Continuous on-line true titrations by feedback-based flow ratiometry. The principle of compensating errors
Continuous on-line true titrations by feedback-based flow ratiometry. The principle of compensating errors
复制标题
通过基于反馈的流量比率测定法进行连续在线真实滴定。
DOI：
10.1021/ac000598t
复制
发表时间：
2000
影响因子：
7.4
通讯作者：
Huang
中科院分区：
文献类型：
--
作者：
Tanaka;Dasgupta;Huang
介绍了一种基于反馈控制流量比法和误差补偿原理的连续在线滴定新概念。该系统已通过将其应用于酸碱中和滴定与基于指示剂的终点检测进行了全面测试。在典型的情况下，总流量（FT，由样品和滴定剂流量组成）保持恒定，而滴定剂（例如，包含指示器的标准基底）流量FB响应于控制器输出电压而线性变化。样品（例如，待滴定的酸性溶液）流量FA构成了补给，因此也变化（FA = FT-FB）。混合液流中指示剂颜色的状态由光学检测器监测，用于控制控制器输出或解释滴定结果。三种方法（基于PID的控制，固定三角波控制，并在PC上实现基于反馈的三角波控制）进行了检查。在最后一种也是最成功的方法中，滴定剂流最初线性地向上倾斜。在检测器感测到颜色变化的瞬间，滴定剂流速FH高于真实当量流速FE，因为第一成分变化与其检测之间存在滞后时间。感测到颜色变化会导致系统输出立即反转其斜坡方向，从而滴定剂流量现在以相同的速率线性下降。在再次感测到颜色变化的瞬间，此时在相反的方向上，滴定剂流速FL比FE低与FH比FE高的量完全相同的量。这种补偿误差的原理（FE =（FH + FL）/2）允许具有优异的再现性和速度的真实滴定（在3秒/滴定时0.6%RSD和在10秒/滴定时0.2%RSD）和低至12微升/滴定的滴定剂体积消耗，并且解决了基于流动的滴定中的旧概念问题。
We introduce a new concept for continuous on-line titrations based on feedback-controlled flow ratiometry and the principle of compensating errors. The system has been thoroughly tested by applying it to acid-base neutralization titrations with indicator-based end point detection. In a typical case, the total flow (FT, consisting of the sample and the titrant flows) is held constant while the titrant (e.g., a standard base containing an indicator) flow FB varies linearly in response to a controller output voltage. The sample (e.g., an acidic solution to be titrated) flow FA constitutes the makeup and thus also varies (FA = FT - FB). The status of the indicator color in the mixed stream is monitored by an optical detector and used either for governing the controller output or for interpreting the results of the titration. Three methods (PID based control, fixed triangular wave control, and feedback-based triangular wave control implemented on a PC) were examined. In the last and the most successful approach, the titrant flow is initially ramped upward linearly. At the instant a change in the color is sensed by the detector, the titrant flow rate FH is higher than the true equivalence flow rate FE because of the lag time between the first compositional change and its detection. The sensing of the change in color causes the system output to immediately reverse its ramp direction such that the titrant flow now goes down linearly at the same rate. At the instant a change in color, in the opposite direction this time, is again sensed, the titrant flow rate FL is lower than FE by exactly the same amount that FH was higher than FE. This principle of compensating errors (FE = (FH + FL)/2) allows true titrations with excellent reproducibility and speed (0.6% RSD at 3 s/titration and 0.2% RSD at 10 s/titration) and titrant volume consumption as little as 12 microL/titration and solves an old conceptual problem in flow based titrations.