An investigation of internal pressures in capillary flow injection systems

Results of an investigation of pressure drops in a capillary flow injection (CFI) system are presented. Peristaltic and syringe pumps were used to drive reagents through a manifold employing fused silica capillaries (75 μm i.d.) as the reactor tubing. A comparison of pressure capabilities, baseline noise levels and reproducibility was performed. The maximum stable pressure for the peristaltic pump and syringe pump were 7.6 and 19.2 bar, respectively. The maximum stable pressures for the syringe pump varies with the inside diameter of the syringe. For the peristaltic pump, the percent relative standard deviation of the pressure drop was less than 2%. When no time was allowed for equilibration, the reproducibility of the syringe pump was between 6% and 10%. When equilibration time was allowed, however the reproducibility was also better than 2%. Reproducibility was also measured by using an enzyme catalyzed reaction with reaction periods as long as 242±1 s. Each pump showed baseline noise levels of less than 5 milliabsorbance units. Based on these observed values, practical considerations for designing CFI manifolds are also reported.