Automatic potentiometric titrator JH-T7 titration method to measure amine value (perchloric acid tit

1. Project background
In the fields of chemical engineering and materials, the amine value of amine curing agent is a key index, which directly affects the product performance. When the traditional acid-base titration method is used to determine the amine value of weak alkaline fatty amines, there are some problems such as the color change of the indicator is not obvious, the potential titration is abrupt and the end point is difficult to judge, which leads to poor accuracy of the results. The automatic potentiometric titrator JH-T7 of Shanghai Jiahang Instrument Co., Ltd. combined with perchloric acid titration method can effectively solve these problems and provide accurate and efficient solutions for the determination of amine values.
2. Instruments and reagents
(1) Instruments
1. Automatic potentiometric titrator JH-T7: With high-precision titration system, the amount of titration liquid can be accurately controlled; With high sensitivity potential detection module, real-time monitoring potential changes; Equipped with intelligent data processing system, it can automatically record data, draw titration curve and calculate the result.

2. Non-aqueous composite electrode: suitable for non-aqueous system titration, to ensure stable and accurate measurement of potential in solutions such as ice acetic acid. Before use, check the appearance of the electrode, no damage, pollution, activation according to the instructions, to ensure the measurement accuracy.

3.10mL burette: equipped with titrator to accurately measure perchloric acid standard titrant. Calibrate before use to ensure the calibration is accurate.

(2) Reagents
1. Perchloric acid standard titration solution (0.1mol/L) : used for titration of samples, its concentration accuracy is crucial. Regular calibration is required to ensure correct concentration. Store in brown bottle, away from light and low temperature, to prevent concentration change.

2. Glacial acetic acid: provides a reaction environment for the sample and enhances the relative alkalinity of the weakly alkaline amine. Select analysis pure level, ensure purity, sealed storage after use, anti-volatilization, water absorption.

3. Trichloromethane: auxiliary sample dissolution. If the sample does not dissolve well in ice acetic acid, add appropriate amount of trichloromethane. Pay attention to its toxicity when using, operate in a well-ventilated place, and dispose of it properly after use.

3. Experimental steps
(1) Sample preparation
Use an analytical balance to accurately weigh the 0.2g sample to four decimal places. Place the sample in a clean and dry titration cup and add 50mL of glacial acetic acid. If the sample is difficult to dissolve, add another 10mL of trichloromethane, place it on the heating device and stir it at slightly warm temperature until the sample is completely dissolved, and cool it to room temperature for use.

(2) Instrument parameter setting
1. Turn on the power supply of automatic potentiometric titrator JH-T7, start the instrument, and wait for the completion of self-test.

2. On the parameter setting screen, set the parameters as follows:

* Titration mode: Select dynamic titration, the instrument automatically adjusts the titration speed according to potential changes to ensure titration accuracy and high efficiency.

* Minimum addition volume: set to 0.02mL, to achieve a small amount of titrant accurate addition, improve titration accuracy.

* Electrode balance time: set to 4s, so that the electrode reaches a stable state before measurement, to ensure accurate potential measurement.

* Pre-mixing time: set to 10s, so that the solution is fully mixed to ensure the uniformity of the reaction.

* Electrode balance potential: set to 1mV to ensure that the electrode is in the best working condition.

* Titration speed: Select standard speed, taking into account reaction adequacy and experimental efficiency.

* End volume: Set to 20mL and adjust according to the expected titration volume and experimental requirements to prevent excessive titration.

* Pre-titration add volume: set to 0mL.

* Potential jump: set to 150 (reference standard and experience value, can be fine-tuned according to the actual situation, for accurate determination of titration endpoint).

* Equilibrium potential before titration: set to 10mV to ensure stable potential before titration starts.

(3) titration operation
1. Carefully insert the non-aqueous composite electrode into the titration cup solution, ensuring that the electrode head is completely submerged and does not touch the cup wall.

2. Install the burette on the titrator to check whether the connection is tight and there is no leakage. Absorb an appropriate amount of perchloric acid standard titration solution to eliminate air bubbles in the titration tube.

3. Start the titrator and start titration. During the titration process, the instrument monitors the change of potential in real time and draws the titration curve automatically. When the potential jump reaches the set potential jump, the titrator automatically determines the end point and records the titration volume.

4. Perform blank experiment at the same time, that is, add glacial acetic acid and trichloromethane (if any) in the same steps, titrate the liquid drop with perchloric acid standard, and record the blank titration volume.

Iv. Data processing and result analysis
(1) Data recording
After each titration, perchloric acid titration solution concentration, sampling quality, titration volume, blank titration volume and other data were recorded in time. Conduct 3-5 parallel experiments to ensure data reliability.

(2) Concentration calculation
According to the formula: Calculate the amine value.

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Formula:

W is the amine value (mgNaOH/g);

V1 is the volume (mL) of perchloric acid standard titrant consumed by the titration sample.

Vo is the volume (mL) of the standard titrant of perchloric acid consumed in the titration blank.

C is the concentration of perchloric acid standard titration solution (mol/L);

m is the mass (g) of the sample taken.

Use the data processing function of titrator to calculate automatically, or compare after manual calculation to ensure the accuracy of calculation.

(3) Evaluation of results
1. Repeatability evaluation: The relative standard deviation (RSD) of parallel experimental results is calculated. If RSD is within the allowable range (such as less than 2%), it indicates good data repeatability and high experimental precision.

2. Accuracy assessment: The standard sample with known amine value is used for determination, the measured value is compared with the standard value, and the relative error is calculated. If the relative error is within a reasonable range (such as ±5%), the experimental method and instrument operation are proved to be accurate and reliable; Otherwise, check all aspects of the experiment, find the reason and retry the experiment.

5. Precautions

1. Before the experiment, comprehensively check whether the equipment is normal and whether the electrode performance is good. Calibrate the titrator regularly and maintain the electrodes to ensure instrument accuracy and stability.

2. Perchloric acid is highly oxidizing and corrosive. Wear protective gloves and goggles during operation in a fume hood and avoid contact with skin and eyes. In case of contact, rinse immediately with plenty of water and seek medical attention.

3. Ice acetic acid has pungent smell and is volatile. It should be sealed and stored after use. Trichloromethane is toxic, maintain good ventilation during operation, avoid inhaling steam, and dispose of waste liquid according to regulations after use to prevent environmental pollution.

4. During titration, avoid solution splashing or electrode collision. If the solution is abnormal (such as discoloration, precipitation), immediately stop titration, analyze the cause and treat.

5. After the end of the experiment, clean the titration cup, electrode and other utensils in time, and properly store the equipment and reagents. Collect the experimental waste liquid by classification and treat it according to the requirements of environmental protection to prevent pollution.