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Detection index and determination method of purified water for medical device production

Issuing time:2021-09-15 10:29

Course Recommendation: (September 25 · Online Course) Operation Training of "Standardized Experiments for Sterile Microbiological Inspection (Laboratory) Inspectors of Medical Devices in the 2020 Chinese Pharmacopoeia"


Process water for medical devices mainly includes: purified water, water for injection and sterilized water for injection. Purified water refers to process water obtained by using drinking water as raw water and removing impurities, ions, suspended solids, etc. from the water by distillation, ion exchange, reverse osmosis or other suitable methods, and does not contain any additives. In order to help companies verify whether purified water meets the requirements of standards such as the Chinese Pharmacopoeia, this article has compiled the testing indicators and measurement methods of purified water for your reference.






1. Conductivity


The electrical conductivity indicates the electrical conductivity of purified water. The higher the purity of the water, the lower the electrical conductivity. The electrical conductivity is related to the gas, impurity ion content, and pH value in the water, and is also related to the temperature, which increases with the increase of temperature.




Measurement method: Measure with a conductivity meter, and the conductivity meter must have automatic temperature compensation. If it does not have the temperature compensation function, a heat exchanger can be installed to control the temperature between 24 and 26 ℃ during measurement or record the water temperature for conversion. . The measurement result should conform to the conductivity ≤0.1Ms/m.




2. Total Organic Carbon (TOC)


Total organic carbon (TOC) refers to the total carbon content of dissolved and suspended organic matter in water. There are many types of organic matter in water, and it is not possible to separate and identify all of them at present, and they are often expressed as "TOC". TOC is a comprehensive indicator for rapid verification. It expresses the total amount of organic matter in water in terms of the amount of carbon.




Measurement method: The purified water sample is transported to the reaction chamber through the peristaltic pump of the total organic carbon analyzer. The reaction chamber is composed of two ultraviolet lamp tubes and a quartz spiral tube. The ultraviolet lamp emits light to cause photolysis of water and oxidize organic compounds. Into carbon dioxide. The instrument automatically detects, analyzes, and obtains results. The determination result should conform to the total organic carbon ≤ 0.5mg/L.




3. Easy to oxidize


Determination method: Take 100ml of purified water sample, add 10ml of dilute sulfuric acid (10%), after boiling, add 0.10ml of potassium permanganate titrant (0.02mol/L), then boil for 10min, the pink color shall not disappear completely.




4. Microbial limit


The total number of microorganisms should be the total number of bacteria, molds and yeasts, and the total number is less than or equal to 100cfu/ml.




Determination method: Use a small amount of pH 7.0 sodium chloride peptone buffer to rinse the filter membrane, take a specified amount of sample purified water and filter through the filter membrane, take out the filter membrane and inoculate it on the R2A medium plate with the inoculum side up, and take the pH 7.0 sodium chloride Peptone buffer 100ml was injected into the filter, filtered, and the filter membrane was taken out and inoculated on the R2A medium plate as a negative control. Place the plate upside down in an incubator at 30-35°C for 5 days and count.




5. pH


Determination method: take 10ml of purified water sample, add 2 drops of methyl red indicator solution, no redness; take another 10ml of purified water, add 5 drops of bromothymol blue indicator solution, no blueness.




6. Ammonia


Determination method: Take 50ml of purified water sample, add 2ml of Nessler's reagent, and leave it for 15 minutes; if it develops color, compare it with 1.5ml of ammonium chloride solution, add 48ml of non-ammonia water and 2ml of Nessler's reagent.




7. Nitrate


Determination method: Take 5ml of purified water sample and place it in a test tube, cool in an ice bath, add 0.4ml of 10% potassium chloride solution and 0.1ml of 0.1% diphenylamine sulfuric acid solution, shake well, slowly add 5ml of sulfuric acid dropwise, shake well, Place the test tube in a water bath at 50°C for 15 minutes. The blue color produced by the solution is 0.3ml with standard nitrate solution, and 4.7ml of nitrate-free water is added. The color after treatment with the same method should not be darker.




8. Nitrite


Determination method: Take 10ml of purified water sample and place it in a Nessler colorimetric tube, add 1ml of dilute hydrochloric acid solution of p-aminobenzenesulfonamide and 1ml of naphthaleneethylenediamine hydrochloride solution to produce pink, and 0.2ml of standard nitrite solution. Add 9.8ml of nitrite-free water, and the color after treatment with the same method should not be darker.




9. Heavy metals


Determination method: take 100ml of purified water sample, add 19ml of water, evaporate to 20ml, let cool, transfer to a 25ml colorimetric tube, add acetate buffer pH 3.5, 2ml and appropriate amount of water, add 2ml thioacetamide solution, shake Evenly, let it stand for 2 minutes. Compared with the color of 1.0ml lead standard solution plus 19ml water and treated with the same method, it should not be darker.




10. Non-volatile matter


Determination method: Take 100ml of purified water from the sample, place it in an evaporating dish with constant weight at 105°C, evaporate to dryness on a water bath, and dry to constant weight at 105°C. The remaining residue shall not exceed 1mg.




Note: Enterprises should select applicable water quality standards based on their own product inspection purposes, raw water quality, and characteristics of purified water preparation methods, and regularly monitor, evaluate and analyze water quality related indicators to ensure continuous and stable production of purified water that meets the requirements.


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