Multicomponent sample preparation techniques

Polymeric materials then, whether natural (such as cellulose, resins, and proteins) or synthetic (such as polyolefins, nylons, and acrylics), behave in reproducible ways when exposed to pyrolysis temperatures. This permits the use of pyrolysis as a sample preparation technique to allow the analysis of complex materials using routine laboratory instruments. Pyrolytic devices may now be interfaced easily to gas chromatographs, mass spectrometers, and FT-IR spectrometers, extending their use to solid, opaque, and multicomponent materials. Laboratories have long made use of pyrolysis for the analysis of paint flakes, textile fibers, and natural and synthetic rubber and adhesives. The list of applications has been expanded to include documents, artwork, biological materials, antiquities, and other complex systems that may be analyzed with or without the separation of various layers and components involved. 

This example further demonstrates the power of neutron scattering to extract structural information of individual components in a complex system by use of the contrast variation method. Contrast variation provides an additional sample preparation technique that allows the extraction of the scattering of a single component in a multicomponent mixture and broadens the utility of neutron scattering into fields such as the study of biological complexes and the structure of diblock copolymers (74). 

The type (e.g., liquid, solid, powder, gel, syrup, emulsion, granule) and range of food samples (raw ingredients to final products) for water activity measurement are immense. The amount of sample required for measurement is typically 5 to 10 ml. A homogeneous and representative sample should be prepared and placed into the sample cup. For the majority of samples, no preparation is necessary the sample is simply placed into the cup. Multicomponent (e.g., muffin with raisins or pizza) and coated samples (e.g., breaded foods or chocolate-covered bar) may have to be sliced, crushed, or ground in order to obtain a representative sample. If sample preparation is necessary, then a consistent technique must be used with each sample to ensure reproducible results. 

Synchronous scanning techniques have also been applied to the quantitative analysis of fluorescent substances. Synchronous scanning involves scanning both the excitation and emission monochromators simultaneously, while maintaining a constant wavelength interval between them. The technique has been employed in the analysis of multicomponent preparations. The technique is reported to simplify the spectra of multicomponent samples and reduce the bandwidths of fluorescence spectra. The equation relating the measured fluorescence to concentration is given by... 

Quantification requires knowledge of the beam path through the sample. Hence, the sample often needs to be modified to allow for a known geometry. Spectral subtraction, least square regression analysis, PLS and spectral deconvolution are some of the spectroscopic techniques widely used to quantify constituents in a multicomponent sample. For almost any type of spectroscopic analysis, this is usually the first step. It is especially important for polymers given the variations in spectra for the same polymer due to molecular weight, conformation, crystallinity, sample preparation, age and sampling method. 

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