The most extensively used interfaces for a GC-MS are electron impact ionization (EI) and chemical ionization selleckbio (CI) modes. However, in modern GC�CMS systems, various other types can be used that allow identification of molecular ion. For example, an orthogonal TOF mass spectrometry coupled with GC is used for confirmation of purity and identity of the components by measuring exact mass and calculating elemental composition. Nowadays, a GC-MS is integrated with various on-line MS databases for several reference compounds with search capabilities that could be useful for spectra match for the identification of separated components. LC-IR The hyphenated technique developed from the coupling of an LC and the detection method infrared spectrometry (IR) or FTIR is known as LC-IR or HPLC-IR.
While HPLC is one of the most powerful separation techniques available today, the IR or FTIR is a useful spectroscopic technique for the identification of organic compounds, because in the mid-IR region the structures of organic compounds have many absorption bands that are characteristic of particular functionalities, e.g., �COH, �CCOOH, and so on. However, combination of HPLC and IR is difficult and the progress in this hyphenated technique is extremely slow because the hyphenated technique’s 237 absorption bands of the mobile phase solvent are so huge in the mid-IR region that they often obscure the small signal generated by the sample components. In addition, as a detection technique, IR is much less sensitive compared to various other detection techniques, e.g., UV and MS.
The recent developments in HPLC-IR technology have incorporated two basic approaches based on interfaces applied in HPLC-IR or HPLC-FTIR. One is a flow-cell approach and the other is a solvent-elimination approach. The approach used with the flow cell in LC-IR is similar to that used in UV�Cvis and other typical HPLC detectors. In this case, absorption of the mobile phase induces the interference of the detection of sample component absorption bands, but some transparent region of the mid-IR range produces detection possibility. For example, if one uses a mobile phase of a deuterated solvent such as heavy water or perdeuterated methanol, IR can monitor many organic compounds that have C�CH structures in the molecules. The solvent-elimination approach is the preferred option in most of the LC-IR operations.
After the mobile phase solvent is eliminated, IR detection is carried out in some medium that has a transparency for IR light. Generally, KBr or KCl salts Brefeldin_A are used for the collection of sample components in the eluent, and heating up the medium before IR detection eliminates the volatile mobile phase solvents. There are two types of interfaces for the solvent-elimination approach: diffuse-reflectance infrared Fourier transform (DRIFT) approach and buffer-memory technique.