Development and Validation of Multi-organism/Multi-application Quantitative Coliform CRM
Oral Presentation
Prepared by E. Morris, M. Hammersla
NSI Lab Solutions, Inc., 7212 ACC Blvd., Raleigh, NC, 27617, United States
Contact Information: [email protected]; 919-789-3000
ABSTRACT
Intro: ISO Guide 17025 requires use of CRMs or secondary refernce materias to monitor validity of all tests.
Purpose: The prupose of this design and development study was to determine if multi-organism/multi-application reference materials could be produed and certified according to ISO Guide 34 having adequate stability, precison and performance to be used as received for commonly performed selective media coliform methods in environmental monitoring laboratories.
Method: E.coli(NCTC9001), K aerogenes(NCTC 8167) P, aeruginosa(NCTC12591) were combined and preserved at 2 levels to produce countable colonies for Total Coliform, Fecal Coliform and E.coli by both MF and MPN methods. Approximately 1000 individual samples were prepared from each formulation lot. Twenty random samples were collected for internal certification by listed methods. Twenty ISO Guide 17025 accredited laboratories were chosen for a 3rd party inter-laboratory proficiency testing study. Archived samples were tested for stability and further evaluated by spiral plate counting on non-selective media. Concurrently, single organism controls were prepared and validated similarly.
Results: Results of internal certification and inter-laboratory proficiency testing were statistically evaluated to determine value assignements and overall performance. Expanded uncertainties of each analyte were determined as per ISO Guide 34 and were calculated at about +/-10%. The standard deviation of the interlaboratory proficiency testing with n=20 was comparable to recent NELAC PT studies. Mixing organisms into a single CRM was documented to have no negative effect relative to single organism formulations. Stability of the CRM exceeds 8 months with testing continuing.
Significance: The performance data indicates that stable, fit for use multi-organism/multi-application CRMs can be developed and produced. Further, these CRMs can be certified with routinely performed environmental methods to yield value assignments and uncertainties applicable to the specific method.
Oral Presentation
Prepared by E. Morris, M. Hammersla
NSI Lab Solutions, Inc., 7212 ACC Blvd., Raleigh, NC, 27617, United States
Contact Information: [email protected]; 919-789-3000
ABSTRACT
Intro: ISO Guide 17025 requires use of CRMs or secondary refernce materias to monitor validity of all tests.
Purpose: The prupose of this design and development study was to determine if multi-organism/multi-application reference materials could be produed and certified according to ISO Guide 34 having adequate stability, precison and performance to be used as received for commonly performed selective media coliform methods in environmental monitoring laboratories.
Method: E.coli(NCTC9001), K aerogenes(NCTC 8167) P, aeruginosa(NCTC12591) were combined and preserved at 2 levels to produce countable colonies for Total Coliform, Fecal Coliform and E.coli by both MF and MPN methods. Approximately 1000 individual samples were prepared from each formulation lot. Twenty random samples were collected for internal certification by listed methods. Twenty ISO Guide 17025 accredited laboratories were chosen for a 3rd party inter-laboratory proficiency testing study. Archived samples were tested for stability and further evaluated by spiral plate counting on non-selective media. Concurrently, single organism controls were prepared and validated similarly.
Results: Results of internal certification and inter-laboratory proficiency testing were statistically evaluated to determine value assignements and overall performance. Expanded uncertainties of each analyte were determined as per ISO Guide 34 and were calculated at about +/-10%. The standard deviation of the interlaboratory proficiency testing with n=20 was comparable to recent NELAC PT studies. Mixing organisms into a single CRM was documented to have no negative effect relative to single organism formulations. Stability of the CRM exceeds 8 months with testing continuing.
Significance: The performance data indicates that stable, fit for use multi-organism/multi-application CRMs can be developed and produced. Further, these CRMs can be certified with routinely performed environmental methods to yield value assignments and uncertainties applicable to the specific method.
