# Metal-Organic Frameworks Characterization via Inverse Pulse Gas Chromatography
## 1 Introduction  
To help identify the potential application of a microporous solid in separation or catalysis, theoretical or experimental determination of its basic adsorption properties and sorption behavior is a beneficial tool. Gathering information about the surface activity of these microporous materials provides a deeper understanding of their performance and continual development. Consequently, it is important to determine the surface properties that indicate the surface's ability to contribute to both dispersive and specific interactions. The adsorption enthalpy and associated physicochemical parameters of a material may be derived directly from calorimetric measurements or indirectly by the adsorption constant temperature dependence obtained by volumetric, gravimetric, or chromatographic adsorption measurements [1; 2; 3; 4; 5; 6; 7; 8; 9]. Alkane adsorption molecular modeling via force fields for zeolites has been improved to such an extent over the last decade that great canonical Monte Carlo models can now be applied to forecast zeolites' adsorption behavior at high levels of pore filling [10; 11; 12]. Inverse gas chromatography (IGC) is recognized as a proper and fast tool for characterizing the surface properties of porous solids, with a minimal adsorbent amount needed for reliable calculations and shorter experimental times compared to other techniques used for thermodynamic characterization. One of the unique features of IGC is that no specific or complicated preparation procedure of samples is necessary. Relative to other surface energy analysis techniques, IGC requires minimal sample preparation [13]. One can easily and accurately use the IGC technique to characterize various crystalline, composite, amorphous, or even fibrous solids. Without the need for any extrapolation, the enthalpies of adsorption measured with IGC and other methods show excellent consistency [14; 15; 16]. Since IGC has a superior efficiency at infinite dilution, it can differentiate between characteristic variations that other methods, such as conventional wettability measurements, do not identify [15]. For example, the probability of observing the differences associated with surface group orientations is one advantage of using IGC in researching acid-base specific properties [15]. Compared to analytical gas chromatography (GC), the mobile and stationary phases and roles are reversed in IGC. In IGC, the explored material represents the stationary phase. The injected known molecules within the mobile phase are considered probes used to investigate the physicochemical properties of the stationary phase. The first attempt to introduce IGC was by Nobel Laureates [PERSON] and [PERSON] in 1941 [17]. In 1960, [PERSON] gave the emerged IGC technique its name [18]. Furthermore, he was a key player in developing chromatography and the field of surface chemistry [19]. GC was identified by [PERSON] and [PERSON] as a versatile \"indispensable analytical instrument\" for applications other than defining mixture constituents [20]. In the 1970s, IGC became more familiar when it proved to be a promising method in investigating the surface and bulk properties of polymers and related materials [21]. Polymeric studies are still the most significant application of IGC judging by the large number of related publications [22]. In principle, IGC experiments can be conducted by either a pulse or frontal technique. For a pulse technique, a specific portion of the tested molecule is injected. With the help of a carrier gas, this pulse is transferred across the system through a column that is packed with the studied material. A chromatographic peak appears as a result of the adsorption and desorption processes within the column. On the other hand, in the frontal technique, the tested molecule is injected perpetually into the system, and consequently, a breakthrough curve will be the output chromatogram [21].