Bjørn Grung

Incomplete healing (scar tissue) after periapical surgery—radiographic findings 8 to 12 years after treatment

Twenty-four cases treated by periapical surgery--which 2 to 6 yr after surgery were classified radiographically as incomplete healings (scar tissue)--were further followed, extending the observation period to 8 to 12 yr. One case healed completely, 1 failed, and 22 were still recorded in the same healing group. All the 22 scar tissue cases were characterized by a reduction of the defect in bone. In 13 cases, continuous periodontal structures were seen and the defect thereby separated from the root. The findings support the conclusion that cases clearly showing features of incomplete healing (scar tissue) at the regular follow-up 1 yr after surgery can be regarded as successes. They need not be recorded for further systematic control. A general follow-up program for apicectomy cases is suggested.

MISSING VALUES IN PRINCIPAL COMPONENT ANALYSIS

Abstract Calculation schemes for principal component analysis are considered for the case when some matrix elements are missing. Iterative solutions are proposed—either a set of multilinear regression problems or as singular-value decomposition problems with iterative imputation of missing values. If mean values are subtracted from the data matrix, they should also be included in the iteration scheme. Test calculations using Matlab show that the regression approach is somewhat faster than the imputation approach. The results with a substantial amount of missing data are different and superior to those obtained with the naive NIPALS algorithm in common use in chemometrics.

Automated curve resolution applied to data from multi-detection instruments

Abstract This work presents a method for automated resolution of multicomponent data. The proposed procedures corrects background, cuts the data into smaller sub matrices, and resolves complex overlapping systems without human intervention. Basic constraints on concentration and spectral profiles are defined and used for determining the number of components and for cutting complex peak clusters into smaller sub matrices. The procedures are applied to multicomponent data from high performance liquid chromatography with diode array detection (HPLC-DAD), flow injection analysis with diode array detection (FIA-DAD), and gas chromatography–mass spectrometry (GC–MS).

Retention time shift adjustments of two-way chromatograms using Bessel's inequality

Abstract For two-way data (data stemming from so-called hyphenated methods), several methods have been developed for quantification of analytes. One of the better known methods is rank annihilation factor analysis (RAFA). However, an effect observed in chromatographic data seriously reduces the usability of this method. Like any other method based on the use of standards, RAFA fails to estimate the correct concentrations in the presence of retention time shifts. Hence, a retention time shift correction method is necessary. Bessels inequality can be used to adjust for the retention time shifting of the data relative to the standards. RAFA can then be used to estimate the concentrations with a high degree of precision. This procedure is demonstrated on four data sets of varying complexity, and is found to perform excellently for all sets.

Elucidation of triacylglycerols in cod liver oil by liquid chromatography electrospray tandem ion-trap mass spectrometry.

Though liquid chromatography electrospray tandem mass spectrometry (LC-ESI-MS(2)) has been widely used in the structural elucidation of triacylglycerols (TAG) in vegetable oils, its potentiality for the identification of TAG molecules in omega-3 rich oils remains unexplored till date. Hence, this article investigates the applicability of LC-ESI-MS(2) for the structural characterization of naturally occurring TAG in cod liver oil without the TAG fractionation during the sample preparation. A computational algorithm was developed to automatically interpret the mass spectra and elucidate the TAG structures respectively. The results were compared against the lipase benchmark method. A principal component analysis study revealed that it is possible to discriminate genuine from adulterated cod liver oil.

Resolution of multicomponent profiles with partial selectivity. A comparison of direct methods

Abstract Three procedures for resolution of multicomponent systems were tested for their ability to deal with partial selectivity. The methods were evolving factor analysis (EFA), heuristic evolving latent projections (HELP) and the method of orthogonal projections. An extensive data simulation, in which five factors were varied according to a full 2 5 factorial design, was carried out to test the methods. The simulations showed HELP to be the most powerful method for resolution. The importance of the design variables was qualitatively studied by means of PLS models. Several parameters, among them the net analytical signal, were found to be unable to alone say anything conclusively about HELPs chances for successfully resolving the systems.

Fatty acid composition of wild mushroom species of order Agaricales—Examination by gas chromatography–mass spectrometry and chemometrics

Applying gas chromatography-mass spectrometry of 4,4-dimethyloxazoline fatty acid derivatives, the fatty acid composition of 15 mushroom species belonging to 9 genera and 5 families of order Agaricales growing in Bulgaria is determined. The structure of 31 fatty acids (not all present in each species) is unambiguously elucidated, with linoleic, oleic and palmitic acids being the main components (ranging between 70.9% (Marasmius oreades) and 91.2% (Endoptychum agaricoides)). A group of three hexadecenoic positionally isomeric fatty acids, 6-, 9- and 11-16:1, appeared to be characteristic components of the examined species. By applying chemometrics it was possible to show that the fatty acid composition closely reflects the classification of the species.

Experimental designs for modeling retention patterns and separation efficiency in analysis of fatty acid methyl esters by gas chromatography–mass spectrometry

The retention behavior of components analyzed by chromatography varies with instrumental settings. Being able to predict how changes in these settings alter the elution pattern is useful, both with regards to component identification, as well as with regards to optimization of the chromatographic system. In this work, it is shown how experimental designs can be used for this purpose. Different experimental designs for response surface modeling of the separation of fatty acid methyl esters (FAME) as function of chromatographic conditions in GC have been evaluated. Full factorial, central composite, Doehlert and Box-Behnken designs were applied. A mixture of 38 FAMEs was separated on a polar cyanopropyl substituted polysilphenylene-siloxane phase capillary column. The temperature gradient, the start temperature of the gradient, and the carrier gas velocity were varied in the experiments. The modeled responses, as functions of chromatographic conditions, were retention time, retention indices, peak widths, separation efficiency and resolution between selected peak pairs. The designs that allowed inclusion of quadratic terms among the predictors performed significantly better than factorial design. Box-Behnken design provided the best results for prediction of retention, but the differences between the central composite, Doehlert and Box-Behnken designs were small. Retention indices could be modeled with much better accuracy than retention times. However, because the errors of predicted tR of closely eluting peaks were highly correlated, models of resolution (Rs) that were based on retention time had errors in the same range as corresponding models based on ECL.

Determination of Omega-3 Fatty Acids in Fish Oil Supplements Using Vibrational Spectroscopy and Chemometric Methods

The potential of Fourier transform infrared (FT-IR), near-infrared (NIR), and Raman spectroscopic techniques combined with partial least squares (PLS) regression (PLSR) to predict concentrations of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and total omega-3 fatty acids (n-3 FAs) in fish oil supplements was investigated. FT-IR spectroscopy predicted EPA (coefficient of determination (R2) of 0.994, standard error of cross-validation (SECV) of 2.90%, and standard error of prediction (SEP) of 2.49%) and DHA (R2 = 0.983, SECV = 2.89%, and SEP = 2.55%) with six to seven PLS factors, whereas a simpler PLS model with two factors was obtained for total n-3 FAs (R2 = 0.985, SECV = 2.73%, and SEP = 2.75%). Selected regions in the NIR spectra gave models with good performances and predicted EPA (R2 = 0.979, SECV =2.43%, and SEP =3.11%) and DHA (R2 = 0.972, SECV = 2.34%, and SEP = 2.60%) with four to six PLS factors. Both the whole and selected NIR regions gave simple models (two PLS factors) with similar results (R2 = 0.997, SECV = 2.18%, and SEP = 1.60%) for total n-3 FAs. The whole and selected regions of Raman spectra provided models with comparable results and predicted EPA (R2 = 0.977, SECV = 3.18%, and SEP = 2.73%) and DHA (R2 = 0.966, SECV = 3.31%, and SEP = 2.56%) with seven to eight PLS factors, whereas a simpler model (three PLS factors) with R2 = 0.993, SECV = 2.82%, and SEP = 3.27% was obtained for total n-3 FAs. The results demonstrated that FT-IR, NIR, and Raman spectroscopy combined with PLSR can be used as simple, fast, and nondestructive methods for quantitative analysis of EPA, DHA, and total n-3 FAs. FT-IR and NIR spectroscopy, in particular, have the potential to be applied in process industries during production of fish oil supplements.

Friedel—Crafts Acylation on Porous Divinyl Benzene Polymer Particles: A Reaction Kinetic Process Studied by Mid- and Near-Infrared Spectroscopy

Porous poly(para-divinylbenzene) and poly(meta-divinylbenzene) particles were synthesized from para-divinylbenzene and meta-divinylbenzene monomers with toluene and 2-ethylhexanoic acid as porogens. The residual vinyl groups in the particles were thereafter reacted with lauroyl chloride by using the Friedel–Crafts reaction. The conversion of vinyl groups was followed by analyzing polymer particles taken from the reaction mixture at different time intervals. Infrared spectroscopy in both the mid- and near-infrared region was used as the analytical technique. The intensity changes in the overtone absorption at 1628 nm due to the vinyl bonds were used as the basis for the quantification of the reaction. Spectra of the particles in the mid-IR region provide understanding of the changes taking place in the polymer matrix during the acylation reaction. The results indicated that the reaction took place at a faster rate in the polymer particles synthesized from para-DVB monomer compared with the poly(meta-DVB) particles. The polymer particles synthesized with toluene as porogen react faster than the polymer particles prepared with 2-ethylhexanoic acid as the porogen. The analysis also indicated that the acylation takes place at the early stages of the reaction and the product formed transforms into more stable products at the latter stages. On the basis of the infrared analysis, mechanisms for the formation of the different products are proposed.