Koch, M.: Interlaboratory Tests© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) Quality Assurance in Analytical Chemistry – Training and Teaching Interlaboratory Tests Michael Koch

Koch, M.: Interlaboratory Tests© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) Quality Assurance in Analytical Chemistry – Training and Teaching Types of interlaboratory tests method validation reference material characterization proficiency testing

Koch, M.: Interlaboratory Tests© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) Quality Assurance in Analytical Chemistry – Training and Teaching Interlaboratory tests for characte- rization 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) Quality Assurance in Analytical Chemistry – Training and Teaching Method specific evaluation

Koch, M.: Interlaboratory Tests© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) Quality Assurance in Analytical Chemistry – Training and Teaching Performance scoring – Z-score  the deviation from the assigned value in standard deviation units the standard deviation is calculated after exclusion of outlier or with robust statistics

Koch, M.: Interlaboratory Tests© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) Quality Assurance in Analytical Chemistry – Training and Teaching Z-score - diagramm

Koch, M.: Interlaboratory Tests© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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 = rel. standard deviation  = distribution function of standard normal distribution 1-  = confidence level (here: 0,955) with g = quality limit for Z and k 1, k 2 =correction factors

Koch, M.: Interlaboratory Tests© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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 – |Z u -score|  2  80 % of the parameters successful

Koch, M.: Interlaboratory Tests© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) Quality Assurance in Analytical Chemistry – Training and Teaching Certificate – example

Koch, M.: Interlaboratory Tests© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) Quality Assurance in Analytical Chemistry – Training and Teaching Collusion  must not be possible as many concentration levels as possible

Koch, M.: Interlaboratory Tests© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) Quality Assurance in Analytical Chemistry – Training and Teaching Level-by-level evaluation for different concentrations  can lead to injustice a procedure for a common evaluation can be found in a German standard (DIN :2003)

Koch, M.: Interlaboratory Tests© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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© Springer-Verlag Berlin Heidelberg 2003 In: Wenclawiak, Koch, Hadjicostas (eds.) 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