Detection of acetochlor pesticides in strawberries

On April 25th, the CCTV Financial Channel “Is it true?” broadcasted a message “The CCTV reporter bought 8 strawberries and all of them contained carcinogenic pesticides”. According to reports, online rumors recently said that strawberry pesticide residues are widespread. CCTV financial reporters randomly purchased 8 samples of strawberries at different strawberry sales locations in Beijing and sent them to Beijing Agricultural College for testing. After testing, the chlorothalonil pesticide residues were all qualified. Acetochlor is at least 1 times higher than the EU standard.

Acetochlor is a widely used herbicide. It is one of the most important herbicides in the world and one of the most widely used herbicides in China. Acetochlor is classified as a B2 carcinogen in the United States. It may cause poisoning and carcinogenicity when consumed for a long time.

According to the corresponding standards, RephiLe specifically recommends the following acetochlor content detection solution for strawberries. The program was tested by GC-MS with a detection limit of 0.01 mg/kg. The detailed solution is as follows:

First, the experimental principle

In the strawberry sample, acetochlor was extracted by extraction solvent, purified by solid phase adsorbent, and determined by gas chromatography-mass spectrometry, and selected by ion qualitative and external standard method .

Second, instruments and reagents

Gas Chromatography-Mass Spectrometry, Solid Phase Extraction, Nitrogen Blowing Apparatus, Analytical Balance, Centrifuge Tube: 100 mL, High Speed ​​Homogenizer Centrifuge, Pipette, Direct-Pure Genie Ultrapure Water System.

N-hexane, ethyl acetate, all of which are chromatographically pure. Anhydrous magnesium sulfate, analytically pure. Nitrogen: 99.99%.

Third, the test method

1 , sample weighing

Weigh 5 g (accurate to 0.1 g) of strawberry sample in a 100 mL centrifuge tube, add 50 mL of ethyl acetate to dissolve, homogenize for 2 min on a homogenizer, centrifuge at 4000 r/min for 10 min, and pour the supernatant into a concentrate bottle. Concentrate to dryness and dissolve in 1 mL of n-hexane.

2 , purification

The above extract was pipetted into a centrifuge tube, and 1.0 g of anhydrous magnesium sulfate, 0.5 g of PSA, 0.5 g of ODS was added, vigorously shaken for 1 min, and then centrifuged at 5000 r/min for 10 min. The supernatant was transferred to a nitrogen blow tube, and blown to near dryness at 40 ° C, and made up to 1 mL with n-hexane for GC-MS detection .

3 , GC-MS determination

3.1 Chromatographic conditions

The column model is DB-5MS, and the temperature is adjusted to allow the column to better separate the target compound at elevated temperatures.

Column: DB-5MS, 30m × 0.25mm × 0.25μm; carrier gas: high purity helium; column flow rate: 1mL / min; detector: mass spectrometry EI detection; inlet temperature: 250 ° C; injection method: no Split injection; injection volume: 1 μL.

Column temperature conditions :

3.2 Chromatographic conditions

Ion source: quadrupole ion source; mass scan range mPz: 50 - 650 amu; ionization mode: EI; electronic energy: 70 ev; interface temperature: 280 ° C; ion source temperature: 230 ° C; quadrupole temperature: 150 ° C.

3.3 Qualitative determination

When performing sample determination, if the retention time of the detected chromatographic peak is consistent with the standard, and in the sample mass spectrum after subtracting the background, the selected ions are present, and the selected ion abundance is higher than that of the standard. The ion abundance ratio is consistent (relative abundance >50%, allowable deviation ±10%; relative abundance >20% - 50%, allowable deviation ±15%; relative abundance >10% - 20%, allowable deviation ±20 %; relative abundance <10%, tolerance ± 50%), it can be judged that the pesticide or chemical is present in the sample. If it is not confirmed, it should be re-injected, determined by scanning (with sufficient sensitivity) or by adding other confirming ions or using other analytical instruments with higher sensitivity.

3.4 Quantitative determination

Single ion quantitative determination by external standard method. The standard for quantification should be prepared by using a blank sample solution to prepare a mixed standard working curve. The concentration of the standard solution should be similar to the concentration of the compound to be tested. Detailed parameter conditions are shown in the table below.

3.5 parallel test

The same sample was tested in parallel according to the above procedure.

3.6 Blank test

Except that the sample is not weighed, it is carried out according to the above steps.

4, expression analysis results

The sample solution and the reagent blank are used to find the concentration values ​​(C and C0) from the standard curve, and then calculate according to the following formula:

In the formula:

Ci----concentration of acetochlor in the sample, mg/kg

Cs----the concentration of acetochlor in the standard, μg/mL

Ai----the peak area of ​​acetochlor in the sample

As----the peak area of ​​acetochlor in the standard

V----final volume, mL

m----sample quality, g

5 , precision

The detection limit of acetochlor in this method is 0.01 mg/kg, respectively .

In the GC-MS detection method, water mainly plays the following roles:

1. Configure blank solution and standard solution. Due to the high sensitivity of GC-MS, the purity of water is very strict, and the TOC level is required to be as low as possible, so as to avoid organic interference.

2. Clean the relevant experimental vessels to prevent interference of foreign impurities on the experimental results and damage to the relevant instruments .

3. Clean the ion source, air filter, etc. of the GC-MS. Metal ion residue can seriously affect the service life of related components .

          To ensure that high-quality ultrapure water can be used in the maintenance of GC-MS. RephiLe specifically recommends the Direct-Pure Genie water purification system for use with analytical instruments such as GC-MS. The Direct-Pure Genie Ultra Pure Water Meter is a product that uses tap water as the influent water to produce both EDI secondary water and ultrapure water. It uses a purification unit such as RO membrane, EDI and refined ion exchange resin to effectively remove trace ions in water, and the water resistivity can reach 18.2 MΩ•cm. The Direct-Pure Genie system also uses EDI and dual-wavelength UV lamps to cycle time to reduce organic levels in the water to below 5 ppb. EDI-Pure Genie's EDI water can be used to configure buffer solutions and clean common laboratory vessels; ultrapure water is used to provide water for most analytical instruments to meet the overall water needs of analytical instrumentation laboratories. RephiLe can provide verification services for pure water systems to help users complete system verification in accordance with ISO, GMP and GLP. Make sure you are at ease, safe, and worry-free.

  To eat strawberries safer, we recommend cleaning the strawberries by following these steps:

1. Rinse continuously with running tap water for a few minutes to remove most of the bacteria, pesticides and other contaminants from the surface of the strawberry.

2. Dip the strawberry in water with 2 tablespoons of baking soda and 1 teaspoon of salt for 3 minutes. Baking soda can decompose the pesticide; salt can make the insects and eggs attached to the surface of the strawberry float, easy to be washed away by water, and there is a certain Disinfection.

3. Rinse off with running tap water.

4. Rinse with clean water (or cold water).

Need to be reminded: Do not remove the strawberry stalk before washing the strawberry, so as to prevent pesticides and pollutants from penetrating into the fruit through the “crush” during the soaking process, which will cause pollution.

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