Injector-internal thermal desorption from edible oils. Part 1: visual experiments on sample deposition on the liner wall

Injector-internal thermal desorption from edible oils or fats enables the analysis of a wide range of compounds in oils or extracts of fatty food without prior removal of the sample matrix. The oil or fat is deposited onto the wall of the injector liner. The solutes of interest are evaporated, leaving behind the sample matrix. The injector is kept at a temperature volatilizing the solutes of interest, but minimizing evaporation of the bulk material of the oil. This technique was optimized regarding sample deposition on the liner wall (Part 1) and desorption of high boiling compounds, such as migrants from food packaging materials into simulant D (olive oil) or fatty food (Part 2). The sample liquid should be transferred to the liner wall and spread to a thin film in order to facilitate the release of high boiling components. Visual experiments with perylene-containing solutions showed that the oil must be diluted to reduce the viscosity (separation from the needle tip). The oil concentration should not exceed 20% in order to rule out that squirting sample liquid drops to the bottom of the vaporizing chamber. Further dilution to about 10% oil improves spreading of the liquid to a thin film. A rather high boiling solvent should be used, such as n-butyl acetate, to prevent thermospray at the needle exit and violent evaporation from the liner wall with sputtering liquid. Using a 5-mm ID liner, 5-10-microL injections of 10-20% oil solutions were at the upper limit.     

Injector-internal thermal desorption from edible oils. Part 2: chromatographic optimization for the analysis of migrants from food packaging material

Injector-internal thermal desorption from edible oil or fat is a convenient sample preparation technique for the analysis of solutes in lipids or extracts from fatty foods. The injector temperature is selected to vaporize the solutes of interest while minimizing evaporation of the bulk material of the oil. This technique has been in routine use for pesticides for some time. Now its potential is explored for migrants from food contact materials, such as packaging, into simulant D (olive oil) or fatty/oily food, which means extending the range of application towards less volatile compounds. The performance for high boiling components was investigated for diisodecyl phthalate (DIDP) and diundecyl phthalate (DUP). Since the injector temperature needs to be as high as 260degreesC, some bulk material of the oil enters the column and must be removed after every analysis. This is achieved by a coated precolumn backflushed towards the end of each analysis. Desorption of the solutes is particularly efficient in the initial phase, when a thin sample film is spread on the liner wall, and is largely determined by the diffusion speed in the oil after the latter has contracted to droplets. An increased carrier gas flow rate during the splitless period supports the transfer into the column. It is concluded that the technique is attractive for migrant analysis, with DUP being at the upper limit of the boiling point.     

Programmed-Temperature Vaporizing (PTV) Liners to Introduce Chlorinated and Sulfur Compounds into a Capillary Gas Chromatograph

Introduction of a sample at a programmed temperature is an attractive approach both for dilute samples in large volumes and to prevent discrimination inside the syringe needle with this injection into a capillary gas Chromatograph. Quantitative data obtained with glass liners packed with trapping materials including glass wool, Tenax TA, Chromosorb 101 and Thermotrap-TA to analyze chlorinated and sulfur compounds are compared. To eliminate the solvent, these vapors were vented through the injection port cap, which provided greater efficiency than through the split line.     

Epoxidized soy bean oil migrating from the gaskets of lids into food packed in glass jars. Analysis by on-line liquid chromatography-gas chromatography

The migration of epoxidized soy bean oil (ESBO) from the gasket in the lids of glass jars into foods, particularly those rich in edible oil, often far exceeds the legal limit (60 mg/kg). ESBO was determined through a methyl ester isomer of diepoxy linoleic acid. Transesterification occurred directly in the homogenized food. From the extracted methyl esters, the diepoxy components were isolated by normal-phase LC and transferred on-line to gas chromatography with flame ionization detection using the on-column interface in the concurrent solvent evaporation mode. The method involves verification elements to ensure the reliability of the results for every sample analyzed. The detection limit is 2-5 mg/kg, depending on the food. Uncertainty of the procedure is below 10%.     

Detection of nitro musks in human fat by capillarv gas chromatography with atomic emission detection (AED) using programmed temperature vaporization (PTV)

Atomic emission detection (AED) has been successfully applied to the determination of nitro musks in the fat of human adipose tissue by gas chromatography at trace concentration levels. Element specific detection with the AED combined with a clean-up procedure for nonpolar substances makes target screening analysis for lipophilic nitro aromatic compounds possible for the first time. The lack of sensitivity, especially in the AED nitrogen and oxygen trace, was compensated by higher concentration of the extracts and injection of larger sample volumes performed by cold programmed temperature vaporization (PTV) in the solvent split mode. The combination of the superior quantification properties of the atomic emission detector with large sample volume introduction makes the quantification of nitro musks down to the ppb level possible. All five nitro musks investigated exhibit linear dynamic ranges going down close to instrumental limits of detection. Moreover, organochlorine compounds could be sensitively detected in the same sample extract by the AED chlorine trace without any interferences from coeluting matrix compounds.     

Optimisation and validation of programmed temperature vaporization (PTV) injection in solvent vent mode for the analysis of the 15 + 1 EU-priority PAHs by GC-MS

This paper presents the optimisation of a programmed temperature vaporization solvent vent (PTV-SV) injection gas chromatographic mass spectrometric (GC-MS) method for the analysis of the 15 + 1 EU-priority PAHs in food extracts. Three operation parameters (vent time, vent flow and vent pressure) were optimised by applying a D-optimal experimental design. Among these variables, vent time showed the highest effect on the analytical response (signal intensity) of the target PAHs.The 15 + 1 EU-priority PAHs were analysed in solvent solutions and in extracts of fortified sausage. In addition, blank lamb meat extracts were prepared and spiked with the target PAHs prior to GC-MS analysis. The performance of the optimised PTV-SV injection GC-MS method was scrutinised for linearity, precision, matrix effects and robustness. All parameters were found satisfactorily. Compared to PTV injection in splitless mode, the PTV-SV injection method provided an enhancement of sensitivity for all target PAHs. Especially significant was the improvement of the S/N ratios of the compounds with the highest molecular mass.