Direct Analysis

Extraction techniques utilising solvent in direct contact with materials have been discussed in previous articles. You can download the eBook of this series.

The next series of articles will cover extraction techniques that rely on direct analysis of the container closure system/device. If we define direct analysis as an approach in which the extraction of an analyte from a material and/or a solution cannot be separated from the actual analysis, then there are an ever-increasing number of analytical techniques that fit this description. The classical techniques for direct analysis would be infrared and Raman spectroscopy. However, these techniques, whilst very useful, do not alter the material being tested and as such are not carrying out an extraction. These will not be discussed further save for that they could be used non-destructively to identify and quantify extraction solutions, as well as identifying materials so as to assist with the identification of likely extractables.

The direct analysis techniques can be divided into two subgroups:

  1. Those that analyse what is on the surface or a few nm into the material.
  2. Those that facilitate the extraction and analysis of species from within the material being tested.

Liquid Extraction Surface Analysis (LESA)

As the title suggests this is a surface technique where extractables are analysed based on what is present on or near the surface.  The LESA process brings the extraction solvent from a pipette tip into contact with the surface of a sample held in the sample plate of an Advion TriVersa NanoMate. The analyte is extracted from the surface [1]. The solvent is then retracted back into the pipette tip and sprayed through the ESI chip in the normal manner, see Figure 1.  There are a number of advantages and disadvantages to this approach.  The advantages can include:

  • Mapping of a surface of a material can be accomplished by taking the analysis at numerous points and producing an extractable map. This could help identify defects.
  • By having and using a very small sample volume high sensitivity can be achieved.
  • Extraction and analysis can be very fast.
  • Could be used as a rapid confirmatory tool.

The disadvantages can include:

  • It may need to be assumed that the surface is homogeneous.
  • Complex solutions may be produced as there is no separation and so an idea of what could be present would be needed.

As with all extraction techniques, it is important to decide on what questions the study is trying to answer and choose the most appropriate extraction technique.

Figure 1 The LESA process (schematic[2])

[1]  V. Kertesz and G.J. Van Berkel, Journal of Mass Spectrometry, 2010, 45, 3, 252

[2]  A Feilden., Update on Undertaking Extractable and Leachable testing ISBN 978-1-84735-455-6