titrimetric estimation of phosphate , molybdate , tungstate and sulphate with lead nitrate solution , using 1,2-naphthoquinone-2-semicarbazone-4-sulphonic acid ( nqs-4s ) and 1,2-naphthoquinone-2-thiosemicarbazone-4-sulphonic acid ( nqts-4s ) as visual indicators .
C0036621
semicarbazone
C0039946
thiosemicarbazone