To increase production and income, the tea gardens have long been using highly effective pesticides to control diseases and pests, leading to excessive pesticide residues in some of the tea products. Red tea as a kind of drink is a target for strict regulation of detection limit in many countries. And this article also introduces the QuEChERS-LC-MS/MS method for extracting and testing 112 types of pesticide residues in red tea.
Weigh 2.0 g of tea powder, and transfer it in a 50 mL centrifuge tube. Add 10 mL of water into the tube, and leave it stand still for 1h. Add 15 mL of acetonitrile, 4.0 g of magnesium sulfate and 1.0 g of sodium chloride (P/N: MS-MG5055). Keep violently oscillating the tube manually for 1min and keep centrifuging the tube at 8,000 rpm for 5min, and then reserve 1 mL of supernate for purification.
Connect Bonna-Agela Cleanert® NANO special purification columns (P/N: IC-NN1510-C) for agricultural complex matrixes in series with 10 mL one-time needle tubes. Extract 1 mL of extracting liquid, and then push out the liquid. Repeat this step for 3 times. Filter the liquid with a 0.22 µm organic membrane for the next LC-MS/MS determination.
Preparation of matrix-mixed standard working solution
Dilute the high-concentration pesticide-mixed standard solution with blank sample matrix solution to the matrix-mixed standard working solution (concentration: 0.02 μg/mL).
Chromatographic columns: Venusil® ASB C18 (5 μm, 150 Å, 2.1 × 150 mm);
Phase A: Formic acid aqueous solution (concentration: 0.1%)
Phase B: Formic acid -acetonitrile solution (concentration: 0.1%);
Column temperature: 30 °C;
Sample size: 10 µL;
Gradient elution conditions (see Table 1);
Ion source: ESI source;
Scanning mode: Positive ion scanning;
ESI voltage: 5500 V;
Atomized gas pressure: 50 psi;
Curtain gas pressure: 15 psi;
Auxiliary gas pressure: 50 psi;
Ion source temperature: 400 °C;
Collecting mode: MRM.
Figure 1 LC Gradient Elution Conditions
Results and Discussion
Figure 1 LC-MS/MS Chromatogram of Mixed Standard Solution (concentration: 0.02 μg/mL)
Figure 2 Blank LC-MS/MS Chromatogram of Black Tea Sample
Figure 3 LC-MS/MS Chromatogram of Black Tea Matrix–mixed Standard Working Solution (concentration: 0.02 μg/mL)
Figure 4 LC-MS/MS Chromatogram of Black Tea Matrix Sample with Standard Addition (content: 0.15 mg/kg)
This experiment establishes the LC-MS/MS method for detecting pesticide residues, and determines the contents of pesticide residues in the black tea on the basis of solid phase extraction technology. The samples (standard addition amount: 0.15 mg/kg) are detected, and the resulted recovery rates are between 60% and 110%, conforming to requirements. The stable QuEChERS effect and good reproducibility of chromatographic columns show this method can be applied to the detection of pesticide residues in the black tea.
Venusil® ASB C18
5 μm, 150 Å, 2.1 × 150 mm
10 mg Nano, 150 mg MgSO4
MAS-QuEChERS Cleanup Kits
15 mg Nano, 150 mg MgSO4
Guard cartridge holder
Suitable for 4.6 × 10 mm and 2.1 × 10 mm
Direct-coupled protect column core
5 μm, 150 Å, 2.1×10 mm, 4/pk
1.5 mL vials
Screw neck vials, 12 × 32 mm
Caps and Septa
Screw neck cap, center hole; red silicone/white PTEE septa, slitted
Syringe Filter (Nylon)
Monofilm, 13 mm, 0.22 μm
Disposable Needle-Free injection systems
2 mL, 100/pk