Laboratory Dyeing Techniques

Laboratory dyeing technique should simulate actual production conditions as closely as possible. It also should allow for a multiplicity of tests in a short period of time. Laboratory equipment permits dyeing of small (5 g) to larger (1 kg) textile samples. Most lab dyeing machines work batchwise, but installations for continuous operation are also available [29],... 

Protein Content. The protein content of milk can be determined using a variety of methods including gasometric, Kjeldahl, titration, colorimetric, and optical procedures (see Proteins). Because most of the techniques are too cumbersome for routine use in a dairy plant, payment for milk has seldom been made on the basis of its protein content. Dye-binding tests have been appHed to milk for determination of its protein content these are relatively simple to perform and can be carried out in dairy plant laboratories. More emphasis will be given to assessing the nutritional value of milk, and the dependence on fat content as a basis for payment will most likely change. 

A fully automated instrumental procedure has been developed for analyzing residual corrosion inhibitors in production waters in the field. The method uses ultraviolet (UV) and fluorescence spectrophotometric techniques to characterize different types of corrosion inhibitors. Laboratory evaluations showed that fluorescence is more suitable for field application because errors from high salinity, contamination, and matrix effect are minimized in fluorescence analysis. Comparison of the automated fluorescence technique with the classic extraction-dye transfer technique showed definite advantages of the former with respect to ease, speed, accuracy, and precision [1658],... 

Center for Healthcare Technologies at Lawrence Livermore National Laboratory in Livermore, potentially capable to measure pH at or near the stroke site29. The probe is the distal end of a 125 pm fibre tapered up to a diameter of 50 pm. A fluorescent pH-indicator, seminaphthorhodamine-1-carboxylate, is embedded inside a silica sol-gel matrix which is fixed to the fibre tip. Excitation of the dye takes place at 533 nm and the emission in correspondence of the acid (580 nm) and basic (640 nm) bands are separately detected. The use of this ratiometric technique obviates worrying about source fluctuations, which have the same effects on the two detected signals. The pH sensor developed was first characterised in the laboratory, where it showed fast response time (of the order of tens of seconds) and an accuracy of 0.05 pH units, well below the limit of detection necessary for this clinical application (0.1 pH units). The pH sensor was also tested in vivo on rats, by placing the pH sensor in the brain of a Spraque-Dawley rat at a depth of approximately 5 mm30. 

Another RP-HPLC technique has been applied for the determination of synthetic food dyes in soft drinks with a minimal clean-up. Separation of dyes was obtained in an ODS column (150 x 4 mm i.d. particle size 5 pm). Solvents A and B were methanol and 40 mM aqueous ammonium acetate (pH = 5), respectively. Gradient conditions were 0-3 min, 10 per cent A 3-5 min, to 25 per cent A 5-8 min, 25 per cent A 8-18 min, to 75 per cent A 18-20 min, 75 per cent A. The flow rate was 1 ml/min and dyes were detected at 414 nm. The separation of synthetic dyes achieved by the method is shown in Fig. 3.35. The concentrations of dyes found in commercial samples are compiled in Table 3.21. The quantification limit depended markedly on the type of dye, being the highest for E-104 (4.0 mg/1) and the lowest for E-102 and E-110 (1.0 mg/1). The detection limit ranged from 0.3 mg/1 (E-102 and E-110) to 1.0 mg/ml (E-104 and E-124). It was suggested that the method can be applied for the screening of food colourants in quality control laboratories [113]. 

Fluorescence assays are considered among the most convenient, sensitive, and versatile of all laboratory techniques. However, the purine and pyrimidine bases yield only weak fluorescence spectra. Le Pecq and Paoletti (1967) showed that the fluorescence of a dye, ethidium bromide, is enhanced about 25-fold when it interacts with DNA. Ethidium bromide, which is a relatively small planar molecule (Figure El3.4), binds to DNA by insertion between stacked base pairs (intercalation). The process of intercalation is especially significant for aromatic dyes, antibiotics, and other drugs. Some dyes, when intercalated into DNA, show an enhanced fluorescence that can be used to detect DNA molecules after gel electrophoresis measurements (see Chapter 4 and Experiments 14 and 15) and to characterize the physical structure of DNA. Two analyses of DNA will be completed in this experiment ... 

Few simple methods exist for estimating pKa for complex dye structures. However, complex artificial intelligence techniques combining the results of fundamental and empirical approaches have been developed which can predict pKa values for dye structures to within the experimental error of laboratory measurements. 

Having obtained (or been provided with) a representative sample the next stage will be to prepare the laboratory sample. There are again a number of points to consider, such as will the sample go off (decompose) or change over a period of time or under certain conditions (for example, the hydrolysis of reactive dyes) and does the sample absorb water from the environment (especially important where accurate weighings are required) as this may affect the results obtained by various techniques ... 

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