Charlotte Bjergegaard

Determination of thiocyanate, iodide, nitrate and nitrite in biological samples by micellar electrokinetic capillary chromatography

Abstract Micellar electrokinetic capillary chromatography (MECC) has been developed as an efficient method for the determination of the thiocyanate ion, iodide, nitrite and nitrate. The use of various alkyltrimethylammonium ions was found advantageous for MECC compared to negatively charged surfactants, as this resulted in low migration times for the anions and thereby fast analysis. Moreover, the MECC system, using positively charged surfactants (dodecyltrimethylammonium bromide, DTAB), was effective in separating the anions of interest from interfering organic anions present in extracts from biological samples such as milk and blood. Detection of the anions was performed by direct UV. The performance of the developed method was satisfying; however, a low number of theoretical plates for the thiocyanate ion indicated the need for some improvements in this respect. The sensitivity of the method increased with a factor two by using a 75 μm I.D. capillary instead of the 50μm I.D. capillary, whereas use of a high-sensitivity optical cell assembly increased the sensitivity an additional nine times. Repeatability with the 50-μm capillary was satisfying with respect to migration time, relative migration time and normalised peak area (except for the thiocynate ion) of the anions, with relative standard deviations varying between 0.24 and 0.29%, 0.07 and 0.16%, and 1.75 and 2.37%, respectively, whereas some improvements are still needed for the normalised and relative normalised peak areas for the thiocyanate ion (13.50 and 13.91%). Apart from the thiocyanate ion ( r 2 = 0.9748), linearity studies gave correlation coefficients between 0.9962 and 0.9975 for the normalised peak areas.

Determination of phenolic carboxylic acids by micellar electrokinetic capillary chromatography and evaluation of factors affecting the method

Abstract Micellar electrokinetic capillary chromatography (MECC) based on cetyltrimethylammonium bromide (CTAB) was developed for separation of individual cinnamic and benzoic acid derivatives. This method was adapted to the separation of the phenolic carboxylic acids from other anions, phenolics and glucosinolates in samples prepared from plant materials. The influence of temperature, voltage, pH, electrolyte and detergent concentrations in the buffer on migration times for the compounds considered, peak areas, resolution and number of theoretical plates were investigated. It is shown that rapid and efficient separations (270 000 plates/m) are possible, even for structural closely related phenolics.

Determination of flavonoids by micellar electrokinetic capillary chromatography

Abstract HPCE based on cetyltrimethylammonium bromide (CTAB) or cholate micellar electrokinetic capillary chromatography (MECC) was found suitable for the separation of individual flavonoid glycosides following a rapid and simple technique of isolation, purification and group separation. Kaempferol and quercetin glycosides with varying degrees of glycosylation, and with or without additional esterification on the carbohydrate part, were included in the study. The influence of temperature and voltage as well as electrolyte, CTAB and organic modifier concentrations in the buffer on the migration order, migration times, and peak areas of the flavonoids was investigated. The method developed gives possibilities for the separation and specific determination of flavonoids isolated from vegetative parts of cruciferous plants.

Comparison of glucose, glucose 6-phosphate, ribose, and mannose as flavour precursors in pork; the effect of monosaccharide addition on flavour generation.

The effect of glucose, glucose 6-phosphate, mannose and ribose on the generation of aroma volatiles in pork was investigated. The monosaccharides were added individually to minced pork prior to heat treatment (160°C for 10min) in the following concentrations: glucose (27.5μmol/g), ribose (1.2μmol/g), mannose (8.3μmol/g) and glucose 6-phosphate (0.5μmol/g). The natural concentrations of the monosaccharides in the pork used were found to be 4.0μmol/g for glucose, 0.1μmol/g for ribose, 0.3μmol/g for mannose and 2.6μmol/g for glucose 6-phosphate. The major aroma compounds identified in the headspace of the heated samples were pyrazines, aldehydes (Strecker and lipid-derived), ketones, and sulphides. Glucose generated the highest amounts of volatiles followed by glucose 6-phosphate. However, when related to the added concentration of glucose 6-phosphate, this phosphorylated monosaccharide showed the highest aroma generating potential. The addition of ribose did not increase the concentration of volatiles compared with pork without the added monosaccharide. The fates of ribose 5-phosphate and ribose in pork were studied over time. The concentrations of ribose and ribose 5-phosphate clearly decreased during 2h equilibration, which may be due to enzymatic activities. These precursors may, therefore, be less important pork flavour precursors than glucose and glucose 6-phosphate.

Separation of desulphoglucosinolates by micellar electrokinetic capillary chromatography based on a bile salt

Abstract Micellar electrokinetic capillary chromatography (MECC) has been developed as a promising method for the determination of 40 desulphoglucosinolates. A sodium cholate based MECC method was found to be efficient for the qualitative and quantitative analysis of desulphoglucosinolates produced in an on-colum, enzymatic step form the corresponding intact glucosinolates. Separation conditions and sensitivity of the method have been optimised with respect to different parameters, including capillary types, where the 75-μm I.D. capillary increased the sensitivity 2.5 times over that of a 50-μ capillary. With use of a high-sensitivity optical cell assembly (Z-cell), the sensitivity was further increased ten times, resulting in detection of picogram amounts, or concentration levels corresponding to 10−6 M. Repeatability with a 75-μm capillary was good, with the relative standard deviation varying between 0.2% and 0.9% for relative migration times and for relative normalised areas between 1.0% and 3.0%. Linearity of the optimised method gave correlation coefficients between 0.99 and 0.9999 for the 50-μm capillary and 0.99 and 0.9997 for the 75-μm capillary. Separation efficiency expressed as number of theoretical plates (N/m) was in the range 250 000–300 000 for the 50-μm capillary and 210 000–250 000 for the Z-cell. Limitations and possibilities of the MECC method here presented are discussed with respect to analyses of glucosinolates occuring in a wide range of cruciferous seed, vegetative plant parts including cabbage varieties, feed and food.

Flavour development in pork. influence of flavour precursor concentrations in longissimus dorsi from pigs with different raw meat qualities.

Flavour development and overall eating quality of pan-fried pork chops of longissimus dorsi from eight different raw meat qualities aged for 4 and 15 days were assessed by a trained sensory panel. The raw meat qualities were obtained through combinations of strategic feeding/fasting (control vs. low glycogen concentration), slaughter live-weight (84kg vs. 110kg), and gender (female vs. castrate). The flavour development was investigated for possible correlation with the concentrations of selected individual flavour precursors present in the raw meat: monosaccharides, IMP and degradation products, fatty acids, lactate and thiamine. Differences in precursor concentrations between the raw meat qualities were observed with feeding/fasting and ageing as the main factors with the largest influence of all experimental factors. However, the concentrations of the precursors could not explain the differences in sensory perception of the pan-fried pork chops. Overall, the differences were small.

Eating quality of pork from pure breeds and DLY studied by focus group research and meat quality analyses.

The eating quality of pan-fried pork chops from the pure breeds of Duroc, Hampshire, Black spotted and Wild pigs, and of the cross-breed of Duroc, Landrace and Yorkshire (DLY) was investigated by focus group research in combination with analyses of raw meat quality. The three focus groups, all consisting of young consumers, generally agreed in their description of the eating quality of the five breeds. The focus group methodology was found to be an informative method for the sensory evaluation of pork chops. Chemical and physical analyses of raw meat quality were performed in parallel with the focus group research, and this combination proved useful. The chemical and physical analyses generally supported the focus group evaluation, and differences between the breeds could be explained. Duroc was the breed with the overall best eating quality, while Hampshire had the lowest overall eating quality. DLY, Black spotted, and Wild pigs were intermediate, though not similar.

Determination of aromatic choline esters by micellar electrokinetic capillary chromatography

Abstract Micellar electrokinetic capillary chromatography (MECC) using sodium dodecyl sulphate (SDS), alkyltrimethylammonium bromide (C 10 to C 18 TAB) or

Chiral separation of aromatic amino acids by capillary electrophoresis

Abstract 3-Carboxyphenyl-substituted amino acids co-occurring with various types of other aromatic amino acids in plants have been investigated with respect to the chirality at the α-carbon atom. A free zone capillary electrophoresis (FZCE) method using cyclodextrin as chiral selector has been developed and found to be suitable for this purpose. Phenylalanine, tyrosine, tryptophan, and all of the 3-carboxyphenyl-substituted amino acids (m-carboxytyrosine, m-carboxyphenylalanine, m-carboxyphenylglycine and m-carboxy-p-hydroxyphenylglycine) separated well into their enantiomers and from other naturally occurring amino acids using the developed FZCE method. Identification of the separated enantiomers has been confirmed by use of authentic reference compounds, by spiking and use of stereospecific aromatic amino acid decarboxylase, l - and d -amino acid oxidases. The influence of various parameters on the separation efficiency has been investigated and optimized. Theoretical plate numbers of up to 460 000 N·m−1 have been obtained, and resolutions between d - and l -forms in the range from 0.70 to 1.26 (SD d - and l -forms of the four meta-carboxy substituted amino acids, with the possibility of the racemisation of these compounds, and as a highly specific and efficient technique for use in amino acid oxidase and decarboxylase assay.

Determination of heterocyclic compounds by micellar electrokinetic capillary chromatography

Micellar electrokinetic capillary chromatography (MECC) based on sodium cholate (NaCh) and sodium dodecyl sulphate (SDS) was developed for the determination of aromatic amino acids and heterocyclic legume constituents. The influence of temperature, voltage, micellar system, pH, zwitterion and modifier concentrations in the buffer on migration times, peak areas, resolution and number of theoretical plates was investigated. This MECC method makes possible the sensitive determination of the individual compounds with detection limits in the picomole range. Up to 300 000 theoretical plates per metre of capillary were obtained together with satisfactory linearity and repeatability of the NaCh method. The applicability of MECC to samples prepared from plant material, following a fast and simple technique of isolation, purification and group separation, is illustrated by selected examples.