Intermediate checking on Working Standards
Working standard bottles
Working standards play a crucial role in
chemical analysis. Comparison with a standard is essential for both
identification and quantification of unknown components of samples. In
other words a standard serves to authenticate an analysis. Ideally a
certified reference material bearing traceability to national or
international standardization bodies is essential every time an analysis
is carried out but this becomes impractical as the cost of certified
reference materials is highly prohibitive so working standards offer a
practical solution.
What is a Working standard?
A working standard is material of
highest grade purity which contains the analyte of interest. The
composition of the working standard relates to the composition of the
certified reference material with which establishes a chain of
traceability to the original standards body.
A working standard has a specific
validity as it decomposes due to several factors such as external
contamination, environmental changes and handling misuse. Before the
expiry date another standard is prepared which bears traceability to the
standard and so on the chain continues.
Working standards stored in recommended
storage conditions are valid for at least three months. If it gets
consumed in less than the validity period should be replaced through a
written request and any amount remaining after expiry date should not be
used any further.
Shelf life Studies
Shelf life conditions are :
+/- 
at 65 % +/-5% RH
Assay and other quantifying parameters
are evaluated at initial, 6months and 12 month periods. On the basis of
results of shelf life is specified. As a general rule purity of working
standard should check at 6 months for expiry of standard having expiry
of 1year and 3 months for other working standards
The parameters usually checked are assay, loss on drying and water
Triple analysis is conducted by three different lenses and the acceptance criteria are
| Test parameter | Acceptance criteria (RSD) |
| Assay by HPLC | +/-0.5% |
| Chemical assay | +/- 1.0% |
| Microbiological assay | +/-2.0% |
| Water | +/- 0.5% |
Packaging and labelling requirements
Working standards should be stored in amber coloured vials and stored at 
C. Records of working standards issued to external parties or to
different units of same laboratory should be maintained. A typical
working standard label is represented below:
C. Records of working standards issued to external parties or to
different units of same laboratory should be maintained. A typical
working standard label is represented below:
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