Pigment purification method

Diatomite is tested from the mining bench through the production process to the bag. Methods depend in part on use. For use in pigments, there are ASTM (12) and military (13) specifications. Other specifications relate to use in the pulp (qv) and paper (qv) industry (14), in water (qv) purification (15), and for use in pharmaceuticals (qv) (16). 

TLC has been traditionally regarded as a simple, rapid, and inexpensive separation method, currently used mainly for preliminary examinations to give an indication of the number and variety of pigments present and help in the selection of suitable separation and purification procedures for further analysis. To avoid epoxy-furanoid rearrangements caused by inherent silica gel acidify, one pellet of a strong alkali such as KOH or NaOH should be added to the water used to make the thin layer, or in case of ready commercial plates, 0.1% triethylamine (TEA) should be added to the mobile phase. 

The solvent method may also be performed either by continuous (in cascades) or by batch operation. Continuous techniques in particular have gained considerable technical importance. A phthalonitrile/copper chloride solution is typically treated at 120 to 140°C in a flow tube furnace and the temperature subsequently increased to 180 to 250°C. The entire process requires approximately 1.5 to 2 hours and affords the pigment in practically quantitative yield. The excellent purity of the product eliminates the need for additional purification with dilute acid or base prior to finishing, a procedure which plays a major role in the baking process. These... 

The results of theoretical calculation using both general rate and transport-dispersive models were in good agreement with the overloaded band profiles determined experimentally, therefore, the method has been found to be suitable for the prediction of band profiles [88], Natural pigments were generally used as a complicated mixture of various compounds with chromophore substructure. Their separation by preparative RP-HPLC is not necessary, and the application of preparative RP-HPLC for the purification of one or more pigment fractions is not expected in the near future. 

As for Basic Protocol 1, the LOX enzyme is prepared according to the Support Protocol. However, more care should be taken to reduce turbidity and other UV-absorbing materials caused by suspended lipid and pigments, especially when low activity is expected (requiring more enzyme addition). Triton X-100 is a UV absorber, and it causes more lipid and pigments to be suspended. Partial purification may be necessary. HEPES and PIPES buffers are not used in this method because of excessive absorption at 234 nm (0.5 to 0.6 absorbance for 0.1 M solutions) MES is useful with limitations (0.2 absorbance for 0.1 M solution). 

No satisfactory method for the quantitative determination of bile pigments in urine has yet been evolved (W9). Direct spectrophotometry is impossible on account of the presence of yellow pigments other than bile pigments. Diazotization procedures necessitate the application of correction factors, which are not entirely adequate. Some purification can be effected by absorption of the bile pigments onto barium sulfate but their subsequent elution is by no means quantitative. 

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