# Metal-Organic Frameworks Characterization via Inverse Pulse Gas Chromatography
## 3 Applications of IGC for the Characterization of MOFs  
IGC is considered a very effective surface energy analysis tool for the characterization of various materials' surface properties. Here, we review recent applications of IGC in analyzing the surface properties of MOF materials. These applications include gases, hydrocarbons, and solvents, which reflect the wide-ranging advantages that can be achieved by applying the IGC technique (Table 1). The IGC evaluations reviewed here were are carried out using conventional GC at infinite dilution, which is usually equipped with a flame ionization detector (FID) or a thermal conductivity detector (TCD).  
The studied MOFs were packed into either metallic or glass columns of 2-80 cm length, with 30 cm being the most commonly used length, and a standard internal diameter (ID) of 3.18 mm with actual utilization of the columns ranging from 0.53 to 5.3 mm ID (Table 1). Whether prepared or purchased, the adsorbent powder was either packed directly into the column or pressed under high pressure (\(\sim\)600 bar) into disks, then broken into fragments and sieved to the proper fraction for a higher homogeneity.  
Packing of the tested material was achieved either through vacuum suction of the dry powder or by pushing the suspended powder into the empty tubing. In either case, good packing was usually accomplished using mechanical vibration or an ultrasonic water bath; thereafter, the column ends were plugged with glass wool to avoid the loss of adsorbent.  
Silica wall-coated open tubular capillary columns have been used successfully for the IGC calculations for the coated material. Capillary columns coated with MOFs have been used in two forms: either a controlled approach using secondary building units (SBUs) for in situ preparation of the MOF material [24], or as a dynamic coating after preparation [73]. Estimating the physicochemical properties of MOFs incorporated into an organic monolithic capillary column as a composite is an unusual platform for IGC studies; however, it was successful [71].  
Generally, high purity nitrogen or helium (\(\geq\)99.99%) is applied as the carrier gas with flow rates ranging from 20 to 60 mL min\({}^{-1}\); exceptions include 1 and 5.3 mL min\({}^{-1}\) flow rates, which were used in the case of open tubular coated columns [24; 73], 5.5 mL min\({}^{-1}\) for lower molecular weight N\({}_{2}\)/O\({}_{2}\) gaseous probes [78], and about 0.6 mL min\({}^{-1}\) for a monolithic column [71].  
Prior to the measurements, the most fulfilling activation procedure of the studied material within the column is performed by heating the column to a suitably high temperature, using a slow ramp heating under a constant flow of the inert carrier gas overnight, that maintained the required thermal stability of the material.  
Then, a trace amount of the probe molecules is then injected as a vapor phase. The adsorption data is collected under a wide range of temperatures, starting from room temperature up to 300 \({}^{\circ}\)C, depending on the nature of the adsorbed probes, with the retention time of the separated probes being the primary information collected during an IGC experiment.