A nitrocellulose matrix for infrared matrix-assisted laser desorption/ionization of polycyclic aromatic hydrocarbons.
A nitrocellulose matrix for infrared matrix-assisted laser desorption/ionization of polycyclic aromatic hydrocarbons.
复制标题
用于多环芳烃红外基质辅助激光解吸/电离的硝化纤维基质。
DOI：
10.1002/rcm.1296
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发表时间：
2004
期刊：
影响因子：
--
通讯作者：
Murray,KermitK
中科院分区：
文献类型：
--
作者：
Jackson,ShelleyN;Dutta,SucharitaM;Murray,KermitK
Matrix-assisted laser desorption/ionization (MALDI) is a powerful mass spectrometry technique, but is primarily used for polar compounds. 1 Application of MALDI to non-polar compounds is difficult due to problems with compatibility of the analyte, matrix, and the solvent in which they are dissolved prior to deposition on the MALDI target. Performing MALDI with polycyclic aromatic hydrocarbons (PAHs) can be particularly challenging due to the vastly different properties of solvents required for matrix and analyte. An elegant method for circumventing the problem in finding a common solvent for matrix and PAH is to dispense with the solvent entirely and mix the matrix and analyte as powders. 2 With mixed powder matrices, the accessible upper mass range for PAHs is 3000Da. A liquid matrix can also be useful if a solvent for the analyte also functions as a matrix or if a suitable mixture of materials can be found. For example, a matrix consisting of K4 [Fe (CN) 6] dissolved in glycerol has been shown to be effective for the analysis of a wide range of hydrophobic compounds. 3 Recently, an infrared laser at 10.6 μm was used with the solvent sulfolane for ionization of PAHs with minimal interferences from matrix and impurities. 4 Nitrocellulose has been used as a matrix for plasma desorption mass spectrometry with great success. 5, 6 Nitrocellulose has also found extensive use as a component of MALDI sample preparation as a ‘co-matrix’along with a traditional solid matrix. A thin layer of nitrocellulose deposited on the MALDI sample target prior to the addition of a matrix and analyte solution improves sample homogeneity and reduces the effects of sample impurities in UV-MALDI. 7, 8 With liquid-matrix IR-MALDI, a nitrocellulose co-matrix improves the sample durability and the shot-to-shot signal stability. 9In this work, nitrocellulose was used as the matrix for mid-infrared MALDI of PAHs. The sample targets were prepared by depositing a thin layer of nitrocellulose onto a metal surface and allowing it to dry. The PAH of interest was then deposited on the nitrocellulose from a solution of dichloromethane. Because the nitrocellulose and PAH solution are deposited sequentially, there is no problem with solvent compatibility or co-crystallization as with conventional MALDI. The mass spectrometer used in this study is a linear time-of-flight instrument with delayed ion extraction that has been described in detail previously. 9 Samples are deposited on a stainless steel target that is inserted into the ion source chamber through a vacuum insertion lock. A Nd: YAG pumped optical parametric oscillator (OPO) that is tunable from 1.45–4.0 μm was used to ionize the sample. The OPO output beam was focused to a spot size of 200 x 300 μm measured using laser burn paper and a measuring microscope. The IR laser energy was attenuated to achieve a fluence of approximately 500 J/m2. The analytes, anthracene (97%, Aldrich Chemical Co., Milwaukee, WI, USA), benzo [a]-pyrene (97%, Aldrich) and dibenz [a,-h] anthracene (97%, Aldrich), were used as obtained from the manufacturer without further purification. The matrices used were nitrocellulose (10% in amyl acetate, Ernest F. Fullman, Latham, NY, USA) and a 10: 1 (v/v) mixture of sulfolane (99%, Aldrich) and glycerol (99.7%, Fisher Scientific, Fair Lawn, NJ, USA). PAH samples were prepared by depositing a 10 μL volume of 0.5% nitrocellulose in acetone on the sample target and allowing it to dry. Next, a 10 μL volume of a 5 mM solution of the PAH of interest in dichloromethane was deposited on the nitrocellulose layer and allowed to dry before the target was inserted into the mass spectrometer for analysis. For
