European Acceptance Scheme
– UK Performance Testing of EAS GCMS General Survey Test
DWI0845
March 2005
EXECUTIVE SUMMARY
To reinforce the UK’s case for the inclusion of an analysis
using gas chromatography-mass
spectrometry (GCMS) to detect unsuspected compounds in migration waters
from non-metallic construction products used in contact with public
water supplies, the performance of the existing UK test method
(BS6920:2001 Part 4) has been assessed by three of the laboratories
approved by the UK regulatory body (the Committee on Products and
Processes (CPP)). This performance test was supervised by WRc-NSF and
the laboratories that participated were WRc-NSF, Law Laboratories and
Intertek.
The performance testing exercise had two components. Firstly, three
batches of migration waters (unchlorinated and chlorinated) prepared
from different products were circulated to the participating
laboratories. As the true concentrations of the compounds detected in
real migration waters are not known, the results from these samples
were used to check the comparability of the data produced by the
different laboratories. Eachlaboratory analysed five samples (test
water, chlorinated test water, migration water, chlorinated migration
water and a laboratory blank) for each of three products. The second
component of the exercise involved an assessment of the
semi-quantitative performance of the method, which was checked by
analysing samples to which known compounds (fifteen) had been added at
known concentrations. Each laboratory analysed three batches of four
samples (test water spiked at a low concentration, chlorinated test
water spiked at a low concentration, test water spiked at a high
concentration, chlorinated test water spiked at a high concentration).
The results from the analysis of real samples indicated that the three
laboratories produced broadly comparable data. For two batches of
migration waters, all laboratories reported very few compounds at low
concentrations. For the other batch of migration waters, where the
concentrations of the compounds detected were very high (hundreds of mg
l -1 ), the variation between the highest and
lowest concentrations reported for the same compounds by the different
laboratories was high (by factors of 2´ to 3´).
Potential reasons for this variation include the use of different GCMS
instruments, GC columns and internal standard solutions by each
participant.
By comparing the relative responses of the internal standards (to one
of these, d10-phenanthrene), it is possible to determine the relative
standard deviations of the responses for eight of the nine internal
standards for each batch of migration waters analysed. It is also
possible to quantify the remaining standards on the basis of their
relative responses compared to d10-phenanthrene, and obtain an
indication of the uncertainty of measurement for the overall procedure,
as the true concentrations of all of the internal standards are known.
It is suggested that each laboratory could maintain a record of their
performance on this basis, which may satisfy UKAS’ concerns
regarding this method.
The data from the analysis of the spiked test water and spiked
chlorinated test water samples containing known compounds at known
concentrations indicated that there may be some bias due to
chlorination, but this is small in relation to the precision of the
analysis. The results from the samples spiked at low concentrations
(0.86 – 2.04 mg l -1 ) confirm that
the ability of the approved laboratories to detect and report the
presence of these determinands is relatively good, with two of the
participating laboratories reporting the concentrations for thirteen of
the compounds present. The compounds that caused problems were
tetrahydrofuran (THF), which is very volatile, N-methylpyrrolidinone
which is polar and basic and bis-phenolA diglycidyl ether (BADGE) which
would normally be determined using a HPLC-based method, rather than
GCMS. These three compounds were included in the spiking mixtures
because they were known to be “difficult” compounds
to analyse using BS6920:2001 Part 4. The results from the samples
spiked at high concentrations (8.6 – 20.4 mg l -1
) were satisfactory, with variation (% relative standard deviation)
being less than 25% for most compounds. The exceptions were the three
“difficult” compounds noted earlier. With respect
to bias (i.e. the deviation between the reported concentrations and the
true concentrations) the results from two laboratories consistently
exhibited negative bias, while those from the other laboratory were
predominantly positively biased. This may be due to the use of biased
internal standard solutions, which could be addressed if internal
standard solutions from a single source were available.
The relative GCMS responses of the compounds used in the spiking
mixtures was determined by WRC-NSF and, on a per nanogram basis, there
was a five-fold variation between the most and least responsive
compound (BHT and BADGE, respectively). Given that there is also
variation in the responses of the individual internal standards which
are used to produce the quantitative estimates of the compounds
detected in migration water samples, the results from the spiked
samples are better than expected, with the bias for the samples spiked
at low concentrations in the range from +150% to – 100%, and
in the range –20% to +15% for the samples spiked at high
concentrations.
Compared to the performance achieved during the EU 5th Framework
programme CPDW
project, where six of the seven laboratories that participated had no
previous experience of applying BS6920:2001 Part 4, the results of this
current exercise are an improvement. This suggests that, as expected,
experienced users can achieve better performance from the method than
inexperienced users, and reinforces the view that following
incorporation of this GCMS method into the EAS other European
laboratories would be able to utilise the method and obtain similar
performance data to the UK laboratories.
It is recommended that:
- the supply of isotopically-labelled internal standards from
a single commercial source should be investigated;
- consideration should be given to modifying BS6920:2001 Part
4 to include specifications for the GC column to be used and
the temperature programme to be used for the GCMS analysis;
additional information on these points will emerge from DG
Enterprise-funded work which will commence in April 2005;
- any compounds of interest which have a boiling point lower
than that of d6-benzene (79°C) should be analysed as
specified compounds using, for example, purge and trap GCMS
rather than the procedures specified in BS6920:2001 Part 4.
Copies of this report may be available as an Acrobat pdf download under the 'Find Completed Research' heading on the DWI website.