Preservation of Throughfall Samples by Chloroform and Thymol

Abstract

Chloroform (trichloromethane) and saturated thymol (5-methyl-2-[1-methyl ethyl]phenol) were used as biocides to preserve synthetic and real throughfall water samples for up to 50 days. Three replicate sealed sample bottles were kept in a cold room in the dark at 2[ddot]C to simulate laboratory storage conditions, and three replicate samples were kept in the dark unsealed, but covered, in a greenhouse at an average of 20[ddot]C to simulate storage in the field.

Both additives maintained the pH, conductivity and NH⁺ ₄ content of both synthetic and real throughfall samples for 50 days in the cold room while only thymol could maintain concentrations beyond 14 days in the greenhouse. In samples without biocide there were some changes of chemical composition after 7 days, even in the cold room. The loss of effectiveness of chloroform at the higher temperature was caused by evaporation from the unsealed bottles, and resulted in mould growth and marked loss of NH⁺ ₄ from solution.

The use of a saturated solution of thymol as a preservative is recommended where throughfall is sampled at weekly (or longer) intervals, to prevent loss of organic acids and NH⁺ ₄ ions, and maintain sample pH prior to collection and laboratory analysis. Without such precautions, measurements of NH⁺ ₄ and NO⁻ ₃ in throughfall are likely to be unreliable indicators of the net flux of N below a forest canopy.

Key Words:

• Throughfall
• ammonium
• biocide
• preservation