Automated sample preparation
Reducing variability in samples and standards
preparation is essential for tackling 50% of
out-of-specification results in QA/QC. Mettler
Toledo shows how precise concentrations
make it easier to identify trends in analytical
results before they cause OOS issues.
Out-of-specification (OOS)
investigations in analytical R&D
and QA/QC laboratories are
costly and time-consuming. Although
analytical instrumentation has seen
impressive innovations in speed and
efficiency over the last ten years, sample
preparation techniques have remained
virtually unchanged for 75 years.
Sample preparation is now reported to be
the most time-consuming, labour-intensive
and error-prone element of the workflow,
with approximately 50% of OOS errors
attributed to either sample processing
steps or human error. These errors could
be prevented by automation.
Consequences of OOS results
Based on OOS results, many groups find themselves
consuming valuable testing and material resources
by
conducting or supporting an analytical lab investigation.
This frequently leads to an uncomfortable deviation
report and an even more expensive corrective and
preventive action (CAPA).
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Figure 1. Quantos automated
powder and liquid dispensing system.
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CAPAs can mount over time and a full-blown root
cause analysis along with follow-up quality/compliance
audits quickly exponentiate costs. Seasoned managers
are valued for efficiently pulling together the
right resources and groups including QA/QC, method
development, R&D and validation to determine
the root cause and laboratory-related errors.
Substantial literature addresses the handling
of these
investigations; however, there remains a need
for more
theoretical and practical information related
to the
prevention of such occurrences.
Accuracy of solutions
Mettler Toledo is changing the way that samples
and
standards are prepared in modern analytical laboratories.
It
is universally accepted that a gravimetric measurement
is
intrinsically more accurate that a volumetric
measurement.
Pipettes and volumetric measuring equipment are
even
calibrated using gravimetric methods. Why then
do we still
weigh our solids and powders on a weighing paper,
transfer
them into a volumetric flask, and subjectively
read the
meniscus to prepare an accurate concentration?
Surely it makes more sense to also add the solvent
gravimetrically to achieve pinpoint accuracy.
In this way, the
exact amount of substance dispensed by
spatula or automated dosing head is
recorded and used to precisely adjust the
amount of liquid added.
Any under or overshoot in powder
weighing doesn’t require you to waste time
adding a tiny amount more or scooping
material off the weighing paper with your
spatula. The automated liquid dispensing
compensates for this and calculates the
exact amount of solvent that needs to be
added. This allows you to achieve the
perfect concentration every time.
Save substance and solvent
Automated solution preparation also allows
you to significantly downscale your consumption
of substance
and solvent. You profit from two effects: firstly,
you are able to
weigh out a smaller amount while adhering to USP
regulations
due to the lower minimum weight achievable with
automated
dispensing, which saves material.
Secondly, you can prepare the exact amount of
solution
that you need for further use, rather than being
constrained
by the volumetric glassware available. There is
no need to
round up the volume prepared to the nearest flask
size; for
example, preparing a 1mg/ml concentration to within
±10%
requires dosing of 90-110mg into a 100ml volumetric
flask.
With Quantos you can weigh in only 10mg and still
comply
with USP. There is ample solution for a typical
HPLC
injection (10-20ìl); you simply have 90%
less to dispose of.
Gravimetric dispensing
Gravimetric solution preparation has several clear
advantages. Automated dispensing of the solvent
reduces
the variability in the concentrations, which will
give you
increased confidence in your analytical results.
Using
automation removes the contribution of human error
to the overall process.
In addition, data transcription or labelling
errors are
eliminated as data is recorded and printed automatically.
The amount of substance and solvent used can be
reduced
by up to 90%, with the added benefit is that analyst
exposure
to potent substances is greatly reduced.
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