We have used MALDI-TOF mass spectrometry to characterize a selection of dyes from the Schweppe dye collection and pigments from the Tate Gallery collection. MALDI-TOF mass spectra of such samples are easily obtained and, through observation of both positive and negative ion spectra, provide a convenient, versatile method for dye characterization and identification. Such pairs of positive and negative ion spectra immediately distinguish between acidic and basic dyes and provide the characteristic mass of either the molecular ion or a simply related fragment ion. This approach is especially useful in situations where very small amounts of analyte are available, as in museum research and forensic analysis. In the case of textile dyes, we have carried out identification on material from single fibers and, with insoluble pigments, have begun to identify components of historically important pastel sticks from submicrogram samples. T he special advantages of matrix assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry have been applied principally to large molecules, such as synthetic polymers, proteins, and nucleic acids. However, there have been some notable applications of this mass spectrometric method to small molecule analytes [1,2]. Simplicity of sample preparation, rapid spectrum acquisition, high sensitivity, and relative tolerance to impurities make MALDI-TOF attractive here. Direct laser desorption ionization (LDI) mass spectrometry, with no matrix, has also been explored for the investigation of inks and dyes [3,4].We assess here the utility of MALDI-TOF mass spectrometry for the identification of dyes and pigments from standard collections; the molecular masses of these substances are in the 200 to 1100 Da range. Application of the new solvent-free vortex grinding method for sample preparation [5,6] is well suited for the small sample sizes available in this work and is also assessed. Experimental Sample PreparationWe have utilized both a traditional overlay method and the new solvent-free vortex grinding method. In the overlay method, 4 L of a saturated methanol solution of 9-aminoacridine (9AA) matrix (Aldrich S517216) was deposited on the stainless steel target and allowed to air dry. One L of methanolic dye solution from the Schweppe collection [7] was then applied near the edge of the matrix spot.For the solvent-free method of Hanton and Parees [5], the sample and matrix were intimately ground in a 4 mL glass vial containing two 4.5 mm diameter zinc-plated steel balls using a vortex mixer. For dyes, we applied 1 L of the dye solution to about 15 mg of dry 9AA matrix in the vial, evaporated the methanol under vacuum, scraped the vial walls with a spatula to free the solid deposit, and proceeded with the vortex grinding. For insoluble pigments, about 15 mg of 9AA matrix was added to a microcentrifuge tube containing a barely visible amount of pigment dust (ϳ0.5 g) and mixed with a spatula; this mixture was then transferred to the 4 mL glass vial with the metal balls for vorte...