ASTM D6277-99

7.Apparatus

7.1Mid-IR Spectrometric Analyzer (of one of the following

types):

7.1.1Filter-based Mid-IR Test Apparatus —The type of

apparatus suitable for use in this test method minimally

employes an IR source,an infrared transmission cell or a liquid

attenuated total internal reflection cell,wavelength discrimi-

nating filters,a chopper wheel,a detector,an A-D converter,a

microprocessor,and a method to introduce the sample.The

frequencies and bandwidths of the filters are specified in Table

1.

7.1.2Fourier Transform Mid-IR Spectrometer —The type of

apparatus suitable for use in this test method employs an IR

source,an infrared transmission cell or a liquid attenuated total

internal reflection cell,a scanning interferometer,a detector,an

A-D converter,a microprocessor,and a method to introduce

the sample.The following performance specifications (through

the ATR cell)must be met:

scan range 4000to 600cm –1

resolution 4cm –1

S/N at 674cm –1>300:1RMS

The signal to noise level will be established by taking a

single beam spectrum using air or nitrogen as the reference and

declaring that spectrum as the background.The background

single beam spectrum obtained can be the average of multiple

FTIR scans,but the total collection time shall not exceed 60s.

If interference from water vapor or carbon dioxide is a

problem,the instrument shall be purged with dry air or

nitrogen.A subsequent single beam spectrum shall be taken

under the same conditions and ratioed to the background

spectrum.The RMS noise of the ratioed spectra,the 100%

line,shall not exceed 0.3%transmittance in the region from

700to 6cm –1.

7.2Absorption Cell —The absorption cell can be either

transmission or attenuated total reflectance.

7.2.1Transmission Cells ,shall have windows of potassium

bromide,zinc selenide,or other material having a significant

transmission from 712cm –1to 660cm –1.The cell path length

of the transmission cell shall be 0.025(+/–0.005)mm.The use

of a wedged transmission cell with the same nominal path

length is acceptable.

7.2.2Attenuated Total Reflectance (ATR)Cells ,shall have

the following specifications:

ATR element material ZnSe beam condensing optics conical,non-focussing optics integral to cell body element configuration circular cross section with coaxial conical ends cone half angle 60°element length 1.55in.element diameter 0.125in.angle of incidence at sample interface 53.8°maximum range of incidence angles +/–1.5°standard absorbance (1428cm−1band of acetone)0.38+/–0.02AU material of construction 316stainless steel seals Chemraz or Kalraz o-rings 8.Reagents and Materials (see Note 1and Note 2)8.1Standards for Calibration,Qualification,and Quality Control Check Standards —Use of chemicals of at least 99%purity,where available,for quality control checks is required when preparing samples.8.1.1tert -Amyl methyl ether,TAME [994-05-8].8.1.2Benzene [1076-43-3].8.1.3tert -Butyl ethyl ether,ETBE [637-92-3].8.1.4tert -Butyl methyl ether,MTBE [1634-04-4].8.1.51,3Dimethylbenzene (m -xylene).8.1.6Ethanol [-17-5].8.1.7Ethylbenzene [100-41-4].8.1.83–Ethyltoluene [620-14-4].8.1.9Heavy aromatic/reformate petroleum stream (high boiling cut:IPB of 150+/−5°C and EP of 245+/−8°C)certified to contain less than 0.025%benzene (an absorbance of less than 0.03at 675cm −1using a 0.2mm cell and a baseline between approximately 680cm −1and 670cm −1)[741-68-0].8.1.10Hexane (an absorbance versus water of less than 0.1at 250nm using a 1cm cell)[110-54-3].8.1.112,2,4-Trimethylpentane (iso octane)[540-84-1].8.1.12Pentane (an absorbance versus water of less than 0.1at 250nm using a 1cm cell)[109-66-0].8.1.13Propylbenzene [103-65-1].8.1.14Toluene [108-88-3].8.1.151,3,5-Trimethylbenzene (mesitylene)[108-67-8].8.1.16m -Xylene [108-38-3].N OTE 1—Warning:These materials are flammable and may be harmful if ingested or inhaled.N OTE 2—Only some of the reagents are required in each calibration or qualification procedure.9.Sampling and Sample Handling 9.1General Requirements :9.1.1The sensitivity of the measurement of benzene to the loss of benzene or other components through evaporation and the resulting changes in composition is such that the utmost precaution and the most meticulous care in the drawing and handling of samples is required.9.1.2Fuel samples to be analyzed by the test method shall be sampled using procedures outlined in Practices D 4057,D 4177,or D 5842,where appropriate.Do not use the “Sam-pling by Water Displacement.”With some alcohol containing samples,the alcohol will dissolve in the water phase.9.1.3Protect samples from excessive temperatures prior to testing.This can be accomplished by storage in an appropriate

TABLE 1Specification for Filters Used in Filter-based Mid-IR Test

Center Wavenumber Bandwidth (in wavelength units)

(+/−0.15%of wavenumber)(full width at half height)

673cm -11%of l c

729cm -11%of l c

769cm -11%of l c

1205cm -11%of l c

1054cm -11%of l c

1188cm -11%of l c

1117cm -11%of l

c

ice bath or refrigerator at 0to 5°C.

9.1.4Do not test samples stored in leaky containers.Discard

and obtain a new sample if leaks are detected.

9.2Sample Handling During Analysis:

9.2.1When analyzing samples by the mid infrared appara-

tus,the sample must be between a temperature of 15to 38°C.

Equilibrate all samples to the temperature of the laboratory (15

to 38°C)prior to analysis by this test method.

9.2.2After analysis,if the sample is to be saved,reseal the

container and store the sample in an ice bath or a refrigerator

at 0to 5°C.

10.Calibration and Standardization of the Apparatus

10.1Calibration Matrix —Calibration standards shall be prepared in accordance with Practice D 4307or appropriately scaled for larger blends and Practices D 5842and D 5854,where appropriate.Whenever possible,use chemicals of at least 99%purity.To minimize the evaporation of light components,chill all chemicals and fuels used to prepare standards.10.1.1Calibration Matrix for Filter Based Mid IR Instruments —Prepare the set of calibration standards as de-fined in Table 2.

TABLE 2Filter Based Mid IR Instrument Calibration Sample Set (mass %)

Sample

Benzene Toluene Xylenes Hvy.Ref.A MTBE EtOH TAME ETBE Isooctane C 5C 6B 1

0.00 2.5012.5 5.000.0000.020.00.0030.030.02

0.00 2.5025.0 2.500.000.000.000.0035.035.03

0.00 5.007.5010.0 1.000.00 2.5015.025.034.04

0.0012.512.5 3.0020.00.00 2.500.0025.024.55

0.0020.010.0 1.000.0010.000.000.0025.034.06

0.0025.07.50 2.500.000.000.000.0040.025.07

0.0025.0 2.507.500.00 4.000.000.0020.041.08

0.250.0010.0 5.000.000.000.0020.0025.039.759

0.25 2.50 6.00 2.500.000.000.000.0035.053.7510

0.25 4.7515.0 1.000.007.500.000.0025.046.5011

0.2510.00.0010.015.000.000.000.0030.034.7512

0.2514.07.50 3.000.00 5.000.000.0030.040.2513

0.50 2.5012.5 5.00 5.000.00 5.00 5.0020.044.514

0.50 5.0010.0 2.000.000.000.000.0030.042.515

0.50 6.007.507.500.000.0020.00.0025.033.516

0.5010.015.0 2.500.0012.50.000.0025.034.517

0.5012.5 4.007.500.000.000.0020.020.035.518

0.5025.010.0 1.000.000.000.000.0025.038.519

0.75 5.0025.0 1.000.000.000.000.0030.038.2520

0.7510.010.0 5.000.000.000.000.0030.044.2521

0.7512.50.0010.00.00 5.000.000.0035.036.7522

0.7512.512.5 1.000.000.000.000.0030.043.2523

0.7525.020.010.00.000.000.000.0014.2530.024

1.0015.0025.0 1.007.500.0015.0

2.5010.02

3.025

1.00 5.007.5010.00.00

2.000.000.0035.039.526

1.007.5010.07.5020.000.000.000.0020.034.027

1.0010.010.0 5.000.0010.00.000.0030.034.028

1.0015.0

2.00 2.515.00.00 2.507.5020.037.029

1.0025.020.00.000.000.000.000.0025.029.030

1.50 5.0015.0 5.00 5.000.0010.00 5.0020.033.531

1.5015.015.0 1.000.000.00 5.0020.020.02

2.532

1.5015.015.0 1.000.000.000.000.0030.037.533

1.5010.0 5.007.500.007.500.00

2.5025.041.034

1.5025.010.00.000.000.000.000.0025.038.535

2.00 5.007.50 2.507.500.00 2.50 2.0030.041.036

2.00 5.0020.00.000.000.000.000.0030.04

3.037

2.0012.512.5 5.000.008.000.000.0025.0035.038

2.0025.0 5.00

3.0020.000.000.000.0020.025.039

2.0025.020.00.000.000.000.000.0020.03

3.040

2.500.0015.0 2.500.000.0015.00.0025.040.041

2.50 5.00 5.0010.015.00.000.000.0025.037.542

2.5015.00.007.500.0010.00.000.0030.035.043

2.5010.015.0 2.50.000.000.0015.025.030.044

2.5020.020.0

3.000.000.000.000.0025.029.545

3.00 5.0025.0 5.000.000.007.507.5020.027.046

3.0010.015.0 5.000.007.500.007.5020.032.047

3.0015.0 5.00 2.00 2.500.0010.0 2.5025.035.048

3.0020.020.0 5.000.000.000.000.0025.027.049

3.0025.010.0 2.000.000.000.000.0030.030.050

4.000.0020.0 2.500.00

5.000.000.0025.043.551

4.00 2.50

5.0010.0 5.000.00 5.00 5.0025.038.552

4.001

5.0 2.50 5.00 2.0010.0 2.000.0020.039.553 4.0020.015.0 2.000.000.000.000.0025.0

34.0

Sample Benzene Toluene Xylenes Hvy.

Ref.A

MTBE EtOH TAME ETBE Isooctane

C5C6B

54 4.0025.020.0 1.000.000.000.000.0025.025.0

55 5.00 5.0025.00 4.000.000.000.000.0025.036.0

56 5.007.50 5.007.500.000.000.0015.025.035.0

57 5.0012.512.5 2.5015.00.000.000.0020.032.5

58 5.0020.0 5.00 5.000.00 5.000.000.0025.035.0

59 5.0020.0 2.50 2.500.000.007.500.0025.037.5

60 5.0025.020.00.000.000.000.000.0020.030.0

A Heavy reformate petroleum stream

B50volume%pentane in hexane

10.1.1.1Measure the density for each of the calibration

standards according to either Practice D1298or Test Method

D4052.

10.1.1.2For each of the calibration standards,convert the

mass%benzene to volume%benzene according to the

equation presented in13.1.

10.1.2Calibration Matrices for FTIR Instruments Using a

PLS Calibration—To obtain the best precision and accuracy of

calibration,prepare two benzene calibration sets as set forth in

Table3and Table4.Thefirst set(Set A)has35samples with

benzene concentrations between0to1.5mass%.The second set(Set B)has at least25samples with benzene concentrations between1to6mass%.Each of the subsets in Set B shall have a minimum offive samples with the benzene concentration evenly spaced over the1to6mass%range.

10.1.2.1Measure the density for each of the calibration standards according to either Practice D1298or Test Method D4052.

10.1.2.2For each of the calibration standards,convert the mass%benzene to volume%benzene according to the equation presented in13.1.If the densities of the calibration standards can not be measured,it is acceptable to convert to volume%using the densities of the individual components measured using Practice D1298or Test Method D4052. 10.1.3Calibration Matrix for FTIR Instruments Using Classical Least Squares Peak Fitting Calibration—Prepare a benzene calibration set as detailed in Table5.The set has samples with benzene concentrations between0to6mass%.

10.1.4Background Correction Mixtures for FTIR Instru-ments Using Classical Least Squares Peak Fitting Calibration —Prepare one mixture containing80mass%hexane and20 mass%of the respective aromatic for each of the six substances(toluene,1,3-dimethylbenzene,3–ethyltoluene, 1,3,5-trimethylbenzene,ethylbenzene,and propylbenzene)as set forth in Table6.

TABLE3FTIR Instruments PLS Calibration Sample Set A

(mass%)

Sample Benzene

(mass%)

Toluene

(mass%)

Mixed Xylenes

(mass%)

Isoctane

(mass%)

1000100 207093 3014086 4021079 50151570 60.250099.75 70.50099.5 80.750099.25 910099

10 1.250.098.75

11 1.50098.5 120.257092.75 130.57092.5 140.757092.25 1517092

16 1.257091.75

17 1.57091.5 180.2514085.75 190.514085.5 200.7514085.25 21114085

22 1.2514084.75

23 1.514084.5 240.2521078.75 250.521078.5 260.75210.78.25 27121078

28 1.2521077.75

29 1.521077.5 300.25151569.75 310.5151569.5 320.75151569.25 331151569

34 1.25151568.75

35 1.5151568.5

TABLE4FTIR Instruments PLS Calibration Sample Set B

(mass%)

Subset

(minimum5

samples)

in each subset)

Benzene

(mass%)

Toluene

(mass%)

Mixed

Xylenes

(mass%)

Isooctane

(mass%)

Subset11–600to100% Subset21–67–90to100% Subset31–614–170to100% Subset41–621–250to100% Subset51–615–1815–18to100%

TABLE5FTIR Instruments Calibration(Classical Least Squares Peak Fitting)Sample Set(mass%)

Sample Benzene Toluene Isooctane 10595

201585

30.5594.5

40.51584.5

51594

611584

7 1.5593.5

8 1.51583.5

92593

1021583

113592

1231582

134591

1441581

155590

1651580

1765

18615

79

10.2Calibration :

10.2.1Each instrument must be calibrated in accordance with the mathematics as outlined in Practice E 1655.This practice serves as a guide for the multivariate calibration of infrared spectrometers used in determining the physical char-acteristics of petroleum and petrochemical products.The procedures describe treatment of the data,development of the calibration,and qualification of the instrument.PLS or a classical least squares peak fitting calibration may be used if a continuous frequency region(s)of the spectrum is acquired,and MLR may be used if absorbances at discrete frequencies are used.

10.2.2Equilibrate all samples to the temperature of the laboratory (15to 38°C)prior to analysis.Fill the sample cell with the calibration standards in accordance with Practice E 168or in accordance with the manufacturer’s instructions.10.2.3For each of the calibration standards,acquire either the digitized spectral data or the absorbances through each specified filter.

10.2.3.1If a filter based mid IR instrument is being used,acquire the absorbances at the wavelengths corresponding to the specified filters for each of the calibration standards.

10.2.3.2If an FTIR is being used,acquire the digitized spectral data over the frequency region from 4000cm –1to 600cm –1for each of the calibration standards.The infrared spectrum is the negative logarithm of the ratio of the single beam infrared spectrum obtained with a sample and the single beam FTIR spectrum with dry air (or nitrogen).For FTIR instruments using a PLS calibration,baseline correct the spectrum using a linear baseline fit to absorbances measured between 712and 658cm –1.

10.2.4For filter based mid IR instruments,develop a calibration model based on the correlation of the set of calibration spectra to known benzene concentrations (volume %)according to Practice E 1655by fitting to the following MLR equation:

C 5a @x #1······1a n x n 1b 1x 673cm–121b 2x 729cm–121e (1)where:C 5concentration of the analyte,volume %,a n and b n 5the regressed coefficients,

x n 5the absorbance at filter wavelength,n,and

e 5the intercept.10.2.5For FTIR instruments using a PLS calibration,two separate calibrations will be developed.

10.2.5.1Develop the first calibration (using samples over the range of 0to 1.5mass %),referred to as the low calibration,using spectra obtained from the samples in calibration Set A detailed in Table 3.This calibration relates the spectrum to the benzene concentration (volume %).Use baseline corrected data in the region of 712to 6cm –1to develop the low calibration.Use mean centering and four latent variables in developing the model.10.2.5.2Develop the second calibration (using samples over the range 1to 6.0mass %),referred to as the high calibration,using spectra obtained from all of the samples in calibration Set B as detailed in Table 4.This calibration relates the spectrum to the benzene concentration (volume %).Use baseline cor-rected data in the region of 712to 6cm –1to develop the high calibration.Use mean centering and four latent variables in developing the model.10.2.6For FTIR instruments using a classical least squares peak fitting calibration a single calibration will be developed.This calibration relates the spectrum to the benzene concen-tration (mass %).In the calibration,the spectra in the region of 710through 660cm –1are used in developing the calibration model.10.2.6.1Measure the spectra of the six background correc-tion mixtures as detailed in Table 6as well as the spectrum of pure hexane in the region of 710through 660cm –1.For each of the mixture spectra,subtract 0.80times the spectrum of hexane from the spectrum of the 20mass %solution.The resulting spectrum is the derived spectrum of the respective aromatic.10.2.6.2Fit the absorption spectrum in the region of 710through 660cm –1using a classical least squares fit (k-matrix method).The fit matrix must include the derived spectra of toluene,1,3-dimethylbenzene,3-ethyltoluene,1,3,5-trimethylbenzene,ethylbenzene,and propylbenzene.10.2.6.3To eliminate spectral overlaps,subtract the derived spectra of toluene,1,3-dimethylbenzene,3-ethyltoluene,1,3,5-trimethylbenzene,ethylbenzene and propylbenzene,multiplied by the coefficients that resulted from the classical least squares fit to the absorption spectrum.In this way,a residual benzene peak is obtained.10.2.6.4Fit the residual benzene peak with a Lorentzian line shape function with a linear background in the region of 691through 660cm –1.The following equation is used for the Lorentzian line shape function L(v):L ~n !5A G 2/@G 21~n 0–n !2#1k n 1d (2)where:A 5peak height,G 5half width,n 05center wavenumber,n 5wavenumber,k 5slope of lines background,and d 5intercept of linear background.The fit parameters for the least squares fit are A ,G ,n 0,k ,and d .10.2.6.5Develop the calibration equation using the peak height of the residual peak (parameter A versus mass %benzene).10.3Qualification of Instrument Performance —Once a calibration(s)has been established,the individual calibrated instrument must be qualified to ensure that the instrument

TABLE 6FTIR Background Correction Mixtures (Classical Least

Squares Peak Fitting)

Sample Hexane Toluene 1,3Dimethyl-benzene 3-Ethyl-toluene 1,3,5-

trimethyl-benzene Ethyl-benzene Propyl-

benzene

(mass %)(mass %)(mass %)(mass %)(mass %)(mass %)(mass %)

1802000000280020000038000200004800002000580000020068000000

20

10.3.2Acquisition of Qualification Data—For each of the qualification standards,measure the benzene concentration, expressed in volume%,according to the procedure established in Section12.The instrument performance is satisfactory if the Standard Error of Validation for the set of qualification standards(as defined in Practice E1655)is equal to or less than 0.12.

11.Quality Control Checks

11.1Confirm the calibration of the instrument each day it is used by measuring the benzene concentration using the proce-dure outlined in Section12on at least one quality control sample of known benzene content.The preparation of known benzene concentration is described in11.1.1and11.1.2. 11.1.1Standard(s)of known benzene concentration shall be made up by mass according to10.1and converted to volume% using the measured density as outlined in Section13.At least one standard shall be made up at1.2(+/–0.2)mass%benzene, that is,nominally1.0volume%.Additional standards may also be prepared and used for quality control checks.

11.1.2Standard(s)should be prepared in sufficient volume to allow for a minimum of30quality control measurements to be made on one batch of material.Package or store,or both, quality control samples to ensure that all analyses of quality control samples from a given lot are performed on essentially identical material.

11.2If the benzene volume%value estimated for the quality control sample prepared at1.2mass%benzene differs from the known value by more than0.12volume%,then the measurement system is out-of-control and cannot be used to estimate benzene concentrations until the cause of the out-of-control behavior is identified and corrected.

11.3If correction of out-of-control behavior requires repair to the instrument or recalibration of the instrument,the qualification of instrument performance described in10.3shall be performed before the system is used to measure benzene content on samples.

12.Procedure

12.1Equilibrate the samples to between15and38°C before analysis.

12.2Clean the sample cell.If a separate baseline using the empty cell is required,and if residual fuel is in the sample cell, remove the fuel byflushing the cell and inlet-outlet lines with enough pentane to ensure complete washing.Evaporate the residual pentane with either dry air or nitrogen.

12.3If needed,obtain a baseline spectrum in the manner established by the manufacturer of the equipment.

12.4Prior to the analysis of unknown test samples,establish that the equipment is running properly by collecting the spectrum of the quality control standard(s),by analyzing the spectrum with the calibration model,and by comparing the estimated benzene concentration to the known value for the QC standard(s).Introduce enough standard to the cell toeinsure that the cell is washed a minimum of three times with the standard solution.

12.5Introduce the unknown fuel sample in the manner established by the manufacturer.Introduce enough of the fuel sample to the cell to ensure the cell is washed a minimum of three times with the fuel.

12.6Obtain the spectral response of the fuel sample. 12.6.1If afilter based mid IR instrument is used,acquire the absorbance for the fuel sample at the wavelengths correspond-ing to the specifiedfilters.

12.6.2If an FTIR is used,acquire the digitized spectral data for the fuel sample over the frequency region from4000cm–1 to600cm–1.

12.7Determine the benzene concentration(volume%)ac-cording to the appropriate calibration equation developed in Section10.

12.7.1Forfilter based mid IR instruments,apply the cali-bration equation determined in10.2.4to convert the absor-bances at each of the wavelengths to the benzene concentration expressed in volume%.

12.7.2For FTIR instruments using a PLS calibration,deter-mine the benzene concentration using the calibration models developed in10.2.5by following the steps outlined as follows.

12.7.2.1Baseline correct the spectrum using a linear base-linefit to absorbances measured between712and658cm–1.

12.7.2.2Estimate the benzene concentration in the fuel sample by applying the low calibration(see10.2.5.1)to the baseline corrected spectrum in the region of712to6cm–1.

12.7.2.3If the estimated benzene concentration(determined in12.7.2.2)is equal to or less than1.30volume%,determine the benzene concentration by applying the low calibration(see 10.2.5.2)to the baseline corrected spectrum in the region of 712to6cm–1.

12.7.2.4If the estimated benzene concentration(determined in12.7.2.2)is greater than 1.30volume%,estimate the benzene concentration by applying the high calibration(see 10.2.5.3)to the baseline corrected spectrum in the region of 712to6cm–1

.

12.7.2.5If the value estimated by application of the high calibration(determined in12.7.2.4)is less than or equal to1.30 volume%,report the value determined by the low calibration (even if the value is greater than1.30volume%).For estimated values greater than1.30volume%(determined in12.7.2.4), report the value obtained.

12.7.3For FTIR instruments using a classical least squares peakfitting calibration,fit the absorption spectrum in the region of710through660cm–1using a classical least squares fit(k-matrix method).Thefit matrix must include the derived spectra of toluene,1,3-dimethylbenzene,3-ethyltoluene, 1,3,5–trimethylbenzene,ethylbenzene,and propylbenzene(as determined in10.2.6.1).

12.7.3.1To eliminate spectral overlaps,subtract the derived spectra of toluene,1,3-dimethylbenzene,3-ethyltoluene,1,3,5-trimethylbenzene,ethylbenzene and propylbenzene,multiplied by the coefficients that resulted from the classical least squares fit to the absorption spectrum.In this way,a residual benzene peak is obtained.

12.7.3.2Fit the residual benzene peak with a Lorentzian line shape function(as defined in10.2.6.4)with a linear background in the region of691through660cm–1and determine the peak height of the residual benzene peak. 12.7.3.3Determine the benzene concentration expressed in mass%in the fuel sample by applying the calibration(see 10.2.6)using the peak height of the residual benzene peak determined in12.7.3.2.

12.7.3.4Determine the density of the fuel sample by Prac-tice D1298or Test Method D4052.

12.7.3.5Convert the determined mass%to volume%for the sample using the equation in Section13.

13.Calculation

13.1Conversion to Volume%of Benzene—To convert the calibration and qualification standards to volume%use Eq3.

V b5M b~D f/0.8844!(3) where:

V b5benzene volume%,

M b5benzene mass%,and

D f5relative density at15.56°C of the calibration or

qualification standard being tested as determined by

Practice D1298or Test Method D4052.

14.Report

14.1Report the following information:

14.1.1Filter instruments(Test Method D6277a).

14.1.1.1V olume%benzene by Test Method D6277a,to the nearest0.01%.

14.1.2FTIR instruments with PLS calibration(Test Method D6277b).

14.1.2.1V olume%benzene by Test Method D6277b,to the nearest0.01%.

14.1.3FTIR instruments with CLS calibration(Test Method D6277c).

14.1.3.1V olume%benzene by Test Method D6277c,to the nearest0.1%

15.Precision and Bias

15.1Interlaboratory tests of each of the procedures(filter instruments,FTIR instruments with PLS calibration,and FTIR instruments with CLS calibration)were carried out using twenty samples that covered the range from0to1.8volume% and at least six laboratories for each of the procedures.An additional sample containing approximately4volume%ben-zene was also included in the interlaboratory results.The precision of the test method as obtained by statistical exami-nation of interlaboratory results6is summarized in Table7and Table8and is as follows:

15.2Repeatability for Filter Based Mid IR Instruments—For benzene concentrations between0.1and1.8volume%,the difference between successive test results obtained by the same operator with the same apparatus under constant operating conditions on identical test samples would,in the long run,and in the normal and correct operation of the test method,exceed the following values only in one case in twenty:

r50.02110.027X(4) where X is the benzene concentration determined.For the one sample at approximately4volume%benzene,the differ-ence between successive test results,obtained by the same operator with the same apparatus under constant operating conditions on identical test samples would,in the long run,and in the normal and correct operation of the test method,exceed 0.18only in one case in twenty.

15.3Repeatability for FTIR Instruments Using PLS Cali-bration Instruments—For benzene concentrations between0.1 and1.8volume%,the difference between successive test results obtained by the same operator with the same apparatus under constant operating conditions on identical test samples would,in the long run,and in the normal and correct operation of the test method,exceed the following values only in one case in twenty.

r50.0131.052X(5) where X is the benzene concentration determined.For the one sample at approximately4volume%benzene,the differ-ence between successive test results obtained by the same operator with the same apparatus under constant operating conditions on identical test samples would,in the long run,and in the normal and correct operation of the test method,exceed 0.14only in one case in twenty.

15.4Repeatability for FTIR Instruments Using a Classical Least Squares Calibration—For benzene concentrations be-tween0.1and1.8volume%,the difference between successive 6Available from ASTM Headquarters.Request RR:D02–1431.

TABLE7Repeatabilities as a Function of Concentration Benzene

Concentration

(volume%)

Filter Instruments

FTIR with PLS

Calibration

FTIR with CLS

Calibration

0.10.020.020.05

0.30.030.030.06

0.50.030.040.07

0.70.040.050.08

0.90.050.060.09

1.10.050.070.09

1.30.060.080.10

1.50.060.090.11

1.80.070.110.12

40.180.14

0.18

test results obtained by the same operator with the same apparatus under constant operating conditions on identical test samples would,in the long run,and in the normal and correct operation of the test method,exceed the following values only in one case in twenty.

r 50.04710.043X

(6)

where X is the benzene concentration determined.For the one sample at approximately 4volume %benzene,the differ-ence between successive test results obtained by the same operator with the same apparatus under constant operating conditions on identical test samples would,in the long run,and in the normal and correct operation of the test method,exceed 0.18only in one case in twenty.

15.5Reproducibility for Filter Based Mid IR Instruments —For benzene concentrations between 0.1and 1.8volume %,the difference between two single and independent results,ob-tained by different operators working in different laboratories on identical test samples would,in the long run,and in the normal and correct operation of the test method,exceed the following values only in one case in twenty:

R 50.1211.012X

(7)

where X is the benzene concentration determined.For the one sample at approximately 4volume %benzene,the differ-ence between two single and independent results,obtained by different operators working in different laboratories on identi-cal test samples would,in the long run,and in the normal and correct operation of the test method,exceed 0.59only in one case in twenty.

15.6Reproducibility for FTIR Instruments Using a PLS Calibration Instrument —For benzene concentrations between 0.1and 1.8volume %,the difference between two single and independent results obtained by different operators working in different laboratories on identical test samples would,in the long run,and in the normal and correct operation of the test method,exceed the following values only in one case in twenty:

R 50.02210.118X (8)

where X is the benzene concentration determined.For the one sample at approximately 4volume %benzene,the differ-ence between two single and independent results obtained by different operators working in different laboratories on identi-cal test samples would,in the long run,and in the normal and correct operation of the test method,exceed 0.47only in one case in twenty.

15.7Reproducibility for FTIR Instruments Using a Classi-cal Least Squares Calibration Instrument —For benzene con-centrations between 0.1to 1.8volume %,the difference between two single and independent results obtained by different operators working in different laboratories on identi-cal test samples would,in the long run,and in the normal and correct operation of the test method,exceed the following values only in one case in twenty.

R 50.0991.031X

(9)

where X is the benzene concentration determined.For the one sample at approximately 4volume %benzene,the differ-ence between two single and independent results obtained by different operators working in different laboratories on identi-cal test samples would,in the long run,and in the normal and correct operation of the test method,exceed 0.23only in one case in twenty.

15.8Bias —Since there were no suitable reference materials included in the interlaboratory test program,no statement of bias is being made.However,the samples of the test program were shared with an interlaboratory study of Test Method D 5769and small biases (see Note 3)relative to that test method were observed.The relative biases were not the same for all procedures,nor were they the same for all samples within each procedure.Because such sample biases are not correctable,users wishing to use this test method to substitute for Test Method D 5769,or conversely,are cautioned to consider the specific source or sources of subject fuels and to assure,through periodic comparative testing,that any differ-ences are consistent and manageable.

N OTE 3—The average bias,relative to Test Method D 5769,was -0.06volume %for the FTIR procedures and +0.06for the filter procedure.After accounting for the averages,the fuel-specific differences exceeded 0.1volume %for only one fuel on one procedure (out of 62combina-tions).

16.Keywords

16.1aromatics;benzene;infrared spectroscopy;spark-ignition engine fuel

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TABLE 8Reproducibilites as a Function of Concentration

Benzene Concentration (volume %)

Filter Instruments

FTIR with PLS Calibration

FTIR with CLS Calibration

0.10.120.030.100.30.120.060.110.50.130.080.110.70.130.100.120.90.130.130.131.10.130.150.131.30.140.180.141.50.14.0.200.151.80.14.0.230.154

0.59

0.47

0.23