Rolf Danielsson

Chromatographic alignment by warping and dynamic programming as a pre-processing tool for PARAFAC modelling of liquid chromatography-mass spectrometry data.

Solutes analysed with LC-MS are characterised by their retention times and mass spectra, and quantified by the intensities measured. This highly selective information can be extracted by multiway modelling. However, for full use and interpretability it is necessary that the assumptions made for the model are valid. For PARAFAC modelling, the assumption is a trilinear data structure. With LC-MS, several factors, e.g. non-linear detector response and ionisation suppression may introduce deviations from trilinearity. The single largest problem, however, is the retention time shifts not related to the true sample variations. In this paper, a time warping algorithm for alignment of LC-MS data in the chromatographic direction has been examined. Several refinements have been implemented and the features are demonstrated for both simulated and real data. With moderate time shifts present in the data, pre-processing with this algorithm yields approximately trilinear data for which reasonable models can be made.

Alignment of chromatographic profiles for principal component analysis: a prerequisite for fingerprinting methods

Abstract In fingerprinting methods, small differences between chromatograms with rather complex appearance have to be detected. Pattern recognition methods based on principal component analysis (PCA) could be a useful tool, but for chromatographic profiles as input data a severe problem is the great impact of chromatographic variations compared with true variations in sample composition. The problem has been analysed in terms of parameter variations for exponentially modified Gaussian peaks, and a procedure has been developed to align a sample chromatogram towards a target chromatogram in order to compensate for (i) small shifts in retention time (not due to different sample components), (ii) common variations in peak area (not due to sample composition) and (iii) variations in level and slope of the baseline. The effects of the alignment procedure on the PCA is demonstrated for a set of chromatographic profiles intended for peptide mapping.

Matched filtering with background suppression for improved quality of base peak chromatograms and mass spectra in liquid chromatography - mass spectrometry

A time domain filter that combines the properties of matched filtering and two-fold differentiation is presented. The filter coefficients are given by the second derivative of a Gaussian model peak, controlled by the setting of two parameters related to the chromatographic system. The fundamental characteristics of the filter were derived, and its applicability demonstrated for real liquid chromatography–mass spectrometry (LC–MS) data. The filter is primarily intended as a fast pre-processing step, for a mass chromatogram with 320 scans over 700 mass channels the computation time was 0.6 s on a standard PC. Base peak chromatograms with improved peak detection capability and mass spectra useful for compound identification were obtained with filtered data. The most significant effect of the described filter is background reduction due to the differentiation, which in combination with the matched filter can be performed with maintained or even improved signal-to-noise ratio.

Pressurized Hot Water Extraction of anthocyanins from red onion: A study on extraction and degradation rates

Pressurized Hot Water Extraction (PHWE) is a quick, efficient and environmentally friendly technique for extractions. However, when using PHWE to extract thermally unstable analytes, extraction and degradation effects occur at the same time, and thereby compete. At first, the extraction effect dominates, but degradation effects soon take over. In this paper, extraction and degradation rates of anthocyanins from red onion were studied with experiments in a static batch reactor at 110 degrees C. A total extraction curve was calculated with data from the actual extraction and degradation curves, showing that more anthocyanins, 21-36% depending on the species, could be extracted if no degradation occurred, but then longer extraction times would be required than those needed to reach the peak level in the apparent extraction curves. The results give information about the different kinetic processes competing during an extraction procedure.

Controlling mechanisms of aluminium in soil solution - an evaluation of 180 podzolic forest soils

To monitor the level of soil acidification in the county of Värmland in the middle west of Sweden 180 podzolic forest soils were investigated. Soil solutions from four horizons were obtained by centrifugation and the soil was sampled for a determination of the exchangeable pool by extraction. The concentrations of inorganic Al and its fraction of the total Al in solution were greater in the south of the county (up to 50%). The factors influencing the total Al and free inorganic Al3+ in the soil solutions were evaluated. Saturation indices (SI) for five different mineral phases were calculated but none implied equilibrium conditions. The relationships between pAl3+ and pH (in the pH range 4-6.2) gave slopes of about 1, which indicated that ion exchange/complexation reactions may be important for determining the Al3+ concentration in the B and C horizons. In the E horizon solutions complexation with soluble organic acids seemed to be the major factor which influenced the Al3+ activity. The influence of organic matter on Al solubility was supported by partial least square (PLS) regressions.

The "mysterious" disease in Swedish moose. Concentrations of trace elements in liver and kidneys and clinical chemistry. Comparison with experimental molybdenosis and copper deficiency in the goat

Moose (Alces alces L.) affected by a disease with unknown aetiology were compared with healthy moose regarding trace element concentrations in liver and kidneys, as well as certain clinical chemical parameters of blood plasma. The diseased moose showed decreased hepatic concentrations of Cu, Cd and Mg. Renal concentrations of Cd, Co, Mg and Mn were also decreased. Substantially increased concentrations in both liver and kidneys were seen for Al, Ca, Fe, Pb and Zn, while Se and Mo were increased in liver tissue. The hepatic levels of Mo in the affected moose were 36% higher and Cu was approximately 60% lower than in reference animals collected in 1982. The most important clinical chemical changes were decreased concentrations of bilirubin, thyroxine (T4) and the liver-specific enzymes GLDH and g-GT. Also, the activities of the enzymes CuZn-SOD and GSH-Px in erythrocytes were decreased. Increases were recorded for free fatty acids (NEFA), the muscle-specific enzyme CK, but especially for urea and insulin. Changes in the plasma protein pattern were also discernible after electrophoresis on agarose gel membranes, indicating chronic immunostimulation. All the observed changes in trace element concentrations and clinical chemical parameters are compatible with molybdenosis and secondary Cu deficiency in ruminants and most of the parameters are in agreement with those found in experimental copper deficiency and molybdenosis in the goat. It is, therefore, suggested that the moose disease with previously unknown aetiology is mainly caused by molybdenosis.

Nova Scotia moose mystery – a moose sickness related to cobalt- and vitamin B12 deficiency

A wasting, debilitating disease with uncertain aetiology affecting moose (Alces alces americana) in Eastern North America has been reported repeatedly ever since the 1910s. Despite the intensive studies during 1930-1960s the cause of the sickness could not be established. In the 1960s a parasitic nematode (Parelaphostrongylus tenuis) was reported as constituting a probable explanation for the sickness, although several clinical and pathological signs remained unexplained. In Sweden, a moose disease with similar signs, has been shown to be caused by molybdenosis resulting from a nutritional imbalance. The findings of this investigation were applied in Nova Scotia to determine trace element concentrations in tissues from indigenous moose. Co deficiency was found in about half of the cases and the investigation was complemented by determining the vitamin B12 level, which proved nutritional Co/vitamin B12 deficiency, further verified by an increased MMA (methylmalonic acid) level in plasma. Deficiencies were found mainly in the Tobeatic and Cape Breton Highland regions. No indications of molybdenosis or other trace element disturbances were found in Nova Scotia. Otherwise, extremely high Cd levels (148 mg Cd/kg kidney wet wt., maximum) were found, though probably not contributing to the moose sickness. The Cd burden of moose on mainland Nova Scotia was more than 50% higher than that of moose in Huntville and Alonquin (Ontario, Canada) and five- to six-fold is higher than the highest Cd levels found in Sweden. To counteract the bio-geochemical effects of Co deficiency in the moose environment, provision of Co-containing salt licks is suggested.

Peak purity assessment in liquid chromatography-mass spectrometry

Fixed-size moving window evolving factor analysis and base peak chromatograms have been used for peak purity detection in data generated with LC-MS. The two methods were evaluated with both real and simulated data and were found to be fast and complementary to each other. When a possibly impure peak is detected, it is suggested that further information can be obtained from local principal component analysis modelling and comparative mass chromatogram plots.

Decomposition of diphenylamine in nitrocellulose based propellants—I. Optimization of a numerical model to concentration-time data for diphenylamine and its primary degradation products determined by liquid chromatography with dual-amperometric detection

The consumption of diphenylamine (DPA) in two nitrocellulose (NC) based propellants subjected to a heat storage test at 85 degrees has been studied. A previously developed method based on reversed-phase liquid chromatography with dual-amperometric detection was used to monitor the concentrations of DPA, 2-nitro-DPA and 4-nitro-DPA during the test. A numerical model based on first order rate equations was fitted to the obtained analytical data with the use of a specially written curve fitting program. The model implemented in the program describes the initial nitrosation and nitration steps of DPA in aging NC propellants. The use of matrices in the calculation of concentration-time (CT) curves enables the introduction of a general algorithm which can be readily changed in order to simulate any system of first order reactions. The program can therefore be used in other applications such as mechanistic studies in organic synthesis. The general simulation algorithm allows inclusion of unknown (not analysed) components in the reaction mechanism. In this application, it was possible to simulate the course of N-nitroso-DPA which is not detectable by the amperometric principle.

FACTORS AFFECTING THE PREPARATION OF PACKED CAPILLARY COLUMNS IN SUPERCRITICAL CARBON DIOXIDE MEDIA

In this study, packed capillary columns were prepared using supercritical carbon dioxide as a packing carrier. A factorial design was used to examine the effect that four selected factors have on the packing performance. The investigated factors were: 1)