ABSTRACT
Objective To observe the influence of sodium citrate concentrations in TISAB on detection of water fluoride,and to explore the feasibility of 0.10 mol/L sodium citrate buffer system in detection of water fluoride.Methods Under pH 5.0 to 5.5,a series of fluoride standards of 0.2,0.5,1.0,2.0 and 5.0 mg/L were measured when sodium citrate concentration was 0.01,0.10,and 1.00 mol/L in the TISAB system.The results of water fluoride measurement were compared,recovery calculated and regression equation of the standard curve was set up.The feasibility of 0.10 mol/L sodium citrate in the TISAB system to detect water fluoride was tested,including interference test,accuracy,confidence limits,as well as precision test.Water fluoride was determined by fluoride ion selective electrode according to the Standard Test Methods for Drinking Water (GB/T 5750.5-2006).Results When the sodium citrate concentrations in the TISAB system were 0.01,0.10 and 1.00 mol/L,and the concentrations of fluoride in the sample were 0.2,0.5,1.0,2.0 and 5.0 mg/L,recoveries of water fluoride were 96.0％,103.0％,179.5％; 80.6％,97.8％,132.2％; 73.3％,97.0％,103.0％; 70.0％,100.0％,87.5％; and 66.4％,102.0％,65.4％.The equation of linear regression was y =lg-1(226.4-E/47.4),y =lg-1(226.4-E/53.4) and y =lg-1(208.1-E/36.9) ; the correlation coefficient(r) were 0.9993,0.9999 and 0.9993.The minimum detectable concentration and limit of quantitation was 0.023 and 0.072 mg/L when sodium citrate was 0.10 mol/L in the TISAB system.Aluminum(Al3+,100 μg),ferrum(Fe3+,800 μg),calcium(Ca2+,1200 μg),Al3+(50 μg) + Fe3+ (800 μg),Al3+(50 μg) + Ca2+(1200 μg) can be masked when sodium citrate was 0.10 mol/L in the TISAB system.The total average recoveries confidence limit R/d was 0.99.The total standard deviation of standard solution,water sample and spiked water sample was less than 5％ of their respective mean concentration.Conclusions High concentration of sodium citrate buffer system has a significant influence on the detection sensitivity and limit of quantification of fluoride ion in water.The capacity of anti-interference of 0.10 mol/L sodium citrate in the TISAB is strong.The confidence limits of precision and accuracy meet the requirements for fluoride determination in a variety of source water and drinking water.