Objective: To establish a continuous flow injection analysis with potassium permanganate for determination of oxygen consumption in water. Methods: The water samples and acid potassium permanganate working solutions were mixed using the continuous flow bubble spacing, and subjected to online heating reaction at 97 ℃. The peak height of the electrical signal of potassium permanganate was measured at the maximum absorption wavelength of 520 nm, and the standard substance, sulfuric acid concentration and potassium permanganate concentration were optimized according to the peak height of the electrical signal. The standard curve was plotted to measure the limit of detection, the limit of quantification, and spiked recovery rate of the method. The CODMn concentration was determined in 40 drinking water samples using acid potassium permanganate titration and continuous flow injection analysis using potassium permanganate, and the determination results of the two methods were compared with paired t-test. Results: Glucose was selected as the standard substance, and the mixture of 17.5% sulfuric acid and 3.2 mmol/L potassium permanganate was selected as the working solution. CODMn had a good linear relationship at concentrations of 0 to 6.00 mg/L, with a correlation coefficient of 0.999 and higher, a detection limit of 0.013 mg/L and a quantitation limit of 0.043 mg/L, respectively. The spiked recovery rates were 90.00% to 105.00% in 40 drinking water samples, with relative standard deviations of 0.12% to 1.36%. The determination results of two permanganate index standard substances were all within the range of standard values. The relative errors of CODMn concentration were 1.55% to 9.26% between the continuous flow injection analysis using potassium permanganate and acid potassium permanganate titration, and there was no significant difference (t=2.023, P=0.185). Conclusion The established continuous flow injection analysis with potassium permanganate is feasible for batch determination of oxygen consumption in water.

Objective:To investigate the value of using ultrasound excited contrast agents to assess extracorporeal hydrostatic pressure on the basis of ultrasound contrast imaging.Methods:An extracorporeal hydrostatic pressure evaluation system was established. The changes in contrast intensity was first evaluated for the same concentration of microbubble contrast agent at ambient pressures of 20, 25, 30, 35, 40, and 45 cmH 2O. Contrast agents with the same initial intensity were placed at different pressures for 1 s, 3 s, and 5 s, and the percentage change in contrast agent intensity was analyzed to select the optimal excitation time. Finally, the contrast agent at different pressures was stimulated using an acoustic excitation device, and correlation analysis was performed using the Pearson product moment correlation coefficient. Linear regression analysis was used to establish the relationship between different pressures and the percentage change in intensity. Results:When the ambient pressure was varied under 6 gradients of 20, 25, 30, 35, 40, and 45 cmH 2O, the contrast strength decreased with the pressure increased, and there was a negative correlation between contrast strength and the pressure ( r=-0.971, P<0.001). Under different pressures, the contrast agent intensity showed different degrees of natural decrease in 1 s, 3 s, and 5 s. The difference in the percentage change in contrast agent intensity in each pressure gradient was not statistically significant in 1 s ( P>0.05), whereas the differences in the percentage change in contrast agent intensity in 3 s and 5 s were statistically significant in each pressure gradient (all P<0.05). After microbubble contrast agent was stimulated by ultrasound excitation for 1s, the percentage change in contrast agent intensity was significantly correlated with ambient pressure ( r=-0.976, P<0.001). A linear regression model was fitted with the percentage change in contrast agent intensity after 1 s of stimulation as the independent variable and the pressure as the dependent variable, with the model equation: y=60.075-2.559×x1, where x1 is the percentage change in contrast agent ( R2=0.952, P<0.001). Conclusions:The percentage change in contrast intensity after 1 s of ultrasound excitation of microbubble contrast agent is a favorable predictor of hydrostatic pressure at 6 pressure gradients of 20, 25, 30, 35, 40, and 45 cmH 2O, which may provide a new method for noninvasive monitoring of portal vein pressure for clinicans.