Applications of DART-MS for food quality and safety assurance in food supply chain : DART-MS FOR FOOD QUALITY AND SAFETY ASSURANCE

A new ion source has been developed for rapid, noncontact analysis of materials at ambient pressure and at ground potential. The new source, termed DART (for "Direct Analysis in Real Time"), is based on the reactions of electronic or vibronic excited-state species with reagent molecules and polar or nonpolar analytes. DART has been installed on a high-resolution time-of-flight mass spectrometer (TOFMS) that provides improved selectivity and accurate elemental composition assignment through exact mass measurements. Although DART has been applied to the analysis of gases, liquids, and solids, a unique application is the direct detection of chemicals on surfaces without requiring sample preparation, such as wiping or solvent extraction. DART has demonstrated success in sampling hundreds of chemicals, including chemical agents and their signatures, pharmaceutics, metabolites, peptides and oligosaccharides, synthetic organics, organometallics, drugs of abuse, explosives, and toxic industrial chemicals. These species were detected on various surfaces, such as concrete, asphalt, human skin, currency, airline boarding passes, business cards, fruits, vegetables, spices, beverages, body fluids, horticultural leaves, cocktail glasses, and clothing. DART employs no radioactive components and is more versatile than devices using radioisotope-based ionization. Because its response is instantaneous, DART provides real-time information, a critical requirement for screening or high throughput.

Paper spray is developed as a direct sampling ionization method for mass spectrometric analysis of complex mixtures. Ions of analyte are generated by applying a high voltage to a paper triangle wetted with a small volume (<10 microL) of solution. Samples can be preloaded onto the paper, added with the wetting solution, or transferred from surfaces using the paper as a wipe. It is demonstrated that paper spray is applicable to the analysis of a wide variety of compounds, including small organic compounds, peptides, and proteins. Procedures are developed for analysis of dried biofluid spots and applied to therapeutic drug monitoring with whole blood samples and to illicit drug detection in raw urine samples. Limits of detection of 50 ng/mL (or 20 pg absolute) are achieved for atenolol in bovine blood. The combination of sample collection from surfaces and paper spray ionization also enables fast chemical screening at high sensitivity, for example 100 pg of heroin distributed on a surface and agrochemicals on fruit peels are detectable. Online derivatization with a preloaded reagent is demonstrated for analysis of cholesterol in human serum. The combination of paper spray with miniature mass spectrometers offers a powerful impetus to wide application of mass spectrometry in nonlaboratory environments.