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Rapid analysis of liquid food products and beverages using Ultrasonic Rapid Evaporative

Ionisation Mass Spectrometry. Daniel Simon1; Tamas Karancsi1; Steve Pringle2; Zoltan Takats3

1Waters Research Center, Budapest, Hungary; 2Waters Corporation, Wilmslow UK; 3Imperial College, London,UK

INTRODUCTION •Rapid Evaporative Ionisation Mass Spectrometry (REIMS) is a powerful tool for rapid classification and identification of complex biological matter based on their mass spectral fingerprint

•The method was proven to be useful when dealing with solid matter, like biological tissue or solid food (chocolate, leaves, etc.) using electrosurgical tools or laser for sample mobilisation, but its performance for liquid samples found to be quite compromised.

•A novel method is described here for REIMS analysis of liquid samples without sample preparation. Its applicability will be illustrated though case studies in food area.

METHODS A Waters Xevo G2-XS QToF masss spectrometer was used for the experiments. All spectra were acquired in negative ion mode.

For the ultrasonic sample introduction, a Sonic Systems P100 sonic processor and transducer was used. The applied transduction was ≈ 10 μm, the frequency was 40 kHz.

The REIMS method and Ultrasonic droplet generation is summarised on figures 1 and 2.

RESULTS Several MS and REIMS standards and commercially available liquid food products were sampled with the ultrasonic and ESI method, the acquired spectra can be found on figures 2 and 3.

A case study was conducted with different energy drinks to see if the system can be used as a quick identification method for liquids. The results are shown below. 20 – 45 spectra were collected per class and used in multivariate statistical analysis.

E-drink case study:

Characterization of disaccharide mixture based on MS/MS:

•Figure 6: An MS/MS case study of different sugars. 0.5mM of lactose and sucrose disaccharides were mixed together in water in different ratios and were introduced to MS/MS analysis. After the spectra was obtained a PCA model was built to differentiate the samples. The algorythm was capable of distinguishing the different ratios without major issues, a good lactose – sucrose ratio can be guessed based on MS/MS spectra.

CONCLUSION

•Here a new method for liquid sample introduction was described for Rapid Evaporative

Ionisation Mass Spectrometry.

•The Ultrasonic REIMS is a feasible method for sampling liquid food products and beverages

without any sample preparation.

•The method is capable of providing spectra for MS/MS studies and multivariate statistics - based food product differentiation

Figure 4: PCA - LDA model of 9 energy drink samples. 100 – 600 mass range was used with 1 Da binning. The 3D plot shows good separation between different flavours, sugar or sweetener content, and a good separation was achieved in general. Leave 20% out cross validation results were 99.3%.

Figure 5:An example of an Energy Drink scandal case. Several similar e-drink adulteration cases were unfolded in recent history, in these cases Ultrasonic REIMS could have been an useful tool in search for counterfeit products.

Figure 1: A general drawing of the Ultrasonic REIMS method. The liquid sample is injected in front of the ultrasonic horn without any sample preparation. Droplets are then generated via the ultrasonic vibration of the horn. Then the sample aerosol is introduced to the Mass Spectrometer through a sampling capillary, then the aerosol droplets hit a heated impactor surface where ions are generated.

Figure 3: Mass spectra of a few beverages. Several key compounds were identified using MS/MS and/or accurate mass measurements, for example: Disaccharides, citric acid, stearic and palmitic acid, sweeteners and flavouring agents.

Figure 2: Comparison between electrospray and Ultrasonic REIMS using lactose (341 Da MS/MS, 20 eV Collision Energy), Angiotensin II and porcine liver extract from Isopropanol.