**4. Results and discussion**

Examples of preset m/z ratios and retention times of *S. aureus* PSMs for qualitative and quan‐ titative analyses are shown in **Table 1**. Retention times may vary according to the LC sys‐ tem and MS detector. (d), (t) and (q) stand for doubly, triply and quadruply charged ions, respectively.

The chromatograms of PSMs extracted from the culture are shown in **Figure 1**. The result indicates that the new method has a high selectivity. Good linearity of the PSMs was achieved in the range 0.5~100 µg/L (*R*<sup>2</sup> > 0.99). Compared with other analytical methods, the pre‐treatment of the new method is simple and rapid, and the high resolution makes the method highly sensitive and selective. The method has been used successfully for the determination of PSMs extracted from different culture mediums, such as milk, beverage, vegetable and meat.


**Table 1.** m/z ratios and retention times of *S. aureus* PSMs.

**Figure 1.** Chromatograms of PSMs extracted from the culture.

## **Acknowledgements**

This work was supported by Science & Technology Project of China General Administration of Quality Supervision, Inspection and Quarantine (2015QK055), Science & Technology Project of Quality Supervision Bureau of Jiangsu Province (KJ155426), Six talent peaks project in Jiangsu Province (SWYY‐031) and Jiangsu Natural Science Foundation (BK20141085).
