt, pH, temperature, and lipids need to be taken into consideration for possible effects on viscosity and solubility. A pH range of 4-7 and a relatively constant temperature of 37°C can generally be expected. Observed solution properties as a function of salt and polymer concentration can be referred to as saline compatibility. Polyelectrolyte solution behavior [27] is generally dominated by ionic interactions, such as with other materials of like charge (repulsive), opposite charge (attractive), solvent ionic character (dielectric), and dissolved ions (i.e., salt). In general, at a constant polymer concentration, an increase in the salt concentration decreases the viscosity, due to decreasing the hydrodynamic volume of the polymer at a critical salt concentration precipitation may occur. 

In DSC the sample is subjected to a controlled temperature program, usually a temperature scan, and the heat flow to or from the sample is monitored in comparison to an inert reference [75,76], The resulting curves — which show the phase transitions in the monitored temperature range, such as crystallization, melting, or polymorphic transitions — can be evaluated with regard to phase transition temperatures and transition enthalpy. DSC is thus a convenient method to confirm the presence of solid lipid particles via the detection of a melting transition. DSC recrystaUization studies give indications of whether the dispersed material of interest is likely to pose recrystallization problems and what kind of thermal procedure may be used to ensure solidification [62-65,68,77]. 

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