The development of analytical methods for the analysis of explosives and peptides are described. Improvements of chromatographic and mass spectrometric methods and/or instrumentation have been accomplished for this purpose. A fast gas chromatography (GC) method was developed for the analysis of organic high explosives (nitrate esters, nitroaromatics and nitramine), which allows the separation of nine compounds in less than 2.5 minutes. The fast separation method was initially developed as a screening method using a pulsed-discharge electron capture detector (PDECD). The detection limits for all the explosives studied varied between 5 and 72 fg on-column.
A novel way to perform tandem mass spectrometry (MS) in quadrupole ion traps (QITs) was then developed to increase the confirmatory power of the detection system while meeting the high duty cycle requirements of the fast separation method. The new tandem MS method is termed dynamic collision-induced dissociation (DCID). DCID performs the excitation of ions during the mass scanning step and therefore reduces the amount of time required for tandem MS analysis. DCID was implemented on a Finnigan PolarisQ mass spectrometer using only software modifications. Combined with faster mass scanning, DCID allows QITs to operate in tandem MS mode at an acquisition rate compatible with fast GC. When interfaced with the fast explosives separation method described above using negative chemical ionization (NCI) and selected reaction monitoring (SRM), DCID permits detection limits varying between 0.5 and 5 pg for the same group of explosives.
Peptides were also analyzed using DCID and fragmentation patterns similar to those obtained with conventional CID were obtained. The identification of peptides from b-y ions in positive mode and some c-z ions as well as b-y in negative mode was demonstrated. The results are compared and contrasted with conventional CID and high amplitude short time excitation (HASTE). The analysis of peptides demonstrated that DCID could fragment larger molecules with greater energetics than conventional CID—as demonstrated by the product ion distribution of leucine enkephaklin—but at typically much lower CID efficiencies (~20%). The analysis of tryptic digests using high-performance liquid chromatography (HPLC) in conjunction with DCID tandem MS is also described. The analysis of tryptic digests demonstrates that DCID must be improved to become a more universal energy transfer method, especially for larger molecules.