Accred. Qual. Assur, Springer, Berlin and Heidelberg, 2014
Quality control in extended measurement campaigns: Selection of contract laboratories
by proficiency testing exemplified for the trace analysis of anilines in groundwater
Roland Becker, Ute Dorgerloh*, Andreas Buchholz, Andrea Hofmann
Federal Institute for Materials Research and Testing, BAM
Richard-Willstätter-Str. 11, 12489 Berlin, Germany
*Corresponding author:
Phone: +49 30 8104 5937 e-mail: ute.dorgerloh@bam.de
Supplementary Material
Content
page
Quantification of anilines ........................................................................................................................ 1
Quantification of monochlorobenzene .................................................................................................... 3
Homogeneity study, monochlorobenzene ............................................................................................... 3
Homogeneity study, anilines ................................................................................................................... 4
Number of pages:
4
Number of figures:
1
Number of tables:
3
Electronic Supplementary Material, page 1
Quantification of anilines
The quantification of anilines during homogeneity and stability testing and reference measurements
were done according the German standard method by LLE-GC/MS.1 Water samples of 100 mL were
extracted thrice with 10 mL of toluene. The unified extracts were concentrated to 1 mL on a rotation
evaporator. Quantification was carried out using a Hewlett Packard 6890 gas chromatograph (GC),
mass selective detector MSD 5973N (Hewlett-Packard, Waldbronn, Germany) equipped with a
CombiPAL autosampler (CTC Analytics, Zwingen, Switzerland). The capillary column used for
aniline compounds separation was a ZB5ms, 30 m length x 0.25 mm ID x 0.25 µm film thickness
(Phenomenex, Torrance, CA, USA). The GC oven was programmed from 70 °C, held for 1 min, to
150 °C at 3 °C min-1 und further to 280 °C at 10 °C min-1. The transfer line was heated to 300 °C. The
flow of carrier gas hydrogen 5.0 (Air Liquide, Berlin, Germany) was 1 mL min -1. Fig. S1 depicts a
chromatogram of the groundwater sampled in the field.
Fig. S1: Full-scan chromatogram of toluene extracts, water samples A and B (LLE – GC/MS)
DIN 38407-16, German standard methods for the examination of water, waste and sludge – Jointly determinable substances
(group F) – Part 16: Determination of aniline derivates by gas chromatography (F16); 1999
1
Electronic Supplementary Material, page 2
Quantification of monochlorobenzene
The quantification of monochlorobenzene (MCB) for homogeneity testing of the sampled groundwater
was done according the German standard method for determination of volatile compounds by
headspace – gas chromatograph/flame ionisation detection (GC/FID).2 The quantification was carried
out using a HP 6890 GC/FID system (Hewlett-Packard, Waldbronn, Germany) equipped with a
CombiPAL autosampler (CTC Analytics, Zwingen, Switzerland). Water samples of 5 mL were
applied in 10 mL vials and thermostatted at 80 °C for 30 min prior to injection. A split/splitless
injector was run with a split ratio of 10:1 and was thermostatted at 150 °C; the injection volume was
250 µL. The capillary column used for compound separation was a VF624ms, 60 m x 320 µm ID and
5 µm film thickness (Varian Inc., Palo Alto, CA, USA). The GC oven was programmed from 40 °C,
held for 1 min, to 200 °C at 70 °C min-1, held for 10 min. The flow of carrier gas hydrogen 5.0 (Air
Liquide, Berlin, Germany) was 1.5 mL min-1. The flame ionisation detector was run at 300 °C,
hydrogen flow of 30 mL min-1, airflow of 300 mL min-1, and make-up gas nitrogen (10 mL min-1).
Homogeneity testing, monochlorobenzene
The first, each 10th and the last bottle of sampled water in order of sampling were selected for
homogeneity testing. These seven bottles were been quantified for monochlorobenzene in triplicate.
The trend analysis was done to demonstrate the homogeneity in order of sampling. The results of
outlier (Grubbs) and trend tests (Neumann) are documented in Table S1.3
Table S1: Homogeneity study for monochlorobenzene, outlier test (Grubbs)
and trend test (Neumann), (α = 0.05)
Item
Unit
Data
a
b
Replicate measurements
µg L-1
Mean (M)
Standard deviation (s)
Variance (s2)
Extreme Value Xext
Grubbs test
Empirical value (G =|xext - M|/s)
Critical value
Outlier?
Neumann test
Differential dispersion (δ2)
Empirical value (P = δ2 / s2)
Critical value
Trend ?
µg L-1
µg L-1
µg2 L-2
µg L-1
20.898
19.647
19.913
19.768
20.098
20.462
20.281
20.15
0.4342
0.1885
20.898
-
1.716
2.097
No
µg2 L-2
-
0.3218
1.707
0.614
No
Each value is the mean of three injection of a subsample
δ2 = Σ (xi – xi+1)2/(n-1)
DIN 38407-9, German standard methods for the examination of water, waste and sludge – Jointly determinable substances
(group F) – Part 9: Determination of benzene and some derivates by gas chromatography (F9); 1991
2
3
Statist 24, Version 2.0, Rev. 4c, © 2000 - 2003 Georg Schmitt / Michael Herbold *,Institut für Rechtsmedizin und
Verkehrsmedizin der Universität, Voßstraße 2, D-69115 Heidelberg * ab 2001 ARVECON GmbH, Walldorf, Germany
Electronic Supplementary Material, page 3
A one way analysis of variance was done to compare the variation within and between the bottles
(Table S2).
Table S2: Analysis of variance table for monochlorobenzene
Source of
Sums of squares Degrees of Mean squares
variation
(SS)
freedom (df)
(MS)
3.396
25.090
28.487
Between bottles
Within bottles
Total
6
14
20
0.566
1.792
F
P value
Fcrit
0.316
0.918
2.848
It is seen that the within-bottle variance exceeds the variance between the bottles. This means that the
scatter of measurement results is domination by the uncertainty of the analytical method. In such a
case the between bottle standard uncertainty sbb can be estimated according to ISO Guide 35 by Eq. 1
as 0.475 µg L-1 (2.4 %).
sbb 
MSwithin
2
4
n
N (n  1)
(Eq. 1)
Homogeneity testing, anilines
The homogeneity was also tested for o-chloroaniline as representative aniline in the contaminated
groundwater and for o-toluidine example for the fortified anilines. For this purpose, the data produced
to assess the stability were used. Four bottles had been analyzed in duplicate on different days each
within the time range of the interlaboratory comparison (1st. 2nd. 4th and 7th day). Results were pooled
and a one-way analysis of variance was performed. Mean squares within (MSwithin) and between bottles
(MSbetween), standard deviations within bottles (swithin). between bottles (sbetween) and the standard
uncertainties between units (sbb, see Eq. 1) are collected in Table S3. It is seen that sbb ranges between
0.5 and 1.2 %.
Table S3: Homogeneity of selected anilines in test sample series B
Aniline
Unit
o-Chloroaniline
o-Toluidine
Mean
MSbetween
MSwithin
swithin
sbetween
sbb
µg L-1
µg2 L-2
µg2 L-2
µg L-1
µg L-1
µg L-1
740.2
6.32
405.5
20.14
2.51
3.524
Electronic Supplementary Material, page 4
126.6
7.14
53.65
7.32
2.67
1.551