Post-column photochemical reaction detection in liquid chromatography based on photosensitized generation of singlet molecular oxygen: Study of reaction parameters and application to the determination of polychlorinated biphenyls

The parameters effecting the sensitivity and selectivity of a photochemical reaction detection scheme based on the reaction of 3-substituted pyrroles with singlet molecular oxygen (O-1(2)) in HPLC are reported. Polychlorinate d biphenyls (PCBs) were chosen as model compounds for the detection scheme. Following separation by reverse-phase chromatography, PCBs are excited by a Hg pen-ray lamp in a crocheted PTFE photochemical reactor. PCBs that are efficient O-1(2)-sensitizers promote ground state O-2((3)Sigma(g-)) to an e xcited state ((1)Sigma(g+) or 1 Delta(g)) which rapidly oxidizes 3-substitu ted pyrroles which are added to the mobile phase. Detection is based on the loss of pyrrole. The reaction is catalytic in nature since one analyte mol ecule may absorb light many times, producing large amounts of O-1(2) Detect ion limits for 4,4'-dichlorobiphenyl and Aroclors 1242, 1248 and 1254 were improved by 1-2 orders of magnitude over optimized UV-absorbance detection. Configuration of the photochemical reactor and judicious choice of the wav elength used to follow the loss of pyrrole were determined to be the most i mportant factors in terms of sensitivity of the detection scheme. Compariso n of three reagents (i.e. 3-substituted-pyrroles) used for trapping O-1(2) demonstrates the effect of substitution on sensitivity and to some extent s electivity of PCB determination.