Pesticide residue rapid test reagent which has the characteristic of well stability and high sensitivity are the matching reagents corresponding to national standard GB/T5009.199-2003, and could be used on various types of pesticide detecting instrument.
1. Principle
Pesticide of organophosphorus and carbamate could inhibit the activity of cholinesterase under certain conditions. Whether the samples contain organophosphorus or carbamate could be determined through the calculation of inhibition rate, which has positive correlation with pesticide concentration .
2. Reagents preparation
2.1 Buffer solution: Dissolve one pack of buffer powder with 500mL pure water or distilled water, store at room temperature.
2.2 Cholinesterase: Use directly, store at 4℃.
2.3 Chromogenic agent: Dissolve one bottle of chromogenic powder with 25mL buffer solution, store at 4℃.
2.4 Substrate: Dissolve one bottle of substrate with 12.5mL pure water or distilled water, store at 4℃.
Special tips: Pesticide residue rapid test reagent can be used in various types of pesticide detecting instrument and spectrophotometer.
3. Sample preparation
3.1 Weigh 2g vegetable samples (weigh 4g if it is tuber), cut the samples into 1cm2.
3.2 Soak the samples with 10mL buffer solution, shake it for 1~2min.
3.3 Pour out the above treated solution and stand it for 2 minutes. If the treated solution is muddy or has so many impurities, filter it first before doing the test.
4.Starting instrument
Connect the instrument with power, press the “enter” button allowing the instrument to self-checking which will take about 1min, instrument is ready to use after self-checking process.
5.Detection
5.1 Blank Control detection:
5.1.1 Suck 2.5mL buffer solution into beaker; add 100μL chromogenic reagent and cholinesterase respectively; stand it for 10mins.
5.1.2 Add 100μL substrate into the beaker, shake them fully and then pour the solution into cuvette, put it in the first channel of the instrument, close the lid and press the “B” botton. After 10 seconds, it tests the variation of absorption value (412nm) in 3 minute(△A0).
5.2 Sample detection
5.2.1 Suck 2.5mL samples solution to text tube; add 100μL chromogenic reagent and cholinesterase respectively; stand it for 10mins.
5.2.2 Add 100μL substrate into the test tube, shake it fully and then pour it into cuvette, put it in 2-8 channel of the instrument, close the lid and press the “M” botton. After 10seconds, it tests the variation of absorption value (412nm) in 3 minute (△At).
6. Results:
Inhibition rate could be calculated by formula: [( ΔΑ 0 －ΔΑ t )/ ΔΑ 0 ]×100%;
Normally, Inhibition rate could be calculated by pesticide detecting instrument automatically,
Inhibition rate≥50%: Positive result, it is recommended to detect again with gas chromatography.
Inhibition rate≤50%: Negative result.
7. Retention Period
This kind of pesticide residue rapid test reagent is very stable, and it can be transported in room temperature. For long term storage, it should be stored at 4℃, and the expiration time is 12 months. If it is stored in room temperature or normal temperature, the expiration time is 3-6 months.
8. Matters need attention
8.1 Pesticide residue test reagent include 10 packages of buffer powder, 10 bottles of cholinesterase, 2 bottles of Chromogenic reagent, and 4 bottles of substrates. All these item could offer 500 times detection.
8.2 When using any reagent, please exhaust the open one before reopening a new one in case they go bad.
8.3 Biochemical reaction will occur immediately when enzyme, substrate and chromogenic reagent meet together. So pipette and container should be labeled ,used alone in order to avoid cross-contamination .
8.4 When sucking the reagent from the bottle, it is strictly forbidden to inject the reagent back to the bottle.
8.5 Control the speed of action during using pipettor to suck reagent or drop reagent , in case the quantity of reagent is not accurate. Besides, it is helpful to protect the pipettor.
9. The limit of the detection
The detection limits of pesticide residue rapid test reagent to several commonly used pesticides are as follows (Unit: mg/kg):
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