Safeguarding cosmetics safety: this DESI/PI imaging source leaves no hiding place for trace amounts of prohibited substances in cosmetics!

Foreword

The illegal addition of hormonal and antihistamine substances to cosmetics can lead to safety risks such as skin dependency, ‘hormone face’ and allergies. Existing detection methods primarily involve quantification following homogenisation and extraction; these fail to provide direct information on the spatial distribution of target substances and suffer from issues such as insufficient detection sensitivity for low-concentration trace additives and cumbersome sample preparation.

This study aims to validate the mass spectrometry imaging capabilities of the DESI/PI-MSI system coupled with Agilent Q-TOF for detecting exogenous cosmetic additives at extremely low concentrations of 10 ppb in a glass slide matrix, thereby establishing a rapid, in-situ, visualised detection protocol for trace prohibited components in cosmetics.

‌Materials and Methods

Instrumentation: Electrospray/Photochemical Ionisation Mass Spectrometry Imaging (DESI/PI) source, Agilent Q-TOF 6545 quadrupole time-of-flight mass spectrometer;

Samples: cosmetics and mixed standard solutions;

Sample preparation method: mix the cosmetics with the mixed standards, dilute to 10 ppb with methanol, dispense 2.5 μL onto a glass slide using a pipette, and vacuum-dry for 30 minutes;

Detection mode: Positive ion Full Scan;

‌Results and conclusions

1. Performance of raw mass spectrometry data

The entire system operated stably under the set parameters; the baseline of the total ion current chromatogram in full scan mode was flat with no interference from spurious peaks, and the signal response intensity for the target compound at a low concentration of 10 ppb was sufficient, meeting the basic requirements for mass spectrometry imaging data acquisition.

Figure 1: Average mass spectrum of the mixture of cosmetics and the mixed standard (10 ppb)

Fig. 1: Average mass spectrum of the mixture of cosmetic product and mixed standard (10 ppb).

2. Analysis of imaging results

Using the in-house imaging software developed for the instrument, the mass spectrometry data cube underwent deconvolution, noise reduction and colour visualisation, resulting in the output of two types of in-situ molecular distribution heatmaps for prohibited additives:

Region A (3×6 mm, antihistamines): With extremely low background baseline noise, the regions enriched with target molecules exhibit distinctly bright signals, allowing clear differentiation between the spiked areas and the blank slide background, and providing an intuitive visualisation of the spatial distribution of the substance at a concentration of 10 ppb;

Region B (3×4 mm, hormones): Signals remain stable at the same ultra-low spiked concentration, and the distribution characteristics of different hormonal components can be clearly distinguished.

Figure 2: DESI/PI imaging of a mixture of cosmetics and a spiked sample (10 ppb) on a glass slide. A: antihistamines; B: hormonal compounds

Fig. 2: DESI/PI imaging of the cosmetic product mixed with a mixed standard (10 ppb) on a glass slide.  A: Antihistamine compounds; B: Hormonal compounds.

Conclusions

Utilising a proprietary DESI/PI hybrid ionisation imaging source coupled with an Agilent Q-TOF mass spectrometer, this method enables in situ visualisation of trace hormones and prohibited antihistamine compounds at 10 ppb in cosmetics without the need for complex sample preparation, detecting 42 types of antihistamines and 24 types of hormonal additives in a single analysis. Thanks to its excellent ionisation efficiency and spatial resolution, it produces clear, low-noise molecular distribution maps. Compared with traditional detection methods, it offers the key advantages of ultra-high sensitivity, simultaneous screening of multiple components and intuitive distribution characterisation, making it suitable for the rapid screening of cosmetic safety.