Pesticide residue detectorThe calibration procedure is a key process to ensure the accuracy and reliability of instrument testing results, usually covering preparation before calibration, calibration operations, sample testing, result analysis and judgment, and subsequent maintenance. The following is a detailed introduction:
1、 Preparation before verification
Standard substances and reagents
It is necessary to use standard pesticide solutions of known concentrations (such as organophosphorus or carbamate standards) to ensure their reliable source and within their expiration date.
Reagents should be prepared according to the instructions, such as enzyme solutions, color reagents, substrates, etc., which should be accurately weighed and mixed evenly to avoid contamination or spoilage.
Instrument status check
Ensure that the instrument is powered on and preheated to a stable state (usually taking 10-30 minutes), and check whether the light source, sensor, colorimetric dish, and other components are clean and undamaged.
Verify whether the self checking function of the instrument is normal, such as whether the display screen, buttons, channel selection and other operation interfaces respond sensitively.
Environmental condition control
The laboratory temperature should be controlled between 10 ℃ -30 ℃, with a relative humidity of ≤ 70%, to avoid strong electromagnetic interference (such as staying away from generators and welding machines).
The control panel should be stable and flame-retardant, with sufficient space (at least 10cm) around the instrument for heat dissipation and operation.
2、 Calibration operation
Set calibration parameters
Select the detection wavelength based on the characteristics of the standard substance (such as 412nm for spectrophotometry), and set parameters such as sensitivity and linear range.
Enter the concentration value of the standard solution to ensure that the instrument recognizes and records calibration data.
Measure the absorbance of standard samples
Pour the standard solution into the colorimetric dish, place it in the measuring tank of the instrument, and start the calibration mode.
Record the absorbance value displayed by the instrument, repeat the measurement three times and take the average to reduce errors.
Draw standard curve
Draw a linear regression curve with absorbance as the y-axis and standard solution concentration as the x-axis.
Verify curve correlation (R ² ≥ 0.99) to ensure measurement consistency of the instrument at different concentrations.
Adjust instrument parameters
If the deviation between the instrument reading and the standard value exceeds the allowable range (such as ± 5%), the gain, zero point, or recalibration should be adjusted until it meets the requirements.
3、 Sample testing
Sample processing
Weigh an appropriate amount of sample (such as 2g of fruits and vegetables), cut it into pieces, and add extraction solution (such as 10ml buffer solution). Shake for 1-2 minutes to dissolve pesticide residues.
After filtration or centrifugation, take the supernatant as the test solution and dilute it to the appropriate concentration if necessary.
Detection operation
Add the test solution, enzyme solution, and color reagent in the test tube in sequence, mix evenly, and let it stand for reaction (e.g. 10 minutes).
Pour the reaction solution into the colorimetric dish, place it in the instrument detection channel, and click the "Sample Test" button to start the detection.
controlled experiment
Simultaneously test the control solution (standard solution without pesticides) to eliminate systematic errors.
Compare the absorbance values of the sample and the control, and calculate the inhibition rate (formula: inhibition rate=(control absorbance - sample absorbance)/control absorbance x 100%).
4、 Result analysis and judgment
data recording
Record the testing time, absorbance, inhibition rate, testing personnel, and other information for each sample.
Save raw data and calibration curves to ensure traceability.
Result determination
If the inhibition rate of the sample is ≥ 50%, it is judged as positive (pesticide residue exceeds the standard) and needs to be tested twice or more to confirm.
Positive samples need to be further validated using confirmation methods such as gas chromatography-mass spectrometry (GC-MS).
issue a report
Prepare a calibration report, including instrument information, calibration curves, sample results, judgment conclusions, and other related content.
The report must be signed by qualified technical personnel and accompanied by a calibration certificate (if applicable).
5Pesticide residue detectorfollow-up maintenance
Cleaning and Maintenance
After the inspection is completed, wipe the surface of the instrument and the colorimetric cell with a dry soft cotton cloth to avoid residual liquid corroding the components.
When not in use for a long time, place the instrument in a dedicated box and store it in a cool and dry place.
Reagent management
Reagents should be stored according to the instructions (such as enzyme solution refrigerated, substrate protected from light), and should be used as soon as possible after opening.
Regularly check the expiration date of reagents, and replace expired or deteriorated reagents in a timely manner.
Regular re inspection
The instrument needs to be calibrated at least once a year, or recalibrated after replacing important components.
Participate in inter laboratory comparisons or proficiency testing to ensure consistency between test results and standard methods.