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Standard Reference Materials

Frequently Asked Questions


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.

I need rubber compounding materials. What has happened to materials like NIST RM 8384 and NBS SRM 384c?

Regarding the former NIST RM 8384/NBS SRM 384e, these rubber compounding materials (formerly distributed by NBS/NIST) are now being distributed as Industry Reference Materials (IRMs). They are value assigned in interlaboratory comparisons by members of ASTM Committee D-11 on Rubber and inventoried and sold by companies in the commercial sector.
Please see: www.astm.org under Committee D-11 Rubber.

Does NIST supply viscosity standards?

NIST does not supply viscosity standards, however, you may want to consult the ASTM Directory of Testing Laboratories at www.astm.org or the International Laboratory Accreditation Cooperation (ILAC) and their list of accredited laboratories at http://www.ilac.org

Does NIST distribute flash point fluids?

NIST no longer distributes the flash point fluids. Please consult the ASTM Directory of Testing Laboratories at www.astm.org or the International Laboratory Accreditation Cooperation (ILAC) and their list of accredited laboratories at http://www.ilac.org/directory.htm

Why do some Standard Reference Materials have no expiration date?

This statement in 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 any SRMs certified for shellfish toxins?

NIST does not have any standards for shellfish toxins. Please contact the Institute of Marine Biosciences of the National Research Council Canada (NRC Canada) at the weblink provided below.

http://www.nrc-cnrc.gc.ca/eng

Does NIST have more finfish and shellfish reference materials certified for trace elements?

The National Metrology Laboratory of Canada (NRC Canada) has a greater number of finfish and shellfish CRMs that are certified for inorganics and organics. They can be contacted at the weblink provided below.

http://www.nrc-cnrc.gc.ca/eng

A complete listing of the international National Metrology Laboratories can be found at the link provided below.

http://www.nist.gov/oiaa/national.htm

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 at the SRM web catalog links given below. 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.

https://www-s.nist.gov/srmors/viewTable.cfm?tableid=235


How can I purchase holmium oxide glass?

NIST no longer sells or recertifies holmium oxide standards. These standards have shown insignificant spectral variation from batch to batch and from one manufacturer to another. Therefore, traceability can be established either through the supplier or by the end user. For more information about this, please see "Holmium oxide glass wavelengths standards," D.W. Allen, Journal of Research NIST, 112,
303-306 (2007). This paper and transmittance and absorbance data for holmium oxide can be found on the NIST Spectrophotometry web page, http://www.nist.gov/pml/div685/grp03/spectrophotometry.cfm.

What is the status of SRM 2034 Holmium Oxide Solution Wavelength from 240 nm to 650 nm?

This item is discontinued. However, as we have NEVER seen any degradation in old samples of SRM 2034, dating back to 1985, we recommend that customers not dispose of old samples when they expire. Purchase a new sample from any number of commercial sources in order to maintain traceability, but use the new sample to self-certify the expired sample as an in-house working standard. This process could be as simple as running annual back-to-back spectra of the current sample and the expired sample and writing up a brief in-house document equating the band positions for the two spectra with properly characterized uncertainties. The acceptable traceability chain can include any number of "links" beyond the measurement provided by a National Metrology Institute (NMI) such as NIST. Consult the NIST web site at www.nist.gov for a full treatment of the ISO conditions for traceability.

For an approach using commercial CRMs and intrinsic properties to meet traceability needs formerly provided by this SRM, see JPCRD, Vol 34, No. 1, 2005. Intrinsic Wavelength Standard Absorption Bands in Holmium Oxide Solution for UV/visible Molecular Absorption Spectrophotometry.

I have been given a method that monitors a reaction at a fixed wavelength (650 nm) using a colorimeter and a wavelength filter. I've been searching for a way to certify/calibrate the instrument at 650 nm specifically, but haven't been very successful. I read a little about the SRM 2034 Holmium Oxide Solution Standard, however, since the colorimeter cannot perform a spectral scan down to 640 nm and below, I'm not sure SRM 2034 is applicable. Are you aware of any other 650-nm wavelength reference materials I would be able to use for calibration of a colorimeter at this fixed wavelength?

It sounds like you need a transmittance scan of your 650 nm filter that is acquired on a wavelength-calibrated spectrophotometer. I know of no way to directly wavelength-calibrate a filter photometer other than to calibrate each filter used with it. All of the NIST wavelength standards are for use with scanning spectrophotometers. If you are worried about certification of the wavelength accuracy of your filter and don't have access to a scanning spectrophotometer yourself, then you have to rely on an appropriately accredited vendor to supply a scan of your filter or to supply a certified filter with a scan included. If you are trying to meet ISO 17025 requirements, then you may want to seek a filter supplier who is ISO 17025 accredited for the calibration of wavelength-selective filters or is ISO 34 accredited for the production of certified reference material filters.

The transmittance scan over your filter would not only document the wavelength accuracy, but also the spectral bandwidth. That parameter should also be of some importance to the method, and is also related to the required wavelength accuracy. In fact, your method should probably specify both a wavelength accuracy and maximum permissible spectral bandwidth, based upon the native spectrum of the monitored reaction.

Finally, a transmittance scan would reveal the efficiency of the filter, or the transmittance at the peak wavelength (hopefully 650 nm). If this efficiency is low (say, 20%), then you are loosing a lot of light and signal-to-noise ratio.

What is the density measurement for SRM 114q?

"The density that was used during the round robin is 3.15 g/cm3. The density that is shown in the certificate is for information only and was measured after the round-robin was completed. Therefore it is suggested that you use 3.15g/cm3.

What about the low-residue issue in SRM 114q?

NIST is aware of the problem to the industry concerning the residue of SRM 114q being so low. Therefore, we are working to certify another SRM with a residue of approximately 6%.

At this time we are not able to provide an availability date, however it will not be before 2007.

"So far we have had no complains regarding the Blaine results, only that the cement is finer and the residue is too low. I can only suggest that you be very careful in following the instruction below (as stated in the certificate). We found that we get better results if we follow this procedure:

"Allow the sealed foil bag to equilibrate to testing temperature before opening. Hold the pouch at one end and cut off the end of the pouch with scissors. Fluff the cement in accordance with ASTM standard C204, Section 3.4 and allow the cement to settle for 2 min, then measure without delay."

A NIST Special Publication (SP 260-161) with all the details of the Certification of SRM 114q--Pt 1 is available on line,

https://srmors.nist.gov/tables/view_table.cfm?table=301-2.htm and then

select the link SP260-161."


What is the difference between SRM 114p and SRM 114q?

The SRM 114p and SRM 114q are real cements that were bought on the market when produced and then characterized using a round-robin involving over 70 companies (for 114q) and 10 companies (for 114p). The data were analyzed using statistics to eliminate outliers and calculate the average and error interval.

As they are real cements, it is expected that the Blaine values are different between the two cements (SRM 114p was bought and packaged in the early 1990s and SRM 114q was purchased in the last year, 2004). It would have been impossible to attempt to match the characteristics of the two cements.

Are there other PCB congeners that are present in SRM 2585 that NIST has not certified?

There are other PCB congeners present in SRM 2585 that NIST has not certified. In order to certify a concentration, we are required to have a neat compound of known purity to prepare our calibration solutions and be able to separate and identify that congener on at least two GC columns. Our current methods look at approximately 80 congeners although there are many more, typically 150 or more, in most environmental samples.

Our company is planning on purchasing a set of Portland Cement SRMs from NIST for XRF spectrometer calibration. However, we have some reservations about the selection of SRMs for our XRF spectrometer calibration. Therefore we are seeking further advice on the SRM selection to develop the calibration curve for Portland Cements. We plan on purchasing the SRMs 1880a, 1881a, 1886a, 1887a and 1888a. Are these SRMs appropriate for our XRF calibration?

Many companies use the NIST 1880a series cement SRMs to calibrate X-ray spectrometers. Some prepare them as pressed briquettes; however, I prefer to use borate fusion. While both preparation approaches work, there are advantages and disadvantages to both.

The SRMs that contain portland cement are 1880a, 1881a, 1884a, 1885a, 1887a, 1888a, and 1889a. We will soon add SRM 634a to the list. SRMs 1882a and 1883a are calcium aluminate cements. SRM 1886a is a white cement, which I think is similar in most ways to an ordinary portland cement except the Fe concentration is much lower. Please note that SRMs 1881a and 1889a have other materials blended into the portland cement.

To my knowledge, there is no published standard test method for analysis of cement using XRF. I think you will be able to find papers in the literature, especially in Advances in X-Ray Analysis, the proceeding of the Denver X-Ray Conference. I recommend you consult with the maker of your XRF instrument for help with appropriate measurement conditions and calibration options.

Recently our SRM 2034 - Holmium Oxide Solution Wavelength Standard came due for  replacement. However, when I contacted NIST I was informed that they no longer supply it. Instead, they sent me a journal article titled "Intrinsic Wavelength Standard Absorption Bands in Holmium Oxide Solution for UV/visible Molecular Absorption Spectrophotometry." While the article was packed with information, I was still left without truly knowing where to turn to next to obtain a traceable standard and what that standard should be. Can you help me?

Please do not dispose of your expired SRM 2034. You can recertify it yourself against a new certified reference material and use it to verify the new one. That last point may seem backwards or circular to you, but it's not. In the journal article you refer to, NIST claims that any properly produced solution of 4 % holmium oxide in 10 % perchloric acid will provide "intrinsic standard" absorption bands whose certified wavelengths are given in the article. The condition for "properly made" is that the spectrum is "congruent" with the known spectrum -- that is, the band depths are right and there are no missing bands or extra bands. The easiest way to do that is to run your new standard and your "expired" one back to back and overlay the spectra. This will assure you that the new one was produced within specifications and the certified values will be those in the journal article. Please do the same "back-to-back" spectral overlay on a periodic basis (say, once a year) to recertify your SRM as an in-house working wavelength standard and keep using it. (You're just verifying that the spectrum hasn't changed.) The ten year expiration is an arbitrary decision made in 1995, after 10 years of producing SRM 2034. In fact, NIST has NEVER seen a degradation of our retained SRM 2034 solutions dating back as far as 1985. To find your new traceable reference material, just use a search engine to search the web for various combinations of key words such as "holmium, oxide, solution, perchlorate, wavelength, standard, certified, traceable", etc. One might use the "advanced" feature of the search engine to exclude "NIST, NBS, CSTL, glass." Several suppliers offer products in individual sealed cuvettes, others in sealed ampoules for use with your own cuvette, and others as part of a suite of certified reference materials (CRMs). Make sure that you don't order a holmium oxide glass filter, as they require individual certification for traceability and the band positions are quite different from the solution. The journal article claims automatic traceability through the published certified values for a properly produced product. If you are uncomfortable verifying the new standard against the expired one, then use the spectrum at http://www.cstl.nist.gov/nist839/839.04/Figure1_Data.xls to verify it instead.

Regarding SRM 2670a – Toxic Elements in Urine, why are the low and high concentrations the same for iodine?

The high and low concentrations are the same because iodine was not spiked into this material for the high level. The concentrations therefore represent natural levels of iodine in urine.

How stable is the iodine in solution for SRM 2670a?

The iodine should be relatively stable if the bottles are stored properly and unopened. Once opened there may be possible losses if exposure to air is excessive or the material starts breaking down. Users will want to avoid contact with acidic medium and exposure to oxygen.

Can NIST recommend any methods to prolong the shelf-life in solution for SRM 2670a?

It may be possible either to reflush the headspace with inert gas, or to freeze the reconstituted material for slightly longer storage periods, but NIST has not verified this information at the present time.

After reconstitution of SRM 2670a, how strict is the 12 hour use by instruction?

It is recommended that after reconstitution, the contents be used immediately or stored between 2? C and 8? C until ready for use, preferably within 12 hours. Once reconstituted, the urine will become a natural body fluid and will immediately start degrading. NIST advises that the material be used within 24 hours at the latest.