UOP 755-2013 Trace Impurities in High Purity Ethyl Benzene by GC.pdf

1、 IT IS THE USERS RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES AND TO DETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. EFFECTIVE HEALTH AND SAFETY PRACTICES ARE TO BE FOLLOWED WHEN UTILIZING THIS PROCEDURE. FAILURE TO UTILIZE THIS PROCEDURE IN THE MANNER PRESCRIB

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3、eserved. Nonconfidential UOP Methods are available from ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959, USA. The UOP Methods may be obtained through the ASTM website, www.astm.org, or by contacting Customer Service at serviceastm.org, 610.832.9555 FAX, or

4、610.832.9585 PHONE. Trace Impurities in High Purity Ethyl Benzene by GC UOP Method 755-13 Scope This method is for determining trace impurities in high purity ethyl benzene by gas chromatography (GC). Specific impurities identified include benzene, toluene, p-xylene, m-xylene, o-xylene, cumene, n-pr

5、opylbenzene, 1,2-diethylbenzene, 1,3-diethylbenzene, and 1,4-diethylbenzene. Non-aromatics and unidentified C9+ aromatics are determined as composites. Benzene and toluene may not be separated from the non-aromatic impurities by this method but, if required, may be determined individually by UOP Met

6、hod 543, “Trace Non-Aromatic Hydrocarbons in High-Purity Aromatics by Gas Chromatography.” The lower limit of detection for any single component is 2 mg/kg (mass-ppm) except for p-xylene, which has a lower detection limit of 10 mg/kg. References ASTM Method D4052, “Density and Relative Density of Li

7、quids by Digital Density Meter,” www.astm.org ASTM Practice D4307, “Preparation of Liquid Blends for Use as Analytical Standards,” www.astm.org UOP Method 543, “Trace Non-Aromatic Hydrocarbons in High-Purity Aromatics by Gas Chromatography,” www.astm.org UOP Method 999, “Precision Statements in UOP

8、Methods,” www.astm.org Outline of Method The sample to be analyzed is injected into a GC that is equipped with a capillary injection port, a fused silica capillary column internally coated with poly(ethylene glycol), and a flame ionization detector (FID). The concentrations of individual or group im

9、purities are determined by the external standard method of quantitation, wherein peak areas of the sample components are compared to the peak areas of a calibration blend analyzed under identical conditions and injection volumes. The concentration of the major component is then determined by subtrac

10、ting the total impurities from 100%. 2 of 8 755-13 Apparatus References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. Balance, readable to 0.0001 g Chromatographic column, 60 m of 0.25-mm ID fused silica capillary, internally coated t

11、o a film thickness of 0.50 m with cross-linked poly(ethylene glycol), Restek, Cat. No. 10641 Gas chromatograph, temperature programmable, built for capillary column chromatography, utilizing a split injection system having a glass injection port insert and equipped with an FID that will give a minim

12、um peak height response of five times the background noise for 2 mg/kg o-xylene when operated under the recommended conditions, Agilent Technologies, Model 7890 Data system, electronic, for obtaining peak areas. This device must integrate areas at a sufficiently fast rate so that narrow peaks typica

13、lly resulting from use of a capillary column can be accurately measured. Agilent Technologies, ChemStation. Refrigerator, explosion-proof or flammable storage, VWR, Cat. No. 55700-340 Regulator, air, two-stage, high purity, delivery pressure range 30-700 kPa (4-100 psi), Matheson Tri-Gas, Model 3122

14、-590 Regulator, hydrogen, two-stage, high purity, delivery pressure range 30-700 kPa (4-100 psi), Matheson Tri-Gas, Model 3122-350 Regulator, nitrogen, two-stage, high purity, delivery pressure range 30-700 kPa (4-100 psi), Matheson Tri-Gas, Model 3122-580 Sample injector, any syringe or injector ca

15、pable of injecting a repeatable 0.5-L volume of sample. The use of an automatic injection device is required to achieve necessary repeatable injection volumes. Agilent Technologies, Model 7683. Reagents and Materials References to catalog numbers and suppliers are included as a convenience to the me

16、thod user. Other suppliers may be used. Air, zero gas, total hydrocarbons less than 2.0 ppm as methane Benzene, 99.9% minimum purity, Aldrich, Cat. No. 270709 Carbon disulfide, low organic impurity, VWR, Cat. No. AA40910-AP Cumene, 99.0% minimum purity, TCI, Cat. No. C0687 Gas purifier, for hydrogen

17、, to remove oxygen and moisture from carrier gas, VICI Mat/Sen, Cat. No. P200-1 Hydrogen, zero gas , 99.95% minimum purity, total hydrocarbons less than 0.5 ppm as methane Nitrogen, zero gas , 99.99% minimum purity, total hydrocarbons less than 0.5 ppm as methane n-Octane, 99.9% minimum purity, Aldr

18、ich, Cat. No. 296988 o-Xylene, 97% minimum purity, Aldrich, Cat. No. 294780 Pipet bulbs, VWR, Cat. No. 15001-362 Pipets, disposable, Pasteur, VWR, Cat. No. 14673-043 3 of 8 755-13 Syringe, replacement, for recommended sample injector, 5-L, Agilent Technologies, Cat. No. 5181-1273 Toluene, 99.9% mini

19、mum purity, Aldrich, Cat. No. 89680 Vials, autosampler, for recommended sample injector, Agilent Technologies, Cat. No. 5182-0864 Calibration Preparation of Calibration Blend Quantitative results are based on the injection of repeatable volumes of both the calibration blend and the sample. Absolute

20、response factors, derived from the calibration blend, are used to relate the peak areas of each known component to mg/kg. 1. Prepare a stock solution as described in ASTM Practice D4307 to contain approximately 1.0 mass-% each of n-octane, benzene, o-xylene, and cumene in toluene. Thoroughly mix the

21、 solution by shaking. Record all weights to the nearest 0.0001 g. Obtain the purest toluene possible to prepare the blend. Analyze it, looking for impurities that elute at the n-octane, benzene, o-xylene, and cumene sites. If impurities in the toluene are present at any of the sites, their concentra

22、tions must be accounted for in the calculation of the respective concentrations of the named components in the blend. This blend will be used as the stock solution in the preparation of the actual calibration blend. Label this mixture as the stock solution. 2. Prepare the calibration blend to contai

23、n approximately 1.0 mass-% of the stock solution in toluene. Thoroughly mix the calibration blend by shaking. Record all weights to the nearest 0.0001 g. If refrigerated, the stock solution and calibration blend should remain stable for several months. 3. Calculate the concentration of n-octane, ben

24、zene, o-xylene, and cumene in the calibration blend to the nearest 1 mg/kg using Equation 1. Using the above dilutions, the resulting calibration blend should contain approximately 100 mg/kg of each added component. EDC BA10M6+= (1) where: A = mass of n-octane, benzene, o-xylene, or cumene in the st

25、ock solution, g B = mass of stock solution in the calibration blend, g C = total mass of the stock solution prepared, g D = total mass of the calibration blend prepared, g E = concentration of n-octane, benzene, o-xylene, or cumene, if any, in the toluene, mg/kg M = concentration of n-octane, benzen

26、e, o-xylene, or cumene in the calibration blend, mg/kg 106 = factor to convert to mg/kg 4. Analyze the calibration blend in triplicate as described under Chromatographic Technique. The peak areas from each of the triplicate runs should not deviate from the average by more than 3% (relative) of the v

27、alue. If greater deviations occur, make certain that there are no problems with the equipment and then make additional runs until the required repeatability is obtained on three consecutive runs. Confirm the stability of the chromatographic system by analyzing the calibration blend again at the end

28、of a series of analyses. If the results differ by more than 5% from the average of the triplicate runs, a problem has developed with the chromatographic system, and the series of samples must be rerun after the problem is resolved. Typical problems to look for include a leaky septum and a dirty or p

29、artially plugged syringe. 4 of 8 755-13 5. Use the average peak areas to calculate the absolute response factor for n-octane, benzene, o-xylene, and cumene to three significant figures, using Equation 2. PML = (2) where: L = absolute response factor for n-octane, benzene, o-xylene, or cumene M = con

30、centration of n-octane, benzene, o-xylene, or cumene in the calibration blend, from Equation 1, mg/kg P = average peak area for n-octane, benzene, o-xylene, or cumene in the calibration blend 6. Use the absolute response factor for n-octane to calculate the concentration of the non-aromatics. Use th

31、e absolute response factor for benzene to calculate the concentration of benzene and toluene. Use the absolute response factor for o-xylene to calculate the concentration of p-xylene, m-xylene, and o-xylene. Use the absolute response factor for cumene to calculate the concentration of cumene, n-prop

32、ylbenzene, each of the three diethylbenzene isomers, and the C9+ aromatics composite of all the unidentified peaks eluting after cumene. Procedure The analyst is expected to be familiar with general laboratory practices, the technique of gas chromatography, and the equipment being used. Dispose of u

33、sed reagents, materials, and samples in an environmentally safe manner according to local regulations. Chromatographic Technique 1. Install the gas purifier in the supply line between the carrier gas source and the carrier gas inlets on the gas chromatograph. Column life is significantly reduced if

34、the gas purifier is not used. 2. Install the fused silica capillary column in the gas chromatograph according to the column and gas chromatograph manufacturers instructions. CAUTION: Hydrogen leakage into the confined volume of the column oven can cause a violent explosion. Therefore, it is mandator

35、y to check for leaks each time a connection is made and periodically thereafter. 3. Establish the recommended operating conditions as given in Table 1. Different conditions may be used provided they produce the required sensitivity and chromatographic separations equivalent to those shown in the Typ

36、ical Chromatogram (Figure 1). 4. Program the column oven to 240C (see Table 1) and maintain this temperature until a stable baseline has been obtained at the required sensitivity. 5. Cool the column oven to a stabilized 80C. 6. Mix the sample by shaking. Fill an autosampler vial with an aliquot of t

37、he sample and place it in the autosampler (or autoinjector) tray. Multiple samples may be prepared in advance for unattended operation. Samples are stable in the vials for several hours. 7. Inject nominally 0.5 L (repeatable) of sample into the gas chromatograph and start the integrator and the colu

38、mn oven programming sequence. The use of an autoinjector or autosampler automates the injection of the sample into the GC, starts the data system, and the GC oven program simultaneously. 5 of 8 755-13 To minimize cross contamination in trace level analyses, an injection of carbon disulfide is to be

39、made between each sample or blend. Also, use carbon disulfide in the syringe wash vial, and replace it after every series of injections. 8. Identify the components in the resultant chromatogram and determine the areas of the impurity peaks. A typical chromatogram is shown in Figure 1. The area of th

40、e p-xylene peak must be measured by performing a tangent skim on the tail of the ethyl benzene peak as shown in Figure 2. Non-aromatics are determined as a composite group that includes all unidentified components eluting before cumene. The C9+ aromatics are determined as a composite group that incl

41、udes all unidentified components eluting after cumene. Table 1 Recommended Operating Conditions Carrier gas hydrogen Mode constant pressure Head pressure 68.9 kPa gauge (10 psig) Linear velocity 80C 22 cm/sec Equivalent flow 70C 0.7 mL/min Split flow 50 mL/min Injection port temperature 230C Column

42、temperature program Initial temperature 80C Initial hold time 24 min Programming rate 20C/min Final hold temperature 230C Final time 13 min Detector flame ionization Detector temperature 240C Hydrogen flow ratea 35 mL/min Air flow ratea 375 mL/min Makeup gas nitrogen Makeup gas flow ratea 30 mL/min

43、Sample size 0.5 L, repeatable aConsult the manufacturers instrument manual for suggested flow rates. Calculations Obtain peak areas for each individual component or group of components except ethyl benzene and calculate the composition of the sample to the nearest mg/kg using Equation 3: Component,

44、mg/kg = 1.000 LS (3) where: L = absolute response factor, previously defined, Equation 2 S = peak area of individual component or group of components 1.000 = correction for the difference in density between the toluene external standard and the ethyl benzene sample, 0.86690.8670 Calculate the concen

45、tration of ethyl benzene in the sample by subtracting the sum of all the measured components from 100% using Equation 4. 6 of 8 755-13 Ethyl benzene, mass-% = 4n1i10V100= (4) where: V = concentration of individual component or group of components, mg/kg 100 = 100% 104 = factor to convert mg/kg to ma

46、ss-% Report each measured component or group of components to the nearest mg/kg. Report the concentration of ethyl benzene to the nearest 0.01 mass-%. Precision Precision statements were determined using UOP Method 999, “Precision Statements in UOP Methods,” from precision data obtained using an aut

47、osampler. Repeatability and Site Precision A nested design was carried out for determining impurities in ethyl benzene by four analysts, with each analyst performing analyses on two separate days, performing two analyses each day for a total of 16 analyses. Using a stepwise analysis of variance proc

48、edure, the within-day and within-lab estimated standard deviations (esd) were calculated at the concentration means listed in Table 3. Two analyses performed in one laboratory by the same analyst on the same day should not differ by more than the repeatability allowable differences shown in Table 3

49、with 95% confidence. Two analyses performed in one laboratory by different analysts on different days should not differ by more than the site precision allowable differences shown in Table 3 with 95% confidence. Table 3 Repeatability and Site Precision, mg/kg (mass-% for Ethylbenzene) Repeatability Site Precision Component Mean Within- Day esd Allowable Difference Within- Lab esd Allowable Difference Non-aromatics 351 6.3 21 10.4 34 Benzene 482 2.5 8 3.2 11 Toluene 150 1.2 4 1.3 4 p-Xylene 8 0.4 1 0.5 2