Fibres, sample preparation methods

See also Fibre Optic Probes in Optical Spectroscopy, Clinical Applications IR Spectrometers IR Spectroscopy Sample Preparation Methods IR Spectroscopy, Theory Medical Science Applications of IR. 

As microwave sample preparation has evolved, standard microwave procedures have been developed and approved by numerous standard methods organisations (ASTM, AOAC International, EPA, etc.), see ref. [64]. Examples are standard test methods for carbon black/ash content (ASTM Method D 1506-97), lead analysis in direct paint samples (ASTM Method E 1645-94), etc. Table 8.15 shows some microwave ashing references (detection weight). A French AFNOR method utilises the atmospheric pressure single-mode microwave method as an alternative sample preparation procedure for Kjeldahl nitrogen determination [84], The performance of a microwave-assisted decomposition for rapid determination of glass fibre content in plastics for QC has been described [85]. 

Elaboration of the method for the identification of colour compounds by RPLC MS should comprise four steps (1) spectral characterization of reference materials (standards) and subsequent optimization of detection parameters, as well as those of their chromatographic separation (2) analysis of natural dyestuffs used as colouring materials in historical objects (3) analysis of model samples (dyed fibres, paintings) prepared according to old recipes (4) application of the acquired knowledge to identification of colourants present in historical objects. 

A fast, direct and non-destructive method involving no sample preparation was developed for recording a well-resolved and reproducible spectmm of special acrylic fibre (SAF), a precursor for carbon fibre using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. A novel method was developed for determining the composition of SAF containing both acrylate and carboxylic acid comonomers. The special feature is that no standard samples (of known composition) are required. 11 refs. 

Another procedure for dealing with samples insoluble in counting solution is to support them on a medium such as paper strips, filter discs, glass fibre or DEAE cellulose prior to adding them to a counting vial [235-237]. As indicated earlier, use of this has been in chromatography where the spot has been cut out of the paper or scraped from the plate. Although useful for materials insoluble in scintillator fluid, self-absorption for tritiated samples may constitute a major drawback in this technique, just as it does for the suspension methods. It should be evident why the recent developments in in combustion procedures are so important in the problem of sample preparation. 

Near-IR light-fibre spectroscopy is particularly well suited for assessing product quality of polymeric materials, with minimal or no sample preparation. This is actually one of the most active fields in the application of NIRS to polymers. However, it is necessary to have reasonably accurate training sets of the types of polymer to be analysed. NIRS has replaced many conventional methods in polymer analysis. Methods exist for the determination of OH number, acid value, chain length and cross-linking, methyl and methylene end-groups, primary... 

The statistical analysis method of discriminant analysis [342] has been combined with NIRA to identify dissimilar textile products. Most textile fibres, yarns, and fabrics have chemical structures which yield complex NIR spectra, and as such these species normally require three or more wavelengths to classify the material. Discriminant analysis is simple to use, rapid, and does not require extensive, time-consuming sample preparation and analysis. Polyester staple fibres of different tenacity levels have different fabric dyeing properties. NIRA method with discriminant analysis successfully identifies and classifies the polyester staple samples by tenacity level and thus provides a quick technique for identification of polyester fibre anticipating quality problems [315]. Mitchell et al [343]... 

As PA-FTIR requires minimal or no sample preparation, it is a well-suited method for nondestructive analysis of fibres. PA-FTIR has been used for single fibre sampling (forensic application) and as a tool for identifying surface coatings on fibres [485]. The PAS method allows investigation of the surface treatment of wool fibres [486]. PA-FTIR polarised light measurements can be used to study molecular orientation in drawn fibres and films. 

The solvent-free micro extraction technique SPME is an important step towards the instrumentation and automation of the SPE technique for online sample preparation and introduction to GC-MS (Zhang et al., 1994 Eisert and Pawliszyn, 1997 Lord and Pawliszyn, 1998). It involves exposing a fused silica fibre coated with a liquid polymeric material to a sample containing the analyte. As an extraction and enrichment technique it compares to P T methods (MacGillivray et al., 1994). Also derviatization steps can be coupled to the extraction process for polar compounds and improved efficiencies (Pan et al., 1997). The typical dimensions of the active fibre surface are 1 cm X100 pm. 

The main features of PC are low cost, need for small sample amount, high level of resolution, ease of detection and quantitation, simplicity of apparatus and use, difficult reproducibility (because of variation in fibres) and susceptibility to chemical attack. Identification of the separated components is facilitated by the reproducible Rj values. Detection methods in PC have been reviewed [368]. Fluorescence has been used for many years as a means of locating the components of a mixture separated by PC or TLC. However, also ATR-IR and SERS are useful. Preparative PC is unsuitable for trace analysis because filter paper inevitably contains contaminants (e.g. phthalate esters, plasticisers) [369]. For that purpose an acceptable substitute is glass-fibre paper [28]. 

The purpose is to test yams intended for use with wool, and which should withstand dyeing by all the methods that may be used for the protein fibre. The yams should be knitted into fabrics for the preparation of the samples. A pieee of the dyed material measuring 10 cmx 4 cm is placed between two pieees of undyed cloth and sewn round the edges. One undyed pieee should be of the same fibre as that of the sample undergoing test, and the other seleeted as follows ... 

---