Pressure Stepped Microwave Assisted Digestion

Abstract

An instrument and method for high pressure microwave assisted chemistry are disclosed. The method includes the steps of applying microwave radiation to a sample in a sealed vessel while measuring the temperature and pressure generated inside the vessel and until the measured pressure reaches a designated set point, opening the vessel to release gases until the pressure inside the vessel reaches a lower set point, closing the vessel, and repeating the steps of opening the vessel at designated pressure set points and closing the vessel at designated pressure set points to the sample until the sample reaction reaches a designated high temperature. Microwave energy can be applied continuously or intermittently during the opening and closing steps. Among other items, the instrument includes pressure and temperature sensors and means for opening and closing the vessel at the set points.

1 . A method of high pressure microwave assisted chemistry comprising:
 applying microwave radiation to a sample in a sealed vessel while measuring the temperature of the sample and measuring the pressure generated inside the vessel and until the measured pressure reaches a designated set point above atmospheric pressure;   opening the vessel to release gases until the measured pressure inside the vessel reaches a lower designated set point above atmospheric pressure;   closing the vessel while the pressure remains above atmospheric pressure; and;   repeating the steps of opening the vessel at designated pressure set points and closing the vessel at designated pressure set points, and applying microwave radiation to the sample until the sample reaction reaches a designated temperature.   
     
     
         2 . A method according to  claim 1  comprising applying microwave radiation during any of the opening or closing steps. 
     
     
         3 . A method according to  claim 1  comprising applying the microwave radiation until the pressure reaches a designated set point above atmospheric pressure. 
     
     
         4 . A method according to  claim 1  wherein the step of repeating the opening of the vessel comprises opening the vessel at two designated measured pressure set points that are different pressures from one another. 
     
     
         5 . A method according to  claim 1  comprising applying a single mode of microwave radiation to the sample. 
     
     
         6 . A method according to  claim 1  comprising applying microwave radiation to a sample and an acid. 
     
     
         7 . A method according to  claim 6  comprising opening the vessel at a temperature above the atmospheric boiling point of the acid. 
     
     
         8 . A method according to  claim 1  further comprising measuring the temperature of the vessel and the sample during any of the microwave-applying, vessel-opening and vessel-closing steps. 
     
     
         9 . A method according to  claim 7  comprising moderating the application of microwave energy in response to the measured temperature. 
     
     
         10 . A method according to  claim 1  wherein the step of opening the vessel comprises flexing a cap. 
     
     
         11 . A method according to  claim 1  wherein the step of opening the vessel comprises lifting a cap. 
     
     
         12 . A method according to  claim 1  further comprising thermally managing the sample temperature. 
     
     
         13 . A method according to  claim 11  comprising proactively cooling the reaction vessel during any one or more of the steps of applying microwave radiation, opening the vessel, and closing the vessel. 
     
     
         14 . A method according to  claim 13  comprising cooling the vessel by directing a fluid into contact with the vessel. 
     
     
         15 . A method according to  claim 1  further comprising moderating the application of microwave energy in response to the measured temperature.