Flow-injection analysis–fluorescence detection for the in vivo on-line determination of calcium in blood with microdialysis sampling Original Research Article

Due to its high selectivity for calcium, calcein can be used as fluorescent indicator for the sensitive determination of calcium. A flow-injection on-line microdialysis system for in vivo monitoring of calcium in blood is developed. A microdialysis probe, implanted in the vein of rabbit, was perfused with perfusate at a flow rate of 5 μl/min. The concentration of calcium in the dialysate was determined on-line with a flow-injection fluorescence system. The dialysate sample volume was about 15 μl. The system was linearly related to the concentration of calcium in the range 0–80 μg/ml (r2=0.9968) with a detection limit (3σ) of 0.01 μg/ml and the sample throughput of 20 h−1. R.S.D. was <5% (n=11). The validation of using the no net flux method of quantitative microdialysis to measure concentration of calcium was evaluated in vitro and in vivo. The accuracy of this method was tested in vitro under steady-state conditions for three test solutions containing known concentration of calcium. The estimated concentration of calcium were 32±2, 42±2, and 49.5±0.9 μg/ml (mean±R.S.D.) in agreement with the actual concentrations of calcium in the test solutions which were 30, 40 and 50 μg/ml, respectively. In vivo, the estimated basal of calcium in dialysis sample from probe in the test animal’s blood was 33 μg/ml.