Quantitative Thin-Layer Chromatography/Mass Spectrometry Analysis of Caffeine Using a Surface Sampling Probe Electrospray Ionization Tandem Mass Spectrometry System

Abstract

Quantitative determination of caffeine on reversed-phase C8 thin-layer chromatography plates using a surface sampling electrospray ionization system with tandem mass spectrometry detection is reported. The thin-layer chromatography/electrospray tandem mass spectrometry method employed a deuterium-labeled caffeine internal standard and selected reaction monitoring detection. Up to nine parallel caffeine bands on a single plate were sampled in a single surface scanning experiment requiring 35 min at a surface scan rate of 44 mum/s. A reversed-phase HPLC/UV caffeine assay was developed in parallel to assess the mass spectrometry method performance. Limits of detection for the HPLC/UV and thin-layer chromatography/electrospray tandem mass spectrometry methods determined from the calibration curve statistics were 0.20 ng injected (0.50 muL) and 1.0 ng spotted on the plate, respectively. Spike recoveries with standards and real samples ranged between 97 and 106% for both methods. The caffeine content of three diet soft drinks (Diet Coke, Diet Cherry Coke, Diet Pepsi) and three diet sport drinks (Diet Turbo Tea, Speed Stack Grape, Speed Stack Fruit Punch) was measured. The HPLC/UV and mass spectrometry determinations were in general agreement, and these values were consistent with the quoted values for two of the three diet colas. In the case of Diet Cherry Coke and the diet sports drinks, the determined caffeine amounts using both methods were consistently higher (by approximately 8% or more) than the literature values.

Determination of Caffeine at a Nafion‐Covered Glassy Carbon Electrode

“…Caffeine concentrations of Table 1 are in agreement with recent literature data [25,26]. In fact, as indicated by the American Beverage Association [26], caffeine level in colas ranges from 2.8 mg to 4.6 mg per US fl.…”

Liquid Microjunction Surface Sampling Probe Fluid Dynamics: Computational and Experimental Analysis of Coaxial Intercapillary Positioning Effects on Sample Manipulation

“…The flow of the solution in the probe follows a similar path to previously published iterations. [1][2][3][4][5][6][7][8][9][10][11][12][13]16] A syringe pump (Harvard Apparatus, South Natic, MA, USA) was used to drive LC/MS grade methanol or water solutions (Fisher Scientific, Fair Lawn, NJ, USA) through the probe at 15 μL/ min. The geometry of the probe, constructed of a 1/16th inch PEEK tee and fittings (Upchurch Scientific, Oak Harbor, WA, USA), directs the extraction solution from the side-arm to the surface via a glass microcapillary (Drummond Scientific Co, Broomwall, PA, USA) externally coaxial to a fused silica capillary (Polymicro Technologies Inc, Phoenix, AZ, USA), which led back through the tee.…”

“…In the most common LMJ-SSP geometry, the extraction solvent is pumped to the surface through the annular space between two coaxial tubes at the sampling end of the probe and is then pulled into and through the inner tube to the ionization source via a self-aspirating electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) emitter. [2][3][4][5][6][7][8][9][10][11][12][13] Recently, a non-coaxial, dual capillary, LMJ-SSP operating at nanoelectrospray flow rates was described and implemented by Roach et al [14,15] The LMJ-SSP has had two general methods of operation, viz., a discrete spot sampling method and a scanning (or imaging) method, each of which can be used either manually or as part of an automated procedure. [16] In the discrete sampling method, selected single spots from a surface are analyzed by forming a liquid microjunction separately at each of those points.…”

Qualitative and Quantitative Control of Carbonated Cola Beverages Using 1H NMR Spectroscopy

“…Another paper described the quantitative determination of caffeine in sugar-free soft drinks on reversed-phase C8 thin-layer chromatography plates using a surface sampling electrospray ionization system with tandem mass spectrometry detection. 22 LODs for HPLC/UV and thin-layer chromatography/electrospray tandem mass spectrometry methods were 0.20 ng injected (0.50 μL) and 1.0 ng spotted on the plate, respectively. Such low limits of detection of caffeine are not possible with NMR spectroscopy but are also not required for the soft drinks, which contain in general around 100 mg/L of caffeine.…”