Easy protocol for making a good E-sinapinic acid matrix for neutral and sulfated carbohydrate MALDI-MS analysis

• Published in: Analytical methods 2015-01, Vol.7 (19), p.8478-8483
• Main Authors: Salum, María L., Schmidt De León, Tobias, Erra-Balsells, Rosa
• Format: Article
• Language: English
• Subjects: Carbohydrates; Irradiation; Isomers; Lasers; Mathematical analysis; Matrix assisted; Raw materials
• ISSN: 1759-9660; 1759-9679
• DOI: 10.1039/C5AY01484K

Since the introduction of 3,5-dimethoxy-4-hydroxycinnamic acid (SA) and α-cyano-4-hydroxycinnamic acid as matrices, the successful application of matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS) started. Cinnamics can exist as two different geometric isomers, the E - and Z -forms. The commercially available cinnamics currently used as matrices are E -cinnamics; they do not perform well in general for carbohydrate analysis. Recently, Z -cinnamic acid properties for matrices were studied and compared with those of the corresponding E -isomer. For the analysis of neutral/sulfated carbohydrates the outstanding performance for Z -SA was demonstrated. As the synthesis of pure Z -cinnamic acids requires several steps and the manipulation of some not friendly chemicals ( i.e. , bad smelling organic amines, toxic compounds, organic solvents, etc. ), here we describe a convenient new one-pot protocol to prepare in situ , in a methanolic solution of commercial E -acid ( i.e. , E -SA), a Z - + E - mixture by photoisomerization (UVB irradiation); then, the only step required is the addition of water to the irradiated solution to become ready as a matrix stock solution for MALDI experiments. This “photo-made at home” matrix performs carbohydrate analysis with similar results to the corresponding Z -acid. The results here show that this novel protocol is a tool of choice for the direct, rapid and sensitive detection of neutral and sulfated carbohydrates without any tedious Z -cinnamic acid preparation and isolation.