AOAC OMA# 2011.14 (Final Action Review)-OMB

2011.14 (Oct. 2018) – MTE-03 Final Action Review FOR ERP USE ONLY DO NOT DISTRIBUTE

( e ) Test portion digestion .—[ Caution : Application of microwave digestion systems involves hot pressurized acid solutions and concentrated acids. Use fume hood and wear full personal laboratory protective clothing, gloves and appropriate eye protection (safety glasses) when using glassware and preparing standards or samples with acid solutions. Follow manufacturer’s directions for safety risk and safety environment of microwave systems. Never remove hot vessels from microwave; wait until they are near room temperature. Keep microwave door closed while vessels are hot. The door is the primary safety device if a vessel vents.] ( 1 ) MDC digestion.– With power setting appropriate to MDC (maximum power of 1600 W), and number of vessels used, ramp MDC temperature from ambient to 200 ± 20°C in 15 min and hold at 200°C for 25 min. Cool vessels to room temperature with cooling system on high for 15 min before venting. Transfer the MDC digests quantitatively to 50 mL volumetric flasks or 25 mL autosampler tubes. Dilute to volume with H 2 O and mix. [ Note : Final dilutions in volumetric flasks (e.g. 50 mL) or autosampler tubes (e.g. 25 mL) require the addition of appropriate amounts of HNO 3 for MDC digests to maintain the proportion of 10% (v/v) HNO 3 in the final solution to be analyzed.] ( Note : A digestion is judged complete when a clear to yellow analytical solution is produced.) ( 2 ) MDO digestion.– With power setting appropriate to MDO models (maximum power of 600 W), and number of vessels used, heat MDO vessels at 200 ± 20°C for 20 min. ( Note: Yellow vapors will be emitted during the hydrolysis in MDO vessels.) Carefully remove the MDO vessels. Allow the vessels to cool down to room temperature. Add 5 mL HCl 35% (w/v) and heat MDO vessels at 200 ± 20°C for 20 min. Cool vessels to room temperature. Transfer the digests quantitatively to 100 mL volumetric flasks or 25 mL