Comparison of Ceramic and Polytetrafluoroethene/Quartz Suction Cups for Sampling Inorganic Ions in Soil Solution

Abstract

Because the widely used ceramic cups are reported to release, adsorb, and filter dissolved nutrients from soil solution samples, inert cups made of poly(tetrafluoroethene) (PTFE) are frequently proposed as a more reliable alternative. A ceramic and a PTFE/quartz cup were compared with each other in this laboratory study. The PTFE/quartz cup was the most suited for pH measurements. Because only the ceramic cup samples both ammonium and nitrate in a satisfactory way, this cup type is recommended for nitrogen (N) balance studies. In most cases, the ceramic cup also performed better in sampling cations [sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺)] than the PTFE/quartz cup. Both cup types seemed inadequate to sample soil solution for aluminum (Al³⁺) determinations. The ceramic cups released chloride (Cl⁻) at low ion concentrations, but sulfate (SO₄ ²⁻) concentrations remained almost unaltered in the sample as compared to the solution outside the cup. In contrast, Cl⁻ and SO₄ ²⁻ were retained by the PTFE/quartz cups. The overall conclusion of this study is that PTFE/quartz cups have no clear advantages over the more widely used ceramic cups for use in ecological studies dealing with dissolved inorganic ions in the soil solution.

Keywords:

• Ceramic
• inorganic ions
• porous suction cups
• PTFE/quartz
• soil solution
• Teflon

Acknowledgments

The study was funded by the Special Research Fund (BOF) of Ghent University. Special thanks to T. Coddens, M. Schatteman, L. Deboosere, L. Willems, and M. De Bruyn for the chemical analyses and S. Meerschman for help with the experimental setup.