Determination of Pesticides in Baby Food by HPLC-MS-MS Using an LC System and Triple-Quadrupole LC-MS

Due to the diversity of pesticides used in food protection and the globalization of the food industry, it is important to monitor programs that cover a large number of pesticides. The application of ultrahigh-performance liquid chromatography (UHPLC) systems combined with the new generation of triple-quadrupole mass spectrometers facilitates the analysis of pesticides in challenging matrices such as food samples. As a result of the high sensitivity and high-scan-rate capabilities of the Agilent 6460A triple-quadrupole mass spectrometer (Agilent Technologies, Santa Clara, CA), the simultaneous qualitative and quantitative multiresidue analysis of a large set of pesticides at trace levels can be performed.

High sensitivity is essential for the analysis of these compounds in derived products, where the concentrations will be a fraction of the concentration in the raw material. In this respect, baby food is a challenging matrix. This article describes the quantitative analysis of 40 pesticides in baby food at levels below the maximum residue level (MRL) (10 µg/kg fruit or vegetable) specified in EC Regulation 396/2005, which was implemented in September 2008.1 A QuEChERS (quick, easy, cheap, effective, rugged, and safe) extraction and dispersive solid-phase extraction (SPE) method was applied to isolate the pesticides from the baby food matrix. An Agilent 1290 Infinity LC was used to perform the separation on a Rapid Resolution High Definition (RRHD) ZORBAX Eclipse Plus column (Agilent). The total analysis time was 10 min (including 1.5 min reequilibration), and detection limits ranged from 10 to 500 ng/kg using Dynamic MRM (multiple reaction monitoring) and two transitions (quantifier and qualifier) per compound. Three different baby food compositions were analyzed. Extraction performance criteria such as repeatability, recovery (accuracy), and sensitivity were investigated.

Experimental

Instrumentation

Table 1    -    Dynamic MRM data acquisition parameters for the compounds under investigation*
Table 1    -    Dynamic MRM data acquisition parameters for the compounds under investigation* (cont.)

An Agilent 1290 Infinity LC system and 6460A triple-quadrupole LC-MS with Agilent jet stream technology were used. The LC system was configured as follows:

Part number/description:

Method parameters:

  • Column: ZORBAX Eclipse Plus RRHD C18, 150 mm L × 2.1 mm i.d., 1.8 µm dp
  • Mobile phase A: 0.05% (w/v) ammonium formate + 0.01% (v/v) formic acid in water; mobile phase B: methanol
  • Flow rate: 0.5 mL/min
  • Gradient:
    0 to 5 min, 10 to 65 %B
    5 to 6.5 min, 65 to 95 %B
    6.5 to 8.5 min, 95 %B
    8.5 to 10 min, 10 %B
  • Temperature: 45 °C
  • Injection: 2 µL, with needle wash (flush port, 5 sec; water/methanol, 1/1)
  • Detection: MS-MS
  • Ionization: electrospray, positive ionization.

Jet stream parameters:

  • Drying gas temperature: 250 °C
  • Drying gas flow: 10 L/min
  • Nebulizer pressure: 30 psig
  • Sheath gas temperature: 340 °C
  • Sheath gas flow: 11 L/min
  • Capillary voltage: 4500 V
  • Nozzle voltage: 500 V.

Acquisition:

  • Dynamic MRM (see Table 1)
  • Delta EMV (electron multiplier voltage): 50
  • Cycle time: 200 msec.