Thiram residues were shown to be stable on frozen whole plums stored in closed plastic boxes at a freezer temperature below -20°C for 500 days (Roland, 1993). At each sampling the plums were analysed by a CS2 evolution method and on three occasions by an HPLC method specific for thiram. The methods were in good agreement. The results are summarized in Table 23.
The method of sample preparation was shown to influence the analytical result. If plums were macerated in a blender thiram was decomposed by exposure to the macerate. Roland (1993) recommended that fruit for residue analysis should be stored whole, subjected to a minimum of cutting (into halves and quarters) while still frozen, and analysed immediately.
Table 23. Stability of thiram in whole plums in closed plastic boxes stored below -20°C (Roland, 1993).
|
Storage period, days |
Thiram, mg/kg |
|
|
By CS2 |
By HPLC |
|
|
0 |
7.9 |
7.1 |
|
35 |
8.3 |
7.9 |
|
90 |
8.8 |
- |
|
183 |
7.6 |
- |
|
363 |
6.9 |
- |
|
500 |
8.1 |
7.8 |
The frozen storage stability of thiram was tested by fortifying apple juice and pomace at 1 mg/kg in extraction vials and storing them in a freezer at -20 ± 5°C (Leppert, 1995). Thiram was determined by a CS2 evolution method. The residues were stable for the periods tested, up to 49 weeks (Table 24).
Table 24. Frozen storage stability of thiram residues in processed apple fractions fortified at 1 mg/kg and stored at -20 ± 5°C (Leppert, 1995).
|
Storage period |
% thiram remaining after storage |
||
|
Apple juice |
Wet pomace |
Dry pomace |
|
|
0 day |
90, 90 |
84, 89 |
95, 88 |
|
2 weeks |
94, 90 |
84, 118 |
104, 83 |
|
35 weeks |
94,84 |
|
|
|
49 weeks |
|
80, 72 |
80, 82 |
