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Why is Alumina Superior

Alumina Is the Superior Desiccant for Most Separation and Environmental Cleanup Applications

While we are happy to sell you our “highest quality in the industry” silica gel, many silica gel users are switching to alumina for their separation and purification needs due to it’s superior performance for many applications.

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Should You Switch to Alumina?

A growing number of silica gel users are switching to alumina for its superiority in separation and purification. While silica gel may seem adequate and users may feel comfortable with it, the multiple advantages offered by alumina make the switch an option to be evaluated and considered by most silica users.

At Dynamic Adsorbents, we recognize the benefits will need to be significant in order to change from silica gel, a product with which most people are more familiar and comfortable. The biggest question for silica gel users is whether it’s worth the change, even with the benefits that alumina provides. We believe that in order to make the best decision, it’s important to understand why alumina is superior, and why this change will benefit your company and/or project. Because our number one goal is to satisfy the requests and needs of our customers, we do supply a full line of silica gel with varying angstrom and particle distribution sizes, but it’s important to understand that there is a superior method for separating and/or purifying your compounds. That answer is alumina!

Alumina is in many ways a miracle substance due to its amphoteric properties that allow it to be used with neutral, acidic and basic compounds. This makes it a superior ingredient for many environmental cleanup and separation applications.  DAI’s proprietary technology used to produce the highest quality and specialized alumina products makes its activated alumina the most effective substance available for the widest range of applications.

Alumina opens up a world of possibilities for technicians, chromatographers, and other scientists working with cell culture systems, proteinomics, chromatography, as well as many other low and high pressure separation methods. No other life science material offers the versatility, the ease of use and the low cost of alumina.

Alumina oxide can be used as a substitute for silica for virtually any problematic separation. As with silica, it can be used for reversed phase chromatography. Furthermore, activated alumina provides superior pH stability over silica. Alumina based reverse phase chromatography packing is prepared by free radical polymerization of cross link polymers to alumina particles or by chemically bonding alkyl groups to alumina. It can be synthesized with appropriate particle size and particle shape to offer whatever surface area is best for your separation needs.

Alumina is an excellent support for preparing chemically bonded C18 phases as well as many other ligands.

Scaling up from TLC to large scale preparative purification is consistent and reproducible.

Limitations of Silica

While silica has a higher sample load, there are several limitations in the use of silica:

  • The silica backbone Si – 0 – Si hydrolyzes at pH . 8
  • Silica hydrolyzes at temperatures greater than 40 degrees C
  • Silica hydrolyzes in the presence of phosphate and carbonate ions
  • Silica is soluble in aqueous/organic media in even slightly alkaline media at even moderately elevated temperatures
  • The siloxane bond is unstable at pH < 4.5 and becomes even more unstable the lower the pH

What makes alumina so unique and superior?

  • Alumina displays amphoteric properties. It acts as a weak ion exchanger. Alumina has amphoteric properties with both cation and anion exchange properties over a broad pH range. The ability of a chemical to act either as an acid or a base is called amphoterism. No separation substrate has more superior amphoteric properties than alumina. This insoluble compound can be made to dissolve by reacting with either acid or base. Of all the metal oxides, alumina performs best in this role as an amphoteric ion exchanger. In comparison the more commonly used silica only allows for a cation exchange due to its low pH pzc.
    Alumina Superior Adsorption Silica Gel Standard Adsorption
    30 Parameters for Selectivity
    A. 3 pH ranges: acid, basic, and neutral
    B. 2 surfaces areas for standard Chromatography…Alumina: 150 m2/gm and 200 m2/gm
    C. 5 Brockman activity ranges: I, II, III, IV, V
    Parameters for SelectivityA. pH ranges 6.5 to 7.5 Limited range
    B. 2 Brockman activity ranges: I and II
  • Alumina is stable. It overcomes the relatively low and high pH instability of silica. Alumina is stable throughout the pH range of 2-13. This is a most important feature. When silica is used in a chromatography column at higher pH, one always gets column collapse associated directly with silica dissolution. This also leads to the consequent development of voids in the column. These complications are characterized by abrupt decreases in plate numbers as well as steep increases in tailing factors before changes are seen in the retention factors. Try running your silica stationary phase column at a temperature of 50o C and a pH of 10 with the mobile phase containing phosphate and watch your silica column dissolve and deteriorate in performance.
  • Alumina has much higher values of pH pzc – at a neutral pH the surface of alumina does not have a negative charge and will not interact with charge bases via electrostatic interactions. At solvent pH values below that of the pK of the alumina surface, the alumina surface has a positive net charge. At the higher pH, the surface charge is negative. The zero point charge (no net charge) of alumina occurs at pH 9.2 but is shifted using buffers.
  • Alumina is well suited for use in high temperature HPLC and does not break down like silica. No other separation material provides you with such stability and versatility. Alumina can be used for such an incredibly wide range of applications. It can be used for pharmaceutical, industrial, biohazard, bioterrorism, research, toxic waste, environmental cleanup, gas and liquid dehydration applications.
  • Alumina has Lewis acid sites that are responsible for ligand exchange ability
  • Alumina has a strong affinity for halides – for example, it is able to elute excess concentrations of fluoride from drinking water, leading to enhanced column packing stability.
  • Alumina can be used to remove:
    • Polychlorinated biphenyls ( PCBs)
    • Insecticides
    • Radioactive contamination
    • Lead
    • Toxic Waste
    • Heavy metals
    • Colors or dyes
    • Chemical Pyrogens
    • Arsenic

Try 100 grams for free

Once you switch to alumina, there is no going back. We are so certain of it that we are willing to provide you with 100 FREE grams of any requested alumina to try in your laboratory. We are so confident that you will enjoy your experience that we are providing this product to you free of charge. Just call us for your sample material, and let us know about your requirements. Our technical support team is available to make sure that the transition is seamless. (This offer is limited to one sample per customer).

For more information, download the following article from Center of Excellence Environmental Analysis and Monitoring, August 2003 New Horizons and Challenges in Fundamental Analysis and Monitoring.


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