An experimental study of sampling time effects on the resolving power of on-line two-dimensional high performance liquid chromatography

The experimental effects of sampling time on the resolving power of on-line LC × LC were investigated. The first dimension gradient time (1tg) and sampling time (ts) were systematically varied (1tg = 5, 12, 24 and 49 min; ts = 6, 12, 21 and 40 s). The resolving power of on-line LC × LC was evaluated in terms of two metrics namely the numbers of observed peaks and the effective 2D peak capacities obtained in separations of extracts of maize seeds. The maximum effective peak capacity and number of observed peaks of LC × LC were achieved at sampling times between 12 and 21 s, at all first dimension gradient times. In addition, both metrics showed that the “crossover” time at which fully optimized 1DLC and LC × LC have equal resolving power varied somewhat with sampling time but is only about 5 min for sampling times of 12 and 21 s. The longest crossover time was obtained when the sampling time was 6 s. Furthermore, increasing the first dimension gradient time gave large improvements in the resolving power of LC × LC relative to 1DLC. Finally, comparisons of the corrected and effective 2D peak capacities as well as the number of peaks observed showed that the impact of the coverage factor is quite significant.