Laboratory basic testing knowledge

Most of the analysis in analytical testing is the analysis of aqueous solutions, so water is the most commonly used solvent. In the laboratory, distilled water or special-purpose pure water is indispensable. Unless otherwise specified, whether the reagent is used for water or the water added during the analysis and inspection operation is distilled water or can be purified to meet the analytical requirements. Ionic water. Distilled water can be prepared by distillation and condensation of ordinary domestic water, or by anion exchange treatment. Inspection and analysis of special items When there is special requirement for the purity of water, the purity requirements of the water and the method of purification treatment are generally indicated in the inspection method.

In order to ensure that the quality of pure water can meet the requirements of analytical work, quality inspection must be carried out for each batch of pure water prepared. Generally, the following criteria should be met:

1 Conductivity measured by a conductivity meter is less than or equal to 530 μs / cm (25 ° C ) .

2 acidity is neutral or weakly acidic, PH=5.0~7.5 (25 °C ). It can be measured by precision pH test paper and acidity meter. It can also be determined by the following indicator method: adding 2~3 drops of 1g/L methyl group in 10 ml water Red indicator, shaken yellow and not red, indicating that the acidity of the water is qualified, neutral ; or add 4~5 drops of 1g/L bromothymol blue indicator in 10 ml of water , shake not blue , indicating that the acidity of the water is acceptable and neutral.

3 No organic matter and microbial contamination. The detection method is as follows: adding 2 drops of 0.1 g/L potassium permanganate solution in 100 ml of water and boiling is still pink.

4 The content of metal ions such as calcium and magnesium is qualified. The detection method is as follows: 2 ml of ammonia - ammonium chloride buffer solution (pH=10) , 2 drops of 5 g/L chrome black T indicator are added to 10 ml of water sample, and shaken. The blue color of the solution indicates that the water is qualified. If it is purple, the water is unqualified.

5 hydrogen ion content is qualified. The detection method is as follows: adding a few drops of nitric acid to 10 ml of water sample, and then adding 4 drops of 10 g/L of AgNO3 solution, and shaking. No white turbidity in the solution indicates that the water is qualified, and if there is white turbidity, the water is unqualified.

2 , the requirements of testing reagents

Chemical reagents are high-purity chemicals that meet certain quality requirements and are the material basis for analytical work. The purity of the reagent is very important for the analytical test. It will affect the accuracy of the result. If the purity of the reagent does not meet the requirements of the analytical test, accurate analytical results cannot be obtained. The correct selection and use of chemical reagents will directly affect the success or failure of the analytical experiment, the accuracy of the experiment and the cost of the experiment. Therefore, the instrument user must fully understand the nature, type, use and use of the chemical reagent.

According to the quality standards and uses, chemical reagents can be broadly divided into standard reagents, common reagents, high purity reagents and special reagents.

1 standard reagent

Standard reagents are standard materials used to measure the chemical amount of other substances. They are usually produced by large reagent plants and are inspected in strict accordance with national standards. They are characterized by high content of the main components and are accurate and reliable.

Standard reagents for titration analysis, which is commonly used as reference reagent (PT) in China , is divided into two grades, C grade ( first benchmark ) and D grade ( work benchmark ) . The volume fraction of the main components is 99.98~100.02% and 99.95~100.05 respectively. % , Class D reference reagents are standard materials in titration analysis, and reference reagents are specified in light green labels.

2 common reagents

Ordinary reagents are general-purpose reagents widely used in laboratories. They can be generally divided into three grades. The specifications and applicable ranges are as follows:

 

 

General reagent specifications and scope of application

3 high purity reagent

The content of the main component of the high-purity reagent is usually equivalent to that of the pure grade reagent, but the impurity content is very low, and the impurity detection item is 1 to 2 times more than the excellent grade or the reference reagent . High-purity reagents are mainly used for the decomposition of samples and the preparation of solutions in microanalysis.

4 special reagents

Specialized reagents are a class of reagents with special purpose. It has a high content of main components and a low impurity content. It differs from high purity reagents in that interference with impurity components in a particular application need only be controlled below the limits that do not cause significant interference. There are many kinds of special reagents, such as spectral pure reagent (SP) , chromatographic pure reagent (GC) , biological reagent (BR) and so on.

All kinds of reagents should be selected reasonably and correctly according to the requirements of the inspection items and the inspection methods, and do not blindly pursue high purity. For example, when preparing a chromic acid washing solution, only industrial K2CrO7 and industrial H2SO4 are needed. If the AR grade K2CrO7 is used , it is a waste. Analytical reagents (AR) are used for food testing . Standard solutions commonly used for titration analysis should be prepared with analytically pure reagents and then with Class D reference reagents ; for enzyme reagents, the correct selection should be based on their purity, viability, and storage conditions and expiration date.

3 , the requirements for inspection of general utensils

(1), the choice of utensils

All kinds of utensils can not be separated from the analysis and inspection. The various utensils required should be selected according to the requirements of the inspection method. Generally rigid glassware should be used; some glass corrosive reagents (e.g., NaOH, etc.), the need is selected from polyethylene bottles reservoir; case photolabile reagent (e.g., AgNO3 / I2, etc.) should be selected brown glass bottles dark storage . Capacity and capacity accuracy and heating requirements should also be considered when selecting.

The various utensils used in the test must be clean, otherwise result in error, which is an extremely important issue in micro and volume analysis.

(2), washing of utensils

Preparation of common washing liquids:

1 soapy water, washing powder water, decontamination powder water: according to the washing situation.

2 Wang Shui: 3 parts of HCL mixed with 1 part of HNO3

3 HCL lotion (1+3) : 1 part of HCL is mixed with 3 parts of water.

4 chromic acid washing solution: Weigh 50g K2CrO7 , add 170~180ml water, heat to dissolve into a saturated solution, and slowly add concentrated H2SO4 to about 500ml under stirring .

5 Alkaline Alcohol Wash: Mix 95% by volume of ethanol with an equal volume of 30% NaOH solution.

Washing method of utensils:

1 new glassware: first rinse with tap water, dry it and soak it with chromic acid solution to remove other adhering substances, then rinse with tap water.

2 oily glassware: first wash with alkaline alcohol wash, then wash with detergent or soapy water, then rinse with tap water.

3 There are Vaseline oil stained utensils: first wipe the vaseline, then cook in the washing powder or soapy water, remove it and rinse it with tap water.

4 rust and scale utensils: soak with (1+3) HCL washing solution, then rinse with tap water.

5 cuvette: first rinse with tap water, then wash with dilute HCL , then rinse with tap water.

6 polyethylene plastic utensils: After washing with dilute HCL , rinse with tap water.

In order to ensure that the utensils can meet the requirements of cleanliness after washing, the tap water should be washed away with distilled water, usually rinsed with distilled water for 2~3 times, and distilled water should be rinsed several times to achieve the purpose of saving distilled water and clean utensils.

Instrument and equipment requirements:

1 Glass gauge requirements: The burettes, pipettes, volumetric flasks, graduated straws, colorimetric tubes, etc. used in the inspection method shall be calibrated or verified according to relevant national regulations and procedures. Glass measuring devices and glassware must be thoroughly cleaned before use.

2 Requirements for temperature control equipment: The constant temperature drying oven and constant temperature water bath used in the inspection method shall be tested and calibrated or verified according to the relevant national regulations.

3 Requirements of measuring instruments: balances, acidity meters, thermometers, spectrophotometers, chromatographs, etc. should be calibrated or verified according to relevant national regulations and procedures.

Note: The instruments listed in the test method are the main instruments required by the method, and the common instruments in the laboratory are no longer included.

Whether the washing of the utensils directly affects the test results directly. Due to the uncertainty of manual cleaning, the Y3600 automatic laboratory ware washing machine and laboratory washing machine are recommended to have good cleaning effect, convenient operation, stable use and guaranteed service.

Sun Guang   Gavin Sun    13321180593

Beijing Jiaxin Yida Technology Co., Ltd.

Phone: 010-89451528   Fax: 010-89452906

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