Volatile losses of sulphur from oven drying plant material

An apparatus is described for the quantitative collection of volatile sulphur compounds released by oven drying plant material. The amount of volatile sulphur released was studied in terms of the effects of operational parameters of the all‐glass collection apparatus, drying temperature, and duration of collection. Losses from shoots and roots of 22 species were then measured. An air stream sweeps volatiles from the sample container in a drying oven to a water‐cooled condenser system where the air stream is dried prior to volatile sulphur compounds being trapped on activated carbon. Tests with 35S‐labelled volatiles of plant origin or 1‐butanethiol gave a mean recovery of about 97%. The initial rate of collection of volatiles was affected by air flow rate through the apparatus but the total amount trapped in 48 or 72 hours was independent of flow rate over the range 1 to 6 1/min. For routine use, a 48 hour collection period and an air flow rate of 3 to 4 1/min were satisfactory. An increase in drying temperature from 50 C to 105 C increased both the rate of release and total amount of volatiles collected in 72 hours. Effects of temperature were generally small between 50 and 80 C but increased substantially above 80°C. Appreciable amounts of sulphur were lost from drying (80° C) shoots and roots of 22 plant species. In 17 species, roots were a richer source of volatile sulphur compounds than shoots. Across the 22 species, the percentage losses of total sulphur were not correlated with total sulphur concentrations in the plant tissues.