- 期刊
微電腦輔助之自動電位滴定
Computer-Controlled Automatic Potentiometric Titration
摘要
傳統的電位滴定(Potentiometric Titration)是以滴定管來進行滴定，在每加入一定量的滴定液後，便記錄所加入的體積以及電位針所測得之電位或pH值，然候在整個滴定過程結束後，再將所記錄之滴定液體積和電位數據在方格紙上逐一描點輸出滴定曲線；此一操作過程，不但煩瑣、費時，而且滴定終點(即當量點)的決定往往亦不甚容易。本實驗改用蠕動泵來取滴定管，並利用微電腦經由數位／類比轉換器(DAC)提供一適當的電位給蠕動泵，以控制其轉速，使其以一恆定流速加入滴定液以進行滴定；同時，由電位計所測得之電位值，則經由運算放大器(Operational Amplifier)作適當放大後，再經過類比／數位轉換器(ADC)轉換成數位訊號後，送回微電路，經由軟體程式設計直接在電腦磁示幕上作立即顯示。整個滴定過程所測得之數據並可經由軟體程式的設計，作各種必要的數據處理，如繪圖、平滑(Smoothing)處理、一次微分、二次微分等，可使當量點的判定快而容易；故藉由蠕動泵及微電腦的應用，可順利地達成電位滴定自動化的目的。本實驗並將此微電腦輔助之自動化滴定系統，應用在電位滴定法中的酸鹼滴定與沉澱滴定，分別測定未知樣品中的碳酸納及氯離子的含量，分析結果與確認值間之相對百分誤差皆在2%以內，證實本系統具有很高的準確性，而適用於真實樣品的滴定分析。
關鍵字
無資料並列摘要
Traditional potentiometric titration was done manually by a buret. After each addition of titrant, the volume added and the corresponding potential (or pH) reading were recorded. At the end of titration, the titration curve was then plotted point by point, which is tedious and time-consumming, In addition, the equivalent point often is not easy to be determined directly. A microcomputer-controlled automatic titration system was presented in this paper. The titrant was added by a peristaltic pump and the speed, start/stop of the pump was controlled by the microcomputer through a D/A converter. The corresponding potential readings were amplified and were then sent back to the microcomputer for storage and immediate display through an A/D converter. At the end of titration, the observed titration curve can be easily smoothed, or through a mathematic operation to obtain the first-derivative or the second-derivative curve from which the eqivalent point can be easily determined. This automatic titration system was applied for the determinations of Na_2CO_3 and Cl^-, respectively, in two reference material. The results were in good agreement with the certified values.