Carl fee
Overview
The moisture in the test of the Carfei minutes is an important and sensitive chemical analysis method, but in addition to a very good measurement instrument, it is necessary to determine the substance There is no interference material exist. According to the amount of moisture in the substance, the appropriate amount of injection is determined, and various factors affecting the accuracy of the measurement are overcome, it can get a good measurement result. In 1935, Karlfischer first proposed a method of determining moisture using capacity analysis, this method is a visual measure of GB6283 "Moisture content in chemical products". Vehicle can only determine moisture of colorless liquid substances. Later, it was developed as a power method. With the development of technology, the coulombium is combined with the capacity method to launch Coulomb. This method is the test method in GB7600 "running transformer oil content determination (coulomb method)". Classification testing and electricity styles are called a capacity method. The Card's method is divided into two major methods of Card's Capacity Method and Kakuron. Both methods are customized by many countries to standard analysis methods to correct other analytical methods and measuring instruments.
Cauluna method is measured by a chemical method. The principle is that the K. reagent in the electrolytic cell of the instrument is injected into the water-containing sample, water to participate in iodine and sulfur dioxide, and the pyridine and methyl sulfate pyridine is formed in the presence of pyridine and methanol. The iodine consumed is produced in an anode electrolysis, so that the redox reducing reaction is continuously carried out until the moisture is exhausted, and the electrolysis generates iodine is a proportional relationship with the electricity consumption of the same electrolysis. The reaction is as follows:
h 2 o + i 2 + so 2 + 3c 5 Sub> > H 5 n → 2c 5 h 5 n · hi + c 5 h 5 N · SO 3
c 5 h 5 n · so 3 @ SUB> 3+ CH 3 oh → c 5 h 5 n · hso 4 ch 3 3 < / p>
During the electrolysis process, the electrode reaction is as follows:
anode: 2i - -2e → i 2
< P> Cathodes: i 2 + 2e → 2i -2h + + 2e → h 2 < / SUB> ↑
It can be seen from the above reaction, ie 1 mole of iodized oxidation 1 mole of sulfur dioxide, requires 1 moles of water. Therefore, it is 1 mole of 1 mole of equivalent reaction, that is, electrolytic iodine is equivalent to electrolytic water, electrolytic 1 mmol iodine requires 2 × 96493 milliguluno electricity, electrolysis 1 mmol water requires electricity amount of 2 × 96493 Coulomb electricity.
The moisture content in the sample is calculated in the following formula:
: W --- Water content in the sample, μg;
< P> Q --- Electrolytic electricity, MC;Press water to 18.015 g / mol calculation;
operation
fee method is iodine Method, the basic principle is to utilize iodide oxide sulfur dioxide, need - quantitative water to participate in the reaction:
i 2 + so 2 + 2h 2 2 2 o → 2Hi + h 2 so4
The above reaction is reversible. When the sulfuric acid concentration reaches 0.05% or more, a reverse reaction can occur. If we let the equation proceed in a positive direction, we need to add appropriate alkaline substances to the acid generated during the reaction. Pyridine is added to the system so that the reaction can be carried out to the right. Experiments have shown that pyridine is the most suitable reagent, and the pyridine also has the effect of binding to iodine and sulfur dioxide to reduce the vapor pressure of both. Therefore, the reagent must be added to the methanol or another solvent containing an active OH group, and the sulfate apripidine is converted to a stable methyl sulfide.
Carl Fischer-Treatment method is a method for sample moisture measurement by carbide a titration with methanol to a titration liquid. This method is simple, high accuracy, widely used in medical, petroleum, chemical, pesticide, dye, grain, etc. Especially suitable for samples that are easily destroyed, not only free water, but also measuring the combined water, often used as a standard analysis method such as moisture, especially trace moisture. However, it is not suitable for samples containing strong reducing in Vc.
Carpeu reagent is a reagent for taking trace moisture in certain substances, its components: methanol, pyridine, iodine, sulfur dioxide. The end point determination method has two types of visual findings and potential methods.
The main components are I 2 , so 2 , c 5 h 5 n, CH 3 oh
The basic principle of Carfei Taxi is i 2 oxidation SO 2 , quantitative h 2 2
i 2 + 2h 2 o = 2HI + H 2 so 4
This reaction is reversible, to carry forward the reaction forward, need to be added to the appropriate alkaline substance and the acid produced by the reaction , Pyridine (C 5 h 5 n) can meet this requirement, adding methanol to avoid side effects
Carfei checkpressure is contained in I2 Display brown, when I2, SO 2 , h 2 O react, i 2 brown faded.
This method appears in brown as a titration end point
Carfei breakfast is non-water titration, all containers need dry, 1L Car fee tensor is mixed in the process of formulation and preservation of 6g Water, the reagent will fail.
Carpeu reagent is a reagent for determining the micro moisture in the organic matter, so it is also known as a water reagent, also known as the Cardi reagent. The initial water reagent is mainly prepared by iodine, sulfur dioxide, methanol, and pyridine. This reagent has malodous and has a large toxicity, poor stability, and the storage period within three months, and does not apply to the determination of aldehyde, ketone organic matter, and the user brings storage and use inconvenience. With the advent of the fully automatic Ka's analyzer, the requirements of the Kappry reagent also improved. Therefore, people have developed various types of water reactors. Due to the model of the water reactor, it is necessary to see a detailed description of each manufacturer.
Carpeu Hui reagents:
single group: no pyridine f ≥ 3 500ml
Methyl hydraulid: nopopyridine f ≥ 3 500ml * 2
a + B liquid: no pyridine f ≥ 3 500 ml * 2
Results
Carfei determination of trace moisture in various substances: When the water is present, The water in the sample and the Carfei Trickarer produced an oxidation reducing reaction in SO 2 to i 2 .
i 2 + 2h 2 o → 2hi + h 2 so 4
However, this reaction is a reversible reaction, and when the sulfuric acid concentration reaches 0.05% or more, it can respond. If we let the reaction take in a positive direction, we need to add the appropriate alkaline substance to the acid during the reaction process. Experiments have been shown that pyridine is added in the system, so that the reaction can be carried out to the right.
3 c 5 h 5 n + h 2 o + i 2 + so 2 → 2 hydroiodate pyridine + sulfate apyridine
Menic acid anhydride is unstable, can react with water, consume some water and interfere with the measurement, in order to stabilize it, We can add anhydrous methanol.
Sulfate + CH 3 oh (anhydrous) → Methyl sulfate
total reactive:
i < SUB> 2+ so 2 + 3 pyridine + CH 3 oh → 2 hydroiodate pyridine + Pyridine
From the reaction, 1 mol of water required for 1 mol of iodine, 1 mol sulfur dioxide and 3 mol pyridine and 1 mol of methanol, resulting in 2 mol of pyridine, 1 mol methyl sulfate. This is theoretical data, but in fact, SO 2 , pyridine, CH 3 oh is excessive, and the excess free iodine is red brown after the reaction is completed. It can be determined to reach the end point.
i 2 : c 5 h 5 n = 1: 3 : 10
