TEST METHOD B - ETHYLBENZENE CONTENT BY MEANS OF A RAPID PACKED COLUMN GAS CHROMATOGRAPHIC ANALYSIS
12. Apparatus
12.1 Chromatograph - Any gas chromatographic instrument complying with the sensitivity described in 5.1, and equipped with a thermal conductivity detector may be used.
12.2 Column - Any column and conditions may be used provided the system meets all the requirements of 14.3 and Section 17. The following column was used to establish the precision found in Section 17: 18-ft (5.5-m) of 1/4-in. (6.3-mm) copper, aluminum, or stainless steel tubing packed with 35 % by weight of N,N-bis (2-cyanoethyl) formamide on 60 to 80 mesh untreated, calcined, pink diatomaceous silica (see Footnote B in Table 1).
NOTE 6 - The column may be prepared in two 9-ft (2.7-m) sections and joined together, if preferred. Such columns may be obtained from most chromatography supply houses that offer packed GC columns.
12.3 Strip Chart Recorder - See 5.2.
12.4 Micro Syringe - See 5.3.
13. Reagents and Materials
13.1 Aromatic Hydrocarbons - Benzene, toluene and ethylbenzene of 99.5 mol % minimum purity (see 1.6).
13.2 Carrier Gas - Helium.
14. Procedure
14.1 Set the gas chromatograph instrument conditions as follows:
14.2 Pipet exactly 1.0 mL of toluene internal standard into a 10-mL volumetric flask. Fill to the mark with the mineral spirits sample, and mix thoroughly by inverting several times.
NOTE 7 - Both ethyl benzene and toluene contents may be determined, if present, by using benzene as the internal standard.
14.3 Inject 3 µL of sample containing the internal standard, and chromatograph under the prescribed operating conditions. Change attenuation, if necessary, so as to measure the area of the internal standard with not less than 25 % nor more than 95 % chart deflection. Ethylbenzene will emerge in about 11 min.
14.4 Purge the column of high-boiling aromatics by raising the temperature to 130°C. After the high-boiling components emerge, reset the column temperature to 100°C.
15. Calculation
15.1 Measure the areas of the ethylbenzene and toluene internal standard peaks.
15.2 If different attenuations are used for the ethylbenzene and internal standard peaks, correct to a constant attenuation basis, as in 9.2.
15.3 Calculate the concentration of ethylbenzene as follows:
Ve = (Ae x 10 x 1.036)/AIS
where:
Ve = volume % of ethylbenzene,
Ae = area of the ethylbenzene peak corrected to a constant attenuation,
10 = volume % of internal standard added,
1.036 = relative response factor for ethylbenzene, and
AIS = area of the internal standard peak.
Duplicate results may be averaged, at the 95 % confidence level, if they differ by no more than 0.2 %, absolute.
NOTE 8 - The suggested response factor for ethylbenzene should be verified for the particular instrument used, in accordance with the procedure described in 7.3, and with the internal standard (toluene or benzene) used for the analysis. The response factor actually determined should be used in the ethylbenzene content calculation.
16. Report
16.1 Report the following information: concentration of ethylbenzene in volume percent to the nearest 0.1 %.
17. Precision and Bias
17.1 The precision estimates are based on an interlaboratory study in which one operator in eight different laboratories analyzed two samples of mineral spirits in duplicate on two different days. The samples contained 1.0 and 8.0 % ethylbenzene, and were prepared by adding ethylbenzene to dearomatized mineral spirits. The results were analyzed in accordance with Practice E 180. The within-laboratory and between-laboratories standard deviations were found at different levels of ethylbenzene content to be as follows:
Based upon these standard deviations, the following criteria should be used for judging the acceptability of results at a 95 % confidence level.
17.2 Repeatability - Two results, each the mean of duplicates, obtained by the same operator on different days should be considered suspect if they differ by more than 0.2 % absolute at the 1 % ethylbenzene level, or by more than 0.3 % absolute at the 8 % ethylbenzene level.
17.3 Reproducibility - Two results, each the mean of duplicates, obtained by operators in different laboratories should be considered suspect if they differ by more than 0.7 % absolute at the 1 % ethylbenzene level, or by more than 0.9 % absolute at the 8 % ethylbenzene level.
17.4 Bias - There was no statistically significant bias of the results compared with expected values for quantitatively prepared standards. Hence, the determination of ethylbenzene in mineral spirits by packed column gas chromatography as described in this test method has no bias.