Fourth Annual DNA Grantees' Workshop
Monday, June 23, 2003
AFTERNOON SESSION
How to Make NIST Traceable Materials
Margaret C. Kline
Biography
DR. SELAVKA: There has been a long history of interaction and cooperative agreement between NIJ and the National Institute of Standards and Technology's (NIST's) Office of Law Enforcement Standards. This cooperative agreement has led to a number of groundbreaking infrastructures that forensic scientists take advantage of, and much of it invisible to us. You use it, but you really don't know much about what goes into it. I think today's presentation by Margaret Kline is going to assist us in understanding just what that means.
I would encourage you to review her extensive biographical sketch in the back of the book. It's very well written. Margaret brings to us nearly 20 years of service to the forensic community, and she has practiced through both interlaboratory comparisons as well as the use and development of reference materials.
Please join me in welcoming Margaret Kline. Kline: Slide 1
MS. KLINE: Thank you. We're going to take a quick tour through what traceability means and what NIST traceability means. This principle can be applied to any NIST standard, but it just doesn't apply to DNA. Kline: Slide 2
Our mission at NIST is to strengthen the United States economy and improve quality of life, and technology measurements and standards are in there. We provide calibrations, like thermometers; standard reference materials, like the ones you've heard of earlier today and ones we continue to make; standard reference data; test methods; proficiency materials; evaluation materials; quality measurement assurance programs (that's where a lot of you know me from—my interlaboratory studies); and laboratory accreditation services. Ultimately, we assist customers in establishing traceability of results, measurements, and values of standards. Kline: Slide 3
The responsibility of traceability is that of the provider. The provider of a NIST traceable standard or a traceable standard is the responsibility of the provider, whether the provider be NIST, another organization, or another national measurement laboratory. Kline: Slide 4
Assessing the validity of the claim is up to the user. So, yes, you can go to the catalog and see things that say "traceable." It's not up to NIST to track that down and say, yes, this is traceable. It's up to the user to find out if he or she has documentation to prove it's NIST traceable and to make sure it's traceable to the right standard and not something entirely different.
What our role is not: We do not define, specify, assure, or certify traceability except for those things that we produce or that we have a direct program/official program in which NIST is the one supplying the certification. Kline: Slide 5
We do develop and disseminate technical information on traceability, as I'm doing now. We also conduct coordinated outreach programs for traceability and other requirements. Kline: Slide 6
We define "traceability" according to the National Vocabulary of Basic General Terms, the VIM. It's been around since 1993. They're working on an updated one, but we don't know when that will be out. The definition is: "A property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated certainties." NIST is the national measurement laboratory for the United States. Kline: Slide 7
Traceability means that things have been compared through an unbroken chain to a standard and have uncertainties surrounding them. The further away from the standard you get, the greater the uncertainty.
So what do you need for a claim of traceability? To provide a measurement or result of a value, you have to document your measurement process. All forensic labs have a documented measurement process. You also have to have a description of the chain of comparisons that you use and a particular standard that you're tracing to. Kline: Slide 8
Common elements include:
- A clearly defined measurand (i.e., what you're measuring). (You won't find that in Webster, but Dave Duewer says it exists, so I'll believe Dave.)
- A complete description of the measurement system.
- Your stated measurement result or value with the documented uncertainty. If it's a temperature, then it's going to be plus/minus a certain degree.
- A complete specification of the stated reference at the time the measurement system or working standard was compared with it. Yes, you didn't run it on a broken system. It was working just fine when you ran it. Kline: Slide 9
Internal measurement assurance can be simple or complex. Level of rigor is how great you want to know your uncertainty level and what is needed to determine your credibility. You're responsible to adapt things to meet your needs. Kline: Slide 10
Now we're going to "make your own" (MYO) NIST traceable material. Prepare one batch of DNA samples; it can be a big batch if it's stable. It can be stains, swabs, cell pellets, extracts, and so on. Kline: Slide 11
We want to ensure that these samples are homogeneous, stable, and reproducible. They will need to be analyzed quite thoroughly to make sure that all of these things are happening. Kline: Slide 12
The next thing you're going to do is you're going to pick the appropriate NIST SRM to work in parallel with your traceable standard. If you make a mitochondrial NIST traceable standard, then you must use a mitochondrial standard. You can't use the 2391B; you have to use the 2392. It's got to be the appropriate standard, and you confirm that your results for the SRM (standard reference material) are in agreement with what you've made. Kline: Slide 13
Keep track of your certificate. We send out a card every time you purchase one that says: Please put a name of somebody here who should receive the certificate updates. If we update a certificate, you need to update your paperwork with your NIST traceable material. Kline: Slide 14
Maintain these records (i.e., how you have your NIST traceable material with the SRM analysis). Now, you can use your NIST traceable material as frequently as you desire, but keep a record of its use. Kline: Slide 15
Remember, the lot of material is traceable, not the source. Your lab technician's blood is not traceable, just that one lot of material that you got from him. If there is ever a discrepancy between the results of your traceable standard against the original lot, then you have to totally reanalyze it in parallel with the correct SRM. Kline: Slide 16
There must always be a correct comparison to the appropriate SRM to be traceable to NIST. If you make a second lot of material and compare it to the one you just made (your MYO), then it's not traceable to NIST—it's traceable to the MYO. As I said before, the level of uncertainty increases the further away you get from the SRM. Kline: Slide 17
This is the Web site (http://www.nist.gov/traceability) that talks about traceability in terms of everything that NIST has, including the peanut butter, the baker's chocolate, the total daily diet, and the whole nine yards. Kline: Slide 18
What about thermometers? We said at the beginning of the talk that we provide calibrations. This Web page (http://www.nist.gov/traceability/suppl_matls_for_nist_policy_rev.htm#Checklist) has a checklist for traceability through calibration. It's a nice checklist that provides everything you need. Kline: Slide 19
To learn everything you ever wanted to know about mercury glass thermometers, once again, go to the Web site for this special publication. What is it? It's the NIST Measurement Service's Liquid-in-Glass Thermometer Calibration Service, which was written in 1988 and includes methodologies that we still use. For example, when you're doing a zero-point ice bath, wear gloves while handling the thermometer so you do not put salt in it that would change the absolute zero point. Everything you want to know is in this 128-page pdf file. Kline: Slide 20
I want to thank you for your attention and NIJ for funding us through the National Office of Law Enforcement Standards. Thank you. Kline: Slide 21
DR. SELAVKA: Any questions?
(No response.)