## 2003/2004 AUDITS OF EPA TRACEABILITY PROTOCOL CYLINDER GASES

Contract No. 68-W-03-033 Work Assignments 0-7 and 1-7

Prepared for

John Schakenbach (6204J) U.S. Environmental Protection Agency 1310 L Street, NW Washington, DC 20005

Prepared by

Scott Shanklin The Cadmus Group, Inc. 6330 Quadrangle Drive, Suite 180 Chapel Hill, NC 27517

November 22, 2004

### November 22, 2004 iii 

## N OTICE AND 

## D ISCLAIMER



## The U.S. Environmental Protection Agency through the Clean Air Markets Division in the Office of Atmospheric Programs funded and managed the prepar ation of this document under Contract No. 68-W03-033. The mention of trade names or commerc ial products does not constitute endorsement or recommendation or use by either the U.S. Environmental Protection Agency or The Cadmus Group, Inc., of the product or manufacturer.

### November 22, 2004 v 

## T ABLE OF 

## C ONTENTS



## Notice and Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi Acronyms and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi i 1.0 INTRODUCTION ............................................................... 1 2.0 SELECTION OF GAS VENDORS .................................................. 2 3.0 PURCHASE OF EPA TRACEABILITY PROTOCOL GASES . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4.0 ANALYTICAL PROCEDURES .................................................... 4 4.1 MACTEC A NALYTICAL 

## P ROCEDURES 

## ............................................. 4 4.2 S PECTRAL 

## I NSIGHTS 

## A NALYTICAL 

## P ROCEDURES 

## ..................................... 6 5.0 RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 5.1 D OCUMENTATION 

## ............................................................. 9 5.2 G AS 

## A NALYSES 

## . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.0 CONSIDERATIONS FOR FUTURE PROTOCOL GAS AUDITS . . . . . . . . . . . . . . . . . . . . . . . . 16

APPENDIX A. GAS MEASUREMENT DATA AND COMPARISONS

### November 22, 2004 vi 

## T ABLES



## 1. U.S. Commercial Manufacturers of EPA Traceability Protocol Gases (as of 2004) .............. 3 2. Gases Purchased for the 2003/2004 Audit .............................................. 3 3. Reference Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Spectral Insights’ FTIR Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5. Vendor Cylinder Gas Certification Using EPA Traceability Protocol ......................... 9 6. NO Component Analysis Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 7. SO 2 

## Component Analysis Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 8. CO 2 

## Component Analysis Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

F IGURES



## 1. MACTEC’s assay apparatus ......................................................... 5 2. Spectral Insights’ assay apparatus ..................................................... 8

### November 22, 2004 vii 

## A CRONYMS AND 

## A BBREVIATIONS



## ASTM American Society for Testing and Materials CAMD Clean Air Markets Division CEMS continuous emission monitoring system CFR Code of Federal Regulations CO 2 

## carbon dioxide CO carbon monoxide DAS data acquisition system EPA U.S. Environmental Protection Agency FTIR Fourier Transform Infrared GC gas chromatograph/chromatography GMIS Gas Manufacturer’s Intermediate Standard ID identification mm Hg millimeters of mercury N 2 

## nitrogen gas NIST National Institute of Standards and Technology NDIR nondispersive infrared detection NO Nitrous oxides NO X 

## nitrogen oxides NTRM NIST-traceable reference materials % percent PC personal computer ppm parts per million QA quality assurance QC quality control RTD resistive temperature device SRM Standard Reference Materials UHP ultra high pure UV ultraviolet

### November 22, 2004 1 § 2.1.4: Certificate of Analysis

cylinder ID

certified concentration of analyte

balance gas

cylinder pressure

assay/certification date

certification expiration date

identification of reference standards used in the assay

protocol statement

analytical method used in the assay

name and signature of analyst and laboratory name

if applicable, statement that certified value has been corrected for analytical interferences

estimate of total uncertainty 

### § 2.1.5: Certification Label

cylinder ID number

certified concentration of analyte

balance gas

cylinder pressure

certification and expiration dates

protocol statement

name of certifying laboratory 

## 1.0 INTRODUCTION

The U.S. Environmental Protection Agency’s (EPA) Clean Air Markets Division (CAMD) is responsible for implementing the Part 75 emission m onitoring acid rain control regulations promulgated on January 11, 1993 and revised on May 1, 2002. An essen tial component of Part 75 is the certification and ongoing quality assurance (QA) activities for continuous emission monitoring systems (CEMS). Under Part 75, calibration gases are used to conduct daily calibration error dete rminations and quarterly linearity tests. Calibration gases are also used to calib rate EPA test method equipment, which, in turn, is used to assess the measurement accuracy of installe d CEMS that regulated sources use to determine emissions. To conduct these QA activities, accurate calibration gases are required.

Part 75 regulations require that the certified c oncentrations for calibration gases be traceable to National Institute of Standards a nd Technology (NIST) Standard Reference Materials (SRMs) according to the requirements of “EPA Traceability Protocol fo r Assay and Certification of Gaseous Calibration Standards” (EPA Traceability Protocol), Septem ber 1997 (EPA-600/R-97/121). The protocol was originally published in 1978 and has been revised several times, most recently in 1997. EPA Traceability Protocol gases deviate from the certified value by no mo re than ± 2 percent, and the concentrations are stable for 12 to 36 months, depending on the components of the gas blend.

The EPA Traceability Protocol specifies two types of documentation that must accompany a calibration gas cylinder: (1) a certification of analysis (§ 2.1.4 Certification Documentation), which may be mailed separately or attached to the cylinder; and (2) a certification tag (§ 2.1.5 Certification Label), which must be attached to the valve under the valve cap.

Section 2.1.10 of the EPA Traceability Protocol states that EPA will periodically assess the accuracy of calibration gases and publish the results. Between 1978 and 1996, EPA’s Office of Research and Development conducted several performance audits of calibration gases from various manufacturers. These audits provided a quality check for gas vendors and connected users with good gas vendors. In the most recent five years of audits, the failure rate of the calibration gases declined from about 27 percent in 1992 to 5 percent in 1996. Because of budgetary constraints, audits of calibration gases have not been performed since 1996, and the activity was transferred to EPA’s Office of Air and Radiation.

In 2003, EPA’s CAMD conducted an audit to ev aluate the accuracy of the specialty gas manufacturers’ reported concentrations for three-com ponent cylinder gas blends. EPA procured tri-blend cylinder gases certified according to EPA’s Traceability Protocol from 14 gas manufacturers, checked the accuracy of the manufacturers’ certifications of concentration, and examined the accompanying documentation. The reported concentrations of the th ree three-component cylinder gas blends (each in a

### November 22, 2004 2 Gas Composition of Audited Cylinders

Concentration Level Sulfur dioxide – SO 2 (ppm) Nitric oxide – NO (ppm) Carbon dioxide – CO 2 (%)

Low 50 50 5

Mid 500 400 12
High 1000 900 18 

## balance of nitrogen) were verified. Two laboratories assayed the cylinder gases using different analytical techniques. MACTEC used standard gas analyzers, and Spectral Insights used a Fourier transform infrared (FTIR) spectrometer. Both laboratories used “Procedure G1: Assay and Certification of a Compressed Gas Standard Calibration Without Dilution” (EPA-600/R-97/121).

The standard for comparison is the relative diffe rence between the vendor-certified values and EPA’s laboratory results, which must be within ± 2.0 per cent. Part 75, Appendix A, Section 5.1.4 requires calibration gases to be within 2.0 percent of the con centration specified on the certification label. The ± 2.0 percent limit accommodates the ±1 percent uncerta inty in the NIST SRM concentrations and the ± 1 percent uncertainty in the balance of the measurement system used to produce EPA Traceability Protocol gases. As such, if the difference between EPA’s value and the gas vendor’s value differs by ± 2.0 percent or less, the two values do not differ statistically.

Vendors were notified in writing if any of the con centrations in their gases differed by more than ± 2.0 percent from those determined by both analytical laboratories, or if their documentation was incomplete. The high-level NO and high-level CO 2 

## gases, however, were compared using data from only one of the two analytical laboratories because of an unresolved NO

x 

## analyzer issue, and the high-level CO 2 

## SRM was emptied before the FTIR analyses were performed.

The audit results are posted on two EPA Web sites: www.epa.gov/airmarkets/monitoring and www.epa.gov/ttn/emc/new . (Scroll to “EPA 2003 Blind Audit of Protocol Calibration Gases for CEMS” after accessing the sites.) Posting on the Web enabl es users of the EPA Traceability Protocol gases to readily judge how well the gas manufacturers’ products performed in the audit.

2.0 SELECTION OF GAS VENDORS

At the beginning of this project in support of CAMD, The Cadmus Group, Inc. conducted a study to identify U.S. commercial gas manufacturers which pr oduce and market gas standards that are prepared and analyzed according to EPA’s Traceability Protocol. Cadmus’ search of the Air and Waste Management Web site, the Internet, and previous EPA audit publications indicated that 25 gas manufacturers marketed EPA Traceability Protocol g ases. Followup by telephone confirmed that 11 of these specialty gas companies produce EPA Protocol gas standards, while the others were only distributors of gas products. These producers are liste d in Table 1, along with the supplier, and the laboratory location where the gas concentrations are certified.

Not listed in Table 1 are a few vendors that were included in earlier EPA audits, but have since been acquired by other companies. For example, AIRCO is now BOC Gases and Airgas; Alphagaz is now Air Liquide; and Liquid Carbonic is now Praxair. Th e latest transaction occurred in July 2004 after completing the audit when BOC sold their U.S. packaged gas business (which included EPA Protocol gases) to Airgas and National Welders.

### November 22, 2004 3 Table 1. U.S. Commercial Producers of EPA Traceability Protocol Gases (as of 2004)
Gas Producer Supplier Laboratory Location Air Liquide A-L Specialty Gases La Porte, TX Airgas Airgas Southwest Specialty Gases Mobile, AL Airgas NCN Specialty Gases Los Angeles, CA Airgas South Specialty Gases Mobile, AL BOC Gases MWSC High Purity Gases Riverton, NJ AGA Gas, Inc. AGA Gas, Inc. Maumee, OH Matheson Tri-Gas Matheson Tri-Gas Twinsburg, OH Messer MG Industries MG Industries – Richmond, VA Morrisville, PA Spec Air Specialty Gases Morrisville, PA National Specialty Gases National Welders Durham, NC Praxair Praxair Los Angeles, CA Scott Specialty Gases Scott Specialty Gases Plumsteadville, PA Scott-Marrin, Inc. Scott-Marrin, Inc. Riverside, CA Spectra Gases, Inc. Spectra Gases, Inc. Alpha, NJ



## 3.0 PURCHASE OF EPA TRACEABILITY PROTOCOL GASES

Cadmus arranged for third-party purchases of EPA Traceability Protocol gases from the 14 vendors. Cadmus selected ARCADIS to purchase the gases, receive the gas cylinders at their facility in Research Triangle Park, North Carolina, and transfer the cyli nders to the primary laboratory for analysis. Cadmus ordered the gases, which ranged in price from $288 to $1,384 per cylinder, in December 2002 and January 2003. The vendor-reported concentrations of the purchased gases are presented in Table 2.

Table 2. Gases Purchased for the 2003/2004 Audit

Gas Vendor Conc. Range Cylinder ID Vendor-Reported Gas Concentrations NO (ppm) SO 2 (ppm) CO 2 (%) Air Liquide Low Mid High CC66623 CC92259 CC60899 54.0 ± 0.8 ppm 401 ± 5 ppm 911 ± 10 ppm 47.5 ± 0.8 ppm 499 ± 4 ppm 981 ± 9 ppm 4.97 ± 0.06 % CO 2 12.1 ± 0.1 % CO 2 17.7 ± 0.2 % CO 2 Airgas Southwest Low Mid High CC148939 CC48489 CC125139 48.90 ± 1 % 406.0 ± 1 % 900.0 ± 1 % 47.73 ± 1 % 496.8 ± 1 % 994.6 ± 1 % 5.01 ± 1 % 12.00 ± 1 % 17.99 ± 1 % Airgas NCN Low Mid High CC152482 CC60532 CC137805 51.4 ± 1 % 388 ± 1 % 845 ± 1 % 50.4 ± 1 % 500 ± 1 % 1000 ± 1 % 5.01 ± 1 % 12.0 ± 1 % 18.0 ± 1 %

Airgas South Low Mid High SG9151036 CC156246 SG9170299 50.05 ± 1 % 397.5 ± 1 % 900.0 ± 1 % 50.23 ± 1 % 502.8 ± 1 % 998.8 ± 1 % 5.041 ± 1 % 12.00 ± 1 % 18.07 ± 1 %
BOC Gases Low Mid High CC24569 XC034007B XC034030B 49.8 ± 1 % 407.8 ± 1 % 900 ± 1 % 50.9 ± 1 % 500.4 ± 1 % 1000 ± 1 % 5.00 ± 1 % 11.98 ± 1 % 18.02 ± 1 %
AGA Low Mid High CC35129 CC91994 CC22914 50.4 ± 0.5 ppm 396 ± 4 ppm 904 ± 9 ppm 48.7 ± 0.5 ppm 466 ± 5 ppm 956 ± 10 ppm 5.20 ± 0.5 % CO 2 12.5 ± 0.1 % CO 2 18.3 ± 0.2 % CO 2 Matheson Tri-Gas Low Mid High SX23321 SX31387 SX16476 48.9 ± 0.4 ppm 410 ± 1 ppm 904 ± 9 ppm 49.5 ± 0.4 ppm 504 ± 5 ppm 988 ± 9 ppm 5.23 ± 0.05 % CO 2 12.2 ± 0.1 % CO 2 17.9 ± 0.1 % CO 2 Messer MG Industries Low Mid High CC6166 CC11490 CC27833 50.0 ± 0.128 ppm 398 ± 1.28 ppm 888 ± 2.99 ppm 50.1 ± 0.507 ppm 501 ± 1.82 ppm 1004 ± 3.1 ppm 5.05 ± 0.0444 % CO 2 12.1 ± 0.0501 % CO 2 18.2 ± 0.0501 % CO 2 Messer MG Industries (Spec Air Gases) Low Mid High CC9159 CC17527 CC2193 50.0 ± 0.131 ppm 403 ± 1.28 ppm 894 ± 2.99 ppm 49.3 ± 0.506 ppm 496 ± 1.82 ppm 1004 ± 3.1 ppm 5.07 ± 0.0444 % CO 2 12.1 ± 0.0501 % CO 2 18.3 ± 0.0501 % CO 2

### Table 2. Gases Purchased for the 2003/2004 Audit

Gas Vendor Conc. Range Cylinder ID Vendor-Reported Gas Concentrations NO (ppm) SO 2 (ppm) CO 2 (%)

1 

### MACTEC Federal Programs, Inc. 2004. A Survey of Commercially Available Compressed Gas Standards – Final Report . June, prepared for The Cadmus Group, Inc.

November 22, 2004 4 Gas Analyzers Used by MACTEC

Model Analyte Measurement Principle

Western Research Model 721M SO 2 ultraviolet (UV) absorption

AMETEK Model 922 NO
x UV detection

California Analytical Model 3300A CO 2 nondispersive infrared (NDIR) detection National Specialty Gases Low Mid High CC129710 SG9151344BAL

CC109625 46.2 ± 1 % 398 ± 1 % 930 ± 1 % 51.8 ± 1 % 500 ± 1 % 991 ± 1 % 4.90 ± 1 % 12.0 ± 1 % 17.8 ± 1 %
Praxair Low Mid High CC134131 CC104955 SA13826 51.2 ± 1 % 406 ± 1 % 914 ± 1 % 50.0 ± 1 % 509 ± 1 % 999 ± 1 % 5.00 ± 1 % 12.18 ± 1 % 17.59 ± 1 % Scott Specialty Gases Low Mid High ALM017308 ALM037407 ALM039857 50.0 ± 1 % 402 ± 1 % 911 ± 1 % 50.4 ± 1 % 503 ± 1 % 1011 ± 1 % 5.04 ± 1 % 12.10 ± 1 % 17.97 ± 1 % Scott-Marrin, Inc. Low Mid High CC103753 CC122611 CC12406 50.8 ± 0.3 ppm 397 ± 2 ppm 886 ± 5 ppm 50.9 ± 0.6 ppm 504 ± 5 ppm 997 ± 10 ppm 5.11 ± 0.05 % CO 2 12.02 ± 0.02 % CO 2 17.92 ± 0.05 % CO 2 Spectra Gases, Inc. Low Mid High CC107089 CC94719 CC88654 50.1 ± 1 % 405 ± 1 % 923 ± 1 % 50.2 ± 1 % 495 ± 1 % 988 ± 1 % 5.02 ± 1 % 12.03 ± 1 % 18.07 ± 1 %



## Reference standards were either SRMs purchased from NIST or NIST-traceable reference materials (NTRMs) purchased from BOC Gases that were certified by NIST. These standards are listed in Table 3.

Table 3. Reference Standards

Component Certification Vendor Sample ID Cylinder ID SRM Sample No. Concentration (in N 2 balance)

CO 2 NTRM B NTRM 81674x XC018106B – 4.811 % CO 2 SRM S SRM 1674b 014632 7-F-43 6.876 % CO 2 SRM S SRM 1674b 014550 7-F-52 6.876 % CO 2 NTRM B NTRM 82745x XC018675B – 19.69 % CO 2 NO SRM P SRM 1683b FF17312 45-T-37 46.7 ppm NO SRM S SRM 2735 0014283 141-B-40 781.8 ppm NO SRM S SRM 2630 09911 46-D-24 1476.2 ppm NO

SO 2 SRM S SRM 1694a 010608 95-G-38 97.6 ppm SO 2 NTRM B NTRM 81661 XC006221B – 486.0 ppm SO 2 SRM P SRM 1662a FF17174 93-G-26 973.3 ppm SO 2 NTRM B NTRM 81662 XC006240B – 997.0 ppm SO 2 Vendor code: B – BOC Gases; S – Scott Specialty Gases; P – Praxair



## 4.0 ANALYTICAL PROCEDURES

4.1 MACTEC A NALYTICAL 

## P ROCEDURES 

## MACTEC performed the cylinder assays using “Procedure G1: Assay and Certification of a Compressed Gas Standard Calibration Without Dilution” (EPA-600/R-97/121). 1 

## Analyses of the compressed gas standards were performed using three commercially available gas analyzers.

The SO 2 

## , NO

x 

## , and CO 2 

## analyzer responses were recorded using strip-chart recorders and a PC-based

### November 22, 2004 5 UHP N 2



### Zero

CO 2 

### Reference

NO x 

### Reference

SO 2 

### Reference

Candidate Reference

Candidate Standard

Candidate Standard Pressure Regulator

Gas Flow Selector Pressure Gauge AMETEK Model 922 NO x 

### Analyzer

Western Research Model 721M SO 2 

### Analyzer CAI Model 100 CO 2 

### Analyzer

Analog Digital Converter Data Acquisition PC



### Vent

Figure 1. MACTEC’s assay apparatus. 

## data acquisition system (DAS)—Workbench  for Windows. The DAS polled each analyzer at 2-second intervals. The data were reduced to 1-minute aver ages, and the average response of each analyzer was calculated. Figure 1 is a schematic diagram of the equipment set up.

Analyzer multi-point calibrations were conducted at the start of each assay session. Each analyzer was calibrated using SRMs or NTRMs according to the procedures outlined in Section 2.1.7 of EPA’s Protocol. Calibration standards were introduced into th e analyzers using a calibration flow panel. The use of the flow panel ensured that gases were introdu ced into each analyzer under consistent flow and pressure conditions. Intermediate calibration points were generated using a dilution panel (this step was the only one during which any gas standard was dilu ted). Using the analyzer responses, the estimated calibration line and the upper and lower confidence bands corresponding to 95-percent uncertainty were plotted.

Forty-two candidate standards were assayed duri ng nine assay sessions over four days. Before the start of each day’s assays, a zero gas and an upscal e reference standard were introduced into each analyzer to assess zero drift and upscale drift relative to the initial calibration curve. If the response of any analyzer to either reference standard differed by mo re than five percent from the multi-point calibration, a new multi-point calibration curve was generated. All da ily drift checks showed that analyzer drift was within acceptable limits.

During each assay session, candidate gases, reference gases, and a zero gas were introduced into the analyzers one at a time. Instantaneous responses were r ecorded on data forms as a ch eck to ensure that the values reported by the DAS corresponded with actual an alyzer responses. At the conclusion of each day, the zero and upscale gas standard were introduced into the analyzers as a final check of instrument drift.

Actual concentrations of each gas component were calculated using MS Excel spreadsheets developed by Research Triangle Institute. The true concentration of each component was calculated based2 

### Spectral Insights, Inc. 2004. FTIR Measurements of Candidate EPA Protocol Standards – Final Report. June, prepared for The Cadmus Group, Inc.

November 22, 2004 6 

## on the analyzer response, the multi-point calibration cu rve, and the daily zero and upscale calibration drift results.

MACTEC performed the NO analyses twice, first using a chemiluminescence analyzer (API Model 200AH) and then using the AMETEK UV analyzer. Th e API NO measurements were low relative to the cylinder tag values because of CO 2 

## quenching. Several unsuccessful atte mpts were made to quantify the CO 2 

## interference effects and to develop a correction that could be applied to the data. Consequently, the NO measurement data obtained using the API chem iluminescence analyzer were discarded, and the NO analyses were repeated using the AMETEK UV analyzer.

With the AMETEK Model 922 UV analyzer, an interference between the NO and SO 2 

## measurement channels occurs. The analyzer measures both NO and SO 2 

## concentrations and automatically corrects the NO measurement data for the SO 2 

## interference. Although AMETEK optimized the analyzer’s operation for analyzing the gas blends and concentration levels before providing it for use in the audit, the data obtained during MACTEC’s analyses showed a low NO bias at the 900-ppm level. The analyzer was therefore returned to AMETEK for a thorough performance evaluation.

To conduct the interference check on the M odel 922 analyzer, AMETEK used EPA Traceability Protocol gases and an Environics gas divider (with nitr ogen as the diluent) to obtain the gas blends of SO 2 

## and NO. The gas blending and injection routine was automated. Each gas blend was run through the analyzer for 4 minutes to obtain stable readings, and a DAS averaged the readings over the next 2 minutes. The system then switched to the next gas (or blend). Two repetitions were performed.

AMETEK’s results confirmed a negative cross-interference of SO 2 

## onto the NO channel. They also found the high-concentration blend readings were about 3 percent low at the 900-ppm NO level. Although AMETEK derived a correction to apply to MACTEC’s NO data, the bias was not corrected. AMETEK noted that the analyzer had a 40-cm path length cell installed, which they would not spec for ranges above 500 ppm. Typically, an 80-cm cell is u sed for measurement ranges up to 250 ppm, and a 10- cm path length cell is used for ranges from 250 – 2000 ppm. Given that the audited gas concentrations ranged from 50 – 900 ppm, however, AMETEK provided the analyzer with a 40-cm cell knowing that accuracy at both ends of the range might be affected.

The high-level NO data from the AMETEK UV analy zer were deemed questionable, because the negative bias was concluded to be likely due to th e analyzer set up. As a result, EPA excluded these results and used only FTIR data obtained by Spectra l Insights (see Section 4.2) for the high-level NO cylinder evaluations.

4.2 S PECTRAL 

## I NSIGHTS 

## A NALYTICAL 

## P ROCEDURES 

## To confirm MACTEC’s results, the EPA Traceability Protocol gas standards were analyzed by Spectral Insights using an FTIR analyzer and “Procedure G1: Assay and Certification of a Compressed Gas Standard Calibration Without Dilution” (EPA-600/R-97/121). 2 

## Sampling was conducted in accordance with EPA’s Traceability Protocol. Analyses were performed using a Nicolet Nexus 760 FTIR spectrometer.

Table 4 provides information on Spectral Insight’s FTIR instrumentation. All sample-wetted components were made of one of the following materials: Stainless steel, polytetrafluoroethylene (i.e., TeflonTM), glass, gold, or nickel-coated aluminum. Figure 2 is a schematic diagram of the apparatus. Spectral Insights did not provide details on the spect ral regions or any algorithms used in the FTIR analysis due to proprietary concerns.

### November 22, 2004 7 Table 4. Spectral Insights’ FTIR Instrumentation

Component/Parameter Specification
Measurement System Spectral Insights Series 2000
Spectral Resolution 0.5 wave number (up to 0.125 wave number)
Spectral Range 600 – 7900 wave numbers
Optical Path Length 3.12 meters (adjus table to nominal 1 to 10 meters)
IR Detector MCT operated at 77 Kelvin
Operating Pressure, Temperature Nominal 760 mm Hg, 25 °C

Cell Pressure Thin-film, 0.1 mm Hg resolution, range: 0 – 1550 mm Hg Vendor-stated accuracy: less than ± 0.25 % full scale
Cell Temperature RTD, 0.1°C resolution, range 0 – 200 °C



## Spectral Insights used the following measurement pro cedure for an analysis run for a given candidate standard range:

1. Measure appropriate SRM or NTRM standard fo r each target analyte and install as reference spectrum for respective analyte.

2. Use a random number sequence generator to de termine measurement sequence of candidate, SRM/NTRM, and zero gases.

3. Vent sample gas manifold and flush and vent manifold with next sample gas at least three times. Ensure that only one source gas valve in manifold is open at any time.

4. Evacuate FTIR sample cell to less than 1 mm Hg absolute pressure and fill with candidate standard gas at or slightly above atmospheric pressure (normally 760 mm Hg).

5. Repeat Step 4 above two more times.

6. Flow candidate (or zero) gas standard at ra te of three times cell volume per minute for two minutes (i.e., flow six cell volumes through cell). Isolate sample in cell.

7. Measure 256 spectral scans (approximately seven minutes). Concurrently measure sample gas temperature and pressure.

8. Perform spectral analysis and record result.

9. Repeat with next standard in sequence starting at Step 3.

### November 22, 2004 8 Candidate, Zero, SRM or NTRM Gas Standards 

### FTIR SpectrometerCell 

### Vacuum Pump

Selector Valve

Isolation Valves Vent

P T

Computer 

### Transducers Check Valves Toggle Valves Vent



### Gas Manifold/Regulator Manifold Vent Valve Vent



### Figure 2. Spectral Insights’ assay apparatus.



## No high-level CO 2 

## SRM or NTRM was supplied to Spectra l Insights because the gas standard was emptied during MACTEC’s analyses. Therefore, Spectral Insights blended a CO 2 

## standard directly in the FTIR gas cell to generate a high-range reference spectrum. Blending was accomplished by adding 153.2 mm Hg of 99.99 percent purity CO 2 

## to the cell and filling to 760.0 mm Hg with UHP nitrogen. After correction for CO 2 

## compressibility (less than 0.1 percent correction at 153.2 mm Hg partial pressure), the calculated concentration was determined to be 20.16 molar percent. A mid-level CO 2 

## standard was also prepared in the same way to check the mid-level response (nominal 12 percent CO 2 

## ) of the measurement system.

Because the principle of operation for FTIR spectromete rs differs from that for gas analyzers, some of the procedures in the EPA Traceability Protocol are not applicable. For example, FTIR spectrometers do not have conventional “zero” and “span” controls. Calibration is conducted by generating “reference” spectra for each analyte at precisely known conditions (i .e., pressure, temperature, optical path length, and concentration) using zero gas (nitrogen) and the SRMs or NTRMs. The spectra of the candidate standards were directly compared to the respective reference spectrum using multivariate least squares, a standard spectral analysis technique. Because this procedure is carried out for each analysis run, there is no drift.

Spectral bands that are too strong in intensity can exhibit non-linearity, which can be predicted (via simulation) and corrected. If the concentration of the reference spectrum is close to those of the candidate standards, and a strong spectral band is used, non-linear corrections are usually not required. In this test program, however, all spectral bands chosen showed lin ear responses for all reference spectra used in the measurement range for the candidate standards.

### November 22, 2004 9 

## 5.0 RESULTS

5.1 D OCUMENTATION 

## The documentation that accompanied each EPA Traceab ility Protocol gas cylinder was complete and conformed to the requirements in the Protocol. Do cumentation included a Certificate of Analysis in accordance with § 2.1.4 of the Protocol, and a Certif ication Label, in accordance with § 2.1.5 of the Protocol. The analytical technique and reference sta ndards used by the gas vendors are listed in Table 5.

Analytical techniques used most commonly fo r NO certification were FTIR and chemiluminesence; two vendors used nondispersive infrared (NDIR) detection. For SO 2 

## certification, five vendors used FTIR, seven used NDIR, one vendor used UV, and one used UV for the low-level concentration and NDIR for the mid- and high-level concentra tions. Five vendors certified the CO 2 

## standards using FTIR, eight used NDIR, and one used gas chromatography (GC).

Most vendors used Gas Manufacturers’ Intermediate standards (GMIS) or NTRMs to certify their gas concentrations. A few vendors used SRMs.

Table 5. Vendor Cylinder Gas Certif ication Using EPA Traceability Protocol

Gas Vendor Gas Conc. Range NO Certification SO 2 Certification CO 2 Certification Analytical Technique Reference Standards Analytical Technique Reference Standards Analytical Technique Reference Standards Air Liquide Low FTIR GMIS FTIR GMIS FTIR GMIS
Mid FTIR GMIS FTIR GMIS FTIR GMIS High FTIR GMIS FTIR GMIS FTIR NTRM Airgas Southwest Specialty Gases Low Chem NTRM NDIR NTRM NDIR NTRM
Mid Chem NTRM NDIR NTRM NDIR NTRM High Chem NTRM NDIR NTRM NDIR NTRM Airgas NCN Specialty Gases Low NDIR NTRM NDIR GMIS NDIR NTRM

Mid NDIR NTRM NDIR NTRM NDIR NTRM High NDIR NTRM NDIR NTRM NDIR NTRM Airgas South Specialty Gases Low Chem GMIS NDIR NTRM NDIR NTRM
Mid Chem NTRM NDIR NTRM NDIR NTRM High Chem NTRM NDIR NTRM NDIR NTRM
BOC Gases Low FTIR SRM FTIR SRM FTIR NTRM
Mid FTIR SRM FTIR NTRM FTIR NTRM High FTIR SRM FTIR NTRM FTIR NTRM
AGA (Linde Gas Group) Low Chem GMIS NDIR GMIS NDIR NTRM/GMIS
Mid Chem GMIS NDIR GMIS NDIR NTRM/GMIS High Chem GMIS NDIR GMIS NDIR NTRM/GMIS
Matheson Tri-Gas Low FTIR SRM FTIR SRM FTIR SRM
Mid FTIR SRM FTIR SRM FTIR SRM High FTIR SRM FTIR SRM FTIR SRM
Messer MG Industries Low Chem GMIS NDIR GMIS NDIR GMIS
Mid Chem GMIS NDIR GMIS NDIR GMIS High Chem GMIS NDIR GMIS NDIR GMIS
Messer MG Industries (Spec Air Gases) Low Chem GMIS NDIR GMIS NDIR GMIS
Mid Chem GMIS NDIR GMIS NDIR GMIS High Chem GMIS NDIR GMIS NDIR GMIS National Specialty Gases Low FTIR GMIS FTIR GMIS FTIR GMIS
Mid FTIR GMIS FTIR GMIS FTIR GMIS High FTIR GMIS FTIR GMIS FTIR GMIS

### Table 5. Vendor Cylinder Gas Certif ication Using EPA Traceability Protocol

Gas Vendor Gas Conc. Range NO Certification SO 2 Certification CO 2 Certification Analytical Technique Reference Standards Analytical Technique Reference Standards Analytical Technique Reference Standards



### November 22, 2004 10 Praxair Low Chem GMIS UV GMIS NDIR GMIS
Mid NDIR GMIS NDIR GMIS NDIR GMIS High NDIR GMIS NDIR GMIS NDIR GMIS Scott Specialty Gases Low FTIR NTRM FTIR NTRM FTIR NTRM

Mid FTIR NTRM FTIR NTRM FTIR NTRM High FTIR NTRM FTIR NTRM FTIR NTRM Scott-Marrin, Inc. Low Chem GMIS UV GMIS GC GMIS
Mid Chem GMIS UV GMIS GC GMIS High Chem GMIS UV GMIS GC GMIS Spectra Gases, Inc. Low Chem NTRM NDIR NTRM NDIR GMIS
Mid FTIR NTRM NDIR GMIS NDIR NTRM High FTIR NTRM NDIR GMIS NDIR NTRM
FTIR – Fourier transform infrared GMIS – Gas Manufacturer’s Intermediate Standard NTRM – NIST traceable reference material Chem – Chemiluminescence NDIR – Non-dispersive infrared SRM – Standard reference material UV – Ultraviolet GC – Gas chromatography



## 5.2 G AS 

## A NALYSES 

## Tables 6, 7, and 8 on pages 12 – 16 present the NO, SO 2 

## , and CO 2 

## concentrations, respectively, determined by the manufacturers and by MACTEC and Spectral Insights, along with the percent differences between the concentration determinations . The percent differences were computed relative to the EPA-determined values. More de tailed audit data are presented in Appendix A, Tables A-1, A-2, and A-3. The MACTEC measurement data are presented in Table A-4, and the Spectral Insights’ measurement data are presented in Table A-5.

The results differed by less than 2.0 percent for 33 of the 42 cylinders for NO, 41 of the 42 cylinders for SO 2 

## , and 38 of 42 cylinders for CO 2 

## .
In April 2004, the manufacturers were notified of th eir audit results in writing without revealing the actual audit concentrations. The manufacturers who se gas concentrations differed by more than ± 2.0 percent from both EPA-determined concentrations (i.e., MACTEC and Spectral Insights results) were offered the opportunity to reanalyze their gases and s ubmit the new results to EPA for inclusion in this report and in the report posted on the EPA Web sit es. Cadmus discussed the audit procedures (to the extent that FTIR information was made available by the Spectral Insights) with various gas vendors and responded to their questions and comments. Most vendors stated that they reviewed all of their laboratory routines and had also re-checked the laboratory documentation for their gases.

Six gas vendors (Air Liquide, Airgas, Praxair, Matheson, BOC Gases, and National Specialty Gases) reanalyzed their cylinders to investigate the discr epancies shown by the MACTEC or Spectral Insights results. All reanalyzed results submitted to EPA were within ± 2.0 percent of the corresponding EPA value.

In most cases, the reanalyzed concentration value w as within ±2 percent of the original certified tag value, which is the specification for EPA Traceability Pr otocol gases, and also was within ± 2 percent of the EPA-determined values. Of the few concentrations that changed by more than ± 2 percent, three were at the low-level NO, one was at the low-level CO 2 

## , and one at the high-level CO 2 

## .
One point to consider is that the 2-percent cr iterion must account for the analytical uncertainty associated with both the gas vendor’s and auditor’s m easurements. If the analyses have an uncertainty of ± 2 percent and the results are in opposite directions , the two measurements can differ by up to 4 percent.

### November 22, 2004 11 

## If the two measurements are made using the same analytical technique, the likelihood of this scenario would be decreased. Regardless, the EPA-determined va lue is deemed to be the “true” for the purposes of the cylinder gas audit, and considering alternatives to the specification is beyond the scope of this study.

The EPA Traceability Protocol is a general analyti cal procedure, which does not allow or disallow specific analytical procedures to measure specific gas mixtures—the laboratory analyst must make this choice. The analyst must balance analytical cost s with uncertainty requirements and other factors. Nevertheless, FTIR is probably a technically be tter method to analyze multiple-component mixtures because interference effects are less likely to occur, provided that (1 ) the FTIR has sufficient spectral resolution, (2) a “clean” peak is measured, (3) linearity problems are not encountered, and (4) accurate gas standards are used for developing the reference sp ectra. Spectral resolution is the ability to distinguish adjacent wavelengths. High-resolution spectra enable fi ne details within a spectrum to be observed, while low resolution shows only gross features of a spect rum. The choice of spectral region to conduct the measurement is important. If a sample contains a mixture of gases (some of which may not be the target gas of interest), the potential exists for spectral bands to overlap. The overlapping bands can cause the target gas to be overestimated. Analysis of a g as sample carried out using multivariate least squares allows constituents in the gas sample that have overl apping spectral bands to be quantified with minimum interference, as long as the measurements are conducted at a high spectral resolution and reference spectra are generated using accurate standards. Non-linear responses can be corrected within the FTIR software to provide accurate results.

The high-level CO 2 

## FTIR results showed some significant de viations from the vendor tag value. For example, the results of two high-level candidate gases with identical CO 2 

## tag values (18.30 percent CO 2 

## ) were significantly different; one gas cylinde r was found to be within 0.1 percent CO 2 

## of the tag value, while the other cylinder result differed from th e tag value by approximately 1 percent CO 2 

## . To confirm the results, the spectra of these two gases were directly compared. The CO 2 

## spectra differed in absorbance by 5 percent, confirming the results. This finding hi ghlights the relatively high degree of differences for these particular standards. Because the high-level CO 2 

## reference spectra were not generated using a NIST standard, however, EPA determined that the high-level CO 2 

## FTIR data would not be used in the data comparisons.

FTIR analysis of the gas standards also revealed an impurity issue that NIST is investigating. A visual scan of the spectra indicated small amounts of impurities in the SO 2 

## and CO 2 

## reference standards. For example, a spectrum of SRM 1694a containing 97.6 ppm SO 2 

## in a nitrogen balance revealed the presence of two impurities: 3.1 ppm NO and 100 ppb carbonyl sulfide. These impurities have no impact on the FTIR analysis, but could be of concern when other methodologies are used. Some of the candidate standards also included impurities. No effort was ma de to identify or quantify impurities in all of the SRM, NTRM and candidate standards. Visual insp ection of the sample spectra, however, indicated that some of the candidate standards contained sma ll amounts of carbon monoxide (CO). The small amounts of CO or any other impurity do not affect the FTIR analysis because they do not have absorption bands near any of the analytes of interest. If an impurity has bands that overlap, measures can be taken to account for the potential interference. No su ch measures were required in these analyses.

Accuracy assessments such as the one performed in this project provide a “snapshot” of the process being evaluated. The results of the assessment presented here should therefore not be regarded as a final statement on the accuracy of EPA Traceability Protocol gases, nor should the individual results be taken as definitive critiques of the analytical capabilities of the individual manufacturers. Instead, the results should be viewed as an indicator of the current stat us of the collective accuracy of the Protocol gases.

### November 22, 2004 12 Table 6. NO Component Analysis Summary

Gas Vendor Gas Conc. Range Vendor-Supplied Information NO Analysis by UV a NO Analysis by FTIR

Tag Value (ppm NO) Reanalyzed Value (ppm) Change in Value

(%) NO (ppm) Orig Tag Value Deviation

(% diff) Reanalyzed Value Deviation

(% diff) NO (ppm) Orig Tag Value Deviation

(% diff) Reanalyzed Value Deviation

(% diff)
Air Liquide Low 54.0 54.9 - 1.6 53.83 0.3

Mid 401 395.9 1.3 392.5 2.2
High 911 b – 905 0.7
Airgas Southwest Specialty Gases Low 48.90 49.89 c 2.0 53.4 - 8.4 - 6.5 49.93 - 2.1 - 0.1

Mid 406.0 405.2 - 0.2 411.7 - 1.4 - 1.6 406.3 - 0.1 - 0.3
High 900.0 909.8 c 1.1 b – – 925 - 2.7 - 1.6
Airgas NCN Specialty Gases Low 51.4 52.21 1.6 53.2 - 3.4 - 1.9 51.50 - 0.2 1.4

Mid 388 384.6 - 0.9 387.2 0.2 - 0.7 382.4 1.5 0.6
High 845 860.9 c 1.9 b – – 870 - 2.9 - 1.0
Airgas South Specialty Gases Low 50.05 51.69 c 3.3 52.7 - 5.1 - 2.0 51.80 - 3.4 - 0.2

Mid 397.5 401 0.9 405.7 - 2.0 - 1.2 400.3 - 0.7 0.2
High 900.0 900.8 0.1 b – – 912 - 1.3 - 1.2

BOC Gases Low 49.8 51.5 - 3.3 50.50 - 1.4

Mid 407.8 406.0 d - 0.4 399.5 2.1 1.6 397.4 2.6 2.2
High 900 896 d - 0.4 b – – 880 2.3 1.8

AGA (Linde Gas Group) Low 50.4 51.0 - 1.1 50.50 - 0.2

Mid 396 390.2 1.5 388.3 2.0
High 904 b – 903 0.1

Matheson Tri- Gas Low 48.9 50.4 e 3.1 51.5 - 5.0 - 2.1 50.57 - 3.3 - 0.3

Mid 410 405.1 e - 1.2 401.6 2.1 0.9 397.7 3.1 1.9
High 904 b – 907 - 0.3

Messer MG Industries Low 50.0 50.4 - 0.9 50.00 0.0

Mid 398 396.9 0.3 391.3 1.7
High 888 b – 887 0.1

Messer MG Industries (Spec Air Gases) Low 50.0 50.8 - 1.5 50.47 - 0.9

Mid 403 399.3 0.9 396.0 1.8
High 894 b – 904 - 1.1

National Specialty Gases Low 46.2 47.3 f 2.4 48.1 - 4.0 - 1.8 48.27 - 4.3 - 2.0

Mid 398 401.3 - 0.8 397.3 0.2
High 930 930 0.0 b – – 948 - 1.9 - 1.9

Praxair Low 51.2 51.9 - 1.3 51.50 - 0.6

Mid 406 405.1 0.2 400.6 1.3
High 914 b – 933 - 2.0
Scott Specialty Gases Low 50.0 51.0 - 1.9 50.30 - 0.6

Mid 402 401.7 0.1 397.2 1.2
High 911 b – 918 - 0.8
Scott- Marrin, Inc. Low 50.8 51.7 - 1.8 51.77 - 1.9

Mid 397 399.9 - 0.7 395.5 0.4
High 886 b – 899 - 1.4

### Table 6. NO Component Analysis Summary

Gas Vendor Gas Conc. Range Vendor-Supplied Information NO Analysis by UV a NO Analysis by FTIR

Tag Value (ppm NO) Reanalyzed Value (ppm) Change in Value

(%) NO (ppm) Orig Tag Value Deviation

(% diff) Reanalyzed Value Deviation

(% diff) NO (ppm) Orig Tag Value Deviation

(% diff) Reanalyzed Value Deviation

(% diff)



### November 22, 2004 13 Spectra Gases, Inc. Low 50.1 51.1 - 2.0 50.80 - 1.4

Mid 405 404.2 0.2 400.8 1.0
High 923 b – 934 - 1.2

a AMETEK Model 922 UV measurements of NO were adjusted for SO 2 interference.

b The high-level NO evaluations were based sole ly on the FTIR results because the AMETEK UV NO
x analyzer setup performed by the manufacturer was not optimum for the 1000-ppm range.

c Gas cylinders were returned to Airgas for NO reanalyses. V endor reported new NO values on April 26, 2004, which differed by less than ± 2 percent from the corresponding EPA-determined va lues. In all but one case, the reanalyzed value was within ± 2 percent of the original tag value. No corrective action was taken by the vendor.

d Mid- and high-level gas cylinders were returned to BOC Ga ses for NO reanalyses. Vendor reported new values on June 9, 2004, which differed by less than ± 2 percent from t he corresponding EPA-determined UV or FTIR values. The two reanalyzed NO values also differed by less than ± 2 percent of original tag value. No corrective action was taken.

e Gas cylinders were returned to Matheson for NO and CO 2 reanalyses. Vendor reported new values on May 10, 2004, which differed by less than ± 2 percent from the corresponding EPA-det ermined values. Two of the th ree reanalyzed values differed by more than ± 2 percent of original tag value. The concentra tions for NO were corrected by shifting to a wave number within a spectral region where CO 2 interference is minimized. Matheson f ound an operator calculation error for the CO 2 concentration in this sample from early 2003, and implement ed data acquisition and calculati on software for their FTIRs in early 2004 to preclude the potential for operator errors.

f Gas cylinders were returned to National Specialty Gases for NO, SO 2 , and CO 2 reanalyses. Vendor reported new values on May 10, 2004, which differed by less than ± 2 percent from the corresponding EPA-determined values. Two of the three reanalyzed values differed by more than ± 2 percent of origi nal tag value. The FTIR problem was corrected during the course of the regular calibration cycle and by using a more experienced analyst.

NOTE : When using data in the tables for procuring EPA Traceability Protocol gases , readers should heed the following points. First, the information in the footnotes must not be ignored. Second, if the difference between EPA’s value and the gas vendor’s value is ± 2 percent or less, the values do not statistically differ because of the uncertainties in the total measurement syst em. Thus, a difference of 2.0 percent would be interpreted as bei ng equal to one of, for example, 0.57 percent. Finally, EPA presen ts this information without assigning a rating to the gas vendors, such as which vendor is appr oved, or which is not approved.



### Table 7. SO 2 

### Component Analysis Summary

Gas Vendor Gas Conc. Range Vendor-Supplied Information SO 2 Analysis by UV SO 2 Analysis by FTIR

Tag Value (ppm SO 2 ) Reanalyzed Value (ppm) Change in Value

(%) SO 2 (ppm) Orig Tag Value Deviation

(% diff) Reanalyzed Value Deviation

(% diff) SO 2 (ppm) Orig Tag Value Deviation

(% diff) Reanalyzed Value Deviation

(% diff)
Air Liquide Low 47.5 48.36 - 1.8 47.93 - 0.9

Mid 499 497.17 0.4 498.5 0.1
High 981 987.26 - 0.6 1004.5 - 2.3
Airgas Southwest Specialty Gases Low 47.73 47.62 - 0.2 47.01 1.5 1.3 47.52 0.4 0.2

Mid 496.8 500.9 0.8 492.10 1.0 1.8 501.3 - 0.9 - 0.1
High 994.6 1003 0.8 994.16 0.0 0.9 1008.2 - 1.3 - 0.5
Airgas NCN Specialty Gases Low 50.4 50.05 - 0.7 49.92 1.0 0.3 49.79 1.2 0.5

Mid 500 504.3 0.9 499.89 0.0 0.9 504.2 - 0.8 0.0
High 1000 1002 0.2 1000.28 0.0 0.2 1006.8 - 0.7 - 0.5
Airgas South Specialty Gases Low 50.23 51.03 1.6 50.25 0.0 1.6 50.58 - 0.7 0.9

Mid 502.8 509.2 1.3 505.89 - 0.6 0.7 507.9 - 1.0 0.3
High 998.8 1012 1.3 1003.99 - 0.5 0.8 1016.1 - 1.7 - 0.4

### Table 7. SO 2 

### Component Analysis Summary

Gas Vendor Gas Conc. Range Vendor-Supplied Information SO 2 Analysis by UV SO 2 Analysis by FTIR

Tag Value (ppm SO 2 ) Reanalyzed Value (ppm) Change in Value

(%) SO 2 (ppm) Orig Tag Value Deviation

(% diff) Reanalyzed Value Deviation

(% diff) SO 2 (ppm) Orig Tag Value Deviation

(% diff) Reanalyzed Value Deviation

(% diff)



### November 22, 2004 14 BOC Gases Low 50.9 50.52 0.8 50.83 0.1

Mid 500.4 499.80 0.1 499.8 0.1
High 1000 1001.47 - 0.1 1015.6 - 1.5

AGA (Linde Gas Group) Low 48.7 48.67 0.1 49.54 - 1.7

Mid 466 461.75 0.9 464.2 0.4
High 956 955.83 0.0 967.3 - 1.2

Matheson Tri- Gas Low 49.5 48.33 2.4 48.95 1.1

Mid 504 502.79 0.2 503.6 0.1
High 988 994.28 - 0.6 1006.5 - 1.8

Messer MG Industries Low 50.1 48.89 2.5 49.26 1.7

Mid 501 506.49 - 1.1 508.5 - 1.5
High 1004 1018.01 - 1.4 1029.3 - 2.5

Messer MG Industries (Spec Air Gases) Low 49.3 48.16 2.4 49.12 0.4

Mid 496 502.94 - 1.4 504.0 - 1.6
High 1004 1018.22 - 1.4 1029.8 - 2.5

National Specialty Gases Low 51.8 51.5 a - 0.6 50.49 2.6 2.0 50.64 2.3 1.7

Mid 500 499.12 0.2 502.2 - 0.4
High 991 992 0.1 995.74 - 0.5 - 0.4 1011.0 - 2.0 - 1.9

Praxair Low 50.0 49.59 0.8 50.36 - 0.7

Mid 509 506.59 0.5 511.6 - 0.5
High 999 1000.59 - 0.2 1008.7 - 1.0
Scott Specialty Gases Low 50.4 49.10 2.7 50.38 0.0

Mid 503 497.63 1.1 503.0 0.0
High 1011 1000.65 1.0 1021.3 - 1.0
Scott- Marrin, Inc. Low 50.9 51.07 - 0.3 51.17 - 0.5

Mid 504 502.94 0.2 507.9 - 0.8
High 997 992.93 0.4 995.9 0.1
Spectra Gases, Inc. Low 50.2 49.19 2.1 49.82 0.8

Mid 495 493.05 0.4 493.1 0.4
High 988 987.60 0.0 998.5 - 1.1

a Gas cylinders were returned to National Specialty Gases for NO, SO 2 , and CO 2 reanalyses. Vendor reported new values on May

10, 2004, which differed by less than ± 2 percent from the corresponding EPA-determined values. Two of the three reanalyzed values differed by more than ± 2 percent of original tag va lue. FTIR problem was corrected during the course of the regular calibration cycle and using a more experienced analyst.

NOTE : When using data in the tables for procuring EPA Traceability Protocol gases , readers should heed the following points. First, the information in the footnotes must not be ignored. Second, if the difference between EPA’s value and the gas vendor’s value is ± 2 percent or less, the values do not statistically differ because of the uncertainties in the total measurement syst em. Thus, a difference of 2.0 percent would be interpreted as bei ng equal to one of, for example, 0.57 percent. Finally, EPA presen ts this information without assigning a rating to the gas vendors, such as which vendor is appr oved, or which is not approved.

### November 22, 2004 15 Table 8. CO 2 

### Component Analysis Summary

Gas Vendor Gas Conc. Range Vendor-Supplied Information CO 2 Analysis by NDIR CO 2 Analysis by FTIR

Tag Value (% CO 2 ) Reanalyzed Value (% CO 2 ) Change in Value

(%) CO 2 (%) Orig Tag Value Deviation

(% diff) Reanalyzed Value Deviation

(% diff) CO 2 (%) Orig Tag Value Deviation

(% diff) Reanalyzed Value Deviation

(% diff)
Air Liquide Low 4.97 5.02 - 1.0 4.991 - 0.4

Mid 12.1 12.09 0.1 11.98 1.0
High 17.7 17.9 a 1.1 18.15 - 2.5 - 1.4 b

– – Airgas Southwest Specialty Gases Low 5.011 5.045 0.7 4.97 0.8 1.5 4.984 0.5 1.2

Mid 12.0 11.95 - 0.4 12.07 - 0.6 - 1.0 12.06 - 0.5 - 0.9
High 17.99 17.97 - 0.1 18.09 - 0.6 - 0.7 b

– – Airgas NCN Specialty Gases Low 5.01 5.064 1.1 5.00 0.2 1.3 4.970 0.8 1.9

Mid 12.0 11.94 - 0.5 12.07 - 0.6 - 1.1 12.04 - 0.3 - 0.8
High 18.0 18.06 0.3 18.15 - 0.8 - 0.5 b

– – Airgas South Specialty Gases Low 5.041 5.057 0.3 5.01 0.7 1.0 4.998 0.9 1.2

Mid 12.0 11.88 - 1.0 12.05 - 0.4 - 1.4 12.17 - 1.4 - 2.4
High 18.07 18.15 0.4 18.18 - 0.6 - 0.2 b

– –
BOC Gases Low 5.0 4.98 0.5 4.973 0.5

Mid 11.98 12.05 - 0.6 11.94 0.3
High 18.02 18.14 - 0.7 b

–
AGA (Linde Gas Group) Low 5.2 5.22 - 0.5 5.146 1.0

Mid 12.5 12.68 - 1.4 12.45 0.4
High 18.3 18.53 - 1.2 b

–
Matheson Tri- Gas Low 5.23 4.94 c - 5.5 4.99 4.8 - 1.0 4.979 5.0 - 0.8

Mid 12.2 12.06 1.2 11.93 2.3
High 17.9 18.07 - 0.9 b

–
Messer MG Industries Low 5.05 5.08 - 0.5 5.023 0.5

Mid 12.1 12.22 - 1.0 12.18 - 0.7
High 18.2 18.27 - 0.4 b

–
Messer MG Industries (Spec Air Gases) Low 5.07 5.09 - 0.5 5.053 0.3

Mid 12.1 12.22 - 1.0 12.18 - 0.7
High 18.3 18.31 - 0.1 b

–
National Specialty Gases Low 4.9 4.9 0.0 4.87 0.5 0.5 4.885 0.3 0.3

Mid 12.0 11.97 0.3 12.09 - 0.7
High 17.8 18.23 d 2.4 18.30 - 2.8 - 0.4 b

– –
Praxair Low 5.00 5.03 - 0.6 4.986 0.3

Mid 12.18 12.17 0.1 12.23 - 0.4
High 17.59 17.82 e 1.3 17.85 - 1.5 - 0.2 b

– – Scott Specialty Gases Low 5.04 5.01 0.6 4.987 1.1

Mid 12.10 12.04 0.5 12.18 - 0.7
High 17.97 18.03 - 0.3 b

– Scott-Marrin, Inc. Low 5.11 5.09 0.4 5.046 1.3

Mid 12.02 12.11 - 0.7 12.07 - 0.4
High 17.92 18.13 - 1.2 b

–

### Table 8. CO 2 

### Component Analysis Summary

Gas Vendor Gas Conc. Range Vendor-Supplied Information CO 2 Analysis by NDIR CO 2 Analysis by FTIR

Tag Value (% CO 2 ) Reanalyzed Value (% CO 2 ) Change in Value

(%) CO 2 (%) Orig Tag Value Deviation

(% diff) Reanalyzed Value Deviation

(% diff) CO 2 (%) Orig Tag Value Deviation

(% diff) Reanalyzed Value Deviation

(% diff)



### November 22, 2004 16 Spectra Gases, Inc. Low 5.02 5.01 0.1 5.003 0.3

Mid 12.03 12.10 - 0.5 12.24 - 1.7
High 18.07 18.08 0.0 b

–

a High-range gas cylinder was returned to Air Liquide for CO 2 reanalysis. Vendor reported a new CO 2 value of 17.9 percent on May

6, 2004, which differed by less than ± 2 percent from the EPA- determined value. Reanalyzed value was also within ± 2 percent of original tag value. No correct ive action was taken by the vendor.

b The high-level CO 2 evaluations were based solely on the NDIR result s because the FTIR data obtai ned at this concentration

level were not supported by an SRM; sufficient high-level CO 2 SRM or NTRM was not available to provide reference spectra for the FTIR.

c Gas cylinders were returned to Matheson for NO and CO 2 reanalyses. Vendor reported new values on May 10, 2004, which

differed by less than ± 2 percent from the corresponding EPA-deter mined values. Two of the thr ee reanalyzed values differed by more than ± 2 percent of original tag val ue. The concentrations for NO were corrected by shifting to a wave number within a spectral region where CO 2 interference is minimized. Matheson f ound an operator calculation error for the CO 2 concentration in this sample from early 2003, and implemented data acquisition and ca lculation software for their FTIRs in early 2004 to preclud e the potential for operator errors.

d Gas cylinders were returned to National Specialty Gases for NO, SO 2 , and CO 2 reanalyses. Vendor reported new values on May

10, 2004, which differed by less than ± 2 percent from the corresponding EPA-determined values. Two of the three reanalyzed values differed by more than ± 2 percent of original tag val ue. The FTIR problem was corrected during the course of the regular calibration cycle and by using a more experienced analyst.

e High-range gas cylinder was returned to Praxair for CO 2 reanalysis based on an initial EPA finding of 18.07 percent CO 2 . Vendor

reported a new CO 2 value of 17.82 percent on May 27, 2004. Praxair had an independent, third-party laboratory (Scott-Marin, Inc.) analyze the cylinder, resulting in 17.77 percent CO 2 . Praxair also sent the cylinder to NIST for analysis, which resulted in 17.85 percent CO 2 . All of the reanalyzed values differed by less than 2. 0 percent from the EPA-determined value. The original tag value was within 2.0 percent of each of the reanalyzed va lues. The original tag value and the vendor-reanalyzed value were within 2.0 percent of the NIST-generated "true" va lue. Therefore, no corrective action was required.

NOTE : When using data in the tables for procuring EPA Traceability Protocol gases , readers should heed the following points. First, the information in the footnotes must not be ignored. Second, if the difference between EPA’s value and the gas vendor’s value is ± 2 percent or less, the values do not statistically differ because of the uncertainties in the total measurement syst em. Thus, a difference of 2.0 percent would be interpreted as bei ng equal to one of, for example, 0.57 percent. Finally, EPA presen ts this information without assigning a rating to the gas vendors, such as which vendor is appr oved, or which is not approved.



## 6.0 CONSIDERATIONS FOR FUTURE PROTOCOL GAS AUDITS

The following are elements of the audit that warrant consideration before th e next audit of blended gases is performed.

• When analyzing multi-component gas blends, the analyst must conduct an interference test to verify instrument vendor claims that the analyzer is free of any interferences or that interference correction is properly applied. The instrument calibration should be well characterized using both single-component and multi-component reference standards. Example interference issues are CO 2 

## quenching in chemiluminescence-based techniques, SO 2 

## interference in the UV measurement of NO, and impurities in the gas standards.

• One instrument vendor stated that cross-interfe rence of 1 percent of full scale is their standard specification. The ± 2 percent acceptance criterion (relative to the analyzed value, not full scale) used for these audits accommodates the ± 1 percen t uncertainty in the concentrations of NIST SRMs and the ± 1 percent uncertainty in the bala nce of the measurement system used to produce Protocol gases. This acceptance criterion becomes mo re stringent with possible interference effects

### November 22, 2004 17 

## in multi-component gas analyses, even though the in terference error may be within the instrument performance specifications.

• EPA’s Traceability Protocol should include detailed procedures that are specific to FTIR-based cylinder gas analysis. Some potential issues arose during this study when making quantitative measurements using FTIR, and NIST occasionally had difficulty trying to correlate gas vendor FTIR results for NTRM analyses with the NIST non-FTIR analyses. Standard operating procedures (SOP) for FTIR analysis of cylinder gases may he lp eliminate potential problems and ensure that all FTIR measurement data are generated using cons istent analytical routines and reported in the

same manner.

An approach to the development of a draft FTIR SOP could include the following steps: (a) review existing public guidance documents from, for example, EPA, ASTM, NIOSH, OEDC, and TUV; (b) survey of gas manufacturers' appro aches to QA/QC in such applications, including reviews of any in-house documents the manufactur ers are willing to submit; (c) development of a list of key SOP elements, with the goal of reaching the broadest possible consensus among manufacturers and analysts; and (d) preparation of a draft SOP containing these elements.

Various approaches can be considered in determining selection criteria for audit targets. Given that the gas vendors use these audit results as a marketing tool, however, the next audit should include all specialty gas companies that produce EPA Protocol gas. Currently, 10 specialty gas companies produce EPA Protocol gas. Considering how transfers of gas business entities between companies have occurred over the past few years, the survey should be repeated to identify any changes in this list of gas producers.

## APPENDIX A. GAS MEASUREMENT DATA AND COMPARISONSTable A-1. NO Component AnalysesGas VendorGasConc.RangeVendor-Supplied Information NO Analysis by UVaNO Analysis by FTIRTagValue(ppm NO)Uncert.(±)ReanalyzedValue(ppm)Changein Value(%)NO(ppm)Uncert.(± ppm)95% CI(ppm)RelativeCI(%)Orig TagValueDeviation(% diff)ReanalyzedValueDeviation(% diff)NO(ppm)95 % CI(ppm)RelativeCI(%)Orig TagValueDeviation(% diff)ReanalyzedValueDeviation(% diff)Air Liquide Low 54.0 0.8 ppm 54.9 1.3 0.2 0.34 - 1.6 53.83 0.43 0.80 0.3Mid 401 5 ppm 395.9 3.0 2.3 0.59 1.3 392.5 0.6 0.15 2.2High 911 10 ppmb– – – – 905 1 0.07 0.7AirgasSouthwestSpecialty GasesLow 48.90 1 % 49.89c2.0 53.4 1.9 0.3 0.51 - 8.4 - 6.5 49.93 0.35 0.70 - 2.1 - 0.1Mid 406.0 1 % 405.2 - 0.2 411.7 3.1 0.4 0.11 - 1.4 - 1.6 406.3 1.5 0.36 - 0.1 - 0.3High 900.0 1 % 909.8c1.1b– – – – – 925 2 0.24 - 2.7 - 1.6Airgas NCNSpecialty GasesLow 51.4 1 % 52.21 1.6 53.2 1.3 0.4 0.73 - 3.4 - 1.9 51.50 0.34 0.66 - 0.2 1.4Mid 388 1 % 384.6 - 0.9 387.2 3.0 0.7 0.18 0.2 - 0.7 382.4 1.4 0.36 1.5 0.6High 845 1 % 860.9c1.9b– – – – – 870 1 0.07 - 2.9 - 1.0Airgas SouthSpecialty GasesLow 50.05 1 % 51.69c3.3 52.7 1.3 0.2 0.45 - 5.1 - 2.0 51.80 0.23 0.44 - 3.4 - 0.2Mid 397.5 1 % 401 0.9 405.7 3.0 1.2 0.30 - 2.0 - 1.2 400.3 2.1 0.52 - 0.7 0.2High 900.0 1 % 900.8 0.1b– – – – – 912 2 0.19 - 1.3 - 1.2BOC Gases Low 49.8 1 % 51.5 1.3 0.4 0.83 - 3.3 50.50 0.20 0.40 - 1.4Mid 407.8 1 % 406.0d- 0.4 399.5 3.0 0.6 0.16 2.1 1.6 397.4 1.1 0.27 2.6 2.2High 900 1 % 896d- 0.4b– – – – – 880 5 0.51 2.3 1.8AGA(Linde GasGroup)Low 50.4 0.5 ppm 51.0 1.3 0.1 0.13 - 1.1 50.50 0.11 0.22 - 0.2Mid 396 4 ppm 390.2 2.4 0.2 0.06 1.5 388.3 2.4 0.61 2.0High 904 9 ppmb– – – – 903 2 0.19 0.1MathesonTri- GasLow 48.9 0.4 ppm 50.4e3.1 51.5 1.3 0.1 0.15 - 5.0 - 2.1 50.57 0.07 0.14 - 3.3 - 0.3Mid 410 1 ppm 405.1e- 1.2 401.6 3.0 1.6 0.41 2.1 0.9 397.7 0.7 0.16 3.1 1.9High 904 9 ppmb– – – – 907 2 0.25 - 0.3Messer MGIndustriesLow 50.0 0.128 ppm 50.4 1.3 0.1 0.20 - 0.9 50.00 0.20 0.40 0.0Mid 398 1.28 ppm 396.9 3.0 0.2 0.06 0.3 391.3 1.7 0.43 1.7High 888 2.99 ppmb– – – – 887 5 0.52 0.1Messer MGIndustries(Spec AirGases)Low 50.0 0.131 ppm 50.8 1.3 0.3 0.58 - 1.5 50.47 0.13 0.26 - 0.9Mid 403 1.28 ppm 399.3 2.5 0.9 0.22 0.9 396.0 2.4 0.62 1.8High 894 2.99 ppmb– – – – 904 5 0.58 - 1.1Table A-1. NO Component AnalysesGas VendorGasConc.RangeVendor-Supplied Information NO Analysis by UVaNO Analysis by FTIRTagValue(ppm NO)Uncert.(±)ReanalyzedValue(ppm)Changein Value(%)NO(ppm)Uncert.(± ppm)95% CI(ppm)RelativeCI(%)Orig TagValueDeviation(% diff)ReanalyzedValueDeviation(% diff)NO(ppm)95 % CI(ppm)RelativeCI(%)Orig TagValueDeviation(% diff)ReanalyzedValueDeviation(% diff)NationalSpecialty GasesLow 46.2 1 % 47.3f2.4 48.1 1.3 0.4 0.92 - 4.0 - 1.8 48.27 0.33 0.68 - 4.3 - 2.0Mid 398 1 % 401.3 2.5 0.6 0.14 - 0.8 397.3 1.9 0.48 0.2High 930 1 % 930 0.0b– – – – – 948 9 0.99 - 1.9 - 1.9Praxair Low 51.2 1 % 51.9 1.3 0.3 0.59 - 1.3 51.50 0.49 0.95 - 0.6Mid 406 1 % 405.1 2.5 0.4 0.11 0.2 400.6 1.00 0.25 1.3High 914 1 %b– – – – 933 1 0.07 - 2.0Scott SpecialtyGasesLow 50.0 1 % 51.0 1.3 0.3 0.63 - 1.9 50.30 0.45 0.89 - 0.6Mid 402 1 % 401.7 2.5 2.2 0.55 0.1 397.2 3.7 0.94 1.2High 911 1 %b– – – – 918 3 0.28 - 0.8Scott- Marrin,Inc.Low 50.8 0.3 ppm 51.7 1.3 0.1 0.14 - 1.8 51.77 0.24 0.46 - 1.9Mid 397 2 ppm 399.9 2.5 0.9 0.22 - 0.7 395.5 0.7 0.16 0.4High 886 5 ppmb– – – – 899 4 0.48 - 1.4Spectra Gases,Inc.Low 50.1 1 % 51.1 1.3 0.3 0.65 - 2.0 50.80 0.00 0.00 - 1.4Mid 405 1 % 404.2 2.5 0.8 0.21 0.2 400.8 1.7 0.43 1.0High 923 1 %b– – – – 934 4 0.39 - 1.2aAMETEK Model 922 UV measurements of NO were adjusted for SO2interference.bThe high-level NO evaluations were based solely on the FTIR results because the AMETEK UV NOxanalyzer setup performed by the manufacturer was not optimum for the 1000-ppm range.cGas cylinders were returned to Airgas for NO reanalyses. Vendorreported new NO values on April 26, 2004, which differed by less than 2 percent from the corresponding EPA-determined values. Inall but one case, the reanalyzed value was within ± 2 percent oforiginal tag value. No corrective action taken by the vendor.dMid- and high-level gas cylinders were returned to BOC Gases for NO reanalyses. Vendorreported new values on June 9, 2004, which differed by less than 2 percent from the corresponding EPAdetermined UV or FTIR values. The two reanalyzed NO values also differed by less than 2percent of original tag value. No corrective action was taken.eGas cylinders were returned to Matheson for NO and CO2reanalyses. Vendor reported new values on May 10, 2004, whichdiffered by less than 2 percent from the corresponding EPA-determinedvalues. Two of the three reanalyzed values differed by more than 2percent of original tag value.The NO concentrations were corrected by shifting to a wave number within a spectral region whereCO2interference is minimized. Matheson found an operator calculation error for the CO2concentration in this sample from early 2003, andimplemented data acquisition andcalculation software fortheir FTIRs in early 2004 to preclude the potential for operator errors.gGas cylinders were returned to National Specialty Gases for NO, SO2, and CO2reanalyses. Vendor reported new values on May 10, 2004, which differed by less than 2 percent from the correspondingEPA-determined values. Two of the three reanalyzed values differed by more than 2 percentof original tag value. FTIR problem was corrected during the course of the regular calibration cycle andusing a more experienced analyst.NOTE: When using data in the tables for procuring EPA Traceability Protocol gases, readers should heed the following points. First,the information in the footnotes must not be ignored. Second, if thedifference between EPA’s value and the gas vendor’s value is ± 2 percent or less, thevalues do not statistically differ because of the uncertainties in the total measurement system. Thus, a difference of2.0 percent would be interpreted as being equal to one of, for example, 0.57 percent. Finally, EPA presents this information without assigning a rating to the gasvendors, such as which vendor isapproved, or which is not approved.Table A-2. SO2Component AnalysesGas VendorGasConc.RangeVendor-Supplied Information SO2Analysis by UV SO2Analysis by FTIRTagValue(ppm SO2)Uncert.(±)ReanalyzedValue(ppm)Changein Value(%)SO2(ppm)Uncert.(± ppm)95% CI(ppm)RelativeCI(%)Orig TagValueDeviation(% diff)ReanalyzedValueDeviation(% diff)SO2(ppm)95 % CI(ppm)RelativeCI(%)Orig TagValueDeviation(% diff)ReanalyzedValueDeviation(% diff)Air Liquide Low 47.5 0.8 ppm 48.36 2.88 0.37 0.76 - 1.8 47.93 0.09 0.19 - 0.9Mid 499 4 ppm 497.17 3.13 0.76 0.15 0.4 498.5 2.3 0.45 0.1High 981 9 ppm 987.26 3.29 1.66 0.17 - 0.6 1004.5 1.5 0.15 - 2.3AirgasSouthwestSpecialty GasesLow 47.73 1 % 47.62 - 0.2 47.01 2.88 0.33 0.70 1.5 1.3 47.52 0.40 0.84 0.4 0.2Mid 496.8 1 % 500.9 0.8 492.10 3.13 3.09 0.63 1.0 1.8 501.3 0.5 0.09 - 0.9 - 0.1High 994.6 1 % 1003 0.8 994.16 3.96 5.08 0.51 0.0 0.9 1008.2 2.0 0.20 - 1.3 - 0.5Airgas NCNSpecialty GasesLow 50.4 1 % 50.05 - 0.7 49.92 2.93 0.01 0.02 1.0 0.3 49.79 0.08 0.16 1.2 0.5Mid 500 1 % 504.3 0.9 499.89 3.17 0.35 0.07 0.0 0.9 504.2 0.3 0.05 - 0.8 0.0High 1000 1 % 1002 0.2 1000.28 3.96 2.43 0.24 0.0 0.2 1006.8 2.3 0.23 - 0.7 - 0.5Airgas SouthSpecialty GasesLow 50.23 1 % 51.03 1.6 50.25 2.88 0.03 0.05 0.0 1.6 50.58 0.08 0.16 - 0.7 0.9Mid 502.8 1 % 509.2 1.3 505.89 3.14 0.39 0.08 - 0.6 0.7 507.9 0.8 0.16 - 1.0 0.3High 998.8 1 % 1012 1.3 1003.99 4.01 1.61 0.16 - 0.5 0.8 1016.1 2.7 0.27 - 1.7 - 0.4BOC Gases Low 50.9 1 % 50.52 2.70 0.15 0.29 0.8 50.83 0.32 0.63 0.1Mid 500.4 1 % 499.80 3.13 0.71 0.14 0.1 499.8 2.6 0.51 0.1High 1000 1 % 1001.47 3.96 0.31 0.03 - 0.1 1015.6 1.9 0.18 - 1.5AGA(Linde GasGroup)Low 48.7 0.5 ppm 48.67 2.70 0.13 0.28 0.1 49.54 0.12 0.24 - 1.7Mid 466 5 ppm 461.75 3.04 5.57 1.21 0.9 464.2 2.0 0.43 0.4High 956 10 ppm 955.83 3.87 2.25 0.24 0.0 967.3 0.7 0.07 - 1.2MathesonTri- GasLow 49.5 0.4 ppm 48.33 2.76 0.22 0.45 2.4 48.95 0.12 0.25 1.1Mid 504 5 ppm 502.79 3.04 1.70 0.34 0.2 503.6 1.0 0.20 0.1High 988 9 ppm 994.28 5.30 7.08 0.71 - 0.6 1006.5 1.7 0.17 - 1.8Messer MGIndustriesLow 50.1 0.507 ppm 48.89 2.70 0.23 0.46 2.5 49.26 0.36 0.73 1.7Mid 501 1.82 ppm 506.49 3.09 0.43 0.09 - 1.1 508.5 0.6 0.11 - 1.5High 1004 3.1 ppm 1018.01 5.36 2.19 0.21 - 1.4 1029.3 1.5 0.14 - 2.5Messer MGIndustries(Spec AirGases)Low 49.3 0.506 ppm 48.16 2.70 0.66 1.38 2.4 49.12 0.27 0.55 0.4Mid 496 1.82 ppm 502.94 3.04 0.66 0.13 - 1.4 504.0 1.7 0.34 - 1.6High 1004 3.1 ppm 1018.22 5.40 1.92 0.19 - 1.4 1029.8 3.3 0.32 - 2.5Table A-2. SO2Component AnalysesGas VendorGasConc.RangeVendor-Supplied Information SO2Analysis by UV SO2Analysis by FTIRTagValue(ppm SO2)Uncert.(±)ReanalyzedValue(ppm)Changein Value(%)SO2(ppm)Uncert.(± ppm)95% CI(ppm)RelativeCI(%)Orig TagValueDeviation(% diff)ReanalyzedValueDeviation(% diff)SO2(ppm)95 % CI(ppm)RelativeCI(%)Orig TagValueDeviation(% diff)ReanalyzedValueDeviation(% diff)NationalSpecialty GasesLow 51.8 1 % 51.5a- 0.6 50.49 2.75 0.22 0.44 2.6 2.0 50.64 0.19 0.38 2.3 1.7Mid 500 1 % 499.12 3.04 3.39 0.68 0.2 502.2 3.2 0.64 - 0.4High 991 1 % 992 0.1 995.74 5.30 2.35 0.24 - 0.5 - 0.4 1011.0 3.8 0.37 - 2.0 - 1.9Praxair Low 50.0 1 % 49.59 2.75 0.19 0.38 0.8 50.36 0.34 0.68 - 0.7Mid 509 1 % 506.59 2.83 3.11 0.61 0.5 511.6 0.9 0.17 - 0.5High 999 1 % 1000.59 5.31 6.58 0.66 - 0.2 1008.7 1.6 0.16 - 1.0Scott SpecialtyGasesLow 50.4 1 % 49.10 2.81 0.18 0.38 2.7 50.38 0.08 0.16 0.0Mid 503 1 % 497.63 2.83 2.63 0.53 1.1 503.0 1.9 0.37 0.0High 1011 1 % 1000.65 3.83 4.28 0.43 1.0 1021.3 0.8 0.08 - 1.0Scott-Marrin,Inc.Low 50.9 0.6 ppm 51.07 2.75 0.12 0.23 - 0.3 51.17 0.13 0.26 - 0.5Mid 504 5 ppm 502.94 2.87 0.88 0.17 0.2 507.9 0.4 0.08 - 0.8High 997 10 ppm 992.93 3.81 3.28 0.33 0.4 995.9 1.2 0.12 0.1Spectra Gases,Inc.Low 50.2 1 % 49.19 2.75 0.18 0.37 2.1 49.82 0.18 0.36 0.8Mid 495 1 % 493.05 2.83 0.85 0.17 0.4 493.1 1.0 0.21 0.4High 988 1 % 987.60 3.85 1.15 0.12 0.0 998.5 5.7 0.57 - 1.1aGas cylinders were returned to National Specialty Gases for NO, SO2, and CO2reanalyses. Vendor reported new values on May 10, 2004, which differed by less than 2 percent from the correspondingEPA-determined values. Two of the three reanalyzed values differed by more than 2 percentof original tag value. An FTIR problem was corrected during the course of the regular calibration cycle andby using a more experienced analyst.NOTE: When using data in the tables for procuring EPA Traceability Protocol gases, readers should heed the following points. First,the information in the footnotes must not be ignored. Second, if thedifference between EPA’s value and the gas vendor’s value is ± 2 percent or less, thevalues do not statistically differ because of the uncertainties in the total measurement system. Thus, a difference of2.0 percent would be interpreted as being equal to one of, for example, 0.57 percent. Finally, EPA presents this information without assigning a rating to the gasvendors, such as which vendor isapproved, or which is not approved.Table A-3. CO2Component AnalysesGas VendorGasConc.RangeVendor-Supplied Information CO2Analysis by NDIR CO2Analysis by FTIRTagValue(ppm CO2)Uncert.(±)Reanalyzed Value(% CO2)Changein Value(%)CO2(%)Uncert.(± % CO2)95 % CI(% CO2)RelativeCI(%)Orig TagValueDeviation(% diff)Reanalyzed ValueDeviation(% diff)CO2(%)95 % CI(% CO2)RelativeCI(%)Orig TagValueDeviation(% diff)ReanalyzedValueDeviation(% diff)Air Liquide Low 4.97 0.06 % CO25.02 0.07 0.01 0.12 - 1.0 4.991 0.027 0.54 - 0.4Mid 12.1 0.1 % CO212.09 0.11 0.02 0.18 0.1 11.98 0.08 0.63 1.0High 17.7 0.2 % CO217.9a1.1 18.15 0.17 0.01 0.08 - 2.5 - 1.4b––– –AirgasSouthwestSpecialty GasesLow 5.011 1 % 5.045 0.7 4.97 0.07 0.01 0.26 0.8 1.5 4.984 0.039 0.78 0.5 1.2Mid 12.0 1 % 11.95 - 0.4 12.07 0.11 0.01 0.11 - 0.6 - 1.0 12.06 0.07 0.56 - 0.5 - 0.9High 17.99 1 % 17.97 - 0.1 18.09 0.17 0.01 0.04 - 0.6 - 0.7b––– –Airgas NCNSpecialty GasesLow 5.01 1 % 5.064 1.1 5.00 0.07 0.01 0.10 0.2 1.3 4.970 0.020 0.40 0.8 1.9Mid 12.0 1 % 11.94 - 0.5 12.07 0.11 0.01 0.09 - 0.6 - 1.1 12.04 0.10 0.84 - 0.3 - 0.8High 18.0 1 % 18.06 0.3 18.15 0.17 0.00 0.01 - 0.8 - 0.5b––– –Airgas SouthSpecialty GasesLow 5.041 1 % 5.057 0.3 5.01 0.07 0.01 0.22 0.7 1.0 4.998 0.008 0.16 0.9 1.2Mid 12.0 1 % 11.88 - 1.0 12.05 0.11 0.01 0.09 - 0.4 - 1.4 12.17 0.04 0.30 - 1.4 - 2.4High 18.07 1 % 18.15 0.4 18.18 0.17 0.02 0.11 - 0.6 - 0.2b––– –BOC Gases Low 5.0 1 % 4.98 0.07 0.01 0.22 0.5 4.973 0.031 0.62 0.5Mid 11.98 1 % 12.05 0.11 0.01 0.06 - 0.6 11.94 0.05 0.44 0.3High 18.02 1 % 18.14 0.17 0.01 0.06 - 0.7b–––AGA(Linde GasGroup)Low 5.2 0.5 % CO25.22 0.07 0.01 0.17 - 0.5 5.146 0.004 0.08 1.0Mid 12.5 0.1 % CO212.68 0.12 0.01 0.04 - 1.4 12.45 0.05 0.38 0.4High 18.3 0.2 % CO218.53 0.17 0.02 0.08 - 1.2b–––MathesonTri-GasLow 5.23 0.05 % CO24.94c- 5.5 4.99 0.07 0.01 0.28 4.8 - 1.0 4.979 0.006 0.12 5.0 - 0.8Mid 12.2 0.1 % CO212.06 0.11 0.01 0.11 1.2 11.93 0.04 0.30 2.3High 17.9 0.1 % CO218.07 0.17 0.00 0.02 - 0.9b–––Messer MGIndustriesLow 5.05 0.0444 % CO25.08 0.07 0.01 0.23 - 0.5 5.023 0.007 0.14 0.5Mid 12.1 0.0501 % CO212.22 0.11 0.02 0.13 - 1.0 12.18 0.06 0.49 - 0.7High 18.2 0.0501 % CO218.27 0.17 0.00 0.02 - 0.4b–––Messer MGIndustries(Spec AirGases)Low 5.07 0.04444 % CO25.09 0.07 0.01 0.12 - 0.5 5.053 0.010 0.20 0.3Mid 12.1 0.0501 % CO212.22 0.11 0.01 0.10 - 1.0 12.18 0.04 0.30 - 0.7High 18.3 0.0501 % CO218.31 0.17 0.00 0.01 - 0.1b–––NationalSpecialty GasesLow 4.9 1 % 4.9 0.0 4.87 0.06 0.01 0.11 0.6 0.6 4.885 0.032 0.66 0.3 0.3Mid 12.0 1 % 11.97 0.11 0.01 0.08 0.3 12.09 0.06 0.48 - 0.7High 17.8 1 % 18.23d2.4 18.30 0.17 0.01 0.04 - 2.8 - 0.4b––– –Table A-3. CO2Component AnalysesGas VendorGasConc.RangeVendor-Supplied Information CO2Analysis by NDIR CO2Analysis by FTIRTagValue(ppm CO2)Uncert.(±)Reanalyzed Value(% CO2)Changein Value(%)CO2(%)Uncert.(± % CO2)95 % CI(% CO2)RelativeCI(%)Orig TagValueDeviation(% diff)Reanalyzed ValueDeviation(% diff)CO2(%)95 % CI(% CO2)RelativeCI(%)Orig TagValueDeviation(% diff)ReanalyzedValueDeviation(% diff)Praxair Low 5.00 1 % 5.03 0.06 0.00 0.05 - 0.6 4.986 0.014 0.28 0.3Mid 12.18 1 % 12.17 0.11 0.02 0.16 0.1 12.23 0.02 0.12 - 0.4High 17.59 1 % 17.82e1.3 17.85 0.13 0.01 0.06 - 1.5 - 0.2b––– –Scott SpecialtyGasesLow 5.04 1 % 5.01 0.06 0.00 0.03 0.6 4.987 0.020 0.40 1.1Mid 12.10 1 % 12.04 0.11 0.01 0.07 0.5 12.18 0.03 0.25 - 0.7High 17.97 1 % 18.03 0.17 0.01 0.07 - 0.3b–––Scott-Marrin,Inc.Low 5.11 0.05 % CO25.09 0.06 0.00 0.03 0.4 5.046 0.032 0.63 1.3Mid 12.02 0.02 % CO212.11 0.11 0.01 0.07 - 0.7 12.07 0.07 0.55 - 0.4High 17.92 0.05 % CO218.13 0.17 0.02 0.12 - 1.2b–––Spectra Gases,Inc.Low 5.02 1 % 5.01 0.06 0.01 0.13 0.1 5.003 0.015 0.30 0.3Mid 12.03 1 % 12.10 0.11 0.01 0.07 - 0.5 12.24 0.01 0.10 - 1.7High 18.07 1 % 18.08 0.17 0.01 0.05 0.0b–––aHigh-range gas cylinder was returned to Air Liquide for CO2reanalysis. Vendor reported a new CO2value of 17.9 percent on May 6, 2004, which differs by less than ± 2 percent from the EPAdetermined value. Reanalyzed value is also within ± 2 percent oforiginal tag value. No corrective action taken by the vendor.bThe high-level CO2evaluations were based solely on the NDIR results because theFTIR data obtained at this concentration level were not supported by an SRM; insufficient high-level CO2SRM orNTRM was available to providereference spectra for the FTIR.cGas cylinders were returned to Matheson for NO and CO2reanalyses. Vendor reported new values on May 10, 2004, whichdiffered by less than ± 2 percent from the corresponding EPA-determinedvalues. Two of the three reanalyzed values differed by more than ±2 percent of original tag value. The NO concentrations werecorrected by shifting to a wave number within a spectral region whereCO2interference is minimized. Matheson found an operator calculation error for the CO2concentration in this sample from early 2003, and implemented data acquisition andcalculation software fortheir FTIRs in early 2004 to preclude the potential for operator errors.dGas cylinders were returned to National Specialty Gases for NO, SO2, and CO2reanalyses. Vendor reported new values on May 10, 2004,which differed by less than ± 2 percent from thecorresponding EPA-determined values. Two of thethree reanalyzed values differed by morethan ± 2 percent of original tag value. FTIR problem was corrected during the course of the regularcalibration cycle and using a more experienced analyst.eHigh-range gas cylinder was returned to Praxair for CO2reanalysis based on an initial EPA finding of 18.07 percent CO2. Vendor reported a new CO2value of 17.82 percent on May 27, 2004. Praxairhad an independent, third-party laboratory (Scott-Marin, Inc.) analyze the cylinder, resulting in 17.77 percent CO2. Praxair also sent the cylinder to NISTfor analysis, resulting in 17.85 percent CO2. Allof the reanalyzed values differed by less than 2.0 percent fromthe EPA-determined value. The original tag value was within 2.0percent of each of the reanalyzedvalues. The original tag value andthe vendor reanalyzed value were within 2.0 percent of the NIST-generated "true" value. Therefore, no corrective action was required.NOTE: When using data in the tables forprocuring EPA Traceability Protocol gases,readers should bear in mind the following points. First, the information in thefootnotes may be important and shouldnot be ignored. Second, if the difference between EPA’s value and the gas vendor’s value differs by± 2 percent or less, then (because of the uncertainties in the total measurement system) statisticallythere is no difference between the two values. Thus, a difference of 2.0 percent would be interpreted as being equal to one of,for example, 0.57 percent. Third, EPA presents this information withoutassigning a rating to the gas vendors, for example, who is the best, who is approved, or who is not approved.Table A-4. MACTEC Analysis DataGas VendorGasConc.RangeNO Analysis by UV SO2Analysis by UV CO2Analysis by NDIRRun 1(ppm)Run 2(ppm)Run 3(ppm)Avg.(ppm)CorrAvg.(ppm) sd95 %CIRun 1(ppm)Run 2(ppm)Run 3(ppm)Avg.(ppm) sd95 %CIRun 1(%)Run 2(%)Run 3(%)Avg.(%) sd95 %CIAir Liquide Low 56.25 55.97 55.97 56.1 54.9 0.16 0.19 48.01 48.65 48.42 48.36 0.33 0.37 5.03 5.02 5.02 5.02 0.01 0.01Mid 397.05 392.96 395.44 395.1 395.9 2.06 2.33 496.63 496.96 497.92 497.17 0.67 0.76 12.07 12.09 12.11 12.09 0.02 0.02High 860.32 859.81 859.40 859.8 889.5 0.46 0.52 985.63 987.67 988.48 987.26 1.47 1.66 18.16 18.15 18.13 18.15 0.01 0.01AirgasSouthwestSpecialty GasesLow 54.71 54.24 54.59 54.5 53.4 0.24 0.27 46.91 47.33 46.77 47.01 0.29 0.33 4.96 4.98 4.98 4.97 0.01 0.01Mid 410.74 410.51 409.99 410.4 411.7 0.39 0.44 489.19 492.51 494.61 492.10 2.73 3.09 12.06 12.07 12.09 12.07 0.01 0.01High 880.90 880.39 881.25 880.8 912.5 0.43 0.49 989.04 996.04 997.40 994.16 4.49 5.08 18.09 18.10 18.09 18.09 0.01 0.01Airgas NCNSpecialty GasesLow 54.71 54.31 54.02 54.3 53.2 0.34 0.39 49.92 49.93 49.91 49.92 0.01 0.01 5.00 5.00 4.99 5.00 0.00 0.01Mid 387.23 386.01 386.62 386.6 387.2 0.61 0.69 499.53 500.07 500.07 499.89 0.31 0.35 12.06 12.08 12.07 12.07 0.01 0.01High 836.38 839.38 838.08 837.9 865.5 1.50 1.70 998.85 999.23 1002.75 1000.28 2.15 2.43 18.15 18.15 18.15 18.15 0.00 0.00Airgas SouthSpecialty GasesLow 53.80 54.09 53.69 53.9 52.7 0.21 0.24 50.22 50.25 50.27 50.25 0.02 0.03 5.02 5.00 5.00 5.01 0.01 0.01Mid 405.78 404.45 403.66 404.6 405.7 1.07 1.21 505.56 505.86 506.24 505.89 0.34 0.39 12.04 12.05 12.06 12.05 0.01 0.01High 870.18 869.09 869.75 869.7 900.2 0.55 0.62 1003.10 1005.63 1003.25 1003.99 1.42 1.61 18.19 18.18 18.16 18.18 0.02 0.02BOC Gases Low 53.05 52.33 52.50 52.6 51.5 0.38 0.43 50.66 50.44 50.45 50.52 0.13 0.15 4.99 4.97 4.97 4.98 0.01 0.01Mid 397.98 398.93 398.98 398.6 399.5 0.56 0.64 499.08 500.22 500.10 499.80 0.63 0.71 12.05 12.06 12.05 12.05 0.01 0.01High 838.89 836.86 836.45 837.4 864.9 1.30 1.48 1001.16 1001.68 1001.56 1001.47 0.27 0.31 18.15 18.14 18.13 18.14 0.01 0.01AGA(Linde GasGroup)Low 52.05 52.10 51.99 52.0 51.0 0.06 0.07 48.57 48.64 48.80 48.67 0.12 0.13 5.23 5.23 5.22 5.22 0.01 0.01Mid 389.75 389.34 389.50 389.5 390.2 0.21 0.23 456.20 463.49 465.56 461.75 4.92 5.57 12.68 12.68 12.68 12.68 0.00 0.01High 867.32 866.90 869.00 867.7 898.1 1.11 1.26 953.67 956.23 957.59 955.83 1.99 2.25 18.55 18.53 18.52 18.53 0.01 0.02Matheson TriGasLow 52.67 52.55 52.55 52.6 51.5 0.07 0.08 48.14 48.52 48.32 48.33 0.19 0.22 5.00 4.99 4.98 4.99 0.01 0.01Mid 402.30 400.02 399.61 400.6 401.6 1.45 1.64 501.68 502.20 504.49 502.79 1.50 1.70 12.07 12.05 12.05 12.06 0.01 0.01High 870.68 870.76 871.86 871.1 901.8 0.66 0.75 987.12 997.03 998.70 994.28 6.26 7.08 18.06 18.07 18.07 18.07 0.00 0.00Messer MGIndustriesLow 51.59 51.42 51.54 51.5 50.4 0.09 0.10 48.66 49.05 48.95 48.89 0.20 0.23 5.09 5.07 5.07 5.08 0.01 0.01Mid 396.27 396.12 395.86 396.1 396.9 0.21 0.24 506.05 506.68 506.74 506.49 0.38 0.43 12.23 12.22 12.21 12.22 0.01 0.02High 851.47 851.96 851.55 851.7 880.5 0.27 0.30 1015.82 1018.71 1019.49 1018.01 1.93 2.19 18.27 18.27 18.27 18.27 0.00 0.00Messer MGIndustries(Spec AirGases)Low 52.14 51.64 51.76 51.8 50.8 0.26 0.30 47.50 48.35 48.63 48.16 0.59 0.66 5.10 5.09 5.09 5.09 0.01 0.01Mid 399.24 397.82 398.03 398.4 399.3 0.76 0.86 502.30 503.05 503.46 502.94 0.59 0.66 12.23 12.22 12.21 12.22 0.01 0.01High 857.83 857.66 857.00 857.5 886.9 0.44 0.50 1016.29 1019.50 1018.87 1018.22 1.70 1.92 18.31 18.32 18.31 18.31 0.00 0.00Table A-4. MACTEC Analysis DataGas VendorGasConc.RangeNO Analysis by UV SO2Analysis by UV CO2Analysis by NDIRRun 1(ppm)Run 2(ppm)Run 3(ppm)Avg.(ppm)CorrAvg.(ppm) sd95 %CIRun 1(ppm)Run 2(ppm)Run 3(ppm)Avg.(ppm) sd95 %CIRun 1(%)Run 2(%)Run 3(%)Avg.(%) sd95 %CINationalSpecialty GasesLow 49.58 49.18 48.80 49.2 48.1 0.39 0.44 50.69 50.49 50.30 50.49 0.19 0.22 4.88 4.87 4.87 4.87 0.00 0.01Mid 399.92 400.29 400.93 400.4 401.3 0.51 0.58 495.71 500.33 501.32 499.12 3.00 3.39 11.98 11.97 11.96 11.97 0.01 0.01High 897.19 895.81 895.81 896.3 929.4 0.80 0.90 993.36 997.19 996.68 995.74 2.08 2.35 18.31 18.30 18.30 18.30 0.01 0.01Praxair Low 53.12 53.12 52.65 53.0 51.9 0.27 0.31 49.75 49.59 49.42 49.59 0.17 0.19 5.03 5.03 5.03 5.03 0.00 0.00Mid 404.46 403.71 403.91 404.0 405.1 0.39 0.44 503.65 507.03 509.09 506.59 2.75 3.11 12.19 12.17 12.15 12.17 0.02 0.02High 894.44 894.52 895.30 894.8 927.8 0.48 0.54 994.02 1005.07 1002.68 1000.59 5.81 6.58 18.05 18.11 18.05 18.07 0.03 0.04Scott SpecialtyGasesLow 52.10 52.33 51.76 52.1 51.0 0.29 0.32 48.92 49.14 49.23 49.10 0.16 0.18 5.01 5.01 5.01 5.01 0.00 0.00Mid 398.45 401.86 401.81 400.7 401.7 1.95 2.21 495.44 497.39 500.07 497.63 2.32 2.63 12.05 12.04 12.03 12.04 0.01 0.01High 871.86 871.94 871.94 871.9 902.7 0.05 0.05 996.88 1000.62 1004.44 1000.65 3.78 4.28 18.03 18.03 18.01 18.03 0.01 0.01Scott-Marrin,Inc.Low 52.89 52.78 52.78 52.8 51.7 0.06 0.07 50.96 51.16 51.10 51.07 0.10 0.12 5.09 5.09 5.09 5.09 0.00 0.00Mid 398.45 398.66 399.87 399.0 399.9 0.76 0.86 502.25 502.78 503.77 502.94 0.77 0.88 12.12 12.11 12.10 12.11 0.01 0.01High 872.62 869.75 869.41 870.6 901.2 1.76 1.99 989.94 993.10 995.73 992.92 2.90 3.28 18.15 18.13 18.11 18.13 0.02 0.02Spectra Gases,Inc.Low 52.54 52.15 51.97 52.2 51.1 0.30 0.33 49.05 49.15 49.37 49.19 0.16 0.18 5.02 5.01 5.01 5.01 0.01 0.01Mid 402.40 403.08 403.90 403.1 404.2 0.75 0.85 492.20 493.33 493.61 493.05 0.75 0.85 12.10 12.09 12.09 12.10 0.01 0.01High 887.13 887.64 887.99 887.6 919.9 0.43 0.49 986.48 987.86 988.46 987.60 1.02 1.15 18.09 18.08 18.07 18.08 0.01 0.01Table A-5. Spectral Insights’ Analysis DataGas VendorGasConc.RangeNO Analysis by FTIR SO2Analysis by FTIR CO2Analysis by FTIRRun 1(ppm)Run 2(ppm)Run 3(ppm)Avg.(ppm) sd95 %CIRun 1(ppm)Run 2(ppm)Run 3(ppm)Avg.(ppm) sd95 %CIRun 1(%)Run 2(%)Run 3(%)Avg.(%) sd95 %CIAir Liquide Low 54.10 54.00 53.40 53.8 0.38 0.43 47.91 48.02 47.86 47.93 0.08 0.09 4.999 5.010 4.965 4.991 0.023 0.027Mid 392.40 393.00 392.00 392.5 0.50 0.57 500.8 497.7 497.1 498.5 1.99 2.25 12.05 11.92 11.96 11.98 0.067 0.075High 905.00 906.00 905.00 905.3 0.58 0.65 1005.7 1004.8 1003.1 1004.5 1.32 1.49 17.55 17.47 17.42 17.48 0.066 0.074AirgasSouthwestSpecialty GasesLow 50.00 50.20 49.60 49.9 0.31 0.35 47.92 47.33 47.30 47.52 0.35 0.40 5.021 4.977 4.953 4.984 0.034 0.039Mid 407.60 405.10 406.30 406.3 1.25 1.41 501.0 501.3 501.8 501.4 0.40 0.46 12.05 12.00 12.12 12.06 0.060 0.068High 927.00 923.00 925.00 925.0 2.00 2.26 1006.4 1008.1 1010.0 1008.2 1.80 2.04 17.80 17.69 17.58 17.69 0.110 0.124Airgas NCNSpecialty GasesLow 51.20 51.80 51.50 51.5 0.30 0.34 49.71 49.82 49.83 49.79 0.07 0.08 4.968 4.988 4.953 4.970 0.018 0.020Mid 383.70 381.30 382.10 382.4 1.22 1.38 504.0 504.0 504.4 504.1 0.23 0.26 12.13 11.96 12.04 12.04 0.085 0.096High 871.00 870.00 870.00 870.3 0.58 0.65 1006.4 1005.0 1009.0 1006.8 2.03 2.30 17.98 17.89 17.92 17.93 0.046 0.052Airgas SouthSpecialty GasesLow 51.60 52.00 51.80 51.8 0.20 0.23 50.66 50.52 50.56 50.58 0.07 0.08 5.006 4.992 4.997 4.998 0.007 0.008Mid 402.70 399.20 398.90 400.3 2.11 2.39 507.1 508.1 508.5 507.9 0.72 0.82 12.18 12.19 12.13 12.17 0.032 0.036High 912.00 914.00 911.00 912.3 1.53 1.73 1017.5 1013.3 1017.5 1016.1 2.42 2.74 17.79 17.88 17.93 17.87 0.071 0.080BOC Gases Low 50.60 50.60 50.30 50.5 0.17 0.20 50.99 51.00 50.50 50.83 0.29 0.32 4.980 4.996 4.942 4.973 0.028 0.031Mid 398.00 396.10 398.00 397.4 1.10 1.24 498.5 502.4 498.5 499.8 2.25 2.55 11.99 11.93 11.90 11.94 0.046 0.052High 880.00 876.00 884.00 880.0 4.00 4.53 1014.5 1014.8 1017.5 1015.6 1.65 1.87 17.32 17.45 17.44 17.40 0.072 0.082AGA(Linde GasGroup)Low 50.60 50.50 50.40 50.5 0.10 0.11 49.56 49.42 49.63 49.54 0.11 0.12 5.146 5.142 5.149 5.146 0.004 0.004Mid 390.00 386.00 389.00 388.3 2.08 2.36 463.0 463.3 466.2 464.2 1.77 2.00 12.48 12.40 12.46 12.45 0.042 0.047High 905.00 903.00 902.00 903.3 1.53 1.73 968.0 966.9 967.1 967.3 0.59 0.66 18.20 18.21 18.23 18.21 0.015 0.017MathesonTri-GasLow 50.60 50.60 50.50 50.6 0.06 0.07 49.07 48.86 48.92 48.95 0.11 0.12 4.985 4.977 4.974 4.979 0.006 0.006Mid 398.00 398.00 397.00 397.7 0.58 0.65 503.0 503.1 504.6 503.6 0.90 1.01 11.97 11.91 11.92 11.93 0.032 0.036High 909.00 907.00 905.00 907.0 2.00 2.26 1005.5 1005.8 1008.3 1006.5 1.54 1.74 17.93 17.97 18.02 17.97 0.045 0.051Messer MGIndustriesLow 49.80 50.10 50.10 50.0 0.17 0.20 48.90 49.37 49.51 49.26 0.32 0.36 5.026 5.016 5.027 5.023 0.006 0.007Mid 392.90 390.00 391.00 391.3 1.47 1.67 508.1 508.3 509.1 508.5 0.53 0.60 12.19 12.12 12.22 12.18 0.051 0.058High 891.00 886.00 883.00 886.7 4.04 4.57 1030.1 1030.0 1027.8 1029.3 1.30 1.47 17.69 17.69 17.67 17.68 0.012 0.013Messer MGIndustries(Spec AirGases)Low 50.40 50.40 50.60 50.5 0.12 0.13 49.32 48.86 49.19 49.12 0.24 0.27 5.063 5.050 5.047 5.053 0.009 0.010Mid 398.50 394.90 394.50 396.0 2.20 2.49 502.3 505.0 504.8 504.0 1.50 1.70 12.15 12.18 12.21 12.18 0.030 0.034High 909.00 901.00 901.00 903.7 4.62 5.23 1026.4 1031.6 1031.4 1029.8 2.95 3.33 17.29 17.27 17.25 17.27 0.020 0.023Table A-5. Spectral Insights’ Analysis DataGas VendorGasConc.RangeNO Analysis by FTIR SO2Analysis by FTIR CO2Analysis by FTIRRun 1(ppm)Run 2(ppm)Run 3(ppm)Avg.(ppm) sd95 %CIRun 1(ppm)Run 2(ppm)Run 3(ppm)Avg.(ppm) sd95 %CIRun 1(%)Run 2(%)Run 3(%)Avg.(%) sd95 %CINationalSpecialty GasesLow 48.60 48.10 48.10 48.3 0.29 0.33 50.45 50.72 50.76 50.64 0.17 0.19 4.905 4.897 4.853 4.885 0.028 0.032Mid 399.10 397.10 395.70 397.3 1.71 1.93 499.0 503.5 504.2 502.2 2.82 3.19 12.04 12.14 12.11 12.10 0.051 0.058High 945.00 957.00 941.00 947.7 8.33 9.42 1013.7 1012.1 1007.3 1011.0 3.33 3.77 17.74 17.87 17.87 17.83 0.075 0.085Praxair Low 52.00 51.20 51.30 51.5 0.44 0.49 50.37 50.66 50.06 50.36 0.30 0.34 4.980 5.000 4.978 4.986 0.012 0.014Mid 401.60 400.30 399.80 400.6 0.93 1.05 510.8 511.8 512.3 511.6 0.76 0.86 12.22 12.24 12.21 12.22 0.015 0.017High 933.00 933.00 932.00 932.7 0.58 0.65 1009.6 1007.1 1009.4 1008.7 1.39 1.57 17.84 17.83 17.86 17.84 0.015 0.017Scott SpecialtyGasesLow 50.30 50.70 49.90 50.3 0.40 0.45 50.34 50.46 50.33 50.38 0.07 0.08 4.998 4.996 4.966 4.987 0.018 0.020Mid 401.00 395.90 394.80 397.2 3.31 3.74 501.2 503.5 504.4 503.0 1.65 1.87 12.15 12.20 12.18 12.18 0.025 0.028High 921.00 917.00 917.00 918.3 2.31 2.61 1020.5 1021.7 1021.7 1021.3 0.69 0.78 17.22 17.19 17.19 17.20 0.017 0.020Scott-Marrin,Inc.Low 51.60 51.70 52.00 51.8 0.21 0.24 51.17 51.29 51.06 51.17 0.12 0.13 5.072 5.051 5.016 5.046 0.028 0.032Mid 396.10 395.30 395.00 395.5 0.57 0.64 507.5 508.2 507.8 507.8 0.35 0.40 12.14 12.03 12.05 12.07 0.059 0.066High 902.60 898.50 895.00 898.7 3.80 4.30 995.7 997.1 995.0 995.9 1.07 1.21 18.05 18.03 18.06 18.05 0.015 0.017Spectra Gases,Inc.Low 50.80 50.80 50.80 50.8 0.00 0.00 49.96 49.85 49.65 49.82 0.16 0.18 5.016 4.989 5.004 5.003 0.014 0.015Mid 402.40 400.40 399.40 400.7 1.53 1.73 492.3 492.9 494.1 493.1 0.92 1.04 12.26 12.24 12.24 12.25 0.012 0.013High 935.00 930.00 936.00 933.7 3.21 3.64 999.8 992.9 1002.7 998.5 5.03 5.70 17.33 17.23 17.30 17.29 0.051 0.058