In laboratory analysis, the cleanliness of the injection needle of the automatic sampler and the pre dilution accuracy of the sample directly affect the reliability of the data. The cleaning of injection needles should follow the principle of "classification treatment, gradient elution". For low viscosity samples dissolved in conventional organic solvents, a "three-step" basic cleaning method is used: first, repeatedly suction and rinse the inner wall of the syringe with the sample solvent, and use the principle of similar solubility to remove surface residues; Rinse with chromatography grade methanol to remove solvent residue; Finally, rinse with ultrapure water and dry with nitrogen. For biological samples containing proteins and oils, it is necessary to upgrade the cleaning strategy: first immerse in a 50% acetonitrile aqueous solution and sonicate to remove large molecule adsorption, then rinse with a 0.1mol/L hydrochloric acid solution to neutralize alkaline residues, and finally clean according to the conventional process. For samples containing strong adsorption components, a combination process of "solvent gradient soaking+pulse flushing" needs to be introduced, such as soaking the needle in a mixed solvent of dichloromethane and methanol, and then repeatedly pushing and pulling the needle cylinder piston to form pulse pressure to promote residual desorption.

The pre sample dilution technique is precisely controlled through automated equipment. Modern automatic samplers are equipped with precision injection pump systems, supporting 1-1000 fold automatic dilution, and the minimum injection volume can reach micro upgrades. The core principle is to mix the sample and diluent in a predetermined ratio through dual pump alternating operation or step-by-step dilution mode. For example, when processing high concentration samples, a 100 fold dilution can be performed first, and then the target concentration can be achieved through multi-stage mixing. Some devices also support online dilution mode, where the liquid is continuously diluted during the flow process, making it suitable for industrial process monitoring. To ensure dilution accuracy, it is necessary to regularly calibrate the pump system and control bubble generation. Some equipment is equipped with a degassing module to eliminate bubble interference during the mixing process. The synergistic optimization of cleaning and dilution techniques can significantly improve the efficiency and reliability of laboratory analysis.