The ARF Wet Lab has a MARS5 instrument with 24 vessels. This Microwave Accelerated Reaction System (MARS) 5 unit was bought with the MarsXpress Temperature Control Option and the Mars Xpress TFM Vessel 40 place Starter Set  55 mL carousel that can hold up to 40 vessels. Our CEM representative is Michael Burnett.

MARS X Method Instructions for ARF organics studies

  • Edit/Create Method -> User Directory -> “New Method”
  • Vessel Type: “XPress”
  • Sample Type: “Organic”
  • Control Type: “Ramp to Temperature”
  • Power: “1600W” <Select>
  • Right arrow, type “100” > “15:00” Ramp
  • > 140/160/180 Temp > “15:00” Hold
  • <Next>
  • Name Method <Next>
  • Method Info <Next>

Additional information below was retrieved from the CEM website and from
http://hydrology1.nmsu.edu/teaching/soil698/Student_Material/microwave/MWSPweb/jkallest/operation_Text.htm

Operation of the Mars 5 Microwave Accelerated Reaction System

General description and features

The microwave accelerated reaction system is designed for digesting, dissolving, hydrolyzing a wide variety of materials in a laboratory setting. The system uses microwave energy to heat samples in polar or ionic solutions rapidly and at elevated pressures. Its main purpose is for preparing samples for analysis by atomic absorption (AA), inductively coupled plasma emission spectroscopy (ICP), gas or liquid chromatography.

The system consists of:

A microwave power system with user selectable power settings (0-1200 Watts),

A fluoropolymer-coated microwave cavity (oven interior),

A cavity exhaust fan and tubing to vent fumes,

A programmable microcomputer that controls and monitors the power, temperature, and pressure within the reaction vessels, and is capable of storing 100 programs with up to five reaction stages per program,

Explosion proof reaction vessels, and one specialized vessel for monitoring temperature and pressure,

An alternating turntable that turns the samples 360 degrees within the microwave field,

A door safety interlock system that prevents microwave emissions when the door is open.

 The Oven

External features:

Push button door opener on the top operates the safety door latch.
On/off switch is located on the side above the air intake.
Microcomputer keyboard and display are on the front.
Exhaust tubing and blower are attached from the back. These remove harmful fumes from the cavity to a fume hood or approved air handling device.
Power cord receptacle and access to fuses are on the back.
The oven also features the Reactiguard system, which senses pressure changes within the oven cavity in the event of a sudden pressure change and then shuts down the power. 

User programmable microcomputer

The oven's microcomputer has a menu of preprogrammed settings. Some of these are EPA methods, and some are methods developed by CEM Corp. The user can also change a number of the ovens parameters including the percentage of power applied, the total wattage, control temperature, pressure, ramp and hold time, and the number of reaction stages or cycles.
The measured values for time, power, pressure, and temperature can be stored and recovered within the computer or sent to a remote computer for analysis on some oven models.

 

Accessories for the MARS 5 supplied by CEM Corp.

Stirring The stirring option provides variable speed stirring in each individual vessel. A magnetic spin bar is placed into the vessel to provide sample stirring. This insures sample homogeneity and eliminates possible temperature gradients. Stirring speed is controllable from the main program software screen. Includes 14 stir bars. This option is recommended for all applications.
Available Stir Bars
Digestion
Extraction - Egg Shaped
Extraction - Octagon Shaped
Extraction - Carboflon Filled (for use with non-polar solvents)
A rotating plate containing magnets is located underneath the MARS cavity floor. The magnetic field couples with a spin bar placed into the vessel to affect sample stirring.
MARSLink™ Software (Version 2.0) This powerful, yet easy-to-use, Windows®-based, multi-tasking software package connects the MARS 5 System to any PC (configured with Windows® 3.1 or higher). The software provides method storage, data collection, real-time graphic display of temperature and pressure profiles and report writing capabilities. Includes program disk (3.5" & 5.25" formats), 12 ft. null modem serial cable with RS-232 connectors and installation guide.
Computer requirements: IBM PC or compatible running Microsoft Windows® Version 3.1 or higher, Windows® 95 or higher, or Windows® NT.
MicroVap Accessory Set Enhance the performance of your CEM microwave digestion system with this accessory for pre- and post digestion processing. The MicroVap makes drying of samples before digestion as easy and clean as possible! It also reduces acid volume after the digestion step and concentrates acidified drinking water samples. Process up to 12 samples at a time using a variety of CEM microwave digestion liners. An optional HEPA filter can be used to control the sample environment. Samples are exposed to microwave energy while under a vacuum to accelerate the sample drying and acid volume reduction steps. An “auto-detect” feature of the MARS 5 system software determines when the sample evaporation step is complete and automatically stops operation. Acid fumes are automatically neutralized by the integrated vapor scrubber module.

 

A typical procedure for preparing plant material for ICP/MS

Dried plant material (0.1 - 0.5 grams of homogeneous material) is weighed out and placed in each reaction vessel.
Concentrated acid (10 ml 70% nitric acid) or dilute acid and oxidizer (5ml H2O + 5 ml 70% nitric acid + 2 ml 30% hydrogen peroxide) are added to each vessel. The precise recipe can vary depending on the material to be digested and who needs the information. For the sake of uniformity, specific methods have been developed that are prescribed by the EPA and ASTM for the digestion of certain material. See the links to methods section. It is recommended that the mixture allow to sit for 15 minutes before tightening the reaction vessel lids to allow any vigorous oxidation to vent.
The vessels are placed in the support modules with the load distributing caps, and tightened with a torque wrench to 5 ft*lbs. Blue pressure caps (with pressure membranes inserted) are to be hand tight. Attach pressure sensor and Thermowell to the control vessel. Place the support modules on the carousel and attach the top ring.
Either select pre-programmed microwave control settings from the menu installed on the oven's computer, or program in parameters for power, control temperature, pressure maximum, ramp time, hold time and stage settings that you select or are specified by a standard procedure. Zeroing the pressure sensor every so often is recommended.
Place the carousel on the drive lug in the oven and attach the pressure sensor and temperature sensor. Close the door, press start.
After the cool down period when the temperature sensor reads below 35 degrees C it is safe to remove the carousel from the oven. Pressure in the reaction vessels should be released slowly by unscrewing the blue cap and venting any remaining vapors in a fume hood.
Samples should be filtered through filter paper or centrifuged and diluted to an appropriate final volume (ICP machines need to have acid concentrations be below 20%).

Sample handling and safety

A number of precautions should be observed for safe operation of the microwave system:

Before subjecting vessels to microwave energy the vessels should be free of particulate matter or drops of liquid such as high salt solutions that can absorb microwaves, which in turn can cause localized heating and damage to the vessel. 
Pressure relief devices should always be used when heating samples.
When working with unknown samples it is suggested that the user allow 15 minutes to predigest the samples before sealing the vessel. This will allow for easily oxidized compounds to exhaust volatile gasses and diminish the pressure inside the vessel during heating.
Never heat high boiling point acids like concentrated sulfuric or phosphoric acid in the microwave.
The user should consult the operation manual for the list of solutions and solvents not recommended for use in the system or in the particular reaction vessel you are using.