Interlaboratory Tests
Michael Koch
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
What are interlaboratory tests?
 Randomly selected sub-samples from a
source of material are distributed
simultaneously to participating
laboratories for concurrent testing
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Types of interlaboratory tests
method
validation
reference material
characterization
proficiency
testing
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Interlaboratory tests
for the validation of a method
 objective: best possible characterization
of the method
 laboratories have to use exactly the
same method
 assistance should be given to assure
this
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Interlaboratory tests for characterization of a reference material
 concentration of the analyte in the
material must be analysed by
experienced laboratories
 less experienced laboratories should
not be allowed to participate
 objective: best possible estimation of
the “true value” of the concentration
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Interlaboratory tests for proficiency
testing of laboratories
 objective: to get an indication of the
performance of an individual laboratory or a
group of laboratories as a whole
 laboratories should work under routine
conditions
 help for the laboratory to improve its quality
 can be used by customers or regulatory
bodies for the selection of qualified
laboratories
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Objectives of proficiency tests
 basic concern is accuracy
 inaccuracy contains systematic and
random effects
 laboratory can determine, whether
imprecision or bias is the reason for its
inaccuracy
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Motivation for the laboratories
 to uncover errors that couldn’t be found
with internal quality control
 use as certificate for competence in this
testing field for clients, authorities and
accreditation bodies
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Limitations
 Interlaboratory tests are always retrospective
 organisation, distribution of samples, analyses,
evaluation take time
 it is dangerous to rely only on interlaboratory tests
 Proficiency tests cover only a small fraction of
the often wide variety of analyses
 Proficiency tests do not reflect routine
analyses
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Standards and guidelines for
proficiency testing - I
 ISO Guide 43: Proficiency testing by
interlaboratory comparisons
 Part 1: Development and operation of proficiency
testing schemes.
 Part 2: Selection and use of proficiency testing
schemes by laboratory accreditation bodies.
 IUPAC, ISO, AOAC (1991): The International
Harmonized Protocol for the Proficiency
Testing of (Chemical) Analytical Laboratories.
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Standards and guidelines for
proficiency testing - II
 International laboratory accreditation
cooperation (ILAC): Guidelines for the
requirements for the competence of
providers of proficiency testing
schemes.
 Draft ISO 13528: Statistical Methods for
the Use in Proficiency Testing by
Interlaboratory comparisons.
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Demands on the provider personnel




special organizational capabilities
technical experts for the analysis
statisticians
all staff have to be competent for the
work it is responsible for
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Demands on the provider –
Planning - I
 The interlaboratory test should be
carefully prepared.
 The planning must be documented
before the start of the test
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Demands on the provider –
Planning - II
 The plan should typically include:
 name and address of the PT provider
 name and address of the coordinator and other
personnel
 nature and purpose of the PT scheme
 procedure for the manner in which the participants
are selected or criteria which have to met before
participation is allowed
 name and address of the laboratory performing
the scheme (e.g. sampling, sampling processing,
homogeneity testing and assigning values) and
the number of expected participants.
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Demands on the provider –
Planning - III
 Planning content (contd.):
 nature of the test items and of the tests selected
 description of the manner in which the test items
are obtained, processed, checked and
transported.
 description of the information that is supplied to
participants and the time schedule for the various
phases.
 information on methods or procedures which
participants may need to use to perform the tests
or measurements.
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Demands on the provider –
Planning - IV
 Planning content (contd.):
 outline of the statistical analysis to be used.
 description of how the assigned value is
determined.
 description of the data or information to be
returned to participants.
 basis techniques and methods used for evaluation
 description of the extent to which the test results
are to made public.
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Demands on the provider –
Data-processing equipment
 Equipment should be adequate for
 data processing
 statistical analysis
 to provide timely and valid results
 Software must be
 verified and
 backed up
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Demands on the provider – Test item
preparation and management - I
 For the selection of the test item all
characteristics that could affect the
integrity of the interlaboratory
comparison should be considered




homogeneity
stability
possible changes during transport
effects of ambient conditions (e.g.
temperature)
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Demands on the provider – Test item
preparation and management - II
 samples used in the proficiency test
should be similar to the samples that
are routinely analysed in the
laboratories
 sample amount
 surplus of sample can be used as
reference material
 surplus can be used to make excessive
effort on the analyses
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Demands on the provider Homogeneity - I
 The PT provider has to ensure that every
laboratory will receive samples that do not
differ significantly in the parameters to be
measured
 documented procedure for establishing this
homogeneity
 degree of homogeneity  evaluation of the
laboratories results must not be significantly
affected
 any variation between the portions must be
negligible in relation to the expected
variations between the participants
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Demands on the provider Homogeneity - II
 true solutions are homogeneous at a
molecular level
 for solid samples  special care on the
homogenisation
 a formal homogeneity check is
described in the „International
harmonized protocol...“
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Demands on the provider Stability - I
 test material must be sufficiently stable
 under the conditions of storage and
distribution to the participants
 for the time period from producing the
samples until the analyses in the
participant’s laboratory
 this stability has to be tested by the PT
provider
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Demands on the provider Stability - II
 Analysing a part of the samples after the
estimated time necessary for the distribution
 differences in the results may be due to instability
or to between-batch variability in the organiser’s
laboratory
 information may be derived from the
organiser’s prior experience or obtained from
technical literature
 accelerated stability testing by worsening the
ambient conditions for the samples
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Demands on the provider Stability - III
 the organiser has to ensure that the
changes due to instability do not
significantly affect the evaluation of the
laboratories’ performance
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Choice of analytical method
 Normally the laboratory should use its
routine method
 the choice might be limited by e.g. legal
regulations
 organiser should ask for details
 to conduct a method specific evaluation
 to give comments on the methods used
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Method specific evaluation
aluminum in groundwater
ICP-MS
GFAAS
80
ICP-OES
70
Photometry
60
50
40
30
20
10
0
too low
low
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
correct
high
too high
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Determination of the assigned
value
 one of the most critical features of a
proficiency test
 inappropriate value will drastically
reduce the value of the scheme
 the same problem as in the certification
of a reference material
 but the organiser of a proficiency test
cannot expend the same amount of effort
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Assigned value –
certified reference material
 ideal test material for a proficiency test
 disadvantages
 high costs
 limited availability
 in the necessary quantity
 and concentration range
 CRM‘s have to be stable for months and PT often
deals with more or less instable samples
(foodstuffs, biomedical, environmental samples)
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Assigned value –
Consensus of „Expert
Laboratories” - I
 mean of analysis by expert laboratories
 with high precision reference methods and
traceable materials for calibration
 if different physico-chemical methods are
used and the same results are obtained, it
is more probable that the value is near to
the „true“ value
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Assigned value –
Consensus of „Expert
Laboratories” - II
 disadvantages
 very much effort to ensure the accuracy of
the reference measurements
 „nobody is perfect“
 there might be doubts among the participants if
the result of the expert laboratories deviates
from the mean of the participants
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Assigned value – Formulated or
“Synthetic” test materials - I
 materials, spiked with the analyte to a known
extent
 can be made with extremely accurate amounts by
gravimetric or volumetric methods
 If material does not contain significant
amounts of the analyte
 assigned value directly from added amount
 If material contains analyte, this amount has
to be characterized very well.
 method to calculate this content from proficiency
test was recently developed by the author
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Assigned value – Formulated or
“Synthetic” test materials - II
 disadvantages
 difficult to achieve sufficient homogeneity,
especially with solid materials
 analyte might be bound in a different
chemical form
 Especially in solid materials the originally
contained analyte might be bound more
strongly to the matrix
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Assigned value –
Consensus of participants - I
 easiest and cheapest way  used very
often
 If method for analysis is easy and
straightforward  good estimate of
„true“ value
 If a „convention method“ (an empirically
defined method) is used, the consensus
value is the only possibility
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Assigned value –
Consensus of participants - II
 disadvantages
 Consensus value might be seriously biased (e.g.
analyses of highly volatile substances)
 there might be no consensus at all
 e.g. if two analytical methods are used, where one is
biased
 these circumstances are not uncommon in trace
analysis
 care should be taken to decide whether a
consensus value really is good choice
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Methods to calculate consensus
value – Arithmetic mean
 requires an outlier test
 but these tests are often not very
satisfactory, especially if many outliers are
present
 outlier tests assume normal distribution
which is normally not true in trace analysis
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Methods to calculate consensus
value – Median
 not affected by outlying data
 makes not full use of the information
content of the data
 if the distribution is skewed, the median
is biased
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Methods to calculate consensus
value – Robust mean
 „trimmed“ data; a certain part of the
data on both tails of the data set is
excluded prior to the calculation of the
mean
 e.g. mean of interquartile range
 mean of data between the first and the
third quartile of the data set
 or Huber statistics
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Methods to calculate consensus value
– Robust mean – Huber statistics
 Iterative process
 define initial value for m as median of all
data
 all data outside m±1.5*STD are set to
m+1.5*STD or m-1.5*STD
 new value for m is calculated as arithmetic
mean of the new data
 repeat until there are no changes
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Performance scoring
 assigned value is the target
 for the assessment of laboratories a
accepted range is necessary
 prescribed range originating from the
demands put on the analysis (fitness for
purpose)
 calculated from the standard deviation of
the data set
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Performance scoring –
Tolerance range from STD
 normally distributed set of data
 95,5% of the values inside a range of ±2σ
 99,7% of the values inside a range of ±3σ
 on a confidence level of 95,5 % all
accurate data are inside µ±2σ
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Performance scoring –
Z-score
 the deviation from the assigned value in
standard deviation units
(x  )
z  score 
s

the standard deviation is calculated
after exclusion of outlier or with robust
statistics
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Performance scoring – Classification
of the Internat. Harmonized Protocol
 |Z-score|2 - satisfactory
 2<|Z-score|3 - questionable
 |Z-score|>3
- unsatisfactory
 Z-scores are common practise in the
assessment of laboratory results
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Z-score - diagramm
10
Z-score
5
0
-5
-10
-15
75 39 40 36 34 20 71 56 3 85 2 59 43 25 54 90 1 80 44 76 64 29 79 73 15 7 57 32 37 72 52 10 17 95 63 49 4
laboratory code
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Statistical distribution
 Data near to the limit of determination
are not normal distributed
 otherwise there should be negative
values with a finite probability
 tolerance limits should be asymmetrical
(more narrow below the assigned value,
more wide above it)
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Solution approaches for
assymetrical tolerance limits
 logarithmic normal distribution
 take the logarithm of the values prior to
statistical calculations
 Modification of Z-scores
g
 k  Z if Z  0
Zu   1
g
  Z if Z  0
 k 2
with g = quality limit for Z
and k1, k2 =correction factors
1
1

 1 2 
 1 2
 k 2   exp  k 2     k1   exp  k1 



 2  
 2 

 1 
1     
  

1
k2    k1   1  
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
 = rel. standard deviation
 = distribution function of standard normal distribution
1- = confidence level (here: 0,955)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Laboratory assessment
 by combination of single value
assessment
 involves danger of misinterpretation
 a laboratory can measure one parameter
permanently wrong, but nevertheless is
positively assessed
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Combined assessment according to
Intern. Harmon. Protocol... - RSZ
 RSZ (rescaled sum of z-scores)
 RSZ = z/√m with m = number of scores
 same scale as z-score
 negative assessment, if all values are
within the tolerance but a little biased in the
same direction
 errors with opposite sign cancel each other
out
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Combined assessment according to
Intern. Harmon. Protocol... - SSZ
 SSZ (sum of squared z-scores)
 different scale, because 2-distributed
 doesn‘t consider the sign of z-scores
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Combination of single values
assessments
 just counting positive and negative
assessments of all values
 the absolute value of the z-score is not
considered
 e.g. assessment in the proficiency tests
of german water authorities
 80 % of the values – |Zu-score|2
 80 % of the parameters successful
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Test scheme reports
 should be distributed to the laboratories
as soon as possible
 normally not later than 1 month after
deadline for the analytical results
 laboratories need quick feedback for
corrective actions
 laboratories should be identified in the
report by test specific codes to maintain
confidentiality
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Test scheme reports –
ISO Guide 43 – contents - I
 Name and address of the organisation conducting
or coordinating the test scheme
 Names and affiliations of persons involved in the
design and conduct of the test scheme
 Date of issue of the report
 Report number and clear identification of the test
scheme
 Clear description of item or materials used,
including details of sample preparation and
homogeneity testing
 Laboratory participation codes and test results
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Test scheme reports –
ISO Guide 43 – contents - II
 Statistical data and summaries, including assigned
values and range of acceptable results
 Procedures used to establish any assigned value
 Details of the traceability and uncertainty of any
assigned value
 Assigned values and summary statistics for test
methods/procedures used by other participating
laboratories (if different methods are used by
different laboratories)
 Comments on laboratory performance by the
coordinator and technical advisers
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Test scheme reports –
ISO Guide 43 – contents - III
 Procedures used to design and implement
the test scheme (which may include
reference to test scheme protocol)
 Procedures used to statistically analyse the
data
 Advice, where appropriate, on the
interpretation of the statistical analysis
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Certificate
 If the proficiency test scheme has regulations
for the assessment of the laboratories on the
basis of the data (successful / not successful)
a certificate should be sent to the laboratory
in case of successful participation.
 In many cases these certificates are used by
the laboratories for demonstrating
competence to their customers, i.e. for
advertising.
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Certificate –
example
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Confidentiality
 normally in all PT schemes the identity of all
laboratories are kept confidential
 public reports about poor performance of a
laboratory in a proficiency test could be the
economic ruin of this laboratory
 identity should be known only to a small number
of persons
 These persons must be regularly instructed about
there duty to keep this information confidential
 the coordinating body may be required to report
poor performance to a particular authority
 participants should be notified of this possibility
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Collusion and falsification of
results
 PT schemes often are not only a help
for the laboratories to improve their
quality but also a control tool for
accreditation bodies, customers and
authorities
 their may be a tendency among some
participants to give a falsely optimistic
impression of their capabilities
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Collusion
 must not be possible

as many concentration levels as
possible
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Number of multiple
measurements
 example from reality:
 routine: single measurement
 asked in proficiency test:
independent double measurement
 executed in proficiency test:
40 (!) measurements
 therefore: limitation of sample amount,
where possible
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Level-by-level evaluation for
different concentrations
 can lead to injustice
tolerance limits /
standard deviation in %
aluminum
120
100
80
60
40
20
0
-20
-40
-60
-80
0,050
0,075
0,100
0,125
0,150
0,175
0,200
concentration in mg/l

a procedure for a common evaluation can be
found in a German standard (DIN 3840245:2003)
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Effort for the laboratory
 analysis of the samples
 should not exceed the effort for routine
samples
 in reality not insignificant
 participation fee
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Participation fee
 normally between 300 US-$ and 1000
US-$ (depending on matrix and
parameters)
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Benefits - I
 regular, external and independent check on
data quality
 Assistance in demonstrating quality and
commitment to quality issues
 Motivation to improve performance
 Support for accreditation/certification to
quality standards
 Comparison of performance with that of peers
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Benefits - II
 Assistance in the identification of
measurement problems
 Feedback and technical advice from
organisers (reports, newsletters, open
meetings)
 Assistance in the evaluation of methods and
instrumentation
 A particularly valuable method of quality
control where suitable reference materials are
not available
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Benefits - III
 Assistance in training staff
 Assistance in the marketing of analytical
services
 Savings in time/costs by reducing the
need for repeat measurements
 A guard against loss of reputation due
to poor performance
 Increased competitiveness
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching
Benefits - costs
 the costs are noticed immediately
 benefits are difficult to quantify in
monetary terms
 the succesful participation often is a
important proof of competence
 and therefore compensate for the costs
of participation
Koch, M.: Interlaboratory Tests
In: Wenclawiak, Koch, Hadjicostas (eds.)
© Springer-Verlag Berlin Heidelberg 2003
Quality Assurance in Analytical Chemistry – Training and Teaching