Jaap van der Weerd

Lysozyme distribution and conformation in a biodegradable polymer matrix as determined by FTIR techniques.

Lysozyme distribution and conformation in poly(lactic-co-glycolic acid)(PLGA) microspheres was determined using various infrared spectroscopic techniques. Infrared microscopy and confocal laser scanning microscopy indicated that the protein was homogeneously distributed inside the microspheres in small cavities resulting from the water-in-oil emulsification step. Part of the protein was observed at or near the cavity walls, while the rest was located within these cavities. Attenuated total reflectance (ATR) and photoacoustic spectroscopy (PAS) also showed that there is hardly any protein at the surface of the microspheres. Since this microsphere formulation gave a large burst release (ca. 50%), this burst release can not be caused by protein at the surface of the particles. Probably, the protein is rapidly released through pores in the PLGA matrix. Conformational analysis of lysozyme in the PLGA microspheres by KBr pellet transmission suffered from band shape distortion and baseline slope. Despite incomplete subtraction of the PLGA background, a characteristic band of non-covalent aggregates at 1625 cm(-1) was observed in the second derivative spectrum of the protein Amide I region. The other Fourier-transform infrared (FTIR) methods yielded similar results, indicating that the sample preparation procedure did not introduce artifacts. The observed aggregation signal may correspond to the protein adsorbed to the cavity walls inside the microspheres.

Simultaneous FTIR Spectroscopic Imaging and Visible Photography to Monitor Tablet Dissolution and Drug Release

PurposePrevious studies of hydroxypropyl methylcellulose (HPMC)-based tablet during exposure to water showed a number of ‘fronts’ moving into the tablet but led to contradictory interpretations. These fronts are related to water penetration into and dissolution of the tablet, but the exact nature can not be derived from visible photographic evidence. A method to study tablet dissolution simultaneously by Fourier transform infrared-attenuated total reflection (FTIR-ATR) imaging and macro-photography can assist in providing correct interpretation of the observed fronts.MethodsTherefore, the combination of macro-photography and FTIR-ATR spectroscopic imaging was developed and used to interpret the physical changes leading to the observed fronts. Buflomedyl pyridoxal phosphate (BPP), a coloured drug, was used as a model drug.ResultsThe quantitative results obtained by FTIR-ATR imaging enabled the attribution of the three observed fronts (inside to outside) to: (1) true water penetration, possibly combined with (partial) dissolution of buflomedyl pyridoxal phosphate (BPP); (2) total gellification of HPMC; (3) erosion front.ConclusionsThe method to study dissolution of a tablet simultaneously by FTIR-ATR imaging and macro-photography has been developed and used to obtain reliable interpretation of the fronts observed during tablet dissolution.

FTIR studies of the effects of pigments on the aging of oil

Abstract This study describes the changes in the infrared spectra of oil paint as a result of aging. The focus is on the influence of pigments on the long-term changes in the oil binding medium. Several naturally aged paints made with different pigments were analysed using Fourier-transform infrared spectroscopy (FTIR). One of the most pronounced effects observed in the infrared spectra of aging paint is the shifting and broadening of the carbonyl band due to the formation of carboxylic acids. Another effect of pigments on the oil binding medium is the catalysis of the hydrolysis of triglycerides, as indicated by the decreasing intensity of the ester absorption. Finally, the nature of the pigment included has a profound effect on the CH stretch absorptions. From these results it is clear that pigments can significantly alter the infrared spectra of drying oil, and should therefore be identified to ensure the correct assessment of the infrared spectra in drying oil paint.

Validation of macroscopic attenuated total reflection-fourier transform infrared imaging to study dissolution of swelling pharmaceutical tablets

Macroscopic attenuated total reflection (ATR) infrared imaging is applied to study the dissolution of realistically sized hydroxypropyl methylcellulose (HPMC) tablets. The water intake into in situ compacted tablets and pre-compacted tablets was studied as a function of compaction pressure. Rigorous analysis of the imaging datasets show that the speed of water intake into HPMC tablet is approximately 4 μm/min and is hardly affected by the studied range of compaction pressures or the type of ATR crystal used (diamond or ZnSe). This constant speed of water intake implies that leakage (“creeping”) of water into the space between the tablet and the ATR crystal does not occur. It is shown that the radius of the HPMC tablet initially expands to twice the original radius due to swelling.

Preparation Methods and Accessories for the Infrared Spectroscopic Analysis of Multi-Layer Paint Films

Abstract Several traditional paint samples were prepared for infrared spectroscopic analysis in a number of different ways. The methods applied include the formation of KBr pellets, squeezing of dissected or multi-layer samples in a diamond cell, embedding in a modern resin, and a new method in which a paint cross-section is embedded in KBr and polished from both sides to obtain a thin layer. Microtoming of a paint cross-section embedded in a modern resin was not successful. The various samples were analysed by infrared spectroscopy to assess the usefulness of these sample preparation techniques in the field of paintings research. The amount of information that can be derived from the infrared spectra obtained appeared optimal for sample preparation methods that allow the application of transmission techniques. The results obtained for specular reflectance techniques were of lesser quality, while no diffuse reflectance spectra could be obtained. The results can best be traced to a specific layer or structure in an inhomogeneous paint system if the layer structure of the sample is left intact, i.e., using specular reflectance of an embedded cross-section or transmission of a thin section obtained by doubly polishing a cross-section embedded in KBr.

Quantitative comparison of striated toolmarks

A comparison of striated toolmarks by human examiners is dependent on the experience of the expert and includes a subjective judgment within the process. In this article an automated method is presented for objective comparison of striated marks of screwdrivers. The combination of multi-scale registration (alignment) of toolmarks, that accounts for shift and scaling, with global cross correlation as objective toolmark similarity metric renders the approach robust with respect to large differences in angle of attack and moderate toolmark compression. In addition, a strategy to distinguish between relevant and non-relevant spatial frequency ranges (geometric details) is presented. The performance of the method is evaluated using 3D topography scans of experimental toolmarks of 50 unused screwdrivers. Known match and known non-match similarity distributions are estimated including a large range of angles of attack (15, 30, 45, 60 and 75°) for the known matches. It is demonstrated that the system has high discriminatory power, even if the toolmarks are made at a difference in angle of attack of larger than 15°. The probability distributions are subsequently employed to determine likelihood ratios. A comparison of the results of the automated method with the outcome of a toolmark comparison experiment involving three experienced toolmark examiners reveals, that the automated system is more powerful in correctly supporting the hypothesis of common origin for toolmarks with a large difference in angle of attack (30°). In return, the rate of toolmark comparisons that yield incorrect support for the hypothesis of common origin is higher for the automated system. In addition, a comparison between estimating known match and known non-match distributions using 2D and 3D data is presented and it is shown that for toolmarks of unused screwdrivers, relying on 3D is slightly better than relying on 2D data. Finally, a comparison between estimating known match and known non-match distributions for two different types of screwdrivers suggests, that the method may be used for comparing marks of other tools as well.

Identification of dyes on single textile fibers by HPLC-DAD-MS.

An HPLC-DAD-MS method is described to analyze textile dyes in different dye classes (reactive, basic, acid, direct, disperse). The described method is sensitive enough to analyze single fibers with a length of a few millimeters or less, which makes it suitable for forensic analyses. The current paper describes the information content of the acquired data as well as the results of a validation study, in which the repeatability, specificity, and limit of detection of the method were assessed by repeated measurements of nine different dyes in the mentioned dye classes. The mass accuracy (deviation generally <2 ppm) and absorbance spectra were found to be highly stable in several measurements over a period of 8 weeks. Deviation in retention times were observed and attributed to small experimental effects and a precolumn blockage. The results show that dye analysis is possible for most fibers with a minimum length of one or a few millimeters.

On the recovery of fibres by tape lifts, tape scanning, and manual isolation.

The recovery of fibre traces via tape lifting, tape scanning and manual isolation is investigated. The recovery efficiency of taping was determined using different tapes, donor textiles, and receptor textiles. It was determined that tape lifts generally recover over 90% of extraneous fibres that had been transferred by direct contact with a donor textile. The recovery via tape scanning was evaluated by the preparation of a set of 15 tapes that contained a number of target fibres on a background of other fibres. The tapes presented varying difficulty and were investigated by trained fibre examiners. The examiners were asked to locate the target fibres and to provide their opinion on the difficulty of the search. As expected, the efficiency decreases for more difficult searches. It was determined that the efficiency of the search was influenced by the microscopic illumination modes used by the examiner. A final experiment investigated the recovery by manual isolation of fibres from non-textile items. It was determined that all fibres from tie cables and knives were recovered, except in those cases where the recipient item contained many fibres. In addition, the examiners correctly sampled each of three fibre populations present on a sample of duct tape.

Understanding the visibility of blood on dark surfaces: A practical evaluation of visible light, NIR, and SWIR imaging

Bloodstains on dark surfaces are often difficult to detect due to a lack of contrast. Infrared photography is in many cases a solution as it enhances the contrast between blood and background. Still, on some surfaces bloodstains cannot be visualized. In this study, we investigate why bloodstains on certain surfaces are not detected and how visibility can be improved. Bloodstains on 166 dark fabrics were photographed by four different cameras and for each, the visibility of the bloodstains was scored. The spectral properties of the dark fabrics were examined as well as the properties of the dyes used to colour the textiles. In addition, spreading of the blood within the textile and the roughness of the material were taken into account. In the investigated set of textiles, visibility of blood is mainly determined by the spectral properties of the textile dye. In addition, a high surface roughness of the textile reduces the visibility.

Tracers as invisible evidence — The transfer and persistence of flock fibres during a car exchange

This study assessed the recovery of flock fibres used as a tracer in a car exchange scenario. Flock fibres were deposited onto a car seat (or model thereof) and their transfer and persistence was investigated after a real or simulated car exchange. The overall aim of this study was to achieve an optimal use of flock fibres as tracers, i.e. to be able to select a fit-for-purpose flock fibre, to be able to predict the amount of flock fibres to be recovered from crime related items, and to be able to use these numbers to exclude accidental uptake. The effect of a number of variables on the transfer and persistence of flock fibres was studied, including flock fibre length, car upholstery, and trousers material. Laboratory based experiments were undertaken first, followed by realistic field based experiments. The flock fibres were captured in a non-destructive manner through fluorescence photography. A Matlab algorithm enabled fast automated counting of flock fibres on the images. Results indicate that an initial rapid loss of flock fibres from garments may be expected as a result of moderate movement. Although the amount of flock fibres to be recovered is affected by the flock fibre length, the type of car upholstery, and the type of trousers materials (if frictional force is taken into consideration), large numbers of flock fibres have been recovered from all target materials throughout the transfer route. These numbers are higher than the amount of flock fibres recovered due to accidental uptake. In conclusion, flock fibres can serve as invisible evidence to reconstruct a series of events.