Fast analysis of caffeinated beverages using laser diode thermal desorption mass spectrometry (LDTD-MS/MS)

ABSTRACT

A rapid method for quantitative caffeine analysis in carbonated and non-carbonated beverages and liquid dietary supplement products was developed based on the direct sample introduction technique of laser diode thermal desorption atmospheric pressure chemical ionisation with tandem mass spectrometry (LDTD-MS/MS). Product samples were diluted with a mixture of methanol, water, and d₃-caffeine internal standard. Sample aliquots were filtered, spotted on a metal-lined LDTD microtitre plate, dried, and thermally desorbed for subsequent ionisation and analysis by MS/MS analysis. Each sample required a 6 s desorption, and sample-to-sample analysis time of less than 30 s per sample. Caffeine yielded a linear calibration curve over the range 0.5–100 μg mL⁻¹ (R² > 0.995). Caffeine recoveries from fortified samples ranged from 97% to 107% with <5% RSD. The caffeine determination was not affected by matrix interferences despite the large range of ingredients, vitamins, sweeteners, extracts, and additives present in the products tested, even though LDTD-MS/MS is a whole-sample desorption technique with no separation of matrix background. The method detection limit was below 0.12 μg mL⁻¹. The method was applied to 33 caffeinated products and LDTD-MS/MS quantitative results closely correlated (R² > 0.998) with the regulatory standard HPLC-UV method (AOAC Official Method 979.08).

Graphical Abstract

KEYWORDS:

• Caffeine
• direct analysis mass spectrometry
• laser diode thermal desorption
• energy drinks
• quantitative analysis

Acknowledgments

The authors acknowledge Andrea Heise, Martha Schwartz, and Thomas Conley for HPLC analysis of energy drink and energy shot samples, and to Susan Carlson for her assistance with manuscript preparation.

Disclosure statement

No potential conflict of interest was reported by the authors. Reference to any commercial materials, equipment, or process does not, in any way, constitute approval, endorsement, or recommendation by the U.S. Food and Drug Administration. In addition, the views expressed in this article are those of the author(s) and may not reflect the official policy of the Department of Health and Human Services, the U.S. Food and Drug Administration, or the U.S. Government.