Rapid analysis of caffeine in various coffee samples employing direct analysis in real-time ionization–high-resolution mass spectrometry

Abstract

The development and use of a fast method employing a direct analysis in real time (DART) ion source coupled to high-resolution time-of-flight mass spectrometry (TOFMS) for the quantitative analysis of caffeine in various coffee samples has been demonstrated in this study. A simple sample extraction procedure employing hot water was followed by direct, high-throughput (<1 min per run) examination of the extracts spread on a glass rod under optimized conditions of ambient mass spectrometry, without any prior chromatographic separation. For quantification of caffeine using DART-TOFMS, an external calibration was used. Isotopically labeled caffeine was used to compensate for the variations of the ion intensities of caffeine signal. Recoveries of the DART-TOFMS method were 97% for instant coffee at the spiking levels of 20 and 60 mg/g, respectively, while for roasted ground coffee, the obtained values were 106% and 107% at the spiking levels of 10 and 30 mg/g, respectively. The repeatability of the whole analytical procedure (expressed as relative standard deviation, RSD, %) was <5% for all tested spiking levels and matrices. Since the linearity range of the method was relatively narrow (two orders of magnitude), an optimization of sample dilution prior the DART-TOFMS measurement to avoid saturation of the detector was needed.

Analytical methods applied for the characterization and the determination of bioactive compounds in coffee

“…The coffee brew sample for this analysis can be placed directly in the DART ion source, and time of flight mass spectrometer enables high-resolution measurement of obtained mass spectra, i.e., high selectivity. Variations of signal due to matrix effect and ion source instability were compensated by addition of isotopically labeled caffeine standard [62].…”

Identification of Drugs in Parenteral Pharmaceutical Preparations from a Quality Assurance and a Diversion Program by Direct Analysis in Real-Time AccuTOFTM-Mass Spectrometry (DART-MS)

“…The individual total ion chromatograms were produced as a function of response vs. time and were analyzed for each of the orifice 1 voltages. An internal mass calibration was completed by analyzing polyethylene glycol (PEG 600) with an average molecular weight of 600 Da diluted in methanol (12). The mass calibration was considered acceptable if the curve fit was less than or equal to 1E-1 over the entire mass range.…”

“…It is used to analyze a wide variety of substances "including chemical warfare agents and their signatures, pharmaceutics, metabolites, peptides and oligosaccharides, synthetic organics and organometallics, drugs of abuse, explosives and toxic industrial chemicals" (11). DART-MS offers advantages over traditional mass spectrometry techniques including direct sample examination, minimal or no sample preparation and high sample throughput (12). By coupling a DART ion source to a time-of-flight mass analyzer accurate mass can be measured for compounds present on the substrate.…”

Multimodal Vacuum-Assisted Plasma Ion (VaPI) Source with Transmission Mode and Laser Ablation Sampling Capabilities

“…Reproducible sampling and quantitation with plasma discharge sources have proven to be complicated, necessitating the use of internal standards [22,23] and automated sampling approaches [24]. Much effort has been dedicated to improving the sensitivity and sampling efficiency of these ionization techniques with the aid of simulations that model gas flow patterns [25,26] and real-time visualization of source gas flow profiles using the Schlieren technique [27][28][29].…”