Materiales de referencia y comparaciones interlaboratorios
93
RESULTS OF AN INTERNATIONAL INTERLAB
STUDY ON SLUDGE SAMPLES FOR PCDD/
DFs, PCBs and PBDEs.
S.Moore (a) ,L.Levert2 (b) ,J.Hughes (b) ,F.Messier (a)
(a) Centre d’expertise en analyse environnementale du Québec,
Ministère du Développement Durable,de l’Environnement et des Parcs,
850 boulevard Vanier,Laval (Québec) H7C 2M7
(b) Centre d’expertise en analyse environnementale du Québec,
Ministère du Développement Durable,de l’Environnement et des Parcs,
2700 Einstein,Québec (Québec) G1P 3W8
Abstract.
Two municipal sludge samples have been tested for PCDD/DFs, PCBs (dioxin-like and markers) and PBDEs through an interna-
tional interlaboratory study.More than 50 laboratories from 20 countries participated in this study.Every participating laboratory received
two sludge samples and one standard solution for every test they registered for.Laboratories were requested to run each sample as dupli-
cate and submit the results of both analysis,along with the detection limits and internal standards used.Additional information,such as the
extraction procedure used,the chromatographic and detection system used,were also requested.
Keywords.
Interlaboratory study, polychlorinated dibenzo-dioxins (PCDDs), dibenzo-furans (DFs), Polychlorinated Biphenyls (PCBs), Poly-
brominated diphenyl ethers (PBDEs).
RESULTADOS DE UN ESTUDIO INTERLABORATORIO DE CARÁCTER INTERNACIONAL EN MUESTRAS DE LODOS MUNICIPALES PARA
PCDD/DFs y PBDEs
Resumen.
Mediante un estudio interlaboratorios de carácter internacional,se analizaron PCDD/DFs,PCBs y PBDEs en dos muestras prove-
nientes de lodos municipales.Participaron del estudio más de 50 laboratorios integrantes de 20 países.Cada laboratorio participante reci-
bió dos muestras de lodos y una solución estándar para cada ensayo en que participara.Se solicito a cada laboratorio correr cada muestra
con un duplicado y registrar el resultado de ambos análisis junto a su límite de detección y estándar interno utilizado.También se requirió
información adicional,como el procedimiento de extracción utilizado,columna cromatográfica y detector.
Palabras claves.
Estudio interlaboratorio, dibenzodioxinas (PCDDs),dibenzofuranos (DFs),Bifenilos policlorados (PCBs),éteres de polibro-
modifenilos (PBDEs)
I. Introduction
Most of the laboratories used high resolution mass spectrometry for the determination of PCDD/DFs
(72%),PBDE (50%),dioxin-like PCBs (66%) andmarker PCBs (62%).Results for the standard solutions gave
an average relative standard deviation of 10.6% for the PCDD/DFs, 17.1% for the PBDEs and 16.0% for
the PCBs,indicating very good skill by the participating laboratories.For the sludge samples,the average
relative standard deviation for PCDD/DFs was 30.2% while it was 27.1% for the PBDEs and 22.4% for the
PCBs. Results are given for each individual congener in each sample.
The main objective of this work was to certify a material and make it available to the international scien-
tific community for proficiency testing use or as quality control material.
II. Method
Sample description
The original sludges come from two different urban community sewage treatment plants. Sludges were
dried at 60 o C for a minimum of 24 hours. A lot number is then assigned to the individual sludges after
being grinded and passed through a 0.2 mm sieve. This lot is then mixed on a “Y”mixer for 30 minutes.
Homogeneity had been previously checked by eleven independent laboratories for Aluminium and the
RSD are 8% for sludge #1 and 14% for sludge #2 and seven laboratories for nitrogen (RSD are 5% and
6%).
Sample distribution
The sludges are distributed on a glass plate and 20 g of each is put in individual containers for shipping
to individual laboratories. Each container has a number associated with it such that at any time it is pos-
sible to know which container a participating laboratory received. Samples were sent to participating
laboratories December 1st, 2005 and results were requested by March 13, 2006.
Interlab participation
56 laboratories accepted to participate in this study;nevertheless,only 52 have been able to submit their
results by the deadline.These 52 laboratories come from 20 different countries (see table 1).
Calculations
Laboratories were requested to run the samples as duplicate (except for the standard solution). A re-
jection test has been run
( |(x-µ
1
)|
/
(f *
s
=
(x
i
−
x)
2
1
n
∑
n
−
1
1
)
, where
x
is the analytical result,
µ
1
is the median of all the
original values,
f
is a factor given by
(0.77 + 1.604/n) * t,
s
=
(x
i
−
x)
2
1
n
∑
n
−
1
1
is the median of absolute deviations,
n
is the
number of reported data points and t is the Student’s t factor at 95% probability) and results > 2 have
been flagged and removed from the calculation of the final median value [1].
The assigned value for each congener is the median of all results, after the application of the rejection
test.
