Potential Scope of Hyphenated Mass Spectroscopic Techniques
Hyphenated techniques involve physical coupling of instruments through a compatible interface. Hyphenation results in a marked improvement of analysis in terms of speed, specificity and sensitivity. The benefits of coupling are realized mainly in chromatographic separations involving the popularGC和HPLCtechniques. Such combinations have received a great deal of attention from analytical chemists for identification and quantification of complex mixtures. The key application areas are:
- 毒品分析
- 毒药及其代谢物
- Clinical screening
- Pesticide residue analysis
- 法医调查
- Foods and flavours
- Petroleum products
Mass spectral libraries are available commercially for common constituents of several synthetic as well as natural compounds. Such libraries and in-house developed libraries offer positive identification of sample constituents in different product categories.
Hyphenation with Gas Chromatography (GC- MS)
GC - MS将气相色谱仪的分离能力与质谱仪的分辨率相结合。它是第一种连通技术，其有助于先进的复合混合物的分离和定量，所述复杂的混合物包含挥发性和半挥发性化合物，其在高温下保持其同一性。GC和MS都相互补充但由于压力范围差异（大气压或更高的压力）和MS（\（10 ^ - ^ 5到10 ^ - ^ - 6 \）Torr的真空）是合适的界面在没有液体携带的情况下两种仪器之间的样品转移所需的样品。
CC – MS provides useful information on volatile mixture components, solvent residues, drugs and poisons and the analyst is able to save valuable time with the help of mass spectral libraries for comparing the data from unknown compounds.
Liquid chromatography-Mass spectrometry (LC – MS)
LC – MS is today is an accepted powerful technique which permits identification and quantification to a very high degree of accuracy. The liquid chromatograph with its wide option of separation column sizes, stationary phases and detectors helps separate sample constituents, impurities and other degradation products while the mass spectrometer helps resolve and identify the various molecular mass fragments on the basis of their mass to charge ratios.
LC - MS在移动相流量通常约为1ml / min时构成独特的挑战。这种流速将大量的液体溶剂引入了需要去除的真空系统中以防止损坏。Different approaches are in useto effectively ionize the molecules and remove the solvent. Electro spray ionization (ESI) and atmospheric pressure chemical ionization (APCI) are two main interfaces which are used for majority of applications.
The soft ionization techniques generally used for large molecules such as poly aromatics, peptides and proteins mainly result in the molecular ion and only a small number of fragmented molecules. Significant improvements in number of ionized species have been achieved through collision – induced subsequent dissociation of the resulting molecular ions. Such high degree of fragmentation is achieved through tandem mass spectrometry (LC – MS- MS). This technique is gaining popularity due to its capacity to provide high levels of separations and low detection limits. Its key features and benefits will be covered in subsequent articles.
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