Quantitative determination of native and methylated cyclodextrins by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A method for the quantitative analysis of cyclodextrins using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry is described. To decouple the quantitative approach from the extreme dependence of the absolute ion signal on the experimental parameters of the MALDI technique, the method relies on the normalization of analyte molecular ion signals relative to internal reference molecular ion signals. For good crystal homogeneity and shot-to-shot reproducibility a new method of sample preparation using 4-hydroxy-α-cyanocinnamic acid as a matrix was developed. Linear calibration curves (r2 = 0.998) were obtained for both permethylated cyclodextrins with homologous standards and β-cyclodextrin using maltohexaose as internal standard. Furthermore, tests on different 2,3- and 2,6-di-O-methylated cyclodextrins were made. An excellent shot-to-shot reproducibility allowed the analysis of byproducts using the molecular ion signal of the product as internal standard. In each instance, the results demonstrate that MALDI is a viable approach for quantification of low-molecular-mass analytes.