A mixed indicator strip for phosphine detection

A rapid, sensitive and reliable mixed indicator paper strip impregnated with dimethyl yellow (0.05%), cresol red (0.1%) and mercuric chloride (1.0%) in methanol has been developed for the detection of phosphine (PH₃) in air at the permissible level (TLV). The paper strip turns red in the presence of phosphine. It is highly sensitive and has better shelf-life than indicator strips impregnated with dimethyl yellow plus mercuric chloride or cresol red plus mercuric chloride.