FAQs

Why don't most SRMs have Lot numbers?

SRM 3000 does not have any additional Lot Number identifier. "SRM 3000"  is the primary SRM numerical identifier and is sufficient for identifying the SRM and assuring metrological traceability.  If a lower case alphabet appears after the number, e.g. SRM 3000a, the lower case 'a' is the renewal issue letter identifier (a=first renewal issue or lot designator). If a lot number or serial number is given for an SRM, it will appear on the Certificate of Analysis (COA) under the SRM number, e.g. Lot No. 791103 or Serial No.  X10001Y. These are specific to 'batch lot produced units' or 'individually certified units', respectively. If there is no lot number or serial number given on the accompanying Certificate of Analysis, then the SRM identifier is simply the SRM number alone. As long as the label on the SRM unit (vial/bottle, etc.) matches the SRM number given in your COA, then this is all the information you need to identify the SRM for QA purposes.

Does NIST Standard Reference Materials offer color standards?

NIST SRM does not have the "color chips". However, there is a new service that is available through the NIST Sensor Science Division that may meet your needs. A new reference instrument for measuring the surface color of materials with high accuracy has been developed by the National Institute of Standards and Technology (NIST) Sensor Science Division, which offered a calibration service for 0 degrees/45 degrees industrial color standards starting in January 2003. Because color often plays a major role in the acceptability of a product, this service is designed to meet a demand for improved measurements and standards to enhance the color matching of products.

The new reference colorimeter measures with the best possible accuracy a non-fluorescent samples spectral reflectance properties, from which color quantities are calculated. The instrument design can perform measurements at all possible combinations of illumination and viewing angles, which is important for accurate image rendering. In addition, the standard 0 degrees/45 degrees geometry (illumination at 0 degrees and viewing at 45 degrees) is highly automated through the use of a sample wheel with a capacity of 20 samples.

The new calibration service will be NISTs first for color measurement in many years, a response to needs articulated in recent reports of the Council for Optical Radiation Measurements. This new service complements ongoing services in reflectance, transmittance, and specular gloss. Industrial customers are expected to send samples (typically colored tiles) to NIST for measurement, and then use these samples as standards to calibrate their own instruments. Users then typically convert a spectral reflectance measurement into the color coordinate system used by that particular industry.

For more information, contact Maria Nadal, (301) 975-4632, maria.nadal@nist.gov.

Why do some Standard Reference Materials have no expiration date?

This statement in nist-quotes below states the NIST Policy on those SRM Certificates of Analysis that do not have a stated date of expiration.

"The certificates for NIST Standard Reference Materials (SRMs) traditionally have been in conformance with guidance criteria issued by the ISO Advisory Committee on Reference Materials. The criteria for the contents of certified reference material (CRM) certificates are contained in ISO Guide 31. Until recently, Guide 31 omitted the rationale and procedures for stating a certificates period of validity and placed such responsibility on the CRM producer. However, in response to ISO 9001 and 9002 requirements, ISO Guide 31 has now been revised to indicate that a period of validity should be stated in every CRM certificate. As a matter of policy, NIST is complying with these revised guidelines by assigning specific Expiration of Certification periods to new and renewal SRMs, but because of the number of SRMs affected, it will be some years before all certificates will have such statements. Thus, for SRMs already in circulation, users should expect that NISTs past policy continues to apply; that is, a specific period of validity for a material is stated on the SRM certificate only when the material is known to be unstable or its stability is not well known. If such a statement does not appear in a certificate, NIST considers the SRMs certification to be valid indefinitely provided the SRM is handled and stored in accordance with the instructions given in the certificate. If no specific instructions are given, then NIST recommends that the SRM be stored at room temperature (approximately 24 C) and protected from moisture and light."

How do I reconstitute freeze-dried Standard Reference Materials and what are the final reconstituted volumes?

The lyophilized (freeze-dried) materials, e.g. human serum or urine are in powdered form in the glass vials and are stored at refrigerator temperatures to maintain stability. These freeze-dried powders are produced in a special process where the water is removed from the liquid matrix (serum or urine) in the vials and the concentrated powder remains. The resulting powders are much more stable over a longer period of time. The user must reconstitute or add water to the powders in the vials with a specified volume of water as designated typically in the first paragraph of the SRM's certificate of analysis. These volumes historically have not been listed on the SRM web detail pages or in the sales software. The unit size for the SRM has always been described only as a set, e.g. 6 x 6 or a set of (2 vials).

Examples of some:

• SRM 968c Reconstituted Vol of Serum per vial 1.0 mL
• SRM 909b Reconstituted Vol of Serum per vial 10.0 mL
• SRM 1507b Reconstituted Vol of Urine per vial 20.0 mL
• SRM 2670a Reconstituted Vol of Urine per vial 20.0 mL

Does NIST have SRMs certified for nutrition composition?

Yes, NIST does have SRMs and RMs that are value-assigned for dietary constituents such as proximates, selected fatty acids, vitamins and minerals. A complete listing can be found in the SRM web catalog. These materials are representative of all nine sectors of the AOAC Food Triangle in which foods are positioned based on their fat, protein, and carbohydrate content.