A method was developed to determine glucosinolates in mustard seeds by reverse phase HPLC using volatile ion-pairing reagents followed by UV detection at 235 nm. Two external standards, phenethylglucosinolate and sinigrin were used to quantify results. The identities of individual mustard glucosinolates were confirmed by negative ion electrospray mass spectrometry as was LC peak purity. This LC/MS method may be used to identify species which are not commercially available as pure standards since mass spectrometry can be used to check for all known glucosinolate anions. Three mustard types were chosen from the Brassica species: yellow (Brassica hirta), brown, and oriental (Brassica juncea). Eleven mustard samples representing harvest areas of southwestern Canada were analyzed in triplicate for glucosinolate content. Percent coefficient of variation between triplicate samples of the same batch was often less than 10%