Analysis of citrate in low-volume seminal fluid samples using a time-gated measurement of europium luminescence

This work aims to develop and validate a rapid analytical method that enables the measurement of citrate in seminal fluid samples. Samples were obtained from men who were within 9 weeks of a vasectomy operation. Two age ranges were examined, between 40–43 and 50–53 years old, with nearly 100 samples in each case. No patient clinical history was available for this anonymous study, simulating a random screening cohort. The concentration of citrate in 0.5 μL seminal fluid samples was assessed, using a europium emission luminescence method. This involves the ratiometric analysis of two well-separated europium(III) emission bands. Spectral data were obtained using a time-gated spectrometer whose construction and modification is described. Citrate values were confirmed by independent measurements using a citrate lyase enzymatic assay and by 700 MHz 1H NMR analysis of the seminal fluid. Citrate concentrations were not statistically different between age groups and averaged 35.0(±14.6) mM for the 40–43 group, and 28.2(±12.7) mM for the 50–53 cohort; in each case a polymodal distribution was observed.