UOP 702-2009 Impurities in Distilled High Purity Cumene 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

2、ED HEREIN CAN BE HAZARDOUS. MATERIAL SAFETY DATA SHEETS (MSDS) OR EXPERIMENTAL MATERIAL SAFETY DATA SHEETS (EMSDS) FOR ALL OF THE MATERIALS USED IN THIS PROCEDURE SHOULD BE REVIEWED FOR SELECTION OF THE APPROPRIATE PERSONAL PROTECTION EQUIPMENT (PPE). COPYRIGHT 1970, 1973, 1990, 2009 UOP LLC. All ri

3、ghts reserved. 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 FA

4、X, or 610.832.9585 PHONE. Impurities in Distilled High Purity Cumene by GC UOP Method 702-09 Scope This method is for determining trace impurities in distilled, high purity cumene by gas chromatography (GC). Benzene and toluene may not be separated from the non-aromatic impurities by this method but

5、, if required, may be determined individually by UOP Method 543. Isoparaffins and/or olefins in the C12 range may interfere with the determination of ethylbenzene. The lower limit of detection for any single component is 5 mg/kg (mass-ppm). References ASTM Practice D4307, “Preparation of Liquid Blen

6、ds 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 Methods,” www.astm.org Outline of Method The sample to be analyzed is injected into a GC that

7、is equipped with a capillary injection port, a fused silica capillary column, and a flame ionization detector (FID). The concentrations of individual or group impurities are determined by the external standard method of quantitation, wherein peak areas of the sample components are compared to the pe

8、ak areas of a calibration blend analyzed under identical conditions and injection volumes. The concentration of the major component is then determined by subtracting the total impurities from 100%. See Note for alternative means of calibration and calculation. Apparatus References to catalog numbers

9、 and suppliers are included as a convenience to the method user. Other suppliers may be used. Balance, readability 0.1-mg Chromatographic column, 60 m of 0.32-mm ID fused silica capillary, internally coated to a film thickness of 0.50 m with cross-linked poly(ethylene glycol), Restek, Cat. No. 10642

10、 2 of 15 702-09 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 minimum peak height response of five times the background noise for 5 mg/kg n-prop

11、ylbenzene 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 typically resulting from use of a capillary column can be accurately measure

12、d. 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 3122-590 Regulator, hydrogen, two-stage, high purity, delivery pressure ra

13、nge 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 capable of injecting a repeatable 0.5-L volume of sample. The use of an

14、automatic injection device is required to achieve necessary repeatable injection volumes. See Appendixes. Agilent Technologies, Model 7683. Reagents and Materials References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. Air, total hyd

15、rocarbons less than 2.0 ppm as methane (zero gas) Benzene, 99.9% minimum purity, Aldrich, Cat. No. 270709 Carbon disulfide, low organic impurity, VWR, Cat. No. AA40910-AP 1,4-Diisopropylbenzene, 97% minimum purity, Aldrich, Cat. No. 126276 Gas purifier, for hydrogen, to remove oxygen and moisture fr

16、om carrier gas, VICI Mat/Sen, Cat. No. P200-1 Hydrogen, 99.95% minimum purity, total hydrocarbons less than 0.5 ppm as methane (zero gas) Nitrogen, 99.99% minimum purity, total hydrocarbons less than 0.5 ppm as methane (zero gas) n-Octane, 99.9% minimum purity, Aldrich, Cat. No. 296988 Pipet bulbs,

17、VWR, Cat. No. 15001-362 Pipets, disposable, Pasteur, VWR, Cat. No. 14673-043 n-Propylbenzene, 98% minimum purity, Aldrich, Cat. No. P5240-7 Syringe, replacement, for recommended sample injector, 5-L, Agilent Technologies, Cat. No. 5181-1273 Toluene, 99.9% minimum purity, Aldrich, Cat. No. 89680, (No

18、te 2) Vials, autosampler, for recommended sample injector, Agilent Technologies, Cat. No. 5182-0864 3 of 15 702-09 Calibration Preparation of Calibration Blend Quantitative results are based on the injection of repeatable volumes of both the calibration blend and the sample. Absolute response factor

19、s, 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 Method D4307 to contain approximately 1.5 mass-% each of n-octane, benzene, n-propylbenzene, and 1,4-diisopropylbenzenene in toluene. Thoroughly

20、 mix the solution by shaking. Record all weights to the nearest 0.1 mg. Obtain the purest toluene possible to prepare the blend. Analyze it, looking for impurities that elute at the n-octane, benzene, n-propylbenzene, and 1,4-diisopropylbenzenene sites. If impurities in the toluene are present at an

21、y of the sites, their concentrations must be accounted for in the calculation of the respective concentrations of the named components in the blend. Analyze the toluene, if needed, using the technique in Appendix A of this method and determine the concentrations of n-octane, benzene, n-propylbenzene

22、, and 1,4-diisopropylbenzene in the toluene. 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 contain approximately 3.0 mass-% of the stock solution in toluene. Thoroughly m

23、ix the calibration blend by shaking. Record all weights to the nearest 0.1 mg. If refrigerated, the stock solution and calibration blend should remain stable for several months. 3. Calculate the concentration of n-octane, benzene, n-propylbenzene, and 1,4-diisopropylbenzene in the calibration blend

24、to the nearest 0.0001 mass-% using Equation 1. Using the above dilutions, the resulting calibration blend should contain approximately 230 mg/kg of each added component. ECDAB10M6+= (1) where: A = mass of n-octane, benzene, n-propylbenzene, or 1,4-diisopropylbenzene in the stock solution, g B = mass

25、 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, n-propylbenzene, or 1,4-diisopropylbenzene, if any, in the toluene as analyzed as described in Appendix A; see b

26、ullet under Step 1, Preparation of Calibration Blend, mg/kg M = concentration of n-octane, benzene, n-propylbenzene, or 1,4-diisopropylbenzene 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.

27、 The peak areas from each of the triplicate runs should not deviate from the average by more than 3% (relative) of the value. 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 co

28、nsecutive runs. Confirm the stability of the chromatographic system by analyzing the calibration blend again at the end 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 s

29、amples must 4 of 15 702-09 be rerun after the problem is resolved. Typical problems to look for include a leaky septum and a dirty or partially plugged syringe. 5. Use the average peak areas to calculate the absolute response factor for n-octane, benzene, n-propylbenzene, and 1,4-diisopropylbenzene

30、to three significant figures, using Equation 2. PML = (2) where: L = absolute response factor for n-octane, benzene, n-propylbenzene, or 1,4-diisoproplybenzene M = concentration of n-octane, benzene, n-propylbenzene, or 1,4-diisoproplybenzene in the calibration blend, from Equation 1, mg/kg P = aver

31、age peak area for n-octane, benzene, n-propylbenzene, or 1,4-diisopropylbenzene in the calibration blend Use the absolute response factor for n-octane to calculate the concentration of the non-aromatics. Use the absolute response factor for benzene to calculate the concentration of benzene and tolue

32、ne. Use the absolute response factor for n-propylbenzene to calculate the concentration of ethylbenzene, p-xylene, m-xylene, o-xylene, isopropylbenzene, n-propylbenzene and -methylstyrene. Use the absolute response factor for 1,4-diisopropylbenzene to calculate the concentration of the composite of

33、all peaks eluting after n-propylbenzene, not including -methylstyrene. Procedure The analyst is expected to be familiar with general laboratory practices, the technique of gas chromatography, and the equipment being used. Chromatographic Technique 1. Install the gas purifier in the supply line betwe

34、en the carrier gas source and the carrier gas inlets on the gas chromatograph. Column life is significantly reduced if 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

35、: Hydrogen leakage into the confined volume of the column oven can cause a violent explosion. Therefore, it is mandatory 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 u

36、sed provided they produce the required sensitivity and chromatographic separations equivalent to those shown in the Typical 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

37、. Cool the column oven to a stabilized 70C. 6. Mix the sample by shaking. Fill an autosampler vial with an aliquot of the sample and place in the autosampler (or autoinjector) tray. Multiple samples may be prepared in advance for unattended operation. Samples are stable in the vials for several hour

38、s. 5 of 15 702-09 Table 1 Recommended Operating Conditions Carrier gas hydrogen Mode constant flow Head pressure 62 kPa gauge (9 psig) Linear velocity 70C 30 cm/sec Equivalent flow 70C 1.7 mL/min Split flow 50 mL/min Injection port temperature 250C Column temperature program Initial temperature 70C

39、Initial hold time 0 min Programming rate 2C/min Final hold temperature 200C Final Time 0 min Rate 2 10C/min Final Temperature 2 230C Final hold time 2 7 min Detector flame ionization Detector temperature 275C Hydrogen flow ratea 35 mL/min Air flow ratea 350 mL/min Makeup gas nitrogen Makeup gas flow

40、 ratea 30 mL/min Sample size 0.5 L, repeatable aConsult the manufacturers instrument manual for suggested flow rates. 7. Inject nominally 0.5 L (repeatable) of sample into the gas chromatograph and start the integrator and the column oven programming sequence. The use of an autoinjector or autosampl

41、er automates the injection of the sample into the GC, starts the data system, and the GC oven program simultaneously. To minimize cross contamination in trace level analyses, an injection of carbon disulfide is to be made between each sample or blend. Also use carbon disulfide in the syringe wash vi

42、al, 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 the o-xylene peak must be measured by performing a tangent skim on the tail of the cum

43、ene peak. Non-aromatics are determined as a composite group that includes all unidentified components eluting before cumene. Calculations Obtain peak areas for each individual component or group of components except cumene and calculate the composition of the sample to the nearest mg/kg using Equati

44、on 3: Component, mg/kg = 1.002 LS (3) 6 of 15 702-09 where: L = absolute response factor, previously defined, Equation 2 S = peak area of individual component or group of components 1.002 = correction for the difference in density between the toluene external standard and the cumene sample, 0.86400.

45、8623 Calculate the concentration of cumene in the sample by subtracting the sum of all the measured components from 100% using Equation 4. Cumene, mass-% = 4n1i10V100= (4) where: V = concentration of individual component or group of components, mg/kg 100 = 100% 104 = factor to convert mg/kg to mass-

46、% Report each measured component or group of components to the nearest mg/kg. Report the concentration of cumene to the nearest 0.01 mass-%. Note The external standard method of quantitation is preferred for best efficiency when analyzing multiple samples. It does, however, require the use of an aut

47、oinjector (or autosampler) for best precision. If an autoinjector is not available or if only one or two samples are to be analyzed, the internal standard or total normalization techniques are suitable alternatives. In the internal standard technique, the peak areas for the impurity components are c

48、ompared to the peak area for a known amount of internal standard weighed into each sample. The procedure for using the internal standard technique is described in Appendix A of this method. Newer GCs may have a wide dynamic range such that sufficient sensitivity for the small impurities can be obtai

49、ned without exceeding the instruments capabilities to measure the major component. If that can be verified, see Appendix B, then the total normalization technique of quantitation may be used. The external standard technique will be the reference in case of dispute. Precision Precision statements were determined using UOP Method 999, “Precision Statements in UOP Methods,” from precision data obtained using an autosampler. Repeatability and Site Precision A nested design was carried out for determining impurities in cumene by four an