| Rapid determination of the concentration of acid and base is required in many industrial control processes. But at present, this kind of analysis was performed by acid-base titrations double-indicator titration method. The titration method was notoriously slow and requires rather large volume of samples and reagents thus not well suited for process control. A flow injection analysis (FIA) system is consisted by peristaltic pump, sample valve, mixed coil and detector. The FIA titration technique has been used in lots of applications, in classical acid-base FIA titration, a sample was injected into a carrier stream which contains indicator. On its way to the detector, the sample is dispersed into the carrier stream and thereby gradually mixed and neutralized in both the leading and tailing edges of the sample zone. The detector senses the output signal of every element of the mixture and the signal was recorded as a typical FIA peak. As the reagent concentration, the volume of injected sample and the flow rate were constants the observed peak width or peak area was proportional to the logarithm of the concentration of the sample. The concentration of the sample was detected by the FIA peak and the linear of the concentration of sample and the peak area or peak width. In recent years, much attention was attracted to flow injection titration for its advantages over conventional titration, including high sampling rate, low reagent and sample consumption, simplicity in instrumentation and versatility in solution handling. Material and time could be saved by using flow injection titration to replace manual batch titration. Traditionally, the detector of the FIA acid-base titration system is spectrophotometer. The method, however, was realized with the traditional indicator principle, which is not applicable to colored or turbid samples. And the color of solution will influence the detect result and precision.In this paper, a FIA titration method based on using a flat pH detector was developed for the first time to solve pH determination problems in industry. A simple, accurate and rapid online determination of acid-base system base on FIA was established. To evaluate the accuracy and feasibility, the total basicity, acidity and the concentration of mixed base was detected by this FIA system. The main results are as follows:(1) The concentration of NaOH and ammonia was detected by this FIA system, and calibration curves with good linearity were obtained in the concentration ranges of 1.93×10-40.0948 mol·L-1 for strong base NaOH and 2.66×10-45.32×10-2 mol·L-1 for weak base ammonia. (2) The concentrations of mixed base of Na2CO3 and NaOH and Na2CO3 and NaHCO3 were detected by this FIA system. And the calibration curves with good linearity were obtained in the total basicity ranges of 9.25×10-40.052 mol·L-1 for mixed base of Na2CO3 and NaOH and 9.96×10-40.061 mol·L-1 for Na2CO3 and NaHCO3.(3) The concentration of acetic acid was detected by this FIA system, and calibration curves with good linearity were obtained in the concentration ranges of 4.639×10-40.212 mol·L-1.(4) The total acid number of oil was detected by this FIA system.The results obtained in this paper indicate that the proposed method could be used in automatic FIA titration of strong base, weak base, acid and mixed base. To some extent, this flow injection analysis titration system can replace conventional titration for its advantages including high sampling rate, low reagent and sample consumption, simplicity in instrumentation and versatility in solution handling. The instrument combine the FIA with the ion selective electrode is easy to be automated and miniaturized. |
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