Method 1311 Section 7.2.11 says: Ambient temperature (i.e., temperature of room in which extraction takes place) shall be maintained at 23 ± 2° C during the extraction period.
Does this mean we have to continuously monitor and record the temperature throughout the 18 hours, or is recording at the beginning and end sufficient? What is the correct procedure to meet the temperature requirement?
Extraction temperature is one of the more critical parameters in TCLP, so some form of control is necessary. As you pointed out, the method only states the temperature shall be maintained at 23 plus or minus 2° C. It does not specify how to monitor the temperature, or that continuous monitoring of the temperature is needed. It then becomes a matter of how well the extraction temperature is documented within allowable limits to the satisfaction of the auditor or regulator. A given auditor or regulator may be satisfied with the laboratory just recording a starting temperature. Another may want to see a starting and ending temperature. Another may want to see a starting, middle, and end temperature. For example, it may happen that extractions run overnight and room heating or cooling is reduced during off hours to save energy. In that case you may drop below or go above the approved temperature range during the night. In such cases, it may be necessary to record temperatures during the night to document that stayed within range. In such cases, an auditor may be satisfied that the temperature at the beginning and end was recorded, and that it is documented the room is on a thermostat control with set points to heat if temperature goes below 70 and cool if above 77 degrees F. Still another auditor may want to see continuous temperature monitoring. That is the most conservative approach and should satisfy all auditors or regulators, including NELAC auditors for laboratory certification.