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Professional Analytical and
Consulting Services, Inc.

Have You Tried a GAED?

Gravimetric Adsorption Energy Distribution

What is a GAED?

The most powerful analytical test method for activated carbon is the method invented by Dr. Mick Greenbank. This method is most commonly called the Gravimetric Adsorption Energy Distribution (GAED) determination.

The GAED provides the characteristic curve for the sorbent material, cleanliness of sample, compares characteristic curve with known activated carbon samples, differential pore volumes of the range of adsorptive binding sites from strong to weak, cumulative pore volume as a function of binding site strength, isotherms for a range of compounds, pore sizes and calculated BET surface area and trace capacity numbers.

If you have not tried a GAED you need to do so. Information on typical GAED applications is available at the PACS website. All activated carbons are not the same. The GAED is a tool which is capable of differentiating the world of activated carbons. A list of some of the situations where the GAED has been demonstrated to be better than the present ASTM performance test methods are below:

• Differentiates activated carbons with the same ASTM Iodine or Butane Number

• The GAED provides the sorbent’s pore volume capable of removing difficult targeted adsorbates known as the trace capacity number

• The GAED provides the sorbent’s total pore volume

• GAED data can be used to provide a calculated BET surface area in m2 per gram

• GAED data can be used to provide a calculated trace capacity number (TCN)

• GAED reveals cleanliness of the initial sorbent’s surface

• River bottom samples with activated carbons can be monitored with GAED

• Carryover of activated carbon to downstream products can be monitored with GAED

• Provides the Freundlich aqueous-phase and gas-phase isotherms with target compounds

• Monitors the degree of reactivation, regeneration and initial activation level

• Differentiates activated carbon supplies from a single production batch from a supply of combined batches of activated lots to meet customer specification

• Provides information about the location of chemical impregnants in activated carbon structure. Comparison of GAED runs for host and impregnated carbon

• Determines the activity of the outside versus the inside of individual GAC granules

• Determines the GAC penalty of carbon blocks compared to free flowing GAC

• Enable the determination of the GAC raw material source; peat, lignite, coal, wood, coconut shell, or other based materials to manufacture the activated carbon

• Inventors of new activated carbons need to compare their new materials against the world of Activated carbons, to quickly determine potential markets.

• Facilitates a marketplace survey for opportunities a client’s new activated carbon offers

• Characterization of a family (0.2-0.8 g/cc apparent densities) of activated carbon Reveals the adsorption energy distribution sites in low iodine number sorbents.

• AED determinations help clients to select the best activated carbon for each application

• Demonstrates your knowledge and willingness to use the best test methodology

• Improved data quality and decisions; precision and accuracy improved which allow small sorbent mass for testing and small differences to be meaningful and useful

• Thin GAC beds, of only 3-5 granules, can be evaluated with this advanced test method. Granules against the containing barrier have been compare with granules not against the barrier that is in the middle of the thin bed

• Forensic analysis cases; is it new or used GAC? What is the raw product source: wood, coconut shell, bituminous coal, etc?

• Data from the GAED method has good agreement with Greenbank’s physical model for activated carbons which needs to replace old structural models for activated carbons. Activity as a function of particle size is possible

• Difference in sorbent performance between thermally cleaned and not cleaned received GAC. Provides a thermogravimetric analysis chromatogram from the sorbent cleaning step

• Provides two comfirmatory thermogravimetric analysis of the sorbent, initial clean-up and the final heat-up to remove the adsorbate

• Provides a simultaneous BET surface area and pore size distribution determination in addition to characterization of the sorbent energy distribution pore volumes

• Can obtain binding sites’ information in a wide variety of materials besides activated carbon

• This method can be automated and comply with GLP and GMP standards

• Determines the location of chemical impregnates of concern; surface or interior, specific areas of transport or adsorption pores, overall evenly homogeneous or heterogeneous spread in GAC

• The instrument could provide mass spectral analysis of the initial off gases and desorbed gases to detect changes in molecular structures

• Provides the high energy adsorption sites information compared to other commerical activated carbons

• Provides the total pore volume of your activated carbon samples compared to other commercial activated carbons

• Provides the only way to monitor changes in the activated carbon manufactured by a supplier

• GAED can be used to determine the adsorptivity characteristics of the activated carbon content on fly ash due to changes in boiler operation

• GAED can be used to reveal the amount of adsorptivity in fly ash containing activated carbon from activated carbon injection (ACI)

• GAED can be used to evaluate nanotubes and buckyballs

• GAED was used to evaluate odor control wound bandage product to evaluate shelf-life of products. Product is a polyurethane matrix containing activated carbon. We used GAED to compare "in date" and "assigned expiration date" to provide client information about odor control capacity in the two products.

• GAED was used to provide information on controlling refrigerator odors. We compared an activated carbon product and sodium bicarbonate using GAED for the client

A typical GAED report is provided for two activated carbon cloth materials. This information could not be obtained with any other existing methods. The GAED provided the client with a clear decision on what material was best for their process. The total difference between the two candidate cloth materials was a factor of 50, a very significant difference.

Try a GAED!


For other laboratory testing service, method development, R&D, software or consulting service needs, contact:


For Carbon Conferences or Short Courses in public sessions or at your time and place, contact us.

PACS provides testing, courses and consulting at the client's time and place, and twice a year carbon conferences.

PACS Positions Available:

  • Laboratory chemist for activated carbon group. Will train!

PACS has positions available for professional scientific service providers and has provided these services for over 38 years. PACS will accept proposals for short courses, consultants, activated carbon conference directors for focused conference subjects, and other needed services. New ideas are welcomed.

PACS, Inc.
409 Meade Drive
Coraopolis, PA 15108