Standard Operating Procedures for Moisture Determination Method
The purpose of the standard operating procedures for moisture determination method is to establish a standard operating procedure for moisture determination method. Suitable for moisture measurement. The main responsibility is for the quality inspector to implement this operating procedure, and the inspection room director is responsible for supervising the correct implementation of this procedure.
The standard operating procedure for moisture determination method is as follows
A. Volumetric titration method
This method is based on the principle that iodine and sulfur dioxide can react quantitatively with water in pyridine and methanol solutions to determine water content. The instrument used should be dry and able to avoid the invasion of moisture in the air. The measurement operation should be carried out in a dry place.
Preparation and calibration of Fischer's test solution (1) Preparation: Weigh 110g of iodine (placed in a sulfuric acid dryer for more than 48 hours), place it in a dry stoppered flask, add 160ml of anhydrous pyridine, pay attention to cooling, shake until all iodine is dissolved, add 300ml of anhydrous methanol, weigh the flask, cool the flask in an ice bath, add dry sulfur dioxide to increase the weight by 72g, and then add anhydrous methanol to make 1000ml. Close the flask, shake well, and place it in a dark place for 24 hours.
This liquid should be shaded, sealed, and stored in a cool and dry place. Calibrate the concentration before use.
(2) Calibrate directly with a moisture meter. Alternatively, take a dry stoppered glass bottle and accurately weigh about 30mg of redistilled water. Unless otherwise specified, add 2-5ml of anhydrous methanol and titrate with this solution until the solution changes from light yellow to reddish brown. Alternatively, use the permanent stop titration method (Appendix VII A) to indicate the endpoint; Conduct another blank test and calculate according to the following equation.
In the formula, F is equivalent to the weight of water in milligrams per 1ml of Feuerbach test solution;
W is the weight of weighed distilled water, mg;
A is the volume of Fisher's test solution consumed for titration, ml;
B is the volume of Fisher's test solution consumed for the blank, in ml.
The measurement method accurately weighs an appropriate amount of the test sample (approximately 1-5ml of Fisher's test solution is consumed), and unless otherwise specified, the solvent is methanol, which is directly measured using a moisture analyzer. Alternatively, place the test sample in a dry stoppered glass bottle, add 2-5ml of solvent, and titrate with Fisher's test solution under continuous shaking (or stirring) until the solution changes from light yellow to reddish brown. Alternatively, use the permanent stop titration method (Appendix VII A) to indicate the endpoint; Conduct another blank test and calculate according to the following equation.
n the formula, F is equivalent to the weight of water in milligrams per 1ml of Feuerbach test solution;
W is the weight of weighed distilled water, mg;
A is the volume of Fisher's test solution consumed for titration, ml;
B is the volume of Fisher's test solution consumed for the blank, in ml.
The measurement method accurately weighs an appropriate amount of the test sample (approximately 1-5ml of Fisher's test solution is consumed), and unless otherwise specified, the solvent is methanol, which is directly measured using a moisture analyzer. Alternatively, place the test sample in a dry stoppered glass bottle, add 2-5ml of solvent, and titrate with Fisher's test solution under continuous shaking (or stirring) until the solution changes from light yellow to reddish brown. Alternatively, use the permanent stop titration method (Appendix VII A) to indicate the endpoint; Conduct another blank test and calculate according to the following equation.
Water content in the test sample (%)
B. Coulomb titration method
This method is still based on the Karl Fischer reaction and uses the permanent stop titration method (Appendix VII A) to determine water content. Compared with volumetric titration, the titrant iodine in Coulomb titration is not added from the burette, but is produced by electrolysis of an anode electrolyte containing iodine ions. Once all the water is completely titrated, a small amount of excess iodine will appear in the anode electrolyte, and the double platinum wire electrode detects this signal to stop the production of iodine. According to Faraday's law, the amount of iodine generated is directly proportional to the current passing through, so the method of measuring the total consumption of electricity can determine the total amount of water. This method is mainly used to determine the moisture content of substances with trace amounts of water (0.0001~0.1%), and is particularly suitable for the determination of moisture in chemical inert substances such as hydrocarbons, alcohols, and esters. The instruments used should be dry and able to avoid the invasion of moisture in the air; The measurement operation should be carried out in a dry place.
Prepare or purchase titration solutions according to the requirements of the Karl Fischer Coulomb Titrator. Because the instrument can measure electricity very accurately, there is no need to calibrate the titration solution.
The measurement method first removes the moisture in the system by pre titration, and then accurately measures an appropriate amount of the test sample (with a moisture content of about 0.5-5mg), quickly transfers it to the anode electrolyte, and directly measures it using a Karl Fischer Coulomb titrator. The endpoint is indicated by the permanent stop titration method (Appendix VII A), and the moisture content in the test sample is directly read from the instrument display screen, where every 1mg is equivalent to 10.72 Coulomb of electricity.Water content in the test sample (%)
In the formula, A is the volume of Fisher's test solution consumed by the test sample, in ml;
B is the volume of Fisher's test solution consumed in the blank, ml;
F is the weight of water equivalent to 1ml of Fisher's test solution, mg;
W is the weight of the test sample, mg
