Colour analysis sample types

Numerous CE separations have been published for synthetic colours, sweeteners and preservatives (Frazier et al., 2000a Sadecka and Polonsky, 2000 Frazier et al., 2000b). A rapid CZE separation with diode array detection for six common synthetic food dyes in beverages, jellies and symps was described by Perez-Urquiza and Beltran (2000). Kuo et al. (1998) separated eight colours within 10 minutes using a pH 9.5 borax-NaOH buffer containing 5 mM /3-cyclodextrin. This latter method was suitable for separation of synthetic food colours in ice-cream bars and fmit soda drinks with very limited sample preparation. However the procedure was not validated for quantitative analysis. A review of natural colours and pigments analysis was made by Watanabe and Terabe (2000). Da Costa et al. (2000) reviewed the analysis of anthocyanin colours by CE and HPLC but concluded that the latter technique is more robust and applicable to complex sample types. Caramel type IV in soft drinks was identified and quantified by CE (Royle et al., 1998). 

Once a series of samples is placed on the carousel, the analysis proceeds automatically with a cycle of approximately 3 minutes (including complete wash-out of the previous samples). When a representative sample flUs the two detector cells, the flow is stopped and the measurements are collected from the instruments. When stable readings are obtained, they are compared with the data on file for the sample type and then presented to the analyst for acceptance. Measurements for colour are also possible with suitable changes in the design. Figure 7.2 shows the communication hnes required and the protocols necessary to consolidate and operate the system. Such a system has been in operation on a routine basis for several years in a major fragrance and flavour company in the UK. 

Vegetation has been classified into a number of reaction types (Ernst, 1993). Within the group of plants that react to their environment (reactors), those with visible (or overt) reactions can be distinguished from those with non-visible (or covert) reactions. In the case of geobotany as defined by Ernst (1993), visibility means to the unaided human eye, that is colour, morphology, presence, abundance or absence of species. Cole has pointed out (Cole and Smith, 1984) that is was not until about 1945, when rapid routine methods of analysis for large numbers of samples became available, that biogeochemistry, that is the study of the chemical composition of plants from various habitats, was used for mineral exploration in many parts of the world. 

Both types of problems are common in the different branches of Chemistry. For example, in Qualitative Chemical Analysis one is frequently faced with a solution containing several unknown cations and anions. The analyst must carry out a pre-established series of reactions, and according to the results must rule out or confirm the presence or absence of the more usual cations and anions. This procedure allows the analyst, depending on the results (formation of precipitates, turbidity, colour reactions in the solution, etc.), to deduce the composition of the problem sample. Qearly, this is an example of a causation problem, because the procedure is pre-established, the results are in plain view and the objective is to know what solution composition is compatible with the results obtained (Martinez-Luaces, 2011). 

In samples 245-256, with narrow red and dark blue stripes, the Cu (red) and Co (blue) are rarely measurable, although the As, which is associated with Co, is often measurable at low levels. This shows that for this type of multi-coloured bead, bulk elemental analysis must be used in conjunction with visual inspection of beads and bead fiagments. 

NIRA was used for the analysis of the dyeabil-ity of textured PA6 carpet yarns (one quality type) with C.I. Blue 127 1 and luminosity measurements of partially oriented polyester-yarns [316]. NIR diffuse reflectance spectroscopy has been used to investigate dye uptake potential of PET fibres [326]. NIRS has been used for evaluating colour deviations in different production batches of the acid dye Tec-tilon Red 2B [327]. If an adequate number of samples are available to generate robust regression models, then NIRS can be used as a QC tool to evaluate the dye using only drying and grinding for NIRS sample preparation. 

See also Chapter 7.) As explained in section 2.3.3, data from a series of mid-IR spectra recorded from consecutive, contiguous, masked or selected regions of a sample may be processed to produce, for example, a species concentration map of the sample area. This map may be based on such as relative absorbance band intensity, an absorbance band ratio, a principal component (PC) derived from a multivariate analysis routine, or a cluster from a classification analysis. The map may be presented as a grey-scale image or a false-colour image based on such as an intensity difference or species type. 

A type of automatic analysis in which samples are mixed with reagents by means of plastic tubes, the solutions then being continuously pumped through a number of modules in which reaction takes place, finally passing to a flow-through colorimeter where the intensity of the colour is measured. The Technicon company manufactured the first commercial continuous flow analyser and since then have produced more sophisticated machines. It is these that will be described ... 

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