北化工 专业英语 质谱
- 格式：docx
- 大小：22.07 KB
- 文档页数：4
Although nominally a spectroscopic method, mass spectrometry is unlike other forms of spectroscopy because it dose not involve electromagnetic radiation. Instead it involves chemical manipulation (such as ionization and fragmentation) and the relative intensity of each peak is a measure of the quantity of the corresponding ionic species.1 mass spectrometry is an analytical tool used for measuring the molecular mass and elucidating molecular structure of a sample. For large samples such as biomolecules, molecular masses can be measured to within an accuracy of 0.01% of the total molecular mass of the sample i.e. within a 4 daltons (Da) or atomic mass units (amu) error for a sample of 40000Da. This is sufficient to allow minor mass changes to be detected, e.g. the substitution of one amino acid for another, or a post-translation modification,. For small organic molecules the molecular mass can be measure to within an accuracy of 5 ppm or less, which is often sufficient to confirm the molecular formula of a compound, and is also a standard requirement for publication in a chemical journal. Structural information can be generated using certain types of mass spectrometers, usually those with multiple analysers which are known as tandem mass spectrometer. This is achieved by fragmenting the sample inside the instrument and analyzing the products generated. This procedure is useful for the structural elucidation of organic compounds and for peptide or oligonucleotide sequencing. 虽然质谱名义上是光谱法，但是质谱法不同于其他形式的光谱，因为它不涉及到电磁辐射。相反，它通过化学方法控制(电离和碎片等)和各峰的相对强度测量的数量相应的离子物种。质谱分析是一种分析工具用于测量分子质量和阐明分子结构的一个示例。对于大样本如生物分子,分子质量可以测量精度内总数的0.01%中分子质量的样本即4道尔顿(Da)或原子质量单位(12)错误的样本40000。这是足以让小质量变化被发现,例如一个氨基酸的替换为另一个,或译后修改。有机小分子的分子质量可以衡量在一个精度5 ppm或更少,这通常是足以证实一种化合物的分子式,也是发表在《化学》标准要求。结构信息可以生成使用某些类型的质谱仪,通常有多个分析器被称为串联质谱仪。这是通过分裂仪器内的样本和分析生成的产品。这个过程是非常有用的为有机化合物的结构说明和肽或寡核苷酸测序。 Mass spectrometers are used in industry and academia for both routine and research purposes, The following list is just a brief summary if the major mass spectrometric applications Biotechnology: the analysis of proteins peptides oligonucleotide Pharmaceutical: drug discovery, combinatorial chemistry, pharmacokinetics, drug metabolism Clinical: neonatal screening, haemoglobin analysis, drug testing Environmental :PAHs, PCBs, water quality, food contamination Geological ：oil composition All mass spectrometers require a sample input system, an ionization source, a mass analyzer, and a detector. The sample has to be introduced into the ionization source of the instrument. Once inside the ionization source, the sample molecules are ionized, because ions are easier tio manipulate than neutral molecules. These ions are extracted into the analyser region of the mass spectrometer where they are separated according to their mass (m) to charge (z) ration (m/z). The separated ions are detected and this signal sent to a date system where the m/z ration are stored together with their relative abundance for presentation in put system or ion source volumes are under vacuum (10-6-10-8 torr in some ion sources, where the ions are initially formed ), so vacuum pumps of various types are required.2 Modern mass spectrometers have all of the components under computer control , with a computer-based data acquisition and processing system. Sample introduction ‘ The method of sample introduction to the ionization source often depends on the ionization method being used, as well as the type and complexity of the sample. The sample can be inserted directly into the ionization source, or can undergo some type of chromatography en route to the ionization source. This latter method of sample introduction usually involves the mass spectrometer being coupled directly to a high pressure liquid chromatography (HPLC), gas chromatography (GC) or capillary electrophoresis (CE) separation column, and hence the sample is separated into a series of components which then enter the mass spectrometer sequentially for individual analysis. Methods of sample ionization Many ionization methods are available and each has its own advantages and disadvantages, this ionization method to the used should depend on the type of sample under investigation and mass spectrometer available. Ionization methods include the following: Atmosphere pressure chemical ionization (APCI) Chemical ionization (CI) Electron impact (EI) Electrospray ionization (ESI) Fast atom bombardment (FAB) Field desorption field ionization (FD/FI) Matrix assisted laser desorption ionization (MALDI) Thermospray ionization (TSP) A chemical ionization (CI) source is considered a soft ionization source；it results in less fragmentation of analyte molecules and a simpler mass spectrum than that resulting from EI. Most importantly, the molecular ion is much more abundant using CI， allowing the determination of the molecular weight. If the CI process is soft enough the spectrum may consist almost entirely of only the molecular ion. Such a lack of fragmentation provides less structural information than an EI spectrum. If a fragmented EI spectrum is absent a molecular ion , then combining data from a CI spectrum containing a strong molecular ion will greatly assist interpretation of an unknown compound`s spectra. 3 The two modes complement one another for identification and quantitation of unknowns. During standard electrospray ionization (ESI), the sample is dissolved in a polar, volatile solvent and pumped through a narrow, stainless steel capillary (75-150 micrometers i.d. ) at a flow rate of between 1 μL/min and 1 mL/min. A high voltage of 3KV or 4KV is applied to the tip of the capillary, which is situated within the ionization source of the mass spectrometer, and as a consequence of this strong electric filed, the sample emerging from the tip is dispersed into an aerosol of highly charged droplets, a process that is aided by a coaxially introduced nebulizing gas flowing around the outside of the capillary.4 This gas, usually nitrogen, helps to direct the spray emerging from the capillary tip towards the mass spectrometer. The charged droplets diminish in size by solvent, are released from the droplets, some of which pass through a sampling cone or orifice into an intermediate vacuum region, and from there through a small aperture into the analyser of the mass spectrometer, which is held under high vacuum. The lens voltages are optimized individually for each sample. The ionization methods used for the majority of biochemical analyser are electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI), and these are described in more detail in section 5 and 6 respectively.
