An effective derivatization method for matrix-assisted laser desorption/ionization mass spectrometry of poly(acrylic acid)

✍ Scribed by Ryuichi Arakawa; Shigeki Egami; Shoji Okuno

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 112 KB
• Volume: 41
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/jms.1016

✦ Synopsis

An effective derivatization method for matrix-assisted laser desorption/ionization mass spectrometry of poly(acrylic acid) Matrix-assisted laser desorption/ionization (MALDI) 1,2 was developed as an effective soft ionization method for mass spectrometry (MS) of high molecular weight and thermally labile compounds that are difficult to analyze by other ionization methods. Various types of polymers have been studied by MALDI-MS. 3 -5 However, intense molecular ions of poly(acrylic acid), which has many carboxyl groups in the molecule, were sometimes not obtained because the polymer binds the contaminating metal cations tightly. Derivatization is a technique that has been widely used in many analytical methods such as gas chromatography (GC) and high-performance liquid chromatography (HPLC) to improve sensitivity. Barry et al. derivatized low molecular weight octylphenol polyethoxylates with phthalate anhydride to estimate accurate average molecular weights of the polymers by MALDI-MS. 6 However, derivatization has not been used extensively in MALDI. In this study effective derivatization methods designed to obtain intense molecular ions from poly(acrylic acid) were investigated.

Poly(acrylic acid) (average molecular weight: Mn, 1000), which has a tert-butyl group (M: 57 Da) and a hydrogen (M: 1 Da) as its end groups, was obtained from Polymer Laboratories (Amherst, MA, USA). Three different methods, which are extensively used for GC and HPLC measurements of carboxyl compounds, of derivatizing the carboxyl groups of the polymer were examined according to previous reports. 7 -9 The reaction procedures are shown in Scheme 1.

After the reaction the polymers (1 mM), 2,5-dihydroxybenzoic acid (100 mM), and sodium iodide (2 mM) were dissolved in O NH F F F