[bssharat]

when doing analysis of sulphur dioxide, by west & Gaeke method, there is no formation of any colour. I added 1ml of standard sulphite-tcm solution,containing 6.4 microgram as SO2, then added 9 ml TCM solution, added 1ml sulphamic acid, waited 10 min, added 2ml formaldehyde,added 2ml pararosaniline chloride, made up volume 25ml with distilled water and waited for 30 min. but there is no colour formation. what went wrong?.