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NISI

PUBLICATIONS

NIST SPECIAL PUBLICATION 260-126

U.S. DEPARTMENT OF COMMERCE/Technology Administration

National Institute of Standards and Technology

Standard Reference Materials:

The NIST Traceable Reference Material Program

for Gas Standards

QC

100

.U57

NO. 250-126 Franklin R. Guenther, William D. Dorko,

1996 Walter R. Miller, and George C. Rhoderick
rhe National Institute of Standards and Technology was established in 1988 by Congress

to "assist industry in the development of technology . . . needed to improve product quality, to modernize manufacturing processes, to ensure product reliability . . . and to facilitate rapid

commercialization ... of products based on new scientific discoveries."

NIST, originally founded as the National Bureau of Standards in 1901, works to strengthen

U.S. industry's competitiveness; advance science and engineering; and improve public health,

safety, and the environment. One of the agency's basic functions is to develop, maintain, and retain

custody of the national standards of measurement, and provide the means and methods for

comparing standards used in science, engineering, manufacturing, commerce, industry, and

education with the standards adopted or recognized by the Federal Government.

As an agency of the U.S. Commerce Department's Technology Administration, NIST

conducts basic and applied research in the physical sciences and engineering, and develops

measurement techniques, test methods, standards, and related services. The Institute does generic

and precompetitive work on new and advanced technologies. NIST's research facilities are located

at Gaithersburg, MD 20899, and at Boulder, CO 80303. For more information contact the Public

Inquiries Desk, 301-975-3058.
NIST Special Publication 260-126

Standard Reference Materials:

The NIST Traceable Reference Material Program

for Gas Standards

Franklin R. Guenther, William D. Dorko,

Walter R. Miller, and George C. Rhoderick

Analytical Chemistry Division

Chemical Science and Technology Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899-0001

U.S. DEPARTMENT OF COMMERCE, Michael Kantor, Secretary

TECHNOLOGY ADMINISTRATION, Mary L. Good, Under Secretary for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Arati Prabhakar, Director

Issued July 1996
National Institute of Standards and Technology Special Publication 260-126

Natl. Inst. Stand. Technol. Spec. Publ. 260-126, 40 pages (July 1996)

CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1996

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
FOREWARD

The National Institute of Standards and Technology (NIST), formerly the National Bureau of

Standards, was established by Congress in 1901 and charged with the responsibility for establishing a measurement foundation to facilitate both national and international commerce. This charge was purposely

stated in broad terms to allow NIST the ability to develop its programs to respond to changing national needs

and priorities.

The evolving linkage between the U.S. and world economy has resulted in an increased awareness of

the need for comparability among chemical data used to assess feedstock and product quality and/or evaluate

processes. The lack of comparability in chemical measurements is also a key factor in the high costs for health-care and environmental assessment, and remediation activities.

As a part of its congressional mandate, NIST develops and maintains reference methods for analysis,

and certifies and distributes Standard Reference MaterialsTM (SRMs). The NIST SRM Program distributes over 1300 different SRMs and has over 60,000 customers, with approximately 25% located outside the

United States. The Certificates of Certification contain certified results and their associated uncertainties,

and are considered to be legal documents. All 1300 available SRMs are described in the Standard Reference

Materials Catalog, Special Publication 260.

The gas NTRM program was established in 1992 in partnership with EPA and Specialty Gas

Companies as a means for providing end-users with the wide variety of certified gas standards needed to implement the "Emissions Trading" provision of the 1990 Clean Air Act. In general, a NIST Traceable

Reference Material is a reference material produced by a commercial supplier with a well-defined traceability

linkage to NIST. This linkage is established via criteria and protocols defined by NIST that are tailored to meet the needs of the metrological community to be served. Reference materials producers adhering to these

requirements will be allowed the "NTRM" trademark. Gas NTRMs are produced and distributed by

Specialty Gas Companies with NIST oversight of the production and involvement in the analysis, and can be

developed for any pollutant, concentration and balance gas combination for which a NIST primary standard

suite exists. Certified concentration values are assigned by NIST according to a protocol provided in this document.

Thomas E. Gills, Chief

Standard Reference Materials Program

Willie E. May, Chief

Analytical Chemistry Division

iii
OTHER NIST PUBLICATIONS IN THIS SERIES

Trahey, N.M., ed., NIST Standard Reference

Materials Catalog 1995-96, NIST Spec. Publ.

260 (1995 Ed.). PB95-232518/AS

Michaelis, R.E., and Wyman, L.L., Standard

Reference Materials: Preparation of White Cast

Iron Spectrochemical Standards, NBS Misc.

Publ. 260-1 (June 1964). COM74-11061**

Michaelis, R.E., Wyman, L.L., and Flitsch, R.,

Standard Reference Materials: Preparation of

NBS Copper-Base Spectrochemical Standards,

NBS Misc. Publ. 260-2 (October 1964).

COM74-11063**

Michaelis, R.E., Yakowitz, H., and Moore, G.A.,

Standard Reference Materials: Metallographic

Characterization of an NBS Spectrometric

Low-Alloy Steel Standard, NBS Misc. Publ.

260-3 (October 1964). COM74-11060**

Hague, J.L., Mears, T.W., and Michaelis, R.E.,

Standard Reference Materials: Sources of

Information, Publ. 260-4 (February 1965).

COM74- 11059**

Alvarez, R., and Flitsch, R., Standard Reference

Materials: Accuracy of Solution X-Ray

Spectrometric Analysis of Copper-Base Alloys,

NBS Misc. Publ. 260-5 (February 1965).

PB168068**

Shultz, J.I., Standard Reference Materials:

Methods for the Chemical Analysis of White

Cast Iron Standards, NBS Misc. Publ. 260-6

(July 1965). COM74-11068**

Bell, R.K., Standard Reference Materials: Methods

for the Chemical Analysis of NBS Copper-Base

Spectrochemical Standards, NBS Misc. Publ.

260-7 (October 1965). COM74-11067**

Richmond, M.S., Standard Reference Materials:

Analysis of Uranium Concentrates at the

National Bureau of Standards, NBS Misc. Publ.

260-8 (December 1965). COM74-11066**

Anspach, S.C., Cavallo, L.M., Garfinkel, S.B., et

al., Standard Reference Materials: Half Lives

of Materials Used in the Preparation of

Standard Reference Materials of Nineteen

Radioactive Nuclides Issued by the National

Bureau of Standards, NBS Misc. Publ. 260-9

(November 1965). COM74-11065**

Yakowitz, H., Vieth, D.L., Heinrich, K.F.J. , et

al., Standard Reference Materials:

Homogeneity Characterization of NBS

Spectrometric Standards II: Cartridge Brass and

Low-Alloy Steel, NBS Misc. Publ. 260-10

(December 1965). COM74-1 1064**

Napolitano, A., and Hawkins, E.G., Standard

Reference Materials: Viscosity of Standard

Lead-Silica Glass, NBS Misc. Publ. 260-11**

(November 1966).

Yakowitz, H., Vieth, D.L., and Michaelis, R.E.,

Standard Reference Materials: Homogeneity

Characterization of NBS Spectrometric

Standards III: White Cast Iron and Stainless

Steel Powder Compact, NBS Misc. Publ.

260-12 (September 1966).

Spijkerman, J.J., Snediker, D.K., Ruegg, F.C., et

al., Standard Reference Materials: Mossbauer

Spectroscopy Standard for the Chemical Shift of

Iron Compounds, NBS Misc. Publ. 260-13**

(July 1967).

Menis, O., and Sterling, J.T., Standard Reference

Materials: Determination of Oxygen in Ferrous

Materials (SRMs 1090, 1091, 1092), NBS

Misc. Publ. 260-14** (September 1966).

Passaglia, E. and Shouse, P.J., Standard Reference

Materials: Recommended Method of Use of

Standard Light-Sensitive Paper for Calibrating

Carbon Arcs Used in Testing Testiles for

Colorfastness to Light, NBS Spec. Publ. 260-15

(July 1967). Superseded by SP 260-41.

IV
Yakowitz, H., Michaelis, R.E., and Vieth, D.L.,

Standard Reference Materials: Homogeneity

Characterization of NBS Spectrometric

Standards IV: Pre-paration and Microprobe

Characterization of W-20% Mo Alloy

Fabricated by Powder Metallurgical Methods,

NBS Spec. Publ. 260-16 (January 1969).

COM74-11062**

Catanzaro, E.J., Champion, C.E., Garner, E.L.,

et al., Standard Reference Materials: Boric

Acid; Isotopic, and Assay Standard Reference

Materials, NBS Spec. Publ. 260-17 (February

1970). PB189457**

Geller, S.B., Mantek, P. A., and Cleveland, N.G.,

Calibration of NBS Secondary Standards

Magnetic Tape Computer Amplitude Reference

Amplitude Measurement "Process A," NBS

Spec. Publ. 260-18 (November 1969).

Superseded by SP 260-29.

Paule, R.C., and Mandel, J., Standard Reference

Materials: Analysis of Interlaboratory

Measurements on the Vapor Pressure of Gold

(Certification of SRM 745). NBS Spec. Publ.

260-19 (January 1970). PB190071**

260-20: Unassigned

Paule, R.C., and Mandel, J., Standard Reference

Materials: Analysis of Interlaboratory

Measurements on the Vapor Pressures of

Cadmium and Silver, NBS Spec. Publ. 260-21

(January 1971). COM74-11359**

Yakowitz, H., Fiori, C.E., and Michaelis, R.E.,

Standard Reference Materials: Homogeneity

Characterization of Fe-3 Si Alloy, NBS Spec.

Publ. 260-22 (February 1971).

COM74- 11357**

Napolitano, A., and Hawkins, E.G., Standard

Reference Materials: Viscosity of a Standard

Borosilicate Glass, NBS Spec. Publ. 260-23

(December 1970). COM71-00157**

Sappenfield, K.M., Marinenko, G., and Hague,

J.L., Standard Reference Materials:

Comparison of Redox Standards, NBS Spec.

Publ. 260-24 (January 1972). COM72-50058**

Hicho, G.E., Yakowitz, H., Rasberry, S.D., et

al., Standard Reference Materials: A Standard

Reference Material Containing Nominally Four

Percent Austenite, NBS Spec. Publ. 260-25

(February 1971). COM74-11356**

Martin, J.F., Standard Reference Materials:

NBS-U.S. Steel Corp. Joint Program for

Determining Oxygen and Nitrogen in Steel,

NBS Spec. Publ. 260-26 (February 1971). PB

81176620**

Garner, E.L., Machlan, L.A., and Shields, W.R.,

Standard Reference Materials: Uranium Isotopic

Standard Reference Materials, NBS Spec. Publ.

260-27 (April 1971). COM74-1 1358**

Heinrich, K.F.J. , Myklebust, R.L., Rasberry,

S.D., et al., Standard Reference Materials:

Preparation and Evaluation of SRMs 481 and

482 Gold-Silver and Gold-Copper Alloys for

Microanalysis, NBS Spec. Publ. 260-28

(August 1971). COM71-50365**

Geller, S.B., Standard Reference Materials:

Calibration of NBS Secondary Standard

Magnetic Tape (Computer Amplitude

Reference) Using the Reference Tape

Amplitude Measurement "Process A-Model 2,"

NBS Spec. Publ. 260-29 (June 1971).

COM71-50282** Supersedes Measurement

System in SP 260-18.

Gorozhanina, R.S., Freedman, A.Y., and

Shaievitch, A.B., (translated by M.C. Selby),

Standard Reference Materials: Standard

Samples Issued in the USSR (A Translation

from the Russian), NBS Spec. Publ. 260-30

(June 1971). COM71-50283**

Hust, J.G., and Sparks, L.L., Standard Reference

Materials: Thermal Conductivity of Electrolytic

Iron SRM 734 from 4 to 300 K, NBS Spec.

Publ. 260-31 (November 1971).

COM71-50563**

Mavrodineanu, R., and Lazar, J.W., Standard

Reference Materials: Standard Quartz Cuvettes

for High Accu-racy Spectrophotometry, NBS

Spec. Publ. 260-32 (December 1973).

COM74-50018**

v
Wagner, H.L., Standard Reference Materials:

Comparison of Original and Supplemental SRM

705, Narrow Molecular Weight Distribution

Polystyrene, NBS Spec. Publ. 260-33 (May

1972). COM72-50526**

Sparks, L.L., and Hust, J.G., Standard Reference

Material: Thermoelectric Voltage of Silver-28

Atomic Percent Gold Thermocouple Wire,

SRM 733, Verses Common Thermocouple

Materials (Between Liquid Helium and Ice

Fixed Points), NBS Spec. Publ. 260-34 (April

1972). COM72-50371**

Sparks, L.L., and Hust, J.G., Standard Reference

Materials: Thermal Conductivity of Austenitic

Stainless Steel, SRM 735 from 5 to 280 K,

NBS Spec. Publ. 260-35 (April 1972).

COM72-50368**

Cali, J. P., Mandel, J., Moore, L.J., et al.,

Standard Reference Materials: A Reference

Method for the Determination of Calcium in

Serum NBS SRM 915, NBS Spec. Publ. 260-36

(May 1972). COM72-50527**

Shultz, J.I., Bell, R.K., Rains, T.C., et al.,

Standard Reference Materials: Methods of

Analysis of NBS Clay Standards, NBS Spec.

Publ. 260-37 (June 1972). COM72-50692**

Richard, J.C., and Hsia, J.J., Standard Reference

Materials: Preparation and Calibration of

Standards of Spectral Specular Reflectance,

NBS Spec. Publ. 260-38 (May 1972). COM72-

50528**

Clark, A.F., Denson, V.A., Hust, J.G., etal.,

Standard Reference Materials: The Eddy

Current Decay Method for Resistivity

Characterization of High-Purity Metals, NBS

Spec. Publ. 260-39 (May 1972).

COM72-50529**

McAdie, H.G., Garn, P.D., and Menis, O.,

Standard Reference Materials: Selection of

Differential Thermal Analysis Temperature

Standards Through a Cooperative Study (SRMs

758, 759, 760), NBS Spec. Publ. 260-40

(August 1972) COM72-50776**

Wood. L.A., and Shouse, P. J., Standard Reference

Materials: Use of Standard Light-Sensitive

Paper for Calibrating Carbon Arcs Used in

Testing Textiles for Colorfastness to Light,

NBS Spec. Publ. 260-41 (August 1972).

COM72-50775**

Wagner, H.L., and Verdier, P.H., eds., Standard

Reference Materials: The Characterization of

Linear Polyethylene, SRM 1475, NBS Spec.

Publ. 260-42 (September 1972).

COM72-50944**

Yakowitz, H., Ruff, A.W., and Michaelis, R.E.,

Standard Reference Materials: Preparation and

Homogeneity Characterization of an Austenitic

Iron-Chromium-Nickel Alloy, NBS Spec. Publ.

260-43 (November 1972). COM73-50760**

Schooley, J.F., Soulen, R.J., Jr., and Evans,

G.A., Jr., Standard Reference Materials:

Preparation and Use of Superconductive Fixed

Point Devices, SRM 767, NBS Spec. Publ.

260-44 (December 1972). COM73-50037**

Greifer, B., Maienthal, E.J., Rains, T.C., et al.,

Standard Reference Materials: Development of

NBS SRM 1579 Powdered Lead-Based Paint,

NBS Spec. Publ. 260-45 (March 1973).

COM73-50226**

Hust, J.G., and Giarratano, P.J., Standard

Reference Materials: Thermal Conductivity and

Electrical Resistivity Standard Reference

Materials: Austenitic Stainless Steel, SRMs 735

and 798, from 4 to 1200 K, NBS Spec. Publ.

260-46 (March 1975). COM75-10339**

Hust, J.G., Standard Reference Materials:

Electrical Resistivity of Electrolytic Iron, SRM

797, and Austenitic Stainless Steel, SRM 798,

from 5 to 280 K, NBS Spec. Publ. 260-47

(February 1974). COM74-50176**

Mangum, B.W., and Wise, J. A., Standard

Reference Materials: Description and Use of

Precision Thermometers for the Clinical

Laboratory, SRM 933 and SRM 934, NBS

Spec. Publ. 260-48 (May 1974). Superseded by

NIST Spec. Publ. 260-113. COM74-50533**

vi
Carpenter, B.S., and Reimer, G.M., Standard

Reference Materials: Calibrated Glass Standards

for Fission Track Use, NBS Spec. Publ. 260-49

(November 1974). COM74-51185**

Hust, J.G., and Giarratano, P.J., Standard

Reference Materials: Thermal Conductivity and

Electrical Resistivity Standard Reference

Materials: Electrolytic Iron, SRMs 734 and 797

from 4 to 1000 K, NBS Spec. Publ. 260-50

(June 1975). COM75-10698**

Mavrodineanu, R., and Baldwin, J.R., Standard

Reference Materials: Glass Filters As a SRM

for Spectrophotometry-Selection, Preparation,

Certification, and Use-SRM 930 NBS Spec.

Publ. 260-51 (November 1975).

COM75- 10339**

Hust, J.G., and Giarratano, P. J., Standard

Reference Materials: Thermal Conductivity and

Electrical Resistivity SRMs 730 and 799, from

4 to 3000 K, NBS Spec. Publ. 260-52

(September 1975). COM75-11193**

Durst, R.A., Standard Reference Materials:

Standardization of pH Measurements, NBS

Spec. Publ. 260-53 (December 1978).

Superseded by SP 260-53 Rev. 1988 Edition.

PB882 17427**

Burke, R.W., and Mavrodineanu, R., Standard

Reference Materials: Certification and Use of

Acidic Potassium Dichromate Solutions as an

Ultraviolet Absorbance Standard, NBS Spec.

Publ. 260-54 (August 1977). PB272168**

Ditmars, D.A., Cezairliyan, A., Ishihara, S., et

al., Standard Reference Materials: Enthalpy and

Heat Capacity; Molybdenum SRM 781, from

273 to 2800 K, NBS Spec. Publ. 260-55

(September 1977). PB272127**

Powell, R.L., Sparks, L.L., and Hust, J.G.,

Standard Reference Materials: Standard

Thermocouple Material, Pt-67: SRM 1967,

NBS Spec. Publ. 260-56 (February 1978).

PB277172**

Cali, J. P., and Plebanski, T., Standard Reference

Materials: Guide to United States Reference

Materials, NBS Spec. Publ. 260-57 (February

1978). PB277173**

Barnes, J.D., and Martin, G.M., Standard

Reference Materials: Polyester Film for Oxygen

Gas Transmission Measurements SRM 1470,

NBS Spec. Publ. 260-58 (June 1979).

PB297098**

Chang, T., and Kahn, A.H., Standard Reference

Materials: Electron Paramagnetic Resonance

Intensity Standard: SRM 2601; Description and

Use, NBS Spec. Publ. 260-59 (August 1978).

PB292097**

Velapoldi, R.A., Paule, R.C., Schaffer, R., etal.,

Standard Reference Materials: A Reference

Method for the Determination of Sodium in

Serum, NBS Spec. Publ. 260-60 (August

1978). PB286944**

Verdier, P.H., and Wagner, H.L., Standard

Reference Materials: The Characterization of

Linear Polyethylene (SRMs 1482, 1483, 1484),

NBS Spec. Publ. 260-61 (December 1978).

PB289899**

Soulen, R.J., and Dove, R.B., Standard Reference

Materials: Temperature Reference Standard for

Use Below 0.5 K (SRM 768), NBS Spec. Publ.

260-62 (April 1979). PB294245**

Velapoldi, R.A., Paule, R.C., Schaffer, R., et al.,

Standard Reference Materials: A Reference

Method for the Determination of Potassium in

Serum, NBS Spec. Publ. 260-63 (May 1979).

PB297207**

Velapoldi, R.A., and Mielenz, K.D., Standard

Reference Materials: A Fluorescence SRM

Quinine Sulfate Dihydrate (SRM 936), NBS

Spec. Publ. 260-64 (January 1980).

PB80 132046**

Marinenko, R.B., Heinrich, K.F.J. , and Ruegg,

F.C., Standard Reference Materials:

Micro-Homogeneity Studies of NBS SRM, NBS

Research Materials, and Other Related Samples,

NBS Spec. Publ. 260-65 (September 1979).

PB300461**

vii
Venable, W.H., Jr., and Eckerle, K.L., Standard

Reference Materials: Didymium Glass Filters

for Calibrating the Wavelength Scale of

Spectrophotometers (SRMs 2009, 2010, 2013,

2014). NBS Spec. Publ. 260-66 (October

1979). PB80104961**

Velapoldi, R.A., Paule, R.C., Schaffer, R., et al.,

Standard Reference Materials: A Reference

Method for the Determination of Chloride in

Serum, NBS Spec. Publ. 260-67 (November

1979). PB80110117**

Mavrodineanu, R., and Baldwin, J.R., Standard

Reference Materials: Metal-On-Quartz Filters as a SRM for Spectrophotometry SRM 203 1

,

NBS Spec. Publ. 260-68 (April 1980).

PB80197486**

Velapoldi, R.A., Paule, R.C., Schaffer, R., et al.,

Standard Reference Materials: A Reference

Method for the Determination of Lithium in

Serum, NBS Spec. Publ. 260-69 (July 1980).

PB80209117**

Marinenko, R.B., Biancaniello, F., Boyer, P. A.,

et al., Standard Reference Materials:

Preparation and Characterization of an Iron-Chromium-Nickel Alloy for

Microanalysis: SRM 479a, NBS Spec. Publ.

260-70 (May 1981). SNQ03-003-02328-1*

Seward, R.W., and Mavrodineanu, R., Standard

Reference Materials: Summary of the Clinical

Laboratory Standards Issued by the National

Bureau of Standards, NBS Spec. Publ. 260-71

(November 1981). PB82135161**

Reeder, D.J., Coxon, B., Enagonio, D., et al.,

Standard Reference Materials: SRM 900, Antiepilepsy Drug Level Assay Standard, NBS

Spec. Publ. 260-72 (June 1981). PB81220758

Interrante, C.G., and Hicho, G.E., Standard

Reference Materials: A Standard Reference

Material Containing Nominally Fifteen Percent

Austenite (SRM 486), NBS Spec. Publ. 260-73

(January 1982). PB822 15559**

Marinenko, R.B., Standard Reference Materials:

Preparation and Characterization of K-411 and

K-412 Mineral Glasses for Microanalysis: SRM

470, NBS Spec. Publ. 260-74 (April 1982).

PB82221300**

Weidner, V.R., and Hsia, J.J., Standard Reference

Materials: Preparation and Calibration of First

Surface Aluminum Mirror Specular Reflectance

Standards (SRM 2003a), NBS Spec. Publ.

260-75 (May 1982). PB82221367**

Hicho, G.E., and Eaton, E.E., Standard Reference

Materials: A Standard Reference Material

Containing Nominally Five Percent Austenite

(SRM 485a), NBS Spec. Publ. 260-76 (August

1982) . PB831 15568**

Furukawa, G.T., Riddle, J.L., Bigge, W.G., et

al., Standard Reference Materials: Application

of Some Metal SRMs as Thermometric Fixed

Points, NBS Spec. Publ. 260-77 (August 1982).

PB83 117325**

Hicho, G.E., and Eaton, E.E., Standard Reference

Materials: Standard Reference Material

Containing Nominally Thirty Percent Austenite

(SRM 487), NBS Spec. Publ. 260-78

(September 1982). PB831 15576**

Richmond, J.C., Hsia, J.J., Weidner, V.R., et al.,

Standard Reference Materials: Second Surface

Mirror Standards of Specular Spectral

Reflectance (SRMs 2023, 2024, 2025), NBS

Spec. Publ. 260-79 (October 1982).

PB84203447**

Schaffer, R., Mandel, J., Sun, T., et al., Standard

Reference Materials: Evaluation by an ID/MS

Method of the AACC Reference Method for

Serum Glucose, NBS Spec. Publ. 260-80

(October 1982). PB84216894**

Burke, R.W., and Mavrodineanu, R. , Standard

Reference Materials: Accuracy in Analytical

Spectrophotometry, NBS Spec. Publ. 260-81

(April 1983). PB832 14536**

Weidner, V.R., Standard Reference Materials:

White Opal Glass Diffuse Spectral Reflectance

Standards for the Visible Spectrum (SRMs 2015

and 2016), NBS Spec. Publ. 260-82 (April

1983) . PB83220723**
Bowers, G.N., Jr., Alvarez, R., Cali, J. P., et al.,

Standard Reference Materials: The

Measurement of the Catalytic (Activity)

Concentration of Seven Enzymes in NBS

Human Serum (SRM 909), NBS Spec. Publ.

260-83 (June 1983). PB83239509**

Gills, T.E., Seward, R.W., Collins, R.J., et al.,

Standard Reference Materials: Sampling,

Materials Handling, Processing, and Packaging

of NBS Sulfur in Coal SRMs 2682, 2683,

2684, and 2685, NBS Spec. Publ. 260-84

(August 1983). PB84109552**

Swyt, D.A., Standard Reference Materials: A

Look at Techniques for the Dimensional

Calibration of Standard Microscopic Particles,

NBS Spec. Publ. 260-85 (September 1983).

PB841 12648**

Hicho, G.E., and Eaton, E.E., Standard Reference

Materials: A SRM Containing Two and

One-Half Percent Austenite, SRM 488, NBS

Spec. Publ. 260-86 (December 1983).

PB84 143296**

Mangum, B.W., Standard Reference Materials:

SRM 1969: Rubidium Triple-Point - A

Temperature Reference Standard Near 39.30°

C, NBS Spec. Publ. 260-87 (December 1983).

PB84 149996**

Gladney, E.S., Burns, C.E., Perrin, D.R., etal.,

Standard Reference Materials: 1982

Compilation of Elemental Concentration Data

for NBS Biological, Geological, and

Environmental Standard Reference Materials,

NBS Spec. Publ. 260-88 (March 1984).

PB84218338**

Hust, J.G., Standard Reference Materials: A FineGrained, Isotropic Graphite for Use as NBS

Thermophysical Property RMs from 5 to 2500

K, NBS Spec. Publ. 260-89 (September 1984).

PB85 112886**

Hust, J.G., and Lankford, A.B., Standard

Reference Materials: Update of Thermal

Conductivity and Electrical Resistivity of

Electrolytic Iron, Tungsten, and Stainless Steel,

NBS Spec. Publ. 260-90 (September 1984).

PB85 115814**

Goodrich, L.F., Vecchia, D.F., Pittman, E.S., et

al., Standard Reference Materials: Critical

Current Measurements on an NbTi

Superconducting Wire SRM, NBS Spec. Publ.

260-91 (September 1984). PB851 18594**

Carpenter, B.S., Standard Reference Materials:

Calibrated Glass Standards for Fission Track

Use (Supplement to NBS Spec. Publ. 260-49),

NBS Spec. Publ. 260-92 (September 1984).

PB85 113025**

Ehrstein, J.R., Standard Reference Materials:

Preparation and Certification of SRM for

Calibration of Spreading Resistance Probes,

NBS Spec. Publ. 260-93 (January 1985).

PB85177921**

Gills, T.E., Koch, W.F., Stolz, J.W., et al.,

Standard Reference Materials: Methods and

Procedures Used at the National Bureau of

Standards to Certify Sulfur in Coal SRMs for

Sulfur Content, Calorific Value, Ash Content,

NBS Spec. Publ. 260-94 (December 1984).

PB85 165900**

Mulholland, G.W., Hartman, A.W., Hembree,

G.G., et al., Standard Reference Materials:

Development of a 1mm Diameter Particle Size

Standard, SRM 1690, NBS Spec. Publ. 260-95

(May 1985). PB95-232518/AS**

Carpenter, B.S., Gramlich, J.W., Greenberg,

R.R., et al., Standard Reference Materials:

Uranium-235 Isotopic Abundance Standard

Reference Materials for Gamma Spectrometry

Measurements, NBS Spec. Publ. 260-96

(September 1986). PB87108544**

Mavrodineanu, R., and Gills, T.E., Standard

Reference Materials: Summary of the Coal,

Ore, Mineral, Rock, and Refactory Standards

Issued by the National Bureau of Standards,

NBS Spec. Publ. 260-97 (September 1985).

PB861 10830**

Hust, J.G., Standard Reference Materials: Glass

Fiberboard SRM for Thermal Resistance, NBS

Spec. Publ. 260-98 (August 1985).

SN003-003-02674-3*

ix
Callanan, J.E., Sullivan, S.A., and Vecchia, D.F.,

Standard Reference Materials: Feasibility Study

for the Development of Standards Using

Differential Scanning Calorimetry, NBS Spec.

Publ. 260-99 (August 1985). PB86106747**

Taylor, J.K., Trahey, N.M., ed., Standard

Reference Materials: Handbook for SRM

Users, NBS Spec. Publ. 260-100 (February

1993). PB93 183796**

Mangum, B.W., Standard Reference Materials:

SRM 1970, Succinonitrile Triple-Point

Standard: A Temperature Reference Standard

Near 58.08° C, NBS Spec. Publ. 260-101

(March 1986). PB86197100**

Weidner, V.R., Mavrodineanu, R., Mielenz,

K.D., et al., Standard Reference Materials:

Holmium Oxide Solution Wavelength Standard

from 240 to 640 nm - SRM 2034, NBS Spec.

Publ. 260-102 (July 1986). PB86245727**

Hust, J.G., Standard Reference Materials: Glass

Fiberblanket SRM for Thermal Resistance,

NBS Spec. Publ. 260-103 (September 1985).

PB86109949**

Mavrodineanu, R., and Alvarez, R., Standard

Reference Materials: Summary of the Biological

and Botanical Standards Issued by the National

Bureau of Standards, NBS Spec. Publ. 260-104

(November 1985). PB86155561**

Mavrodineanu, R., and Rasberry, S.D., Standard

Reference Materials: Summary of the

Environmental Research, Analysis, and Control

Standards Issued by the National Bureau of

Standards, NBS Spec. Publ. 260-105 (March

1986). PB86204005**

Koch, W.F., ed., Standard Reference Materials:

Methods and Procedures Used at the National

Bureau of Standards to Prepare, Analyze, and

Certify SRM 2694, Simulated Rainwater, and

Recommendations for Use, NBS Spec. Publ.

260-106 (July 1986). PB86247483**

Hartman, A.W., and McKenzie, R.L., Standard

Reference Materials: SRM 1965, Microsphere

Slide (10 /xm Polystyrene Spheres), NIST Spec.

Publ. 260-107 (November 1988).

PB89 153704**

Mavrodineanu, R., and Gills, T.E., Standard

Reference Materials: Summary of Gas Cylinder

and Permeation Tube Standard Reference

Materials Issued by the National Bureau of

Standards, NBS Spec. Publ. 260-108 (May

1987). PB87209953**

Candela, G.A., Chandler-Horowitz, D., Novotny,

D.B., et al., Standard Reference Materials:

Preparation and Certification of an

Ellipsometrically Derived Thickness and

Refractive Index Standard of a Silicon Dioxide

Film (SRM 2530), NIST Spec. Publ. 260-109

(October 1988). PB89133573**

Kirby, R.K., and Kanare, H.M., Standard

Reference Materials: Portland Cement Chemical

Composition Standards (Blending, Packaging,

and Testing), NBS Spec. Publ. 260-110

(February 1988). PB88193347**

Gladney, E.S., O'Malley, B.T., Roelandts, I., et

al., Standard Reference Materials: Compilation

of Elemental Concentration Data for NBS

Clinical, Biological, Geological, and

Environmental Standard Reference Materials,

NBS Spec. Publ. 260-111 (November 1987).

PB88156708**

Marinenko, R.B., Blackburn, D.H., and Bodkin,

J.B., Standard Reference Materials: Glasses for

Microanalysis: SRMs 1871-1875, NIST Spec.

Publ. 260-112 (February 1990).

PB902 15807**

Mangum, B.W., and Wise, J. A., Standard

Reference Materials: Description and Use of a

Precision Thermometer for the Clinical

Laboratory, SRM 934, NIST Spec. Publ.

260-113 (June 1990). PB90257643**

Vezzetti, C.F., Varner, R.N., and Potzick, J.E.,

Standard Reference Materials:

Bright-Chromium Linewidth Standard, SRM

476, for Calibration of Optical Microscope

Linewidth Measuring Systems, NIST Spec.

Publ. 260-114 (January 1991). PB91 167163**

X
Williamson, M.P., Willman, N.E., and Grubb,

D.S., Standard Reference Materials: Calibration

of NIST SRM 3201 for 0.5 in. (12.65 mm)

Serial Serpentine Magnetic Tape Cartridge,

NIST Spec. Publ. 260-115 (February 1991).

PB9 1187542**

Mavrodineanu, R., Burke, R.W., Baldwin, J.R., et

al., Standard Reference Materials: Glass Filters as a Standard Reference Material for

Spectrophotometry-Selection , Preparation

,

Certification and Use of SRM 930 and SRM

1930, NIST Spec. Publ. 260-116 (March

1994). PB94-188844/AS**

Vezzetti, C.F., Varner, R.N., and Potzick, J.E.,

Standard Reference Materials: Antirerlecting-Chromium Linewidth Standard, SRM

475, for Calibration of Optical Microscope

Linewidth Measuring Systems, NIST Spec.

Publ. 260-117 (January 1992). PB92-149798**

Williamson, M.P., Standard Reference Materials:

Calibration of NIST Standard Reference

Material 3202 for 18-Track, Parallel, and

36-Track, Parallel Serpentine, 12.65 mm (0.5

in), 1491 cpmm (37871 cpi), Magnetic Tape

Cartridge, NIST Spec. Publ. 260-118 (July

1992). PB92-226281**

Vezzetti, C.F., Varner, R.N., and Potzick,

Standard Reference Materials: AntireflectingChromium Linewidth Standard, SRM 473, for

Calibration of Optical Microscope Linewidth

Measuring System, NIST Spec. Publ. 260-119

(September 1992)

Caskey, G.W., Philips, S.D., Borchardt., etal.,

Standard Reference Materials: A Users' Guide

to NIST SRM 2084: CMM Probe Performance

Standard, NIST Spec. Publ. 260-120 (1994)

Rennex, B.G., Standard Reference Materials:

Certification of a Standard Reference Material

for the Determination of Interstitial Oxygen

Concentration in Semiconductor Silicon by

Infrared Spectrophotometry, NIST Spec. Publ.

260-121 (1994) PB95-125076/AS

Gupta, D., Wang, L., Hanssen, L.M., Hsai, J.J.,

and Datla, R.U., Polystyrene Films for

Calibrating the Wavelength Scale of Infrared

Spectrophotometer (SRM 1921). NIST Spec.

Publ. 260-122 (1995) PB95-226866/AS

Development of Technology and the Manufacture

of Spectrometric SRMs for Naval Brasses

(MC62 M63). NIST Spec. Publ. 260-123 (IN

PREP)

Strouse, G.F., SRM 1744: Aluminum Freezing

Point Standard. NIST Spec. Publ. 260-124

(1995) SN003-003-03342-1

Schiller, S.B., Statistical Aspects of the

Certification of Chemical Batch Standard

Reference Materials. NIST Spec. Publ. 260-

125 (IN PREP)

*Send order with remittance to: Superintendent of

Documents, U.S. Government Printing Office,

Washington, DC 20102. Remittance from

foreign countries should include an additional one fourth of the purchase price for postage.

**May be ordered from: National Technical

Information Services (NTIS), Springfield, VA

22161.

For information phone (703-487-4650)

To Place an Order with PB# phone (800-553-

6847)

xi
CONTENTS

1. INTRODUCTION 1

2. PROGRAM OVERVIEW 2

2.1 Description 2

2.2 Qualification of Producer 2

2.3 Batch Planning and Scheduling 3 2.4 Batch Production 3 2.5 Producer Analysis 3

2.6 NIST Data Review 4

2.7 Batch Certification 4

2.8 Maintenance of NTRM Batches 4

2.9 Batch Certification Cost 5

3. BATCH PRODUCTION AND ANALYSIS 6

3.1 Overview of Producer Responsibilities 6

3.2 Batch Preparation 6

3.3 First Analysis 7

3.4 Second Analysis 8

3.5 Batch Stability and Homogeneity 9

4. BATCH CERTIFICATION 11

4.1 Overview 11 4.2 NIST Analytical Protocol 11 4.3 Producer's Data Validation and Batch Value Assignment 12

4.4 Value Uncertainty 12

4.5 NTRM Documentation 13

4.6 NTRM Rejection Criteria 13

5. MAINTENANCE OF NTRM BATCHES 14

5.1 Batch Recertification 14

5.2 Customer NTRM Cylinders 14

5.3 Customer NTRM Recertification 15

6. TRACEABILITY TO NIST 16

6.1 NTRM Batch Traceability 16

6.2 Mixtures Produced Referencing NTRMs and SRMs 16

References 18

Appendix 1: Definition of Terms 19

Appendix 2: Production and Certification Flow Chart 21

Appendix 3: NTRM Specifications 22

Appendix 4: Data Submission Form 24

xii
1. INTRODUCTION

A NIST Traceable Reference Material (NTRM) is a reference material produced by a commercial

supplier with a well-defined traceability (the definition of emphasized words can be found in Appendix 1, "Definition of Terms") to the National Institute of Standards and Technology (NIST). This traceability is established via criteria and protocols defined by NIST that are tailored to meet the needs of the metrological

community to be served. The NTRM concept was established to allow NIST to respond to the increasing

needs for high quality reference materials with constant human and financial resources. Reference material

producers adhering to these requirements are allowed to use the "NTRM" trademark to identify their product.

The gas NTRM program was established in 1992 in partnership with U.S. Environmental Protection

Agency (EPA) and specialty gas companies as a means for providing end-users with the wide variety of

certified gas standards needed to implement the "Emissions Trading" provision of the 1990 Clean Air Act. Gas NTRMs are produced and distributed by specialty gas companies with NIST oversight of the production

and maintenance, and direct involvement in the analysis. NTRMs can be developed for any pollutant,

concentration and balance gas combination for which a NIST primary standard exists. The gas standards

prepared according to this program are related, within known limits of uncertainty [Ref. 1]), to specific

gaseous primary standards maintained by NIST.

This program is jointly administered by the NIST Analytical Chemistry Division and the NIST

Standard Reference Materials Program. The purpose of the program is to produce gas mixtures (NTRMs) to supplement the supply of existing gaseous Standard Reference MaterialsTM (SRMs) and to be used where

SRMs have been used in the past. The program is also designed to replace the EPA Certified Reference

Material (CRM) program. The EPA has agreed to accept an NTRM in place of a CRM.

The procedures described herein are based on NIST experience relative to the production and

certification of gaseous SRMs, and are intended to assure the development of reliable NTRMs. The integrity

of the gas NTRMs produced through this program is assured by NIST through active quality assurance measures. These measures include; NIST oversight of the production and analysis of the NTRM by the producer; NIST analysis of cylinders representative of the NTRM; NIST assignment of the NTRM certified value and associated uncertainty; documentation supplied by NIST, including details of the NTRM

certification, a Certificate of Traceability, and cylinder labels; and, NIST oversight of the long-term

maintenance of the NTRM batch by the producer.

1
2. PROGRAM OVERVIEW

2.1 Description

This section gives an overview of the entire program (see Appendix 2 for flow chart). Where needed,

subsequent sections explain various parts of the program in greater detail.

A NIST Traceable Reference Material (NTRM) is a reference material produced by a commercial

supplier with a well-defined traceability to the National Institute of Standards and Technology (NIST). This

traceability is established via criteria and protocols defined by NIST that are tailored to meet the needs of the metrological community to be served. The NTRM concept was established to allow NIST to respond to the increasing needs for high quality reference materials with constant human and financial resources. Reference

material producers adhering to these requirements are allowed to use the "NTRM" trademark to identify their product.

A gas NTRM consists of a multi-cylinder batch (the definition of emphasized words can be found in Appendix 1, "Definition of Terms") prepared in such a manner that all the cylinders contain a gas mixture

identical in composition and concentration. The cylinders, cylinder treatment, reagent gases, and gas

blending procedure must assure mixture stability for a minimum period of time. The concentration of the

NTRM must be within the bounds of a suite of gaseous NISTprimary standards (Appendix 3). The

concentration of an NTRM is determined by analysis with specific NIST standards. The uncertainty assigned

to the concentration depends on the combined uncertainty in the NIST standards, the producer's homogeneity

analysis, and the analysis performed at NIST. A single certified concentration and uncertainty value are assigned to the batch. The certified concentration and uncertainty, the period of time during which the concentration of the NTRM is certified, the presence of any impurities of consequence, and a list of all the

cylinders included in the batch is given in a NIST Report of Analysis. A Certificate of Traceability is issued

for each successful NTRM, along with labels to be affixed to each cylinder.

2.2 Qualification of Producer

In order to qualify for participation in the NTRM program, the producer must meet certain minimum

requirements. These requirements are intended to assure the high quality of NTRMs and their availability to U.S. laboratories. There are three requirements;

1) The producer must have in place a documented quality system This should follow international or

national guidelines (ISO Guide 25, ANSI/NCSL Z540-1-1994 or equivalent).

2) The producer must have the necessary facilities, equipment, and personnel to produce and analyze the gas mixture in the manner described in this document. NIST may require a meeting with key personnel

and/or a site visit to the producer's facility.

3) The producer must agree to one or more of the following; a) make the NTRMs available for sale to U.S. customers; b) demonstrate that traceable standards produced from NTRMs (as described in section 6.2) will be made available to U.S. customers; or, c) will be used to produce gas standards

according to the EPA protocol standards document [Ref. 2].

2
2.3 Batch Planning and Scheduling

Before an NTRM batch is prepared, the producer must contact NIST for discussions, including the establishment of a production/certification schedule agreeable to both parties. At this time any questions can be addressed so that there is a mutual understanding of procedures. The producer must submit a plan

describing the analytical procedures to be used, including the identification of the batch standard and

calibration standards to be used. NIST will supply the producer with technical specifications the NTRM is expected to meet or exceed in order to be certified. After concurrence on pertinent points the batch

preparation can proceed.

NIST will provide to all NTRM producers a certification schedule that will detail the optimum dates

for submission of NTRM batches for certification analyses. The schedule will detail, by chemical

component, when NIST will best be able to deliver certification results within a minimum time period.

NTRM batches submitted within the schedule will be given higher priority over those submitted outside the optimum submission period. NIST will complete it's certification measurements within 3 months of receipt

of the NTRM cylinders for analysis. NIST may need additional time to certify NTRMs submitted out of

sequence.

2.4 Batch Production

Each NTRM must be prepared as a multi-cylinder homogeneous batch (minimum 10 cylinders).

The cylinders must be clean, of standard size and construction, and of known compatibility and history with

the composition of the proposed NTRM. All NTRM cylinders within the batch must be identical with respect

to size, construction, valve, and cylinder treatment. The cylinders must be equipped with valves of the appropriate material that conform to Compressed Gas Association (CGA) recommendations for the particular

gas mixture. The reagent gases used must be of high purity and quality to ensure that impurity levels and

mixture stability meets NIST technical specifications.

Care must be exercised when filling the cylinders in order for the batch to meet NIST homogeneity

specifications. Any one of several fill methods can be used, including; 1) from a bulk mixture prepared in a single container; 2) from several containers connected together in such a manner that delivery occurs simultaneously from each container; 3) by use of a dynamic blending system; or, 4) other fill method shown

to meet NIST batch homogeneity specifications. A diagram of the filling manifold, which includes the

position of each of the cylinders, will be maintained as part of the NTRM batch records. All cylinders will be

reported to NIST referencing the cylinder number stamped permanently on the cylinders, along with a sequential sample number assigned to each cylinder. Further details on batch production can be found in Section 3.

2.5 Producer Analysis

The responsibility of the producer is threefold; 1) to determine the concentration relationship among

all of the cylinders in the batch (batch homogeneity); 2) to establish the average concentration of the batch;

and, 3) to establish a baseline from which to compare future analyses performed to evaluate batch stability.

To accomplish this, one or more NIST certified standards (see Definition of Terms) are to be used. The

producer's data are used to assess batch homogeneity and are included in the overall expanded uncertainty in

3
the concentration of the batch. Thus it is imperative that the producer generates high quality data in order for the expanded uncertainty to be minimized. Section 3 provides more details on the analysis phase of NTRM

batch production.

2.6 NIST Data Review

The producer must submit to NIST all the data generated from activities described in sections 2.4

and 2.5. The producer should review these data prior to submission to determine if the batch meets NIST

specifications. Once the producer is confident that the batch meets specifications, the producer should submit

the data using a NIST approved data format. NIST will review the data to determine if the batch meets NIST

specifications and to select representative cylinders from the batch for NIST evaluation. Upon request, the

producer will provide NIST with any additional data and/or information relating to the production and

analysis of the NTRM batch. Proprietary information is generally not needed for this review, however NIST

can enter into nondisclosure agreements if necessary.

Data that must be sent to NIST include; 1) cylinder fill date and method; 2) manifold fill position

with cylinders identified by cylinder and sample number; 3) identification of batch standard; 4) analytical

data including cylinder concentration, calibration standards, and order of analysis; and, 5) impurity data for specified species. The data will be submitted to NIST using the data submission form in Appendix 4, or by

electronic means, such as a computer floppy disk, in a comma-separated variable (CSV) file format.

NIST will review the data to determine if; 1) the analytical method yields reliable results; 2) the batch

homogeneity meets NIST specifications; and, 3) the batch concentration meets target values. If the data

supports it, NIST will proceed to the certification phase by selecting a minimum of 2 cylinders for NIST

evaluation. The batch standard will most likely be included in the selected cylinders. The producer will then

send to NIST these cylinders plainly labeled with sample number, producer, specie, and concentration. If the

batch is rejected at this point due to evidence of inhomogeneity in the submitted data, NIST may ask the

producer to perform additional analytical work and resubmit the batch. However, if the inhomogeneity is due to the fill method, the batch can not be certified.

2.7 Batch Certification

After NIST reviews the data the producer must send the selected cylinders to NIST for evaluation.

NIST will evaluate the cylinders for concentration and may analyze for impurities. The NIST analysis will involve comparisons of the NTRM cylinders against NIST standards. NIST standards that may be used in these analyses include primary standards, SRMs, and SRMlot standards. In general the analyses that NIST

performs to value assign NTRM batches will be identical to those used in the certification of SRMs. The

NTRM will be certified for a specific period of time dated from the NIST Report of Analysis. At the end of

this period the producer must submit recertification data to NIST in order for the certification period to be

extended. As long as the producer maintains the batch as described in Section 5, a customer purchasing an NTRM cylinder will have a certified period extending from the date of sale. More details on the NIST

certification process can be found in Section 4.

4
2.8 Maintenance of NTRM Batches

It is the responsibility of the producer to maintain the NTRM batch over the potential lifetime of the individual cylinders. In general the batch standard is used to measure the stability of the entire batch. Periodic analysis of the batch standard against a NIST certified standard will allow a determination of the batch stability over time. NIST must be notified if the batch standard shows a change in concentration

greater than half of the stated uncertainty for the batch. NIST will recommend a course of action to further assess batch stability. Actions that may be recommended include; 1) NIST reanalysis of the batch standard;

2) analysis of some or all remaining batch cylinders by the producer; or, 3) recall of selected cylinders for analysis by the producer. More details on the maintenance of NTRM batches can be found in Section 5.

2.9 Batch Certification Cost

NIST is compensated directly by the producer for the certification of each candidate NTRM batch. Fees are established on a yearly basis and are effective on October 1 of each year. Fees are based on the number of cylinders in the batch with an additional surcharge if the certification requires interpolation

between primary standards. Also included in the fee is a charge for preparation of the Certificates of

Traceability and the cylinder labels. A purchase order must be submitted to NIST before any work can

proceed.

5
3. BATCH PRODUCTION AND ANALYSIS

3.1 Overview of Producer Responsibilities

The NTRM batch must be blended in such a way as to assure gas mixture homogeneity and stability.

After blending, the contents of each cylinder in the batch must be analyzed by the producer. The analytical

procedure recommended here is considered to be the minimum effort necessary to adequately evaluate each

batch for homogeneity and stability. All NTRMs must be stable, and each batch should be homogeneous in composition and concentration. An unstable batch must be rejected, while a batch exhibiting a small

inhomogeneity in concentration may be acceptable, providing that the resulting overall expanded uncertainty

in the concentration does not exceed the desired level. The NTRM program is based on a batch certification;

all cylinders comprising the batch are assigned the same absolute concentration. Thus, any batch

inhomogeneity will increase the uncertainty assigned to the certified value of the batch.

The objective of the producer's analysis is to compare each cylinder mixture (sample) in the batch to one or more NIST certified standards. The simplest procedure would involve direct analysis of each NTRM

sample with a NIST certified standard, but with most analytical methods this approach would use a large

proportion of the available gas. Consequently, it is recommended that the concentration be determined on a

relative basis by selecting one sample from the batch, designated the batch standard, to which all of the other

samples are compared. The batch standard is then analyzed against one or more NIST certified standards.

The concentration of all the other samples can be determined from the measured ratio to the batch standard.

Analyses for impurities which might compromise the use and stability of the NTRM will be

performed using procedures determined by the producer. Maximum impurity levels are given in Appendix 3.

3.2 Batch Preparation

Before an NTRM batch is prepared, the producer must contact NIST for discussions, including the establishment of a production/certification schedule agreeable to both parties. At this time any questions can be addressed so that there is a mutual understanding of procedures. The producer must submit a plan

describing the analytical procedures to be used, including the identification of the batch standard and

calibration standards to be used. NIST will supply to the producer with technical specifications the NTRM is expected to meet or exceed in order to be certified. After concurrence on pertinent points the batch

preparation can proceed.

Each NTRM must be prepared as a multi-cylinder homogeneous batch (minimum 10 cylinders). The

cylinders which will contain the NTRM mixture must be clean and of known compatibility and history with

the composition of the proposed NTRM. All cylinders must be identical with respect to size, construction,

valve, and cylinder treatment. The cylinders must be equipped with valves of the appropriate material that conform to Compressed Gas Association (CGA) recommendations for the particular gas mixture.

Care must be exercised when filling the cylinders in order for the batch to meet the NIST

homogeneity specifications. Any one of several fill methods can be used including; 1) from a bulk mixture

prepared in a single container; 2) from several containers connected together in such a manner that delivery occurs simultaneously from each container; 3) by use of a dynamic blending system; or, 4) other fill methods

shown to be effective by the producer. The reagent gases must be of high purity and quality to ensure that impurity levels and mixture stability meets NIST specifications. The concentration of the component of

6
interest (analyte) must be at, or bracketed by, NIST primary standards (Appendix 3). A diagram of the

filling manifold, including the position of each of the cylinders, must be maintained as part of the NTRM

batch records. The identities of all cylinders will be reported to NIST referencing the cylinder number

stamped permanently on the cylinders, along with a sequential sample number assigned to each cylinder. The

sample numbers will span from one through the number of cylinders in the batch and will be permanently

assigned to the cylinders throughout the valid certification periods of the NTRM.

Multicomponent NTRM mixtures may be produced as long as every component which is to be

certified has a concentration at, or bracketed by, NIST primary standards. Chemical interactions between

components of the NTRM must not occur, or must have completed by the time the producer initiates the fust

analysis. The balance gas, cylinder walls, and valve must be chemically inert with respect to the certified components. Certification of each component is performed independently of all other components.

3.3 First Analysis

An initial analysis of the NTRM batch should be performed two or more days after preparation (see

Appendix 3 for incubation period). One analytical protocol that may be used is to select one cylinder from

the batch, designated the batch standard, to which all other samples from the batch are compared. The batch

standard must be analyzed against appropriate SRM(s) or other NIST certified standards to determine

concentration and to establish a reference for later analyses intended to confirm the stability of the batch. The

batch standard should be analyzed at least six times using a NIST certified standard to calibrate the instrument. This analysis should consist of at least six alternations of the batch standard and the NIST

standard. All of the remaining samples are then analyzed in duplicate, using the batch standard as a

reference.

During the first analysis the producer must analyze for impurities using procedures determined by the producer. NIST reserves the right to identify cylinders to be analyzed. For nitric oxide mixtures, all cylinders

must be analyzed for nitrogen dioxide.

3.3.1 Instrument Performance

The general characteristics of the analyzer response relative to concentration must be known and

demonstrated. This is accomplished by constructing a calibration curve using a minimum of three gas

mixtures. The gas mixture nearest in concentration to the nominal batch concentration must be a NIST

certified standard. If the analyzer has a significantly nonlinear function then a minimum of four calibration

standards are required. If a model using a straight line instead of a quadratic fit results in a predicted

concentration different by 0.5 % or more, then four or more standards and a quadratic fit must be used. The

standards must include a NIST certified standard above and below the concentration of the NTRM (if such

standards are available). Obviously this is not possible when the NTRM is being compared to either the lowest or highest concentration NIST certified standard available in a particular analyte series; these

situations will be addressed on a case-by-case basis considering the limits of NIST analytical capabilities.

Extrapolation beyond the calibration curve is not recommended without technical justification. Thus,

the NTRM concentration should be adjusted to lie within the concentration bounds of the available

calibration gases.

7
The principal elements that contribute to the imprecision of measurement include instrument

sensitivity and drift. The sensitivity of the instrument should be high enough so that differences in concentration of 0.2 % relative can be easily measured. Instruments are available that are capable of

measuring all current SRMs with this sensitivity. However, most instruments exhibit a certain amount of

signal drift. The drift has two components, short term drift (noise), and a long term drift characterized by a slowly changing signal under constant operating conditions. The effect of short term drift can be minimized

by a number of techniques including multiple analysis of each sample, and signal averaging. The effect of

long term drift can be minimized by frequent recalibration of the instrument. The characteristics of each

analytical system should be considered individually to determine the optimum frequency of calibration and

the approach taken to compensate for or control the effect of noise. It should be noted that the effort expended in minimizing the effects of drift will improve the precision of the analyses relating the NTRM to the NIST certified standard. In general, if duplicate analyses of single samples consistently agree within

0.2 % relative, then the effect of noise is at an acceptable level, and if repeated analysis of the same sample

performed at intervals during the analysis of a batch agree within the same limits, then the long term drift is at an acceptable level.

3.3.2 Preliminary Data Evaluation

Some preliminary conclusions regarding the homogeneity and stability of a batch may be drawn from

the results of the first analysis. If the batch is homogeneous when filled, and if no subsequent reactions have

occurred randomly in the cylinders, the concentration of all samples should be the same within the limits of

precision of the analytical method. If inhomogeneity among the samples is observed, it will not be possible at this time to determine whether such inhomogeneity is due to improper preparation or to reactions in the

cylinders.

If the first analysis indicates that no serious problem exists, the entire batch is set aside for 30 days.

If the data indicate that the batch may be bad, NIST should be notified.

3.4 Second Analysis

After the required minimum 30-day hold period has passed, all samples in the batch must be

analyzed in the same manner as the first analysis using the same NIST certified standard(s). The first analysis served to define the concentration of the NTRM and to test for batch homogeneity. Decisions

regarding stability depend on the second analysis. Sufficient time will have elapsed so that reactions in individual cylinders, which were of too low a rate to be recognized by the distribution of concentrations

obtained in the first analysis, can be measured through this subsequent analysis.

8
3.5 Batch Stability and Homogeneity

The stability and homogeneity of an NTRM batch must be carefully evaluated. The batch is considered stable if the concentration in each NTRM cylinder has not changed appreciably (less than the measurement uncertainty) between the first and second analyses. If no change is detected, the batch is most

likely stable and the producer may proceed. However, if an inspection of the data from the first and second

analyses reveals gross instability the batch must be discarded and remade. NIST will assist the producer in analyzing the data if there are questions concerning significance of the differences found.

If cylinder-to-cylinder differences within the batch are observed, then the producer and NIST must

decide if this inhomogeneity will result in an unacceptably large expanded uncertainty. An NTRM is useful

only if the expanded uncertainty in the concentration is at or below a certain level. In general the expanded

uncertainty should be less than two times the maximum stated uncertainty of the NIST certified standards

used for calibration. If the inhomogeneity is small enough then this level will not be exceeded. If it is large

and the acceptable expanded uncertainty level will be exceeded, then the batch should be remade.

The concentration of the analyte(s) in all of the cylinders of an NTRM batch should be identical. Differences in concentration observed among cylinders should reflect only the combined uncertainty in the measurement process [Ref. 1]. Differences greater than this combined uncertainty may arise from several

sources. There can be differences that result from faulty mixing, or from dilution by residual gases left in the cylinder prior to transfer of the bulk mixture. A more critical source arises from reactions, chemical or

physical, that occur in the cylinder after transfer. Because these reactions are largely due to wall effects, and

because no two cylinder walls are alike, the reactions generally proceed at different rates in different

cylinders. The two effects may be differentiated by sets of measurements made over a period of time

sufficiently long so that the extent of reaction is greater than the measurement uncertainty in the analysis. If a batch is analyzed immediately after preparation and individual samples are found to have concentrations that vary more than the measurement uncertainty, then the mixture is either inhomogeneous, or some or all of the samples in the batch are unstable. If the batch is reanalyzed after some time and each sample has essentially

retained its previous value, then the samples are probably stable, but the batch is inhomogeneous. If the concentration of one or more of the samples has changed significantly, then it is plausible to conclude that the

batch is unstable.

It may not be necessary to discard an inhomogeneous batch, but an unstable batch must be discarded.

An inhomogeneous but stable batch may be used if the inhomogeneity is sufficiently small that the expanded

uncertainty does not exceed the acceptable level. If during blending, several large cylinders are connected

together to allow simultaneous delivery, then some inhomogeneity in the batch may result if the

concentrations in the source cylinders differ slightly. In the special case of large scale dynamic dilution

systems where two components are mixed under constant flow conditions and are then compressed into the

cylinders in the batch, some inhomogeneity may result, depending on the design of the delivery system. If variations in concentration are observed in a batch prepared by this method, the variation may be related to the position of individual cylinders on the manifold, and it is therefore important to record the manifold

position of each cylinder.

The nature of the concentration distribution of samples in a batch may give significant information

concerning both the homogeneity and stability of the batch. A batch which has concentrations that vary no more than can be accounted for by the measurement uncertainty of the analytical method, is probably

9
homogeneous and stable. A batch in which the range of values exceeds significantly what might be expected on the basis of measurement uncertainty, and in which several samples are considerably below the average, is probably unstable. A batch in which the range of values is large but all concentrations are essentially

symmetrically distributed around the average, was probably not prepared or transferred in such a way that homogeneity was assured. Occasionally, one or more samples in a batch will be found with concentrations

appreciably different from the average for the batch. These may represent faults in the preparation or filling

of the cylinder. These cylinders may be removed from the batch, provided the batch is otherwise shown to be

stable and homogeneous.

All of the data at this stage ofNTRM production must support the assumption that the batch is stable, homogeneous, and meets all other specifications for an NTRM. If there is any suspicion that the batch

may be unstable or inhomogeneous, then further analytical work should be conducted before a final decision

is made to proceed.

At this point there should be sufficient data for the producer to decide whether or not the batch will qualify as an NTRM. This decision must be based on the measured concentration, stability and homogeneity.

Ultimately the decision will be subject to an independent examination of the data and to a NIST analysis of

selected samples from the batch for concentration value assignment.

10
4. BATCH CERTIFICATION

4.1 Overview

After the producer submits the required data to NIST (see sec. 2.6), the data will be reviewed and a minimum of two cylinders from the batch will be selected to be sent to NIST for analysis. Procedures that are similar to those used for SRM certification will be used to analyze the selected NTRM cylinders. The

analyses will be used to determine the concentration of the analyte(s) and any impurities that may

compromise the use of the NTRM. This process will normally be completed within three months of sample

submission. A Report of Analysis, Certificates of Traceability, and cylinder labels will be prepared by NIST

and issued to the producer for all approved NTRMs. A Report of Analysis will also be issued to the producer

for rejected batches detailing the reasons the NTRM failed certification.

4.2 NIST Analytical Protocol

NIST analysis of the selected cylinders from the NTRM batch is modeled on the procedures used by

NIST to analyze SRMs. In a typical NTRM certification procedure, the producer's batch standard is analyzed

using a NIST reference method. Typically this method is an instrumental procedure calibrated with a gas

reference material, such as gravimetrically prepared NIST primary standards, SRMs, or SRM lot standards.

Then the same instrumental procedure is used to compare the remaining selected cylinders to the NTRM

batch standard. The instrumentation used in these analyses is chosen based on; 1) a stable and noise free signal to ensure a high degree of precision in the intercomparisons; and, 2) an adequate signal resolution to detect small (0.25 %) concentration differences. The same instrumentation used for the certification of an SRM is used for the analysis of the corresponding NTRM.

Since the concentration of an NTRM batch can be at or between NIST primary standard

concentrations, two possible cases exist for the analysis of the selected cylinders. Where the NTRM and

NIST primary standard concentration are close, an SRM, SRM lot standard, or primary standard will be used

to analyze the producer's batch standard. Where the concentration of the NTRM falls between NIST primary

standard concentrations, more standards will be used. The number and range of standards used to analyze

this type of NTRM will depend on instrument function and the concentration of the NTRM.

In both cases, the producer's batch standard is analyzed by comparing it to a NIST standard(s) a minimum of five times on each of two different days. Potential instrument drift is corrected by alternately

analyzing the NIST standard and the producer's batch standard. The NTRM response data is then correlated

to the NIST standard response data using a linear or a quadratic instrument response function. Most of the

instruments used by NIST have a linear response function.

After the producer's batch standard is analyzed, the instrumental procedure is used to compare the other selected cylinders to the batch standard. The same basic analytical sequence is followed, analyzing the

producer's batch standard frequently to correct for instrument drift. A minimum of five comparisons of each

sample to the producer's batch standard is made. The goal of the certification model is to minimize the

measurement uncertainty.

11
4.3 Producer's Data Validation and Batch Value Assignment

The NIST concentration value for the producer's batch standard will be compared to the

concentration determined by the producer. Since the producer is not responsible for final concentration value

assignment, the producer's value need not be the same as NIST's, but it should be close. A factor (F) is determined using the equation;

F —

QjIST ' ^Producer

where is the concentration of the batch standard as determined by NIST, and CProducer is the

concentration of the batch standard as determined by the producer. This factor is used to adjust the

producer's analysis of the NTRM batch to the NIST analysis. If this factor is 1.000 ± 0.005, certification can

proceed and the producer's data can be validated. If the factor deviates from unity more than 0.5 % the

certification may proceed but NIST will work with the producer to identify the reason for the deviation. If, after reconciliation between NIST and the producer, the factor still deviates from unity more than 0.5 % the

batch will be rejected.

NIST will also examine the data to determine if the ratio of the concentration values between the

selected cylinders and the batch standard are the same as determined by both NIST and the producer. If the

ratios determined by NIST are the same (within measurement uncertainty) as that determined by the producer,

then the producer's data can be considered valid and certification can proceed. However, if the ratios do not match within measurement uncertainty the NTRM batch will be rejected.

Once the producer's data have been validated, NIST will examine the data for overall batch

homogeneity. If the producer's data show that the batch is homogeneous and stable the batch can be certified. If the batch shows a percent relative standard deviation in the concentration of greater than 0.5 %, the batch

will be rejected. A possible exception can be made where homogeneous batches are difficult to prepare due

to the chemical nature of particular analytes.

If the batch is found to be homogeneous, and the producer's data have been validated, then NIST will proceed to assign a concentration value. NIST first adjusts the producer's homogeneity data using factor F so each cylinder's concentration value reflects NIST's value assignment of the batch standard. The final certified concentration value for the batch is the average of the producer's NIST adjusted homogeneity data.

4.4 Value Uncertainty

The uncertainty [Ref. 1] of the NTRM concentration value is estimated using a three-component

additive analysis of variance model. The components are: 1) the assigned uncertainty of the standards used in the NIST analysis; 2) the measurement uncertainty of the NIST analysis of the NTRM batch standard; and, 3)

the batch homogeneity measured by the producer.

A combined uncertainty for the NIST standard, uPS, is derived from the assigned 95 % confidence

interval of the standard (UPS) using the appropriate coverage factor (example: an assigned 95 % confidence

interval of 1.5 % would yield a combined uncertainty of 0.75 %, using a coverage factor of 2). A

measurement combined uncertainty, uA, is established from analytical experience and replicate measurements.

A batch homogeneity combined uncertainty, uH, is established from the producer's analysis of all the

cylinders in the batch.

12
This model is used when an NTRM that is close in concentration to a NIST primary standard and the concentration value assignment can be accomplished by direct comparison. In the case where the NTRM

concentration falls between that of two NIST primary standards and its concentration is determined by

interpolation, uPS is larger than just the combined uncertainty of one primary standard since more than one

standard is used in the analyses.

The combined uncertainty of the NTRM batch is estimated from the experimental combined

uncertainties and is calculated using the following equation;

uc = (uPS

2 + uA2 + uH2)'/2

The NTRM expanded uncertainty U is calculated using the following equation;

U = kuc

with the coverage factor k being equal to 2. The true concentration is asserted to lie within the interval defined by the batch certified value ± U with a level of confidence of approximately 95 percent [Ref. 1].

4.5 NTRM Documentation

After the certification process is completed, the NTRM cylinders are returned to the producer and

NIST generates a Report of Analysis (ROA), which is issued to the producer. The ROA contains; 1) the NIST-assigned NTRM batch concentration value and it's uncertainty; 2) the certification period; 3) a

description of the NIST value assignment procedure including the determination of the concentration factor

(F); 4) a description of the NIST standard(s) used; 5) a listing of the NTRM samples analyzed by NIST along

with the NIST and producer's concentration values; and, 6) a listing of all the certified cylinders in the NTRM

batch and the concentration value for each as calculated by NIST.

Certificates of Traceability and cylinder labels are also prepared and sent to the producer. Each

Certificate of Traceability displays the NTRM logo, the batch identification number, the concentration and

uncertainty, and the certification period. The cylinder labels also display the NTRM logo, the NTRM batch

identification number, and the batch concentration value and uncertainty.

4.6 NTRM Rejection Criteria

NIST will reject an NTRM for any one of the following reasons: 1) impurity concentrations are too

high; 2) the concentration factor (F) diverges from unity more than 0.5 % after reconciliation between NIST

and the producer; 3) the producer's and/or NIST's homogeneity data shows a concentration spread > 0.5 %

relative; and, 4) NIST's concentration ratios to the batch standard do not agree within measurement

uncertainty with the producer's concentration ratios. In all these cases NIST will work with the producer to resolve the problem for future NTRM work. NIST may reconsider the certification of a rejected batch if additional analytical work is performed by the producer and the batch resubmitted for certification.

13
5. MAINTENANCE OF NTRM BATCHES

5.1 Batch Recertification

An NTRM batch is certified from the date of the NIST Report of Analysis for a specified period of

time, defined as the certification period. When that time period expires, all cylinders comprising that NTRM batch are no longer certified. Customers who purchase an NTRM from a producer may receive a

certification for the entire certification period commencing from the date of sale. However, if the NTRM

batch expires and subsequently loses certification, the customer's NTRM cylinder likewise loses certification. Thus it is very important that the producer maintains the NTRM batch certification status for the projected

lifetime of the individual cylinder mixtures.

Batch recertification is the process the producer must follow in order to maintain certification of the

NTRM. The purpose of this process is to verify batch concentration and to assure continuing stability of the

gas mixture. To accomplished this, a cylinder(s) that is representative of the batch must be analyzed using a NIST certified standard. Two methods to accomplish this are; 1) if the producer has retained the batch

standard, and the batch standard was a member of the original batch production, then the batch standard may

be analyzed as the representative of the batch; or, 2) a minimum of two cylinders from the batch must be

analyzed. If the producer no longer has the two required cylinders, due to distribution to customers, the cylinders may have to be recalled for analysis. Also, it is recommended that the entire stock of cylinders from

the batch that are still under the producer's control be analyzed.

Analysis of the batch standard, or the two representative cylinders, must be accomplished using the same procedure originally used by the producer. A NIST certified standard must be used to assign

concentrations to these cylinders. The data generated by this analysis must then be sent to NIST. NIST will review the data and determine if the certification period should be extended. Usually if the data from the

analysis match the original data within measurement uncertainty, or within half of the stated uncertainty from

the original certified concentration, the certification period will be extended and a new certificate issued.

NIST reserves the right to recall cylinders (usually the batch standard) from the producer for analysis by

NIST. If the batch fails to be recertified, the producer must contact customers in possession of the NTRM

cylinders. NIST reserves the right to request a listing of the disposition of all cylinders in the NTRM batch.

The recommended method of handling recertification of the NTRM batch is to analyze, prior to shipment, a customer's NTRM cylinder and the batch standard against a NIST certified standard. If the data

continues to show good stability for the batch, e.g., the concentration is within half the stated uncertainty of

the original certified value, the cylinder can be shipped. When the batch certification period expires, these

data can be supplied to NIST as evidence for recertification. This approach is best used when the entire batch

is expected to be sold or used prior to the expiration date. NIST will use the last analysis date as the basis for the extended certification period.

5.2 Customer NTRM Cylinders

A customer who purchases an NTRM cylinder from a producer receives a certificate with a

certification period commencing from the date of sale and extending over a set period of time. The length of

this period of time is identical with the original batch certification period. As outlined in section 5. 1, the

certification period is linked with the batch certification, which is the responsibility of the producer to

14
maintain. Regardless of the batch certification period, the customer's certification expires at the end of the date of sale certification period. The customer must then contact the producer about recertification of their cylinder.

5.3 Customer NTRM Recertification

The producer is responsible for the recertification analyses of NTRM cylinders sold to its customers. The recertification analysis is accomplished in one of three ways; 1) against the original batch standard used

to maintain the batch certification; 2) against a batch standard from a batch similar in composition,

concentration and uncertainty that is currently still in certification; and, 3) against a NIST certified standard

that is similar in composition and concentration. The analysis should provide at least three data points

against the designated standard and demonstrate an instrumental variance well within the original stated

uncertainty.

The data must be submitted to NIST which will give the final approval for recertification. NIST

reserves the right to analyze the cylinder before approval is granted. If the submitted concentration is within

the original certified concentration interval, recertification will usually be granted. If the submitted

concentration is outside the original certified concentration uncertainty interval, recertification will be granted

under the following conditions; 1) there is a known cause for the discrepancy that NIST acknowledges, and it does not impact on the usability of the standard; 2) impurities introduced into the cylinder by the customer

has not compromised the standard; and, 3) the producer can demonstrate, through calibration data, that its analytical system is capable of reliably assigning a concentration distant from the original concentration.

Once notified that the recertification is granted, the producer can issue to the customer written

notification of the certification status. Certification will be extended for the current certification period from

the date of the recertification report.

15
6. TRACEABILITY TO NIST

6.1 NTRM Batch Traceability

The traceability of a gas NTRM batch relies on the unbroken chain of comparisons to NIST's

primary gas standards. Through gravimetric preparation of the primary gas standards, NIST assures

traceability to the mole, a basic unit of the International System of Units, known as SI. Since the beginning of

the NIST gas standards program, the NIST primary gas standards have been the foundation of the gas SRM

program. They are prepared and maintained by NIST, and regularly undergo stringent internal evaluation and

intercomparisons with other international gas standards. In the national hierarchy of gas standards, they are at the pinnacle. The NIST certified standards, such as gas SRMs, are compared to these primary gas standards

before certification. These NIST certified standards enable producers to prepare and maintain the NTRM

batches that are provided to the public or used to produce other NIST traceable gas standards.

There is an unbroken series of analyses comparing NTRM gas mixtures to NIST certified standards,

and a direct NIST involvement in the NTRM certification. NIST maintains records of certified NTRMs and

certification periods. If an NTRM batch is still in use after the certified period expires, it must be reanalyzed

and the data submitted to NIST for concurrence concerning stability. NIST reserves the right to request any

NTRM cylinder be sent to NIST for analysis if there are any questions concerning stability or concentration.

The direct involvement of NIST in the quality assurance of each NTRM batch should provide continued

acceptability of the certified concentrations with time.

6.2 Mixtures Produced Referencing NTRMs and SRMs

Not all of the analytical activities of gas analysis laboratories require the stringent traceability of an SRM or NTRM. In these instances a gas mixture with a somewhat lower level of traceability may be all that

is required. Gas mixtures prepared using a protocol referencing gas SRMs or NTRMs may be declared as NIST traceable if the general guidelines given below are followed. It is important to realize that these

guidelines represent the minimum required in order for NIST to recognize a gas mixture as traceable. The

minimum requirements for a NIST traceable gas mixture are;

1) The cylinders will be clean, of standard size and construction, and of known compatibility and

history with the composition of the proposed standard. The cylinders will be equipped with valves of

the appropriate material that conform to Compressed Gas Association (CGA) recommendations for the particular gas mixture. The reagent gases must be of high purity and quality to ensure that impurity levels and mixture stability meets NIST specifications.

2) The concentration of the mixture is within 5 % relative of the SRM or NTRM concentration to which

it is related by analysis . The composition of the mixture should be identical to that of the SRM or NTRM. Multicomponent mixtures may be traceable to binary mixtures as long as there are no component interactions, and the balance gas is identical to the referenced mixtures (or chemically

inert to the components). Stability must be assured through procedures similar to section 3.5 or demonstrated by data available to customers.

16
3) All sources of uncertainty in the concentration assignment are included in the final uncertainty

statement. The model given in section 4.4 should be followed. The combined uncertainty of the referenced SRM or NTRM must be included in the mixtures expanded uncertainty.

4) An expiration date for the mixture must be given to the customer. The period of time the standard is valid will not exceed the original certification period of the corresponding SRM or NTRM.

Example: If the original NTRM was certified for 2 years, the mixture can be given a maximum

validation period of 2 years.

5) Documentation provided the customer will include concentration, expanded uncertainty, expiration

date, significant impurities, and the specific SRM or NTRM referenced.

An excellent document describing a method to prepare a gas mixture referencing an SRM or NTRM is given

in reference 3.

17
References

1) Guide to the Expression ofUncertainty in Measurement, ISBN 92-67-10188-9, 1st Ed. ISO, Geneva,

Switzerland, 1993. See also Guidelines for Evaluating and Expressing the Uncertainty ofNIST

Measurement Results, B. N. Taylor and C. E Kuyatt, NIST Technical Note 1297, 1994 Edition

2) EPA Traceability Protocolfor Assay and Certification ofGaseous Calibration Standards, U.S.

Environmental Protection Agency, EPA-600/R93/224, September 1993

3) A Procedurefor Establishing Traceability ofGas Mixtures to Certain National Institute ofStandards

and Technology SRM's, E. E. Hughes and J. Mandel, NBSIR 8 1-2227 (revised 1989).

4) International vocabulary ofbasic and general terms in metrology (VIM), 1993, issued by BIPM, IEC,

ISO, IUPAC, IUPAP and OIML.

5) ISO Guide 30: 198 1, Terms and definitions used in connection with reference materials. See also ISO

8402, Quality -Vocabulary, 1986.

18
Appendix 1: Definition of Terms

This section provides definitions of terms used in this document. The initial use of each of these terms within

this document is signified by emphasized print. These terms may be defined differently in other documents

released by NIST.

Batch: A group of gas mixtures, contained in gas cylinders, prepared by a producer in such a manner that all the gas mixtures are identical in composition and concentration. For the purposes of this program, each batch

will contain a minimum of 10 cylinders.

Batch Standard: A gas mixture, similar in concentration and uncertainty to the NTRM batch, to which all cylinders of the batch are related through chemical analysis. The batch standard is usually a randomly chosen

member of the NTRM batch. If the batch standard is not a member of the NTRM batch, it's concentration

must be within 5 % of the batch nominal concentration.

Certification Period: The period of time a gas mixture is certified for component concentration.

Concentration: The amount-of-substance (SI unit: mole) of the subject compound within the cylinder. This

is usually expressed as the amount-of-substance fraction (SI unit: mol/mol).

Homogeneity: A measure of the concentration spread exhibited by an NTRM batch. Usually measured as a percent relative standard deviation from the average concentration.

Homogeneous: Having a concentration spread of less than 0.5 % relative standard deviation.

Impurities: Unwanted chemical compounds within a gas mixture. Their concentration must not be large

enough to jeopardize the intended use of the mixture.

Incubation Period: The period of time after production the gas mixtures are required to mature before

analyses are performed. This period allows the gas mixture to stabilize to their final concentration, giving a

better measure of batch homogeneity.

Inhomogeneous: Having a concentration spread in excess of 0.5 % relative standard deviation.

NIST Certified Standard: Gas mixtures that have been certified by NIST and which are within the valid

certification period. Documentation in the form of a NIST Report of Analysis or Certificate must be

available for inspection. An SRM is a valid certified standard, however Research Gas Mixtures (RGM)

should be approved by NIST before use in NTRM production.

NIST Primary Standards: Gas mixtures maintained by NIST, which have been prepared gravimetrically at NIST, to which all measurements are ultimately compared.

NIST Traceable Reference Material (NTRM): A reference material produced by a commercial supplier

with a well-defined traceability linkage to the National Institute of Standards and Technology (NIST). This

linkage is established via criteria and protocols defined by NIST that are tailored to meet the needs of the

19
metrological community to be served. Reference material producers adhering to these requirements will be

allowed the "NTRM" trademark.

Quality System: The organizational structure, responsibilities, procedures, processes and resources for implementing quality management.

Recertification: A process that must be completed in order for the gas mixture's certification period to be

extended.

Research Gas Mixture (RGM): A gas mixture produced cooperatively by NIST and a producer. The gas

mixture's concentration must be outside a current NIST Primary Standard suite or has a composition not

currently supported by NIST.

Resolution: An instrument's ability to detect small changes in signal and report this change in the output data

stream.

Sample Number: A sequential number assigned to the cylinders of an NTRM. The sample numbers span

from one through the number of cylinders in the batch. They are permanently associated with the cylinders

throughout the lifetime of the NTRM.

Selected Cylinders: Cylinders from the NTRM batch which are selected by NIST to be sent by the producer

to NIST for value assignment.

Sensitivity: An instrument's ability to distinguish a true analytical signal from background noise.

SRM Lot Standard: The batch standard used by NIST to certify an SRM lot. The lot standard is also used

to track the stability of the SRM lot.

Stability: A measure of the concentration drift of a gas mixture over time. A gas mixture is stable if the concentration drift is small relative to the absolute concentration over time. For NTRMs the concentration

drift must be within half of the stated uncertainty from the certified concentration over the entire certification period.

Standard Reference MaterialTM (SRM): Certified reference materials issued by NIST. These are well- characterized materials produced in quantity to improve measurement science. SRMs are certified for specific chemical or physical properties, and are issued by NIST with certificates that report the results of the characterization and indicate the intended use of the material.

Traceability: The property of a result of a measurement whereby it can be related to appropriate standards,

generally national or international standards, through an unbroken chain of comparisons [Ref. 4,5].

Uncertainty: A parameter, associated with concentration, that characterizes the dispersion of the values that attributed to the concentration assignment. A reported concentration value must have an associated

uncertainty [Ref. 1,4,5].

20
Appendix 2: Production and Certification Flow Chart

(With Sections Referenced)

Producer Determines Need (2.2)

f Discussions between NIST/Producer (2.3)

i

Producer Blends Batch (3.2)

1

Producer Analyzes Batch (3.3 and 3.4)

Producer Reviews Data for

Stability and Homogeneity (3.5)

I

Producer Submits Data to NIST

NIST Reviews Data (2.6)

I

NIST Selects Cylinders for Analysis

Producer Sends Cylinders to NIST (2.6/2.9)

T

NIST Analyzes Selected Cylinders

NIST Validates Producer's Data (4.2)

Batch Out of Specification

Batch Discarded

Batch Out of Specification (4.6)

Batch Discarded or Reanalyzed

Data Out of Specification (4.6)

Batch Discarded or Reanalyzed

NIST Value Assigns NTRM (4.3 and 4.4)

Sends Report, Certificates, Labels (4.5)

I

Producer Maintains Batch (Section 5)

Sells or Uses NTRMs Internally

21
Appendix 3: NTRM Specifications

A partial listing of some primary gas standard suites which may bound NTRMs:

Mixture Components Amount of Substance Range

Carbon Monoxide in Nitrogen

Carbon Monoxide in Air

Carbon Dioxide in Nitrogen

Propane in Air

Propane in Nitrogen

Methane in Air

Oxygen in Nitrogen

Nitric Oxide in Nitrogen

Sulfur Dioxide in Nitrogen

Volatile Organics

10 //mol/mol to 13 % mol/mol

10 //mol/mol to 45 //mol/mol

0.5 % mol/mol to 20 % mol/mol

3 //mol/mol to 500 //mol/mol

100 //mol/mol to 4 % mol/mol

1 //mol/mol to 100 //mol/mol

2 % mol/mol to 21 % mol/mol

5 //mol/mol to 3000 //mol/mol

50 //mol/mol to 3500 //mol/mol

Contact NIST

This list is not complete, any questions concerning other constituents and/or concentrations can be

answered by contacting NIST.

Minimum incubation period before first analysis:

Two days for CO, C02 , C3 H8 , CH4 and 02 then 30 days between the first and second analyses.

Four days for NO and S02 then 30 days between the first and second analyses.

Maximum allowable impurity levels:

Carbon Monoxide Mixtures

Water vapor

Carbon dioxide

Methane

Hydrocarbons

5 //mol/mol

1 //mol/mol or 0.1 % of the CO value whichever is greater

0.1 % of the CO value

0.1 //mol/mol as methane

Carbon Dioxide Mixtures

Water vapor

Carbon monoxide

Nitrous oxide

Hydrocarbons

5 //mol/mol

0.01 %ofC02 value

0.1 % of C02 value

0.1 /^mol/mol as methane

Propane Mixtures

Water vapor

Other hydrocarbons

5 //mol/mol

0.4 % of the propane value expressed as propane

Methane Mixtures

Water vapor

Other hydrocarbons

5 //mol/mol

0.5 % of methane value

22
Oxygen Mixtures

Water vapor

Hydrocarbons as methane

Argon in 2 % mol/mol oxygen

Argon in 10 % mol/mol oxygen

Argon in 2 1 % mol/mol oxygen

Total other impurities

Nitric Oxide Mixtures

Water vapor 5 /^mol/mol

Nitrogen Dioxide 1 % of NO value (all batch cylinders analyzed)

Hydrocarbons 2 yumol/mol expressed as methane

Sulfur Dioxide Mixtures

Water vapor 5 ^mol/mol

Hydrocarbons 2 /^mol/mol expressed as methane

5 /^mol/mol

3 yumol/mol

30 /umol/mol

50 ^mol/mol

100 /^mol/mol

15 ^mol/mol

23
Appendix 4: Data Submission Form

The following form may be used to report the producer's NTRM information and analysis results to NIST. This form is available from NIST on a floppy disk.

24
FORM A - Producer's Report of Analysis of Candidate NTRM

Report

Prepared by:

Date: Company Name:

Address:

Phone and FAX #: Individual preparing report:

Description: NTRM Composition:

Corresponding SRM No.:

Date Blended:

Blending Location:

(Address, Phone, FAX and Contact Person)

Blending Method:

Manifold fill position diagram attached upon request:

Cylinders:

Size:

Material:

Manufacturer:

Treatment Process:

Previous Use:

Valve:

CGA#:

Straight or Tapered Threads:

Manufacturer:

25
Form A (continued)

NIST Certified Standards Used as Calibrants:

(If SRM) Concentration

No. Cylinder No. Sample No. and uncertainty Certification Date

1. 2.

3.4.

Brief Description of Analytical Method:

26
Form A (continued)

Instrument Calibration Procedure:

Calibration Date.

Analytical Sequence (order in which cylinders were analyzed):

Na

1. 2.

3.4.

5.

etc.

Calibrant Concentration

Instrument Response

Analysis ofNTRM Batch Standard:

Analysis Date:

Batch Standard Description:

Analytical Sequence (order in which cylinders were analyzed):

Na

12

3

4

56

7

8

9

10

Cylinder or

Calibrant

Form A (continued)

Instrument ResponseCalculated

Concentration

Average =

Std. Dev.

% Relative SD =

27
Analysis ofNTRM Cylinders against Batch Standard:

Date:

Analytical Sequence (order in which cylinders were analyzed)

Sample Cylinder Calculated

No. Number Concentration

12

34

56

789

10

1112

13

14

15

16

17

18

19

20

etc. Average

Std. Dev.

% Relative SD =

Impurity Analyses:

Impurity Concentration Analytical Method

12

34

28
Technical Publications

Periodical

Journal of Research of the National Institute of Standards and Technology—Reports NIST research and development in those disciplines of the physical and engineering sciences in which the Institute is active. These include physics, chemistry, engineering, mathematics, and computer sciences. Papers cover a broad range of subjects, with major emphasis on measurement methodology and the basic technology

underlying standardization. Also included from time to time are survey articles on topics closely related to the Institute's technical and scientific programs. Issued six times a year.

Nonperiodicals

Monographs—Major contributions to the technical literature on various subjects related to the

Institute's scientific and technical activities. Handbooks—Recommended codes of engineering and industrial practice (including safety codes) devel- oped in cooperation with interested industries, professional organizations, and regulatory bodies. Special Publications—Include proceedings of conferences sponsored by NIST, NIST annual reports, and

other special publications appropriate to this grouping such as wall charts, pocket cards, and bibliographies.

National Standard Reference Data Series—Provides quantitative data on the physical and chemical

properties of materials, compiled from the world's literature and critically evaluated. Developed under a worldwide program coordinated by NIST under the authority of the National Standard Data Act (Public

Law 90-396). NOTE: The Journal of Physical and Chemical Reference Data (JPCRD) is published

bimonthly for NIST by the American Chemical Society (ACS) and the American Institute of Physics (AIP).

Subscriptions, reprints, and supplements are available from ACS, 1155 Sixteenth St., NW, Washington, DC

20056.

Building Science Series—Disseminates technical information developed at the Institute on building

materials, components, systems, and whole structures. The series presents research results, test methods, and

performance criteria related to the structural and environmental functions and the durability and safety

characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of

a subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NIST under the sponsorship of

other government agencies.

Voluntary Product Standards—Developed under procedures published by the Department of Commerce

in Part 10, Title 15, of the Code of Federal Regulations. The standards establish nationally recognized

requirements for products, and provide all concerned interests with a basis for common understanding of

the characteristics of the products. NIST administers this program in support of the efforts of private-sector

standardizing organizations.

Order the following NIST publications—FIPS and NISTIRs—from the National Technical Information

Service, Springfield, VA 221 61. Federal Information Processing Standards Publications (FIPS PUB)—Publications in this series

collectively constitute the Federal Information Processing Standards Register. The Register serves as the

official source of information in the Federal Government regarding standards issued by NIST pursuant to the Federal Property and Administrative Services Act of 1949 as amended, Public Law 89-306 (79 Stat. 1127), and as implemented by Executive Order 11717 (38 FR 12315, dated May 11, 1973) and Part 6 of

Title 15 CFR (Code of Federal Regulations).

NIST Interagency Reports (NISTIR)—A special series of interim or final reports on work performed by

NIST for outside sponsors (both government and nongovernment). In general, initial distribution is handled

by the sponsor; public distribution is by the National Technical Information Service, Springfield, VA 22161.

in paper copy or microfiche form.
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