SCIENCES of SOILS, Rel. 2, 1997 - http://www.hintze-online.com/sos/1997/Articles/Art3

Methodologies for Resin Capsules:

Capsule Storage and Ion Recovery

Skogley E.O.*, Dobermann A.**, Yang J.E.***, Schaff B.E.*, Adviento M.A.A.** and Pampolino M.F.**

* Department of Plant, Soil, and Environmental Sciences, Montana State University, Bozeman, MT 59717-0312, USA

** Soil and Water Sciences Division, International Rice Research Institute, P.O. Box 933, Manila 1099, Philippines

*** Division of Biological Environment, Kangwon National Univ., Chuncheon, Korea 200-701

e-mail: a.dobermann@cgnet.com


Key Words

ion-exchange resin, resin capsule, capsule storage, ion recovery, soil testing


Abstract

A simple, accurate, universal extraction methodology has been developed, based on use of mixed-bed ion-exchange resin capsules. Capsules can be used in the laboratory or in the field. To obtain repeatable results, capsules must be used and handled properly, including during storage following their use and prior to analysis. The analysis process must also be one which assures reasonably complete, uniform recovery of adsorbed ions by the stripping solution. The objectives of this research were to 1) determine effects of time, temperature, and resin drying on retention of adsorbed ions during storage, and 2) evaluate several methods of desorbing ions. After allowing capsules to accumulate standard quantities of ions, they were stored at -20, 2, or 20 C for up to 56 days. Capsules were also placed in an oven at 35 C for up to 48 h, with containers either open or closed. Results indicate that resins effectively retain ions as long as capsules are maintained in a clean, capped container, even when stored at high temperatures. Greater retention occurred at 2 C as compared to -20 C, suggesting that storage under cool, but not freezing, conditions is recommended. Two studies were conducted using different approaches to ion adsorption, followed by several methods of desorption from capsules. Results from these studies indicate that a variety of methods provide reasonably efficient, uniform recovery of adsorbed anions as well as cations. Three serial desorptions with 20 ml of 2 M HCl each time is essentially as effective as the standard method involving metering acid over the capsule with a multi-channel pump. Similar results were also obtained by opening the capsule so that the resin is free, placing it in a funnel fitted with filter paper, pouring 5 10-ml portions of acid over the capsule, and allowing complete draining between each portion. The standard procedure, along with most alternative methods, provided good repeatability with CVs of less than 5%.