Dionex ASE 150, Руководство оператора

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Doc. 065207-02 9/08
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E • Theory of ASE
E.1 Introduction
Scientists are continually striving to develop means to accomplish desired results
faster, better, cheaper, and more efficiently. However, the application of new
technologies to sample preparation has often lagged behind the advances in the
determinative steps of the overall analytical scheme. Consider the major
technological changes in chromatography that have occurred in the last few years.
What a contrast exists between the first commercial gas chromatographs (GC)
introduced in the late 1950s and the modern GCs we have today! On the other
hand, analytical chemists can still be seen preparing samples for chromatographic
analysis using the same type of Soxhlet apparatus that was used to prepare
samples for the first GC instruments. In fact, Soxhlet apparatus has been in use
with few modifications for over 100 years. Traditional extraction techniques
suffer from several shortcomings. They often take long periods of time (several
hours), use large quantities of solvent (hundreds of milliliters per sample), and
require a great deal of labor and user intervention.
In addition to the costs associated with sample preparation, studies have shown
that the biggest bottleneck and source of errors in any analytical process are found
in sample preparation. If we want to have the biggest impact on improving the
performance of any analytical method, we would be well-advised to attack the
sample preparation portion of the method. That is one reason that Dionex has been
involved in research dealing with sample preparation for many years. Accelerated
solvent extraction (ASE) was developed by Dionex to address the problems
inherent with traditional extraction techniques, such as Soxhlet and sonication,
that use copious amounts of solvent and long and laborious periods of time.
ASE is an automated extraction technique that uses elevated temperatures and
pressures to achieve extractions in very short periods of time (for example, 10 g of
sample can be extracted in less than 15 minutes, using less than 15 mL of solvent).
Why would we do extractions at elevated temperatures and pressures? There are
several physicochemical reasons for this. First, let's consider temperature.
It is a well-known fact that the use of higher temperatures increases the capacity
of solvents to solubilize analytes. For example, the solubility of anthracene
increases nearly 13-fold as we increase temperature from 50 to 150 °C. Increasing