The use of this MS/MS-based approach offers high specificity allowing TNT labels to be detected in a background of fragmentation noise. In addition, the MS/ MS detection means that tags can share the same mass as long their tag fragment ions are distinguishable from each other. This means that many TNTs can be detected in a compressed mass range. This feature combined with the relatively low overall mass required for TNTs, means that TNT technology will be able to exploit lower cost compact and portable ESI-MS/MS instrumentation that is currently under development (31) (32) (33) (34) (35) (36) .