Titration method (1) Potentiometric titration method: The beaker containing the test solution is placed on a magnetic stirrer, immersed in the electrode, stirred, and the titration solution is added dropwise from the burette; at the beginning, a larger amount can be added at a time. Stir and record the potential; until near the end point, add a small amount each time, stir, record the potential; until the jump point has passed, still continue to add several titrations, and record the potential. Tilmicosin Dosage,Tilmicosin Antibiotics,Tilmicosin Animal Health,Tilmicosin Pneumonia Shandong Shengli Bioengineering Co., Ltd , https://www.shenglipharm.com
The permanent stop titration method uses two identical platinum electrodes. When a low voltage (for example, 50 mV) is applied between the electrodes, if the electrode is polarized in the solution, only a small or no current is passed when the titration end point is not reached. However, when the end point is reached, the titrant is slightly excessive, the electrode is depolarized, and current is passed through the solution, and the galvanometer pointer is suddenly deflected and no longer returns. Conversely, if the electrode is changed from depolarization to polarization, the galvanometer pointer is deflected back to zero and does not change.
The potentiometric titration of the instrument device can be performed by a potentiometric titrator, a pH meter or a potentiometer. The permanent stop titration can be performed by a permanent stop titrator or as shown.
The sensitivity of the ammeter is 10<-6>A/div when measuring moisture and 10<-9>A/div for diazotization unless otherwise specified. The electrodes used can be selected as shown in the table below.
The determination of the end point of the titration is performed by using the coordinate paper with the potential (E) as the ordinate and the volume of the titration solution (V) as the abscissa, and plotting the E-V curve, and the center of the steeply rising or falling portion of the curve is the end point of the titration. Or by △ E / ΔV (that is, the ratio of the potential difference between two adjacent and the volume difference added to the titration solution) as the ordinate, and the titration volume (V) as the abscissa, draw (ΔE / ΔV) - The V curve, the volume corresponding to the maximum value of ΔE/ΔV, is the end point of the titration. The second derivative can also be used to determine the endpoint. According to the obtained ΔE/ΔV value, calculate the difference between adjacent values, that is, △<2>E/△V<2>, and draw (△<2>E/△V<2>)-V curve The volume at which the curve crosses zero is the end point of the titration.
For the selection of the color change domain of the indicator, the indicator is added before the titration, and the color change from the end point to the end point is observed to select the color of the indicator at the end of the variety.
(2) When the permanent stop titration method is used as the end point indication of the diazotization method, the R<[1]> is adjusted so that the voltage applied to the electrode is about 50 mV. Take the appropriate amount of test sample, accurately weighed, placed in the beaker, unless otherwise specified, can add 40ml of water and hydrochloric acid solution (1 → 2) 15ml, and then placed on a magnetic stirrer, stir to dissolve, then add potassium bromide 2g After inserting the platinum-platinum electrode, insert the tip of the burette into the liquid surface at about 2/3, and titrate rapidly with sodium nitrite titration solution (0.1mol/L or 0.05mol/L). The tip of the burette is raised to the liquid surface, the tip is rinsed with a small amount of water, the washing solution is incorporated into the solution, and the titration is continued slowly until the galvanometer pointer suddenly deflects and no longer returns, which is the end point of the titration.
When used as the end point indication for moisture determination , R<[1]> can be adjusted so that the initial current of the ammeter is 5~10μA, and the current is suddenly increased to 50~150μA, and it will not be returned for several minutes, which is the end point of titration. .
Potentiometric titration uses two different electrodes. One of the electrodes is an indicating electrode whose electrode potential changes with the change of the ion concentration of the analyte in the solution; the other is a reference electrode whose electrode potential is fixed. When the end point of the titration is reached, the potential of the analyte is sharply changed to cause a sudden drop or sudden increase in the potential of the indicator electrode. This turning point is called a jump point.