Sezione Prove Interlaboratorio INFORMATION ON PROFICENCY TEST PROGRAM PIOG

Transcription

1 INFORMATION ON PROFICENCY TEST PROGRAM PIOG Odorants in natural gas and liquefied petroleum gas (LPG) (*) Year of activation 2006 Test n in Acronym PIOG-3 Organizer UNICHIM Davide Faedo Secretariat Raffaella Poma, Tel r.poma@unichim.it Organization and management of the Proficiency Test Conforms to UNI CEI EN ISO/IEC 17043:2010. Accreditation issued by ACCREDIA (N. 0003) Subcontracted activities 1) Preparation and shipment of test materials 2) Homogeneity tests Subcontractors SIAD S.p.A., Cinisello Balsamo (MI) (*) Proficency Test scheme not under accreditation Group of Experts in charge of managing the Proficiency Test (PT): Alejandra Casola Lopez Paola Comotti Andrea Gallonzelli Roberto Madella Enrico Mana Snam Rete Gas Innovhub Stazioni Sperimentali per l Industria Divisione Stazione Sperimentale per i Combustibili Innovhub Stazioni Sperimentali per l Industria Divisione Stazione Sperimentale per i Combustibili CPL Concordia ITALGAS This document contains all the "information" which, according to the requirements of the cited standard, have to be provided to the laboratories interested in participating in the PT. The document containing detailed "instructions" on PT (PIOG-3_ISTRU) will be available before the start of the PT. Head of Proficiency Test Division UNICHIM P.le R. Morandi, Milano Tel: 02/ Fax: 02/ pag. 1/6

2 1. Purpose Information and planning of the PT PIOG-3 The purpose is to offer to each of the participating laboratories the opportunity to check their analytical performance in the determination of the odorants in LPG and natural gas by gas chromatography, and to objectively demonstrate their skills to customers, accreditation body and any inspection body. An additional aim is to: o extend the scope of UNI/TR 11422:2011 (Petroleum products - Determination of the concentration of tert-butyl mercaptan in liquefied petroleum gas in the gas phase by gas chromatography), confirming or improving its precision; o extend the scope of TBM and THT in natural gas, as reported in Table 1 (point ) of UNI 7133: , confirming or improving its precision; UNICHIM reserves the right to use statistical data obtained in this PT for evaluations of the performance of techniques, methods, or specific conditions in which the test is conducted. 2. How to join the PT Implies the payment of the costs for preparation and shipping of the test materials, assigned by UNICHIM to a third party (SIAD SpA, Cinisello Balsamo). The payment shall be made directly to the latter, according to the conditions set in the attached document (PIOG-3_offerta SIAD.pdf). By joining the 2014 program the participant shall dispatch to the secretariat of UNICHIM the document PIOG-3_Registration Form, duly completed and signed, which commits the participants to respect the rules and the conditions for the participation established by the PT organizers. Expected participants: - about 10 for LPG; - about 15 for natural gas. 3. Confidentiality In order to ensure the anonymity, UNICHIM assigns to each participating laboratory an alphanumeric code. In the Test Report, UNICHIM will use this code (User ID) as the only identifier of the data source. The code is known only to UNICHIM and the laboratory itself. The test report will be available, starting from the date stated in the PT program, inside the restricted area of the website which can be accessed only by those who are in possession of the assigned code (received during association to UNICHIM or during PT like this one). The participating laboratory must ensure that the code will not be disclosed to third parties; on the same time UNICHIM is committed to the obligation of confidentiality. The participating laboratory agrees not to exchange information with other participants on the results of the determinations made during this PT. If there is an objective evidence of collusion between participants or falsification of results, UNICHIM can decide to exclude from the PT who have been guilty of such conduct. 4. Test material The test material, prepared under the instructions of the PT Manager, consists of: - a synthetic gas mixture that simulates a liquefied petroleum gas containing TBM dispersed in liquid propane in six different concentrations (6 bottles) in the range 3-55 mg/sm 3 ; pag. 2/6

3 - a synthetic gas mixture that simulates a natural gas containing THT and TBM dispersed in methane, in six different concentrations (6 bottles) in the range 2-45 mg/sm 3 (TBM) and 5-90 mg/sm 3 (THT). Depending on what is indicated in the application form, the participant lab will receive the following: - a set consisting of 6 cylinders containing pure propane and TBM; or - a set consisting of 6 cylinders containing pure methane, TBM and THT. or both. The test material will be delivered by courier at the address indicated by each registered laboratory. It is guaranteed the availability of a certain number of additional sets of test material, no later than the time set for the execution of the tests. Sending additional test materials is limited to cases of non-delivery by the courier or accidental damage during transport. 5. Test parameters LIQUEFIED PETROLEUM GAS PARAMETER Tert-butyl mercaptan (TBM) METHOD UNICHIM PROTOCOL* NATURAL GAS Tert-butyl mercaptan (TBM) Tetrahydrothiophene (THT) PARAMETER METHOD INTERNAL METHOD ** INTERNAL METHOD ** * Preparated by the working group "GPL" of the Commission "Petroleum products and lubricants" of UNICHIM, on the basis of UNI/TR (ex MU 2397). It will be available on the website (access with username and password) in the "Consultation and download documents" section. ** An analytical technique linked to UNI EN ISO shall be used. 6. Analytical methods The test methods to be used are given in clause 5, for each of the test parameters. The partecipant will be required to provide, in addition to the analytical result, additional information regarding: - the column used and the analytical conditions; - the type of detector used; - the calibration blends used filling out the form that will be attached to the file-piog 3_ISTRU, provided prior to the test. 7. Repeats All test results have to be provided in duplicates. pag. 3/6

4 8. Transmission of results The results have to be transmitted to UNICHIM in the "Data Entry" page of web site Each laboratory can access via the user ID (alphanumeric code) and the password previously assigned, selecting the appropriate PT. Instructions are provided on the website to help the user in this operation. 9. Information on the results The data obtained, together with the statistical and performance evaluation of the laboratories will be reported in a Test Report, available in the UNICHIM website. As already stated in clause 3, in the test report the laboratories are only identified by the code number assigned to them. 10. Statistical processing and evaluation of the performance of laboratories The purpose of this PT, as clarified in clause 1, is two-fold. The statistical evaluation is necessarily different for the two purposes, as stated in the following paragraphs Extension of the scope of test methods With regard to the objective of extending: - the scope of UNI/TR 11422: 2011; - the scope of the TBM and THT components as shown in Table 1 of point of UNI 7133: the statistical evaluation will be performed according to the indications of UNI EN ISO 4259: Proficiency test For both the test material specified in clause 4, the first of the two results (see clause 7) of the sample having the odorant concentration closer to the one required by Italian regulation will be used. The statistical analysis of these data will be made by means of the "robust analysis" (Algorithm A of Annex C of ISO 13528: 2005), thereby resulting in a "robust mean" and "robust standard deviation" of the PT. In case the robust analysis is not applicable, the approach provided by UNI ISO : for the exclusion of outliers will be used. Criterion for assessing the performance of an individual laboratory (z-score) 1) Assigned Value, X a : " Consensus value from participants" ( 5.6 of ISO 13528), determined by "robust analysis" of the data provided by all laboratories. (UNICHIM reserves the right to use the value specified by the manufacturer of the material as the assigned value) 2) Uncertainty of the assigned value, u Xa = s/ n, where: s is the standard deviation of the values obtained by all laboratories; n is the number of laboratories submitting results. (ISO Guide 35:2006 and IUPAC Technical Report) 3) Assigned standard deviation, s a : standard deviation of the method (LPG) and standard deviation of the test (Natural Gas). pag. 4/6

5 4) z-score = (x i X a )/s a (x i is the value provided by the i - laboratory) In accordance with the specifications of ISO 13528, the performance of the laboratory is to be considered "adequate" when the z-score is in the range Values outside this range indicate a "not adequate" performance, which will be reported in a test report with the notation: - W (Warning), if the z-score is between +2 or ; - A (Action), if the z-score is less than or greater than -3 to +3. In this case, the laboratory must implement a corrective action. Acceptance criterion for the performance assessment (Technical Report IUPAC) u Xa 2 /s a 2 0,2 the z-score is to accept unconditionally; 0,2 < u Xa 2 /s a 2 0,5 the z-score is purely for information; The calculation of the z-score is not executed when: 1. the ratio u Xa 2 / s a 2 is greater than 0,5; 2. the number of participating laboratories is less than 8; 3. when the reproducibility data of the test method are not available and the standard deviation of the test is greater than 30% of the test mean. The condition n.1 is part of the criteria proposed by IUPAC Technical Report. The condition n.2 is in UNI ISO :2004. As regards condition n.3, it should be noted that by using, as the assigned standard deviation, the one of the test (if the standard deviation of the method is not available), than the value of the ratio u Xa 2 / s a 2 is equal to 1/n (u Xa 2 = s a 2 /n), meaning that depends only on the number of laboratories and not on the dispersion of the results. For this reason it is necessary to set an upper limit of acceptability to the test reproducibility. 11. Time schedule Registration deadline By the end of September 2014 Deadline for receiving test Deadline for transmission of Test Report publication materials the results By the end of January 2015 By the end of February 2015 By mid-march 2015 UNICHIM will promptly notify any change in the program should be necessary Reference documents - ISO/IEC 17043:2010, Conformity assessment -- General requirements for proficiency testing - ISO :2004, Accuracy (trueness and precision) of measurement methods and results Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method - ISO :2004, Accuracy (trueness and precision) of measurement methods and results Part 5: Alternative methods for the determination of the precision of a standard measurement method - ISO 13528:2005, Statistical methods for use in proficiency testing by interlaboratory comparisons. pag. 5/6

6 - Thompson M., Ellison S.L.R., Wood R., The International Harmonized Protocol for the proficiency testing of analytical chemistry laboratories (IUPAC Technical Report), in Pure and Applied Chemistry, Vol.78, No 1, pp , EN ISO 4259:2006, Petroleum products Determination and application of precision data in relation to methods of test (ISO 4259:2006). - UNI/TR 11422:2011, Prodotti petroliferi - Determinazione della concentrazione di terbutilmercaptano nel gas di petrolio liquefatto in fase gassosa mediante gascromatografia - UNI :2014, Odorizzazione di gas per uso domestico e similare - Parte 2: Requisiti, controllo e gestione CONFIDENTIALITY AGREEMENT Hereby, the Head of the Proficiency Test Division of UNICHIM, in the name and on behalf of the Coordinator and the Group of Experts appointed for conducting the test, with the objectives, methods, timing and conditions for participation above indicated is committed to: - ensure that the results of each laboratories will be managed in a confidential way and will not in any way be identified by the other participating laboratories; - provide all participating laboratories the results of statistical analysis, in such a way that the results of each laboratory is identifiable only under the assigned number code; - refrain from expressing assessments about the results achieved by an individual laboratory. In faith. Head of Proficiency Test Division pag. 6/6