Preparation of PHC standards

To avoid filtration of large volumes of water, particulate material (PM) is preferably concentrated by continuous centrifugation. All operations are carried out at room temperature and in polyethylene (PE) flasks. Alkaline agents liberate silicate from glass, which may become incorporated in the humic acid to be isolated and hence increase the ash content. 

If desired, fulvic acids can be obtained from the humic acid free supernatants by adsorption on hydrophobic resins such as XAD-2 or XAD-8 (see Malcolm, 1990 for details). 

---