Comparatively few papers are devoted to the high-performance liquid chromatographic (HPLC) analysis of basic' compared to acid dyes2g3 and most of this literature is concerned with individual or a narrow range of basic dyes1v4.
The aim of this study was to develop an HPLC system which would be capable of separating and detecting a range of synthetic basic dyes used in the dyeing of acrylic fibres.
A silica column with a buffered (pH 9.7) water-methanol eluent was found to provide an acceptable separation system for the twenty-one commercial basic dyes available. A gradient elution program was used which varied the buffer concentration while maintaining a 9:l ratio of methanol and buffer.
EXPERIMENTAL
The equipment consisted of two Waters Assoc. Model 510 HPLC pumps, a Water Assoc. Model 680 gradient controller and a Shandon (160 x 4.5 mm I.D.) stainless-steel column. This was packed with Phase Sep Spherisorb silica (5 pm). A Rheodyne valve injector fitted with a 20-~1 sample loop was used. Detection was mainly by a Waters 990 photodiode array detector coupled to a NEC-APCl 11 computer and Waters 990 printer/plotter. Initial experiments were carried out using a Pye-Unicam LC-UV detector and Phillips PM8251 single pen recorder.
UV-VIS spectra were determined between 200 and 800 nm on a Hewlett-Packard HP 8450 diode array spectrophotometer using a l-cm pathlength.
Reagents Mobile phase.
A volume of 94 ml of concentrated ammonia and 21.6 ml of concentrated acetic acid were added to 884 ml of glass distilled water and the pH adjusted to pH 9.76 using either cont. ammonia or cont. acetic acid. The buffer was diluted with glass distilled water (1:3) as required for solvent B. 100 ml of buffer was mixed with 900 ml of HPLC-grade methanol (Fisons) and the eluents filtered under vacuum through a Gelman 0.2~pm FF Vericel TM membrane filter. All solvents were degassed for 30 min in the Decon FS200 ultrasonic bath before use.
Standards. Fifteen basic dyes were obtained from Ciba Geigy and nine from Bayer U.K. (see Table I). Basic blue 7 was obtained from Aldrich. Solutions of these