Microwave-assisted sample digestion techniques excel in decomposing sample completely by raising the temperature of acid higher than the boiling point. The key to increasing the boiling point of acids is their entrapment in Teflon® lined close digestion vessel.
It is recommended that samples are weighted in Teflon® liners directly and digestion reagents are added to the liner. Recently microwave digestion systems have increased the number of samples that can be processed at a time from 12 to 40 on average. Weighing and adding reagents to many samples presents the challenge of being accurate in dispensing and that of missing a reagent addition to a sample in rush. At the end of digestion-cycle samples can not be diluted in liners as they are not transparent. Typically, Samples are transferred to the transparent standard flask for post digestion sample-prep. This essential process of sample transfer to another flask demands a lot of labour work and is time-consuming. Thus, even though the samples are digested in the time period of about 30 min it takes a long time before samples are available for analyzing on spectroscopy instruments.
Automation around the microwave digestion system can relieve analysis from repetitive and time-consuming chores. The automated reagent dispensing, and dilution system Vulcan from Questron Technologies Corp. is ideally suited for such a situation. It comes with a rack suitable for holding the liners from the microwave digestion system. Before samples are presented to the microwave digestion system, Vulcan can dispense required reagents to liners. At the end of digestion, samples are diluted to set level and homogenized in the same liners. Dilution is performed using an ultrasonic sensor followed by a precise diluent addition either by a peristaltic pump or by syringe base dispensing system. A short burst of air bubbles is used to agitate sample to facilitate mixing of sample and diluent. Diluted samples can even be transferred to an autosampler rack for presenting them for analysis.
The use of an automated system for reagent dispensing and post digestion work-up helps microwave digestion base sample digestion process to handle many samples, bringing superior accuracy and consistency in sample-prep tasks.