Sealed vessels are another very simple technique; the sample is placed in the solvent again with appropriate levels of sample and solvent to achieve appropriate method limits of detection.  This important area of sample to solvent ratio will be discussed in a future blog.

A sealed vessel in its simplest form is an oven, which can be simply static or with agitation using an orbital shaker as an example.  A way of putting more energy into the extraction process can be achieved by using an autoclave that uses high pressure steam for heating, which allows the solvent in the sealed vessel to increase significantly without solvent loss.

Other pressurised systems such as microwave assisted extraction or pressurised solvent extraction will be discussed in more detail in later blogs.

Sealed vessel or autoclave extraction is predominately used with aqueous media, whether with pure water or pH adjusted water.  Typical conditions involve temperatures at 121 °C with various extraction times [1].

The conditions in USP <381> Elastomeric Closures for Injections is as follows: ‘Heat in an autoclave so that a temperature of 121 ± 2 °C is reached within 20 to 30 minutes, and maintain this temperature for 30 minutes. Cool to room temperature over a period of about 30 minutes’.

The use of organic solvents is much less common, but examples do exist with the use of alcohols [2] and these tend to be very specialist applications.

If an organic solvent was to be used then general conditions of heating with the solvent at 10 °C below the boiling point of the solvent are recommended.[3]

  1. D. R. Jenke, E. K. Chessa and G Jakubowskia International Journal of Pharmaceutics Volume 108, Issue 1, 25 July 1994, Pages 1-9
  2. C.B. Muchmore, J.W. Chen, A.C. Kent and K.E. Tempelmeyer, American Chemical Society, Division. Fuel Chemisty. Preprints, 30(2) (1985) 24-34.
  3. D. R. Jenke, J Castner et al PDA J Pharm Sci and Tech 2013, 67 448-511