Direct deposit interface FTIR

Figure 3 Schematic of direct deposition GC-FTIR interface (based on Bio-Rad/Digilab Tracer).

Consequently, the major experimental options for the analyst are packed or capillary SFC, mobile phase with/without modifier and off-line or on-line mode, namely direct deposition (DD-SFC-FUR) vs. flowcell. Both small-bore packed columns and narrow-bore open-tubular columns have been used for SFC-FTIR analysis using a pressure-stable, thermostated, flow-cell or solvent elimination interfaces. 

There are three different types of GC/FTIR interfaces light-pipe, matrix isolation (MI), and cryo-deposition (also direct-deposition, cryotrapping). In the two latter techniques, the sample is deposited on a surface before measurement of spectra. All three techniques have been used for the analysis of CWC-related chemicals. Light-pipe interface has been the most popular, even though the usage of cryodeposi-tion in this type of analysis has been increasing over the years. 

Cryodeposition is the newest interface type for a GC/FTIR instrument. In this system, the eluents in the GC effluent are frozen on an IR transparent slide, which is cooled using liquid nitrogen. The carrier gas evaporates in the process so that the chemicals are directly deposited on the slide surface. Transmission spectra are then measured through the slide. These spectra are like normal condensed phase spectra, with rare exceptions. The sensitivity is five times better than in light-pipe, and the same or even slightly better than in GC/MI/FTIR. 

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