Other Reagent Gases in PICI

Isobutane is an especially versatile reagent gas, because i) it provides low-fragmentation PICI spectra of all but the most unpolar analytes, ii) gives almost exclusively one well-defined adduct ([Mh-C4H9], [M+57]) if any (Fig. 7.7), and iii) can also be employed for electron capture (Chap. 7.4). 

Example In an overdose case where evidence was available for the ingestion of Percodan (a mixture of several common drugs) the isobutane-CI mass spectrum of the gastric extract was obtained (Fig. 7.8). [29] All drugs give rise to an [Mh-H] ion. Due to the low exothermicity of protonation by the tert-C Hi) ion, most [Mh-H] ions do not show fragmentation. Solely that of aspirin shows intense 

Reagent Gas Reactant Ions Neutral from Reactant Ions PA of Neutral Product Analyte Ions 

Note Resulting from the large excess of the reagent gas, its spectrum is of much higher intensity than that of the analyte. Therefore, Cl spectra are usually acquired starting above the m/z range occupied by reagent ions, e.g., above m/z 50 for methane or above m/z 70 for isobutane. 

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