With PRIMUS, Fluka GmbH introduces certified
primary multi-ion standards to the market. These «ready-to-use» standards
allow the validation of analytical methods in a very
simple way. PRIMUS standards contain 10 mg/kg of each Br-, Cl-,
F-, NO3-,
PO43-, SO42- (anion solution) or Ca2+, Li+, K+, Mg2+,
Na+ (cation solution).
Two metrological institutes – EMPA (Switzerland) and BAM (Germany) – together
characterized primary materials and issue a joint certificate. The solutions
are produced at EMPA using the facilities of their metrological laboratories.
This is why PRIMUS standards are characterised by their traceability to SI as
well as a unique low degree of uncertainty of <0.2%.
Increasing demand on CRMs
From a review of recent years certain terms
stand out with respect to chemical analysis. These are: «certification», «validation» and «compliance».
The demands placed on both the quality and the documentation of
the analytical work have continually increased over the last years.
A very central part within these requirements is the validation
of analytical methods whereby the so-called «performance
qualification» can always only be as accurate as the standards
with which they are carried out. This is why certified standards
are playing an increasingly important role in analytical procedures.
Directives, for example those issued by the European Union, require that a
CRM (CRM = Certified Reference Material) must be used for checking the correctness
of analyses, whenever available [1]. The American FDA (Food and Drug Administration)
stipulates the use of reference standards in analyses in its «Inspection
Guide». The ISO (International Organization for Standardization) has
also issued more than six publications on the subject of reference materials
[2].
PRIMUS Multi-ion standards
« PRIMUS» stands for Primary Multi-Ion Standards
and is a joint project of EMPA, Fluka GmbH and Metrohm whereby
BAM (Federal Institute for Materials Research and Testing) acts
as a partner institute for certification. The standards are prepared
gravimetrically based on the kilogram as one of the seven basic
SI-units. In gravimetric production the quality of the original
substances used is of crucial importance. This is why a dual approach
has been selected for the certification of the primary materials
for PRIMUS: as many as possible of the trace impurities in the
primary materials are quantified or their non-existence is demonstrated
(below detection limit). This involves the analysis of up to 85
parameters per substance including cations, anions and non-metals.
Residual water is eliminated by drying temperatures up to 500 °C
and the successful completion of the drying process is checked
by TGA (TGA = thermogravimetric analysis).
 The
purity calculated in this way is then confirmed by an independent
high-precision measurement of the contents by coulometry or titrimetry.
This additionally substantiates the accuracy of the certified
content and the correct stoichiometry of the compound.
Weighing out the primary materials as well as the 50 liter batch
is carried out on high-precision balances from Mettler-Toledo
in an air-conditioned weighing room (OIML class E2). The primary
materials are dissolved in ultrapure water or diluted high-purity
HCl in specially manufactured PVDF containers and then mixed for
12 hours in an overhead shaker.
The solutions are then filled off into pre-cleaned 50 mL HDPE
containers under clean-room conditions.
The high-precision analysis of one analyte in the bottled solutions provides
a final check of the manufacturing procedure and corresponds to a type of double
safeguard.
In order to prevent evaporation losses the containers are sealed
in Al-coated bags. Long-term tests have shown that solutions packed
in this way have a stable shelf life of at least three years
Metrohm highly recommends the use of PRIMUS Standards for the
internal calibration and validation of their instruments. Each
new Metrohm IC apparatus contains a PRIMUS pack with multianion
and multication.
Additional sets are available from Fluka (Sigma-Aldrich).
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