A standard commercial thermospray interface was modified by replacing the stainless-steel capillary by another stainless-steel capillary with a larger internal diameter. A fused-silica capillary was then placed within the whole length of the stainless-steel capillary and connected to the liquid chromatograph. A thermospray interface modified in this way exhibits a more inert inner surface, resulting in an increased sensitivity for analysing sulfonzited azo dyes. Analysis of sub-microgram quantities is possible only with the modified interface.The azo dye 2-hydroxy-4-sulfonic acid-6-nitro naphthalene-1 ,lr-azo-2'-hydroxy naphthalene (AZO 4) is an intermediate product which is used for the synthesis of metal-complex azo dyes. A by-product formed during the synthesis of A Z O 4 was detected by UV and it needed to be analysed and characterized in order to improve the yield of A Z O 4.
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