T/LZZLXH 062-2021 Chemical analysis pipetting procedures for inspection and testing organizations

Scope

Main technical content: 7. Liquid transfer operations 7.1 Single-scale pipettes and graduated pipettes for liquid transfer 7.1.1 Extracting a solution: - Use the thumb and middle finger of one hand to pinch the upper end of a single-scale pipette or graduated pipette. - Insert the lower end of the pipette into the solution to a depth that prevents air from being drawn in. - Use a pipette bulb to extract the solution according to the rinsing method. - When the solution level rises about 5 mm above the marked line, remove the pipette bulb and immediately block the upper end with the index finger. 7.1.2 Adjusting the solution level: - Lift the pipette away from the solution surface. - Dry the external surface of the pipette with a clean filter paper. - Place the pipette upright in a clean small beaker, with the tip firmly against the inner wall of the tilted beaker. - Gently loosen the index finger and twist the pipette to allow the solution level to drop steadily until the meniscus of the solution touches the required marking line. - Immediately press the pipette tip with the index finger to maintain the upright position of the pipette and remove the last drop of solution from the outlet. 7.1.3 Dispensing the solution: - Tilt the receiving container appropriately while keeping the pipette upright. - Position the outlet against the inner wall of the container. - Release the index finger to allow the solution to flow down the wall naturally. - When the solution level drops below the tip, wait approximately 3 seconds before removing the last drop from the outlet with the inner wall of the container. - Remove the pipette. 7.1.4 For pipettes marked with "blow," discharge any residual solution from the outlet.

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