Evaluation of the QA forms used for deposition analyses

Transcription

1 EU/UN ECE - International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests Working Group on QA/QC in Laboratories Meeting of the Heads of the Laboratories Zadar, Croatia, September 2013 Evaluation of the QA forms used for deposition analyses Aldo Marchetto, Gabriele Tartari & Rosario Mosello, C.N.R. Institute of Ecosystem Study, Verbania (Italy) r.mosello@ise.cnr.it

2 Aims of the presentation Since 2009 it is mandatory to include the information on analytical methods and laboratory QA in the trasmission of atmospheric deposition results.

3 Methods (source of information)

4 Aims of the presentation Since 2009 it is mandatory to include the information on analytical methods and laboratory QA in the trasmission of atmospheric deposition results. Taking account of the different analytical techniques, the presentation will focus on anomalous reported values (e.g. for LOQs) and missing or wrong information, which highlight problems in the laboratories or in the transmission of data.

5 Life+ FutMon - Working Group on QA/QC in Laboratories Meeting of the Heads of the Laboratories October 2009 in Warsaw Limit of Detection (LOD) and Limit of Quantification (LOQ) estimation and use in the chemical lab Aldo Marchetto, Gabriele Tartari & Rosario Mosello C.N.R. Institute of Ecosystem Study, Verbania (Italy) a.marchetto@ise.cnr.it 5

6 Internal and external QC Internal quality control October 2009 in Warsaw calibration blank control charts mean control charts LOD & LOQ result validation using ion balance andconductivity check External quality control use of certified standard analyses of certified samples participation to WRTs 6

7 Why to estimate LOD and LOQ? October 2009 in Warsaw To evaluate the suitability of the used analytical technique and conditions to the aims of the monitoring. To compare the quality of the determination with other published results in order to evaluate if there is necessity and possibility of improvement. 7

8 Evaluation of LOD and LOQ October 2009 in Warsaw If you have mean control charts at different concentration, use them to evaluate LOD and LOQ else, if calibration slope is very stable (i.e. spectrophotometry) use SD of the blanks (if possible) or of a control sample of low concentration or of the lowest standard used for calibration else, apply Hubax-Vos method, or use the variability of the calibration standards 8

9 mg L Using control chart Single control chart in use from Nov 2006 to Aug UCL UWL LWL LCL October 2009 in Warsaw Statistics mg L -1 Average Standard Deviation Standard Deviation recommended RSD % 2.7 RSD % recommended 5.0 Minimum 0.47 Maximum 0.54 N. data R.S.D. Control Charts All control charts used in the lab for IC determinations (in 20 years) RSD = 3.37 (mg/l) Chloride Ion Chromatography mg L -1 9 C.N.R.- I.S.E. Verbania - Italy

10 Conclusions October 2009 in Warsaw Quality Control is an important tool to criticize analytical activity, to improve it and to assure that it is suitable for the purpose of monitoring. The estimation of LOD and LOQ is an important part of Quality Control. LOD and LOQ can be simply evaluated using results of control charts, blank samples or calibration curves. If you do not store these data yet, please store them anywhere and in a few years you will have years of data... 10

11 LOQs LOQs of mandatory variables

12 LOQs of mandatory variables Strong outliers LOQs

13 Values of LOQ obtained in each laboratory should be compared with those suggested in Arcachon (2011) LOQ Arcachon (2011) LOQ Arcachon (2011) Alkalinity 10 µeq/l Ca mg/l Conductivity 2 µs/cm Mg mg/l Cl mg/l Na mg/l S-SO 4 = 0.1 mg/l K + 0.4mg/L N-NO mg/l N-NH mg/l Total N 0.2 mg/l DOC 1 mg/l P-PO mg/l

14 LOQs LOQs of mandatory variables

15 LOQs LOQs of mandatory variables

16 Other problems rising from the QA forms Only 38 labs out of 47 sent the quality form; Only 13 labs sent quality data for 13 mandatory variables for 3 years. Common errors: Same control chart for several years (is it an error?) Control chart mean < LOQ LOQ = 0 Missing control chart for alkalinity, conductivity or ph Missing LOQ for alkalinity and conductivity (ph is OK) Wrong ring test number, or results from a ring test different from the last one Wrong unit for optional metals (mg instead of µg)

17 Control chart mean < LOQ

18 LOQ = 0

19 Missing control chart for: alkalinity conductivity ph Missing LOQ for: alkalinity conductivity (ph is OK)

20 Wrong ring test number, or results from a ring test different from the last one Correct WRT number: 3 for

21 Mean values of the control charts vs the deposition concentrations

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24 wrong unit?

25 wrong unit?

26 Cd for example is correct!

27 Suggestions for an optimal use of control charts 1. Select CC mean values at least 3 times LOD, best around the median of the measured values. 2. Populate CC with 2-4 measurement each day for at least 20 days. 3. Stabilize CC sample with chloroform (by acid to ph 4 for NH and DOC). 4. Use CC with different mean concentrations in the next run, in order to have at the end plots of control chart R.S.D. vs CC mean R.S.D. Control Charts All control charts used in the lab for IC determinations (20 years!) mg L -1 CC mean

28 Conclusions The highest care is needed in the QA/QC practices and documentation in the laboratory. The comparison of LOD and other QC parameters among laboratories gives information on the reliability of the applied methods and the possibility of improvements. The highest attention should be used in the transmission of results and details on the methods and QA/QC, as essential documentation for the evaluation of the quality of data produced in the laboratory.

29 Thank you for your attention