Trace Analysis

Trace Analysis - Certified Reference Calibration Standards by BAM

Most results of chemical analytical measurements are directly related to reference materials which are used for the calibration of the measurement process. Two decisive preconditions must be fulfilled in order to obtain a result which is traceable to the SI. First, the used reference material itself must carry an SI-traceable value and an attached uncertainty. Second, the whole measurement procedure - from sampling to calculation of the result - must be fully validated and the uncertainty must be evaluated according to common rules (GUM, Eurachem guide). While the analyst has to validate his procedure and to evaluate his measurement uncertainty by himself, he may take it for granted, that the value which is declared on the label of the reference material is traceable to the SI. Thus, the reference material plays a most important role as it serves as a transfer standard in the traceability chain.


Reference materials are available from a large number of producers. Among them are private companies, federal research laboratories, metrology institutes and others. ISO has set up several rules to assure a suitable quality of reference materials which should be clearly indicated in a certificate.



Table 1

ISO Guide Number
Content
17025
General requirements for the competence of testing and calibration laboratories
30 (1992)
Terms and definitions used in connection with reference materials
31 (1996)
Contents of certificates of reference materials
32 (1997)
Calibration of chemical analysis and use of certified reference materials
33 (1989)
Use of certified reference materials (under revision)
34 (1996)
Quality system guidelines for the production of reference materials
35 (1989)
Certification of reference materials - General and statistical principles (under revision)


There also have been several discussions on how the traceable value has to be assigned to the reference material and who is in charge of this duty. However, there is still no valid guideline at present, which is generally accepted. In fact, one has to face a contradictory situation today. On the one hand, there is a growing demand for reference materials which carry traceable values. On the other hand, assigning a traceable value means putting much effort in a primary measurement which at least for a private producer will often be in contrary to economical requirements. Thus it is by far not self-evident, that all the produced reference materials carry traceable values. As the need for reference materials will keep growing, a division of tasks may be the most suitable way, where different institutes and companies focus on their different skills and core activities. While a private company may be able to produce a reference material most efficient in a large scale, the assignment of a traceable value will not be a special skill as this was not explicitely required in the past. So far, the declared value was simply regarded as the truth by most analysts. In contrary to that, federal institutes and among them especially the metrological institutes are predestinated to assign a traceable value, because normally it is one of their core tasks to provide the ultimative link to the SI by performing a primary measurement. However, they often may not be equipped well enough for an efficient production. Regarding the large bunch of reference materials that are already available, one could state, that there is already enough production capacity. There is, however, a lack of capacity for a serious value assignment. As a consequence, it would be more effective to combine the different skills in a complementary way.


The way described above has been chosen by EMPA and FLUKA GmbH. From the beginning, BAM (Federal Institute for Materials Research and Testing) was involved as partner. A suitable quality assurance system was required from each partner. An ISO 9001/2000 certification is in place at EMPA and FLUKA. BAM and EMPA are accredited according to ISO/IEC 17025. After having agreed to the criteria of EMPA for the value assignment, FLUKA produces the reference material according to ISO guide 34 and eventually further requirements defined by EMPA. EMPA controls the batch for its homogeneity and approximate content before the material is released for bottling and packaging. The certification analysis is performed by EMPA and BAM using randomly chosen bottles. Two different methods of measurement are applied. The results are combined to the certified value. Long term stability tests are carried out by EMPA in parallel. A certificate is provided only when all criteria including stability are met.


Each certified standard is accompanied with a certificate which states:

  • The certified property values and their uncertainty
  • The primary methods of analysis used for certification
  • The intended use, storing and handling instructions, the expiry date

And a certification report which states:

  • analysis report of EMPA and BAM
  • the ion standard solutions and the ion chromatography standard solutions the amount of trace impurities
  • the titrimetric standards the homogeneity report

Label of each bottle contents:

  • Fluka catalogue number
  • Fluka product name
  • Certification number
  • Batch number
  • Expiry date
  • Certified property value and the confidence limit


Table 2: These anionic standard solutions for Ion Chromatography (1000 mg/L) are certified
in a cooperation project with BAM and Sigma-Aldrich
Catalog No.
Product Name
Produced from
Example Certificate
87969
Bromide NaBr
87603
Chloride NaCl
80373
Fluoride NaF
86576
Nitrate NaNO3
81193
Phosphate Na2HPO4
80218
Sulfate Na2SO4
These certified standards are prepared with high-purity salts and water and are supplied in 100 mL HDPE bottles.


For our range of Certified Ion Chromatography Standards please click here.



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Table 3. Titrimetric Substances

Catalog No.
Product Name
Use
Assay
Cas No.
Package Size
17971
Arsenic trioxide Reductometric standard
~ 99.5%
1327-53-3
10 g
12353
Benzoic acid Acidimetric standard
~ 99.5%
65-85-0
25 g
15194
Lead nitrate Complexometric standard
~ 99.5%
10099-74-8
25 g
21067
Calcium carbonate Complexometric standard
~ 99.5%
471-34-1
25 g
60357
Potassiumhydrogenphthalate Acidimetric standard
~ 99.5%
877-24-7
50 g
60386
Potassiumiodate Reductometric standard
~ 99.5%
7758-05-6
50 g
71363
Sodium carbonate Basimetric standard
~ 99.5%
497-19-8
50 g
71387
Sodium chloride Argentometric standard
~ 99.5%
7647-14-5
25 g
71804
Sodium oxalate Reductometric standard
~ 99.5%
62-76-0
25 g
93440
Tris hydroxymethyl aminomethane Basimetric standard
~ 99.5%
77-86-1
50 g



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