This memorandum recommends that SW-846 users not follow the cautionary notes in Section 9.3.1 of Method 3500C (organic extraction and sample preparation), Section 11.5 of Method 3545A (pressurized fluid extraction, and Section 11.3 of Method 3550C (ultrasonic extraction). Instead of adding surrogates and spike compounds to samples before adding drying agents, SW-846 users should spike samples AFTER adding drying agents to prevent low recoveries for certain semi-volatile and non-volatile organic compounds. 

• Memo to Regions: Spiking (Prior To vs After Sample Drying) Issue in SW-846 Organic Extraction Methods (PDF)(2 pp, 556 K, August 5, 2010)