Method for making pH test paper

production principle

Produce basic materials

• filter paperGenerally, filter paper with uniform texture, certain water absorption, and relatively stable chemical properties is selected as the base material for the test paper. It can adsorb and carry various reagent components added later, such as quantitative filter paper, which is commonly used.
• acid-base indicatorYou can choose a suitable mixture of universal acid-base indicators or indicators that have good color changing effects specifically for the pH detection range of common fish tank water, such as bromocresol green, methyl red, thymol blue, etc., mixed in a certain proportion, so that they can present a clear and distinguishable color change gradient in the usual pH range of fish tank water (generally around 6-8, with differences in suitable ranges for different fish species), making it easy to accurately determine the pH value.
• Buffer solution (optional)Sometimes, in order to make the color development of the test paper more accurate and stable, buffer solutions with different pH values can be prepared for calibration or pre-processing of the test paper to ensure that its response to the corresponding pH value meets expectations.
• Other additives (optional)For example, some reagents that can enhance the color rendering effect of indicators and help fix indicators on filter paper, such as certain surfactants, adhesives, etc., but it is necessary to ensure that they do not interfere with the normal acid-base indicator color change reaction and do not pollute the water quality.

Production steps

1. Prepare indicator solutionDissolve the selected acid-base indicator in an appropriate amount of organic solvent (such as ethanol, etc., considering its volatility, safety, etc., and not affecting the indicator performance and subsequent drying of the test paper) or water in a suitable proportion to prepare a uniform indicator solution. If multiple indicators need to be mixed, they should be thoroughly stirred to ensure that the mixed solution can exhibit accurate color transition changes at different pH values.
2. Processing filter paperCut the filter paper into a suitable size (usually convenient for handheld operation, immersion in water samples, etc., such as long strips and other common specifications) and place it flat. Use clean tweezers or other tools to pick up the filter paper, carefully soak it in the prepared indicator solution, ensure that the filter paper is fully soaked, and allow the indicator solution to evenly adsorb onto the fibers of the filter paper. The soaking time can be determined through pre experiments to achieve ideal adsorption and color development effects, usually ranging from a few seconds to several tens of seconds.
3. Drying treatmentRemove the filter paper soaked with the indicator from the solution and let it air dry naturally in a clean, ventilated, and dry environment, or use a low-temperature (generally not exceeding 40 ℃ to avoid damaging the indicator and other components) oven or other equipment to dry the filter paper completely. Only in this way can the test paper be easily stored and used in the future.
4. Calibration and Marking (optional but recommended)You can use a standard buffer solution with a known pH value to test the prepared test paper, observe its color development, and compare and calibrate it with a standard color chart (you can make it yourself, test and record the corresponding color under the same conditions with a standard buffer solution, or refer to a professional color chart style). If there is a deviation, you can adjust the production process appropriately. At the same time, important information such as the applicable range and approximate colorimetric pH range should be labeled on the test paper packaging or the test paper itself, making it convenient for users to accurately detect the water quality of the fish tank.

Required conditions

• experimental environmentIt is best to make the test paper in a relatively clean, dry, well ventilated indoor environment with stable temperature and humidity to avoid impurities, dust, water vapor, and other factors affecting the quality of the test paper and the performance of the indicator.
• instrument and equipmentSome basic laboratory instruments are required, such as scissors for cutting filter paper, measuring cylinders for accurately measuring reagents, glass rods for stirring solutions, beakers for holding solutions, adjustable temperature ovens (for drying filter paper, if natural drying conditions are suitable, they can also be omitted), as well as tweezers for picking up filter paper and other operations, to ensure that the operation process is as accurate as possible and meets hygiene requirements, and to prevent the test paper from being contaminated.
• Operation safety protectionDue to the use of some chemical reagents, especially organic solvents, which may have certain volatility, irritability, and even toxicity, it is necessary to carry out relevant operation steps involving the volatilization of organic solvents in a fume hood, and operators should wear suitable gloves, goggles, and other protective equipment to ensure personal safety.