In our previous blog, we explained the differences between NanoPak-C All Carbon microbeads and alkyl bonded silica. In this blog, we delve into a follow-up question we often receive: "How is NanoPak-C different from other types of commercially available carbon-based media?" This question requires a nuanced response.
There are a variety of commercially available carbon media. For simplicity, we are categorizing them into two broad groups:
Group 1. Graphitized carbon blacks (GCBs). These products are adsorbents similar to activated carbon. They vary from very weak to medium/strong – the strongest sorbents. Their shape is spherical or irregular and size is typically greater than 40 µm. Thus, depending on this strength, they will capture an analyte very efficiently, but the release or elution of these adsorbed analytes is poor to suboptimal. Their primary use is during sample clean-up to remove impurities or nuisance compounds. Thus, these products are widely used in solid phase extraction workflows. Carbograph, Carbopack, Carboxen, and Carbotrap are some examples of GCBs.
Group 2. Porous graphitic carbons (PGCs). These products are stationary phase media suitable for reverse phase chromatography. Their shape is spherical, with a size ranging from 3µm to tens of µm [1]. Thus, depending on this size, they are available for applications in reverse phase analytical HPLC or SPE. Hypercarb, Supel Carbon are some examples of PGCs.
Our current suite of NanoPak-C All Carbon microbeads are suitable as reverse phase chromatography media. Thus, for this blog, when we are differentiating them from other types of carbon media, we are referring to PGCs.
We have published a blog titled “Why all carbon marks a new milestone in Chromatography” where we list a table with fundamental properties of stationary phase media and the benefits to end-users. The table also presents these properties for NanoPak-C All Carbon microbeads and PGC-based stationary media used for reverse-phase chromatography. We have included the table below (Table 1). The technical points of this table can be distilled into two key differentiators.
Customizable. NanoPak-C All Carbon Microbead’s structure is a network of sp2 (natural graphite) & inter-graphite sp3 (covalent) carbon bonds (via crosslinker). Other than graphite, sp2 carbon sources can be fullerene, carbon nanotubes, or graphene. This crosslinker can be either hydrophobic (e.g., alkyl chains) or hydrophilic (e.g., polyethylene glycol) and may feature various functional groups (e.g., epoxides, proteins).
Starting materials along with adjustments in process parameters during manufacturing allow us to control structure (diameter, porosity, pore size) and composition (hydrophobicity, functionalization) [2].
In contrast, Porous Graphitic Carbons (PGCs) are synthetic graphite structures. They have a sp2 graphite layer, and unlike natural graphite, each layer is connected by sp3 carbon bonds. These materials are produced through a process called pyrolysis, where a precursor carbon-rich material is subjected to high temperatures (> 2000°C) in the absence of oxygen. This process causes the decomposition of the precursor material and the formation of a synthetic porous graphitic carbon structure (see Figure 1). Thus, the PGC manufacturing process offers no control over composition and limited control of structural properties (diameter, porosity, pore size). The predominant surface area of PGCs is characterized by densely packed arrays of carbon atoms, complicating the direct attachment of functional groups to modify their composition.
Scalable: Our microfluidic-based droplet materials discovery and manufacturing platform facilitates simple, eco-friendly, and economical synthesis of the NanoPak-C all-carbon beads, it allows seamless scalability to continuous and distributed manufacturing processes.
This scalability is conducive to transitioning from analytical to preparative chromatography saving cost and time for end users.
In contrast, porous graphitic carbon compositions have been manufactured using carbon-rich molecules or polymers coated onto sacrificial inorganic templates, followed by template removal and high-temperature graphitization. These are energy-intensive procedures requiring extensive post-processing steps rendering them more complex and less environmentally friendly. Further, this complex process leads to higher manufacturing costs and limits scalability.
References
1.West, C., et al. (2010). "Porous graphitic carbon: a versatile stationary phase for liquid chromatography." Journal of Chromatography A 1217(19): 3201-3216.
2.Parente, M. J. and B. Sitharaman (2023). "Synthesis and Characterization of Carbon Microbeads." ACS omega 8(37): 34034-34043.
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