Microwave-assisted sample preparation in analytical chemistry

The speed and efficiency of instrumentation for chemical analysis has improved dramatically over the past twenty years. Until recently, however, methods of sample preparation had not changed to keep pace, so this had become the slowest step in analytical chemistry methodology. The widespread adoption of domestic microwave ovens during the past twenty-five years has eventually led to their usage in chemical laboratories. Microwave technology has now advanced to the point where it is revolutionizing chemical sample preparation and chemical synthesis. Since the first application of a microwave oven for sample preparation in 1975, many microwave-assisted dissolution methods have been developed - these are applicable to virtually any kind of sample type. This review attempts to summarize all the microwave-assisted dissolution and digestion methods reported up to and including 1994. In addition, some very recent developments in continuous-flow automated dissolution systems are discussed, as is the emergence of databases and software packages related to the application of microwave technology to sample dissolution. There are 344 references.     

Improved locally adaptive least-squares detection of differences in images

We introduce a method for change detection under nonuniform changes of intensity using an improved least-squares method. A locally adaptive normalizing window is correlated with the two images, and a morphological postprocessing is then applied to isolate objects that have been added or removed from the scene. We use a modification of the least-squares solution to get rid of clutter caused by intensity changes that do not satisfy the model assumed for the least-squares solution.     

Non-linear absorption and fluorescence of chlorophyll a excited by a ruby laser

Excitation of chlorophyll a in solution by a Q-switched ruby laser permits the determination of the two-photon and excited singlet state cross sections from fluorescence and transmission measurements.     

Refinements to the diastereoisomer-specific method for the analysis of hexabromocyclododecane

The emergence of hexabromocyclododecane (HBCD) as a bromine-based flame retardant of concern is partly attributable to recent measurements on the environmental occurrence of the individual diastereoisomers (alpha, beta and gamma). These measurements were fuelled by a newly developed liquid chromatography/tandem mass spectrometric (LC/MS/MS)-based analytical method. However, in the course of our recent studies on the environmental fate and behaviour of the diastereoisomers of HBCD, some interesting features of the LC/MS/MS method became apparent. For example, the ion signal of the native ions was found to be dependent on the final extract volume. This was true for both biotic and sediment samples and was found to arise from the suppression of the ion signal due to endogenous material in the extracts that escape clean-up. We have also found differences in the stability of the diastereoisomers in different solvents. If left unaccounted for, both factors can compromise analytical measurement data. By way of a series of controlled experiments conducted at our two laboratories [Department of Fisheries & Oceans Canada (DFO) and Environment Canada (EC)], we illustrate these features and demonstrate that use of newly synthesized labelled HBCD isomers [(13-carbon (13C) and deuterium (d18)] can minimize and often circumvent matrix-related effects.     

Tailoring photonic crystals with nanometer-scale precision using polyelectrolyte multilayers

In this paper, we describe a rapid, accurate, and convenient method for postsynthetically tuning the optical properties of colloidal photonic crystals. High quality photonic crystal films are first synthesized and then coated iteratively with layers of water-soluble polyelectrolytes. The coating process results in nanometer-scale shifts in the photonic stop band, a process which has been monitored by theoretical modeling. The results suggest a fundamentally different, reproducible layering mechanism inside the confined spaces of the colloidal crystal where polyelectrolyte multilayers are less densely packed.     

Homomorphic cameo filter for pattern recognition that is invariant with changes in illumination

We introduce a new matched filter method that yields correlation peaks that are invariant with changes in the illumination of any targets. A scene containing objects at unknown locations is first subjected to a logarithmic transformation that changes the multiplicative constant to an additive background, which is then discriminated against by means of a composite filter containing a cameo of the true target and a term with which to discriminate against other false targets. Experimental results are shown.