Material Digestion System
The Hot Block is made of graphite and other non-metallic materials that eliminate corrosion and reduce contamination of your samples. The Hot Block is part of a digestion system that simplifies and speeds your digestions by use of low cost disposable digestion tubes. These polypropylene tubes also serve as both graduated cylinders and sample storage containers. The specially designed flat bottom tubes can easily withstand the temperatures required to heat samples to the 95°C necessary for EPA Methods 3005, 3010 and 3050.
The Hot Block will digest thirty-six 50mL samples simultaneously—all in just a 15" by 15" foot print. By using the two 18-place polycarbonate racks that are included with the Hot Block, all 36 samples may be loaded or unloaded in a matter of seconds. The use of additional racks allows the analyst to prepare a second batch of 36 samples "offline" while the initial batch is being digested.
The use of the polypropylene digestion tube eliminates the need for glassware and glassware cleanup. The digestion tubes contain no detectable background contaminants and require no acid-rinsing prior to use. There is no need for beakers or expensive microwave vessels that have to be washed, acid washed, dried and inventoried. All the transfer steps normally required in the digestion process are eliminated. The digestion tube is graduated at 10mL, 25mL and 50mL, eliminating the need for a graduated cylinder. After digestion, the sample is brought up to volume and capped for storage. WIth the system there is no need for the extra expense and storage space of a separate container. Also, the 50mL tube will fit directly into many autosamplers and can be supported on the bottom and used as a centrifuge tube.
Because the Hot Block's heat envelops the digestion cup, it requires less energy and radiates less waste heat than acid digestions with hot plates. Using a maximum of 600 watts, the amount of electricity required per sample is reduced by as much as 75%. The low surface temperature of the block makes sample handling safer as well. The sides of the digester are barely warm to the touch when in operation and you can comfortably pick up a sample cup any time during digestion with the gloved hand.
The uniform heat delivery of the Hot Block allows all the samples to digest at the same rate. Unlike hotplate digestions, the temperature of the digesting sample does not increase as the sample volume decreases. Similar samples heat at the same rate, achieve the same digestion temperatures and evaporate at the same rate. Because of this uniformity, the time spent on monitoring the digestion process, moving beakers around or watching for "hot spots" is greatly reduced. In addition, since the samples are heated at the same rate, their vapor pressures are equal, ensuring that there is little opportunity for cross contamination between samples. Uniform temperatures also mean more uniform recoveries. Volatile elements such as lead, cadmium, arsenic, and antimony are not lost due to the accidental overheating that can occur on a hot plate.
Heat energy is provided by a silicone heating mat attached to the entire 12" x 12" bottom surface of the graphite block. Unlike heating rods that are commonly found in digestion blocks, the heating mat evenly distributes the heat across the Hot Block for a point to point uniformity of +/-0.5 °C. Temperature is controlled by a PID controller that provides a set point uniformity of +/-0.1 °C. This uniformity and control makes it possible to control sample temperatures to +/-1.5 °C.
Environmental Express, 490 Wando Park Blvd., P.O. Box 669, Mt. Pleasant, SC, 29465. Tel: 800-343-5319; Fax: 803-881-3964.