Q Exactive quadrupole-electrostatic field orbitrap high resolution mass spectrometry for rapid screening and confirmation of 555 pesticide residues in fruit and vegetable matrices

Q Exactive quadrupole - electrostatic field orbitrap high resolution mass spectrometry for rapid screening and confirmation of 555 pesticide residues in 6 vegetable and fruit substrates

Cheng Mingchuan Jiang Yan

Thermo Fisher Scientific (China) Co., Ltd.

Key words

Orbitrap high-resolution mass spectrometry, Q Exactive, TraceFinder, rapid screening for large-scale pesticide residues

introduction

Pesticide residues have become a hot issue of concern to the society at this stage. China's national standard GB 2763-2012 National Food Safety Standards for Maximum Residues of Pesticides in Foods will be replaced by the latest 2014 editions in less than 2 years. The new version of GB 2763 is more stringent than ever, with 3,650 limits for 387 pesticides in 284 foods, a significant increase from the 2012 edition. Among the newly released standards, the Codex Alimentarius Commission has established 1999 standards, of which 1811 national standards are equivalent to or stricter than the International Codex Alimentarius standards, accounting for 90.6%. Increasingly stringent standards and specifications require more accurate, sensitive and fast methods for pesticide screening. At present, the triple quadrupole LC/MS system is widely used in the analysis of toxic and harmful residues or illegal additives in food, but triple quadrupole mass spectrometry requires standard materials to optimize instrument parameters, and the number of compounds that can be analyzed simultaneously is limited. Scale screening or completely unknown residue identification has certain limitations. At the same time, it belongs to unit-resolved mass spectrometry, which is characterized by the relative abundance of characteristic ions, and there is a certain risk of false positives in the analysis of complex matrix samples.

Based on the unique high resolution and high quality accuracy measurement principle of Orbitrap electrostatic field orbital technology and excellent stability and operability, Q Exactive Quadrupole - Electrostatic Field Orbitrap High Resolution Mass Spectrometry has a resolution of up to 140,000 FWHM, single time The external standard method corrects the mass axis and maintains the mass accuracy of less than 3ppm for more than 1 week, ensuring the reliability of the analysis results; comparable to the sensitivity and wide linear range of the high-end triple quadrupole for easy analysis of trace compounds in complex matrices; matching UHPLC The scanning speed meets the high throughput analysis needs. Q Exactive can be accurately and reliably applied to food safety related non-target compound rapid screening confirmation and high sensitivity and high throughput multi-residue analysis. In this paper, Q Exactive completed rapid screening of sub-ppb levels of 555 pesticide residues in 6 matrix samples of tomato, pepper, spinach, cabbage, cucumber and green beans in 20 minutes. The experiment used full scan + ddms / ms (full scan + automatic trigger secondary mass spectrometry) to collect data, using high-resolution two-level full scan data to confirm, to ensure the accuracy of the experimental results.

Experimental condition

Instrument device

The HRAM LC-MS/MS analysis was performed using a Thermo Scientific Ultimate 3000RSLC and a Q Exactive Orbitrap benchtop high resolution mass spectrometer.

Thermo Scientific Xcalibur and Thermo Scientific TraceFinder software are used for data acquisition and processing, respectively.

Liquid chromatography parameters

Column: Thermo Scientific Accucore aQ (150 x 2.1 mm, 2.6 μm)

The mobile phase composition and gradient elution conditions are shown in Tables 1 and 2.

Table 1. Mobile phase composition

Table 2. Gradient elution tables

Mass spectrometry parameter

Table 3. Mass Spectral Scan Parameter Settings

Screening parameters

Table 4. TraceFinder screening parameter settings

Sample Preparation

Refer to the method described in QuEChERS AOAC 2007.01

Experiment and discussion

In this experiment, 555 pesticides were analyzed in a 20-minute liquid phase gradient. Using full scan+ddms/ms to acquire data, the first-order mass spectrometry XIC map of the target compound and its second-order full-scan mass spectrum were obtained simultaneously, as shown in Figure 1. . Q Exactive can achieve high sensitivity and high resolution uniformity, that is, the resolution is not significantly affected by the sensitivity of the method, and most of the compounds have a good response, and the detection level of the sub-ppb level can be achieved. At the same time, at a high resolution of 70,000 FWHM, the method has good selectivity and the target compound is not affected by co-eluting components and matrix (Fig. 2). Even with 2 scan events in a single scan, Q Exactive can meet UHPLC analysis requirements, as shown in Figure 3. In peak-dense areas, each peak (about 0.1 min) is guaranteed to be sufficient. Scan points (> 15) to meet accurate quantitative and qualitative requirements, and the quality accuracy of each scan point is less than 3ppm.

Figure 1. Typical map of Fluoxastrobin (m/z 459.0866) in a pepper matrix.

(A. Extracted ion chromatogram, B.ddMS2 acquisition point, C. Secondary full scan mass spectrum)

Figure 2. Partial compound 1ppb matrix spiked chromatogram and blank matrix chromatogram

Figure 3. A: Scanning speed meets the requirements of UHPLC analysis (0.1 min peak is greater than 15 scan points); B: mass accuracy map for each scan point

The experimentally collected data was intelligent and fast automated data analysis using Thermo High Resolution Mass Spectrometry Screening Software TraceFinder. TraceFinder is a versatile process software that collects data as well as analytical data. Can be used for simultaneous screening, confirmation and quantitative analysis of multiple components. Qualitative confirmation of compounds, in addition to accurate masses, TraceFinder also provides a variety of methods such as retention time, isotope distribution, primary secondary fragment confirmation and secondary mass spectrum similarity comparison, and comprehensive judgment to obtain accurate qualitative results. Minimize the occurrence of false positive results.

In the analysis of matrix spiked samples, the results were confirmed by four screening indicators such as accurate mass number, retention time, isotope distribution and secondary fragment ions to ensure the accuracy of the screening results. Figure 4-6 shows the results of the quenching of the pepper matrix. The matching results of the exact mass and retention time are shown in Fig. 5. The actual measured m/z deviation from the theoretical value is 1.62 ppm, and the deviation of the retention time is 0.01 min. The matching results of the isotopes are shown in Fig. 6. The isotope distribution matching score of the measured results is 100%, and the m/z of 8 isotope peaks is within the deviation range from the theoretical value (< 5 ppm). The matching results of the secondary fragment ions are shown in Figure 6. The measured fragment ions match the five fragment ions in the self-built database.

In addition to its powerful screening function, TraceFinder also supports high-resolution mass spectrometry quantitative data analysis. Figure 7 shows the quantitative analysis results of thiacloprid in pepper matrix, ranging from 0.1ppb to 50ppb, R2=0.9998 (n=6); Accuracy < 5%; precision RSD < 2% (10 ppb, n=3).

Figure 4. Screening results for quenching net Ametryn accurate mass and retention time in pepper matrix

Figure 5. Screening results for the quenching of the Ametryn isotope distribution in the pepper matrix

Figure 6. Screening results for quenching net Ametryn secondary fragments in pepper matrices

Figure 7. Quantitative analysis of Thiacloprid in the pepper matrix

in conclusion

With high resolution, high quality accuracy, high sensitivity and wide dynamic range, Q Exactive is a mass spectrometry platform with both qualitative and quantitative functions for large-scale screening, confirmation and quantitative analysis of non-target compounds in food safety. In this paper, Q Exactive and the screening component TraceFinder were used to establish a method for simultaneous screening and confirmation of 555 pesticide residues in 6 kinds of vegetable melon and fruit substrates. The method is simple, rapid, accurate and sensitive, and can simultaneously complete multi-agricultural residues. Qualitative and quantitative analysis. A database of 555 compounds containing information on compound names, molecular formulas, exact masses, retention times, and fragment ions was also established. The experimental conditions and database of this paper have good reproducibility. Different instruments, different laboratories and different analysts can get high matching screening results, saving method development, database establishment time and a large number of standard samples. Cost, facilitate the large-scale promotion and application of methods.

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