Validating gc/ms arson analysis procedure,
FAME can be prepared with other acidic catalysts.
The major stages of a typical analytical method processing are [ 5 ]: The samples themselves may be a source of contaminants or artefacts, e. These techniques have been employed to identify and quantify glycerides and FAME.
Non-lipid contaminants or non-ester by-products of esterification reactions like cholesterol can be removed by preparative TLC on plates coated with silica gel G and developed in a solvent system of hexane-diethyl ether 9: Gaseous hydrogen chloride is available commercially or can be prepared when needed by dropping concentrated sulfuric acid onto fused ammonium chloride or into concentrated hydrochloric acid in a Essay fiesta apparatus [ 920 ].
If the sample is in an aqueous solvent, first evaporate to Validating gc/ms arson analysis procedure then use neat or dissolved in an organic, non-polar solvent. This must facilitate the reaction but should not cause unwanted side effects. Introduction The numerous sources of hydrocarbons combined with the variety of available techniques and analytical methods have created confusion among the end users of data in regards to the appropriate methodologies.
With the dilute reagent and moderate temperatures, however, there is no evidence for side effects, and under such conditions the reagent was approved by the Instrumental Committee of the American Oil Chemists' Society even though it has the same drawbacks as other acidic catalysts with sensitive fatty acids [ 9 ].
A qualitative method yields information on the chemical identity of the species in the sample.
Hydrolysis of Fatty Acids Hydrolysis results in a mixture of fatty acids and glycerol from triglycerides as indicated by the following reaction reaction 1 in which R1, R2 and R3 are linear carbon chains: For precise quantitative analysis, it is essential to Hook up oakville the GC—FID system using calibration standards for each analyte.
Retention time specificity for the sample and the standard methyl esters are determined as well as the calibration curve and the correlation coefficient.
Capillary GC-FID is widely used for the quantitative analysis of hydrocarbon compounds and oil analyses [ 11 ]. Palm oil from Elaeis guineensis Jacq.
For example, they can be isolated as pure lipid classes or remain as a mixed lipid extract. On the other hand, special precautions are necessary to ensure quantitative recovery of short-chain esters. It has been claimed that spurious components, which may interfere with GC analyses, are formed in hydrogen chloride-methanol solutions [ 9 ].
Esterification is illustrated in reactions 2 and 3. The FID response for hydrocarbons is generally proportional to the carbon number of the analyte [ 12 ].
It may be possible to obtain water-free conditions by adding anhydrous sodium sulfate to the reaction medium [ 926 ]; a better practice in general is to operate with dry reagents and glassware. The preferred conditions for acid-catalyzed esterification of carboxylic acids or transesterification of existing esters are therefore a large excess of the appropriate alcohol and the absence of water [ 49 ].
Further on in the project, it may be worthwhile to make efforts towards automation and convenience in the method [ 13 ].
Fatty Acid Analysis Analysis of fatty acids from biological or food samples generally involves three steps: It is not inconvenient to have more than one method in routine use in the laboratory, i. All solvents including water and reagents should be of the highest grade and may have to be distilled before use to remove non-volatile impurities, especially when preparing very small quantities of esters.
Processing involves sampling, sample preparation, analytical chromatography, detection and data processing, while output is the analytical results [ 13 ]. Esterification of Fatty Acids The esterification of fatty acids to fatty acid methyl esters is performed using an alkylation derivatization reagent.
The following typical esterification procedure using BCl3-methanol can be used as a guideline and could be altered to meet the needs of a specific application [ 4 ]: However, in the presence of water, which is a stronger Ppl dating donor than are aliphatic alcohols, formation of the intermediate is not favoured and esterification will not proceed fully [ 9 ].
There is some evidence that artefact formation is most likely with aged reagents [ 9 ].
The response factor method determined by the analysis of standard materials or other methods prior to measurement of the analytes is also used for calibration of the GC—FID.
The information obtained from fatty acid analysis is useful in relating to dietary fat intakes to health outcomes [ 5461 ].
Determining the degree of fatty acid unsaturation of a product is difficult because foods can contain a complex mixture of saturated, monounsaturated, and polyunsaturated fatty acids with a variety of carbon chain lengths [ 4 ].
Sampling In method development and validation, it is important to write a sampling plan with the aim of utilizing the information to check the sampling protocols [ 15 ].
It is thus necessary to calibrate each instrument or equipment and devise a specific method for the analysis of each sample type. Quantitative analysis of test compounds is sometimes carried out using one of the compounds in the samples as an internal calibration standard, and the analytical results compared with the reference values.
The solvent layer is washed with dilute potassium bicarbonate solution to remove excess acid and dried over anhydrous sodium or magnesium sulfate or anhydrous calcium chloride and the esters are recovered after removal of the solvent by evaporation under reduced pressure on a rotary film evaporator or in a gentle stream of nitrogen [ 9 ].