Buchi SpeedExtractor E-914, Operation Manual

Page: 46 / 107

6 Operation
45
SpeedExtractor E-916 / E-916XL / E-914 Operation Manual
6.3 Preparing the sample
The following sections describe all operations being involved to prepare the sample for the actual
extraction process.
6.3.1 Sample preparation
To maximize extraction efficiency, samples that are coarse, lumpy or rocky must first be ground and/or
sieved to achieve a uniform particle size. Conversely, fine mesh samples may form tightly compressed
beds which restrict solvent penetration and impede solvent discharge. Such samples must be mixed
with a drying (diatomaceous earth) or dispersing (sand) agent before loading the extraction cell. If a
successful sample pretreatment procedure from another extraction method is known, also follow this
particular procedure for the Speed Extractor. However, for new samples the following guidelines may
be helpful:
• Dry samples work best, because water often tends to co-extract. Wet samples must be air or oven
dried before extraction. Wet samples reduce extraction efficiency and may cause blowback due to re-
stricted flow through the sample bed. To dry and/or disperse samples, blend them with diatomaceous
earth (DE) (P/N 053201) or extraction sand (P/N 037689) in order to decrease sample density, achieve
uniform flow and increase analyte recovery. Generally, diatomaceous earth dries samples more quickly
than sodium sulfate and hence provides a cleaner transfer of the mixture to the cell. On the other
hand, sodium sulfate tends to clump the sample, making transfer more difficult.
• The use of sodium sulfate with very wet samples (i.e. moisture content approx. 30 %) may result in
recrystallization of sodium sulfate and hence clogging of the metal frit in the extraction cell. This is
the case particularly with solvent mixtures with acetone. In these cases blending the samples with DE
before loading into the extraction cell is highly recommended.
• Never use sodium sulfate with polar extraction solvents such as methanol, because this drying agent
is partly dissolved at the temperatures typically used for SpeedExtraction methods.
• For samples which are easily extracted particle sizes of 1 – 2 mm provide generally good results.
For more critical samples particle sizes 500
μ
m are recommended.
• The material of the bottom filter (which is placed between the metal frit and the sample) may influ-
ence the speed and efficiency of the discharge and flushing step significantly. The standard glass
fiber filter is suitable for all applications. For samples with easy discharge and flush, the cellulose
filters (P/N 049569) can be an alternative.
NOTE
Consider the SpeedExtractor Application Booklet for general information about preparation of
different types of samples. It also includes application notes with reference settings for the most
frequently used application particularly in the environmental and food market. Sample types such
as polymers may soften or dissolve in solvent media such as dichloromethane and subsequently
extrude through the fluid transfer lines resulting in plugged tubing and valves. Therefore it is recom-
mended to use extraction thimbles. Additionally, some analytes are prone to precipitate after being
cooled down rapidly by passing the cooling unit. For critical samples it is therefore recommended to
use a smaller cooling unit instead (P/N 053682). Exchange of the cooling unit, however, requires an
authorized service technician. Please contact BUCHI or your local dealer.
6.3.2 Extraction cell selection
NOTE
The process parameters are optimized to each type of extraction cell. Therefore, never mix extraction