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In analytical work, washing glassware is not only a necessary preparatory step before experiments but also a technical task. Whether the instruments are washed properly affects both the accuracy and precision of the test results. Different analytical tasks have varying requirements for instrument cleaning; we will introduce the methods for cleaning instruments, focusing on conventional quantitative chemical analysis. (1) Cleaners and their areas of use The most commonly used cleaners are soap, soap solutions (specialized products), laundry detergent, stain removers, cleaning liquids, organic solvents, etc. Soap, soap solution, laundry detergent, degreasing powder, for instruments that can be scrubbed directly with a brush, such as flasks, Erlenmeyer flasks, reagent bottles, etc ； Laundering solutions are commonly used for instruments that are difficult to clean with brushes, such as burettes, pipettes, volumetric flasks, distillers and other instruments of special shapes. They are also used to clean dishes and utensils that have not been used for a long time, as well as to remove scale that cannot be removed by brushing. Washing instruments with a cleaning solution takes advantage of the chemical reaction between the solution itself and the dirt to remove it. Therefore, it needs to be soaked for a certain period of time to allow full effect ； Organic solvents are used to deal with the oily nature of certain types of dirt; they enable the dissolution of oils and fats, thereby removing them. Alternatively, some organic solvents can mix with water and act quickly, allowing instruments washed with water to be cleaned effectively. For example, toluene, xylene, gasoline, etc., can be used to remove oil stains, while alcohol, ether, and propanone can be used to rinse instruments that are still wet after cleaning. (II) Preparation of cleaning solution and precautions for its use. A cleaning solution is simply referred to as a detergent; there are various types of detergents depending on different requirements. The more commonly used ones are introduced below. 1. Strong acid oxidizing agent solution: This solution is prepared using potassium dichromate (K2Cr2O7) and concentrated sulfuric acid (H2SO4). In acidic solutions, K2Cr2O7 possesses strong oxidizing properties, and it has little erosive effect on glass instruments. Therefore, this type of wash solution is the most widely used in laboratories. The preparation concentrations vary, with various levels ranging from 5% to 12%. The preparation method is roughly the same: Take a certain amount of K2Cr2O7 (an industrial-grade product will suffice), heat it in water at a ratio of about 1–2 parts water per part of the compound until it dissolves. After it cools slightly, slowly add the required volume of industrial-grade concentrated H2SO4 to the K2Cr2O7 solution (under no circumstances should water or the solution be added to H2SO4). Stir while adding the acid using a glass rod, being careful not to let any liquid spill out. Once well mixed, allow the mixture to cool before transferring it to a bottle for later use. The newly prepared wash solution is reddish-brown and has a strong oxidizing capacity. When the cleaning solution turns black-green after long use, it indicates that it no longer has oxidizing cleaning power. For example, prepare 500 ml of a 12% wash solution. Take 60 grams of the industrial product K2Cr2O7 and place it in 100 ml of water (the amount of water used is not fixed; it should be enough to dissolve the substance). Heat the mixture to dissolve it, then cool it. Slowly add 340 ml of concentrated H2SO4 while stirring continuously. After cooling, transfer the mixture to a bottle for later use. When using this wash solution, it is essential to be careful not to let it splash on the body, to prevent burning the clothes and damaging the skin. Pour the cleaning solution into the instrument to be cleaned, ensuring that all surfaces of the instrument are fully submerged; wait for a moment before pouring it back into the bottle. After rinsing the newly soaked instruments with a small amount of water for the first time, do not pour the wastewater into sinks or sewers, as this can cause corrosion over time. It should be poured into a waste liquid container; once the container is full, it should be disposed of as trash. If there is no such container, pour the wastewater into the sink while flushing it with plenty of water at the same time. 2. Alkaline wash solution: Alkaline wash solutions are used to clean instruments contaminated with oil. These solutions are applied using a long-term soaking method (over 24 hours) or a boiling method. When removing the instruments from the alkali wash solution, wear latex gloves to avoid skin burns. Commonly used alkaline cleaning solutions include: sodium carbonate solution (Na2CO3, also known as soda ash), sodium bicarbonate (Na2HCO3, or baking soda), sodium phosphate solution (Na3PO4, trisodium phosphate), and disodium hydrogen phosphate solution (Na2HPO4), among others. 3. Alkaline potassium permanganate solution: Using alkaline potassium permanganate as a cleaning solution, its action is slow, making it suitable for cleaning utensils contaminated with oil. Preparation method: Take 4 grams of potassium permanganate (KMnO4), dissolve it in a small amount of water, and then add 100 ml of 10% sodium hydroxide (NaOH). 4. Pure acid and pure alkali cleaning solutions: Depending on the nature of the dirt on the utensils, these solutions can be used by immersing or boiling the utensils in concentrated hydrochloric acid (HCl) or concentrated sulfuric acid (H2SO4), as well as concentrated nitric acid (HNO3). The temperature should not be too high, as otherwise the volatile acids can cause irritation. Soda ash cleaning solutions typically use solutions with a concentration of 10% or more of concentrated caustic soda (NaOH), potassium hydroxide (KOH), or sodium carbonate (Na2CO3) to soak or boil the utensils (boiling is possible). 5. Organic solvents: For utensils with fatty stains, they can be scrubbed or soaked using organic solvents such as gasoline, toluene, xylene, propanol, alcohol, trichloromethane, and ether. However, using organic solvents as cleaning solutions is quite wasteful; for large instruments that can be cleaned with a brush, alkaline cleaning solutions should be used whenever possible. Organic solvents are used for cleaning only small parts or instruments with special shapes that cannot be cleaned with a brush, such as the inner bore of pistons, the tips of pipettes, the tips of burettes, the bore of burette pistons, droppers, and small bottles. 6. Disinfectant: For vessels used in testing carcinogenic chemicals, in order to prevent harm to the human body, they should be soaked in a disinfectant that can break down these carcinogenic substances before being washed. Disinfectants commonly used in food testing include 1% or 5% sodium hypochlorite (NaOCl) solutions, 20% HNO3 solutions, and 2% KMnO4 solutions. 1% or 5% NaOCl solutions have a destructive effect on aflatoxin. Soaking the contaminated glassware in a 1% NaOCl solution for half a day, or in a 5% NaOCl solution for a short period of time, is sufficient to destroy aflatoxins. Preparation method: Take 100 grams of bleaching powder and add 500 ml of water, stirring well. Meanwhile, dissolve 80 grams of industrial Na2CO3 in 500 ml of warm water. Then combine the two solutions, stir, allow it to clarify, and filter. The filtrate contains 2.5% NaOCl ； If bleaching powder is used, the weight of NaCO3 should be doubled, resulting in a solution concentration of about 5%. If a 1% NaOCl solution is required, the aforementioned solution can be diluted in proportion. 20% HNO3 solution and 2% KMnO4 solution are effective in destroying benzo(a)pyrene; glassware contaminated with benzo(a)pyrene can be soaked in 20% HNO3 for 24 hours, after which the remaining acid should be rinsed off with tap water before further cleaning. Latex gloves and microsyringes contaminated with benzo(a)pyrene can be soaked in a 2% KMnO4 solution for 2 hours before being washed. (III) Steps and requirements for washing glass instruments 1. Washing instruments by the usual method: When cleaning instruments, one should first wash hands with soap to prevent oil from hands from sticking to the instruments, which would make cleaning more difficult. If the instrument has accumulated dust over time, rinse it first with clean water, and then clean or wash it using a detergent as appropriate. If a cleaning powder is used, dip the brush in a small amount of it and scrub the inside and outside of the instrument thoroughly. Then rinse while continuing to scrub until no traces of the cleaning powder are visible to the eye. Wash it with tap water 3 to 6 times, followed by rinsing it with distilled water three times or more. A clean and fine glass instrument should be such that no water droplets remain on it. If water droplets remain, it still needs to be washed again. When rinsing with distilled water, use a wall-following rinsing method and shake thoroughly; the instrument after rinsing with distilled water should be neutral as checked with an indicator. 2. Glassware used for trace metal analysis should be soaked in a 1:1 to 1:9 HNO3 solution, and then washed using conventional methods. 3. When performing fluorescence analysis, glass instruments should not be washed with laundry detergent (as laundry detergent contains fluorescent brighteners that can cause errors in the analysis results). 4. When analyzing carcinogenic substances, appropriate cleaning solutions should be used for soaking, followed by washing using conventional methods. (IV) Drying of glass instruments: Instruments that are used frequently in experiments should be washed and dried after each experiment before being set aside for use. Different experiments have varying requirements regarding dryness; generally, instruments such as beakers and Erlenmeyer flasks used for quantitative analysis are sufficient as long as they are clean. However, many instruments used for food analysis require to be dry – some demand the absence of any traces of water, while others require complete dryness. Drying instruments should be selected according to different requirements. (1) Air-dry: For instruments that are not needed immediately, rinse them with distilled water, then place them upside down in a dust-free environment to allow excess water to drain, and let them dry naturally. Instruments can be placed on shelves with wooden pegs or in glass cabinets with ventilation holes. (2) Drying: The cleaned instruments have their moisture removed, and they are placed in an oven to be dried at a temperature of 105–110°C for about 1 hour. It can also be dried in an infrared lamp drying oven. This method is applicable to general instruments. Vials and similar containers should be placed in a desiccator to cool down and be stored after drying. For instruments with solid glass stoppers and thick walls, it is important to raise the temperature slowly during drying, and the temperature should not be too high to avoid cracking. Measuring instruments should not be placed in an oven for drying. Rigid test tubes can be heated and dried using an alcohol lamp; start heating from the bottom with the tube opening facing downward to prevent water droplets from flowing back and causing the tube to crack. Once no water droplets remain, turn the tube opening upward to remove any remaining water vapor. (3) Drying with hot (cold) air: This method can be used for instruments that need to be dried quickly or for larger instruments that are not suitable for being placed in an oven. Typically, a small amount of ethanol or acetone is poured into the device from which water has been removed, and it is shaken; afterward, a hair dryer is used – cold air is applied for 1–2 minutes at first, and once most of the solvent has evaporated, hot air is used to dry it completely. Finally, cold air is used to remove any remaining vapor, preventing it from condensing back inside the container.