Coupling photochemical reaction detection based on singlet oxygen sensitization to capillary electrochromatography

Despite the impressive separation efficiency afforded by capillary electroc hromatography (CEC), the detection of UV-absorbing compounds following sepa ration in capillary dimensions remains limited by the short path length (5- 75 mu m) through the column. Moreover, analytes that are poor chromophores present an additional challenge with respect to sensitive detection in CEC. This paper illustrates a new photochemical reaction detection scheme for C EC that takes advantage of the catalytic nature of type II photooxidation r eactions. The sensitive detection scheme is selective toward molecules capa ble of photosensitizing the formation of singlet molecular oxygen (O-1(2)). Following separation by CEC, UV-absorbing analytes promote groundstate O-3 (2) to an excited state (O-1(2)) which reacts rapidly with tert-butyl-3,4, 5-trimethylpyrrolecarboxylate, which is added to the running buffer. Detect ion is based on the loss of pyrrole. The reaction is catalytic in nature si nce one analyte molecule may absorb light many times, producing large amoun ts of O-1(2). The detection limit for 9-acetylanthracene, following separat ion by CEC, is similar to 6 x 10(-9) M (S/N = 3). Optimization of the facto rs effecting the S/N for four model compounds is discussed.