Chemical Methods and Separations Group, Chemical Sciences Department, Pacific Northwest Laboratory, P.O. Box 999, MS P8-19, 99352, Richland, WA, USA.
J Am Soc Mass Spectrom. 1993 Jul;4(7):566-77. doi: 10.1016/1044-0305(93)85018-S.
A novel electrospray ionization/Fourier transform ion cyclotron resonance mass spectrometer based on a 7-T superconducting magnet was developed for high-resolution accurate mass measurements of large biomolecules. Ions formed at atmospheric pressure using electrospray ionization (ESI) were transmitted (through six differential pumping stages) to the trapped ion cell maintained below 10(-9) torr. The increased pumping speed attainable with cryopumping (> 10(5) L/s) allowed brief pressure excursions to above 10(-4) torr, with greatly enhanced trapping efficiencies and subsequent short pumpdown times, facilitating high-resolution mass measurements. A set of electromechanical shutters were also used to minimize the effect of the directed molecular beam produced by the ES1 source and were open only during ion injection. Coupled with the use of the pulsed-valve gas inlet, the trapped ion cell was generally filled to the space charge limit within 100 ms. The use of 10-25 ms ion injection times allowed mass spectra to be obtained from 4 fmol of bovine insulin (Mr 5734) and ubiquitin (Mr 8565, with resolution sufficient to easily resolve the isotopic envelopes and determine the charge states. The microheterogeneity of the glycoprotein ribonuclease B was examined, giving a measured mass of 14,898.74 Da for the most abundant peak in the isotopic envelope of the normally glycosylated protein (i.e., with five mannose and two N-acetylglucosamine residues (an error of approximately 2 ppm) and an average error of approximately 1 ppm for the higher glycosylated and various H3PO4 adducted forms of the protein. Time-domain signals lasting in excess of 80 s were obtained for smaller proteins, producing, for example, a mass resolution of more than 700,000 for the 4(+) charge state (m/z 1434) of insulin.
一种基于 7-T 超导磁体的新型电喷雾电离/傅里叶变换离子回旋共振质谱仪被开发出来，用于对大生物分子进行高分辨率精确质量测量。使用电喷雾电离（ESI）在大气压下形成的离子通过（经过六个差分抽气阶段）传输到保持在 10^-9 托以下的囚禁离子阱中。低温泵的抽吸速度可达 10^5 L/s，允许压力短暂上升到 10^-4 托以上，从而大大提高了捕获效率，随后的抽气时间缩短，便于进行高分辨率质量测量。还使用了一组机电快门来最大限度地减少 ES1 源产生的定向分子束的影响，并且仅在离子注入期间打开。结合使用脉冲阀气体入口，囚禁离子阱通常在 100 ms 内填充到空间电荷限制。使用 10-25 ms 的离子注入时间，可以从 4 fmol 的牛胰岛素（Mr 5734）和泛素（Mr 8565）获得质谱，分辨率足以轻松分辨同位素包络线并确定电荷状态。糖蛋白核糖核酸酶 B 的微异质性也得到了检查，给出了正常糖基化蛋白质同位素包络中最丰富峰的测量质量为 14898.74 Da（即具有五个甘露糖和两个 N-乙酰葡萄糖胺残基（误差约为 2 ppm），并且对于较高糖基化和各种 H3PO4 加合物形式的蛋白质的平均误差约为 1 ppm。对于较小的蛋白质，获得了持续时间超过 80 s 的时域信号，例如，胰岛素的 4+电荷状态（m/z 1434）的质量分辨率超过 700000。
