UOP 919-2011 Trace Hydrocarbons in Udex Solvent 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 1992, 2011 UOP LLC. All rights reserve

3、d. 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 610.83

4、2.9585 PHONE. Trace Hydrocarbons in Udex Solvent by GC UOP Method 919-11 Scope This method is for determining low concentrations of hydrocarbons in lean UOP Udex process solvent. Benzene, toluene, C8 aromatics composite, and C9+ aromatics composite are determined. Light non-aromatics through C9 para

5、ffins, if present, are reported as a composite. Higher non- aromatics, i.e., greater than C9, may interfere with the determination of benzene. The lower limit of quantitation for each aromatic component is 3 mg/kg (mass-ppm). References ASTM Practice D4307, “Preparation of Liquid Blends for Use as A

6、nalytical Standards,” www.astm.org Scanlon, J. T. and Willis, D. E., Journal of Chromatographic Science, 23, 333-340 (1985) UOP Method 999, “Precision Statements in UOP Methods,” www.astm.org Outline of Method The sample is injected into a gas chromatograph that is equipped with a fused silica capil

7、lary column internally coated with poly(ethylene glycol), an autosampler, and a flame ionization detector. 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 peak areas o

8、f a calibration blend analyzed under identical conditions and injection volumes. Apparatus References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. Balance, readability 0.0001 g Chromatographic column, 60 m of 0.32-mm ID fused silica

9、capillary, internally coated to a film thickness of 0.50 m with cross-linked poly(ethylene glycol), Restek, Cat. No. 10642 Gas chromatograph, temperature programmable, built for capillary column chromatography, utilizing a split injection system having a glass injection port insert and equipped with

10、 a flame ionization detector that will give a minimum peak height response of 10 times the background noise for 3 mg/kg of toluene when operated at the recommended conditions, Agilent Technologies, Model 7890 2 of 8 919-11 Data system, electronic, for obtaining peak areas. This device must integrate

11、 areas at a sufficiently fast rate so that narrow peaks typically resulting from use of a capillary column can be accurately measured. Agilent Technologies, ChemStation. Leak detector, gas, Grace Davison, Cat. No. 60229 Refrigerator, flammable-materials storage, Fisher Scientific, Cat. No. 97-938-1

12、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 range 30-700 kPa (4-100 psi), Matheson Tri-Gas, Model 3122-350 Regulator, nitrogen, two-stage, high purity, delivery

13、 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 1.0-L volume of sample. The use of an automatic injection device is required to achieve necessary repeatable injection volumes. Agilent Technologies, Mo

14、del 7693. Vortex mixer, VWR, Cat. No. 58816-121 Reagents and Materials References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. Air, zero gas, total hydrocarbons less than 2.0 ppm as methane Benzene, 99.9% minimum purity, Sigma-Aldric

15、h, Cat. No. 270709 Cumene, 98.0% minimum purity, Sigma-Aldrich, Cat. No. 28230 Ethylbenzene, 99.8% minimum purity, Sigma-Aldrich, Cat. No. 296848 Gas purifier, for hydrogen, to remove oxygen and moisture from carrier gas, VICI Mat/Sen, Cat. No. P200-1, and (optional) indicating oxygen trap, Restek,

16、Cat. No. 22010, see Procedure, Chromatographic Technique, Step 1 Hydrogen, zero gas, 99.99% 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 Pipets, disposable, Pasteur, VWR, Cat. No. 14673-043

17、Pipet bulbs, VWR, Cat. No. 15001-362 Propylene glycol (1,2-propanediol), 99.5% minimum purity, Sigma-Aldrich, Cat. No. 398039 Syringe, replacement, for recommended sample injector, 10-L, Agilent Technologies, Cat. No. 5181-1267 Tetraethylene glycol, 99% minimum purity, Sigma-Aldrich, Cat. No. 110175

18、 Toluene, 99.9% minimum purity, Sigma-Aldrich, Cat. No. 650579 Vials, autosampler, for recommended sample injector, with caps, Agilent Technologies, Cat. No. 5182-0864 3 of 8 919-11 Procedure The analyst is expected to be familiar with general laboratory practices, the technique of gas chromatograph

19、y, and the equipment being used. 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 the gas purifier is not used. Replace the gas purifier at intervals de

20、termined by good laboratory practice. An indicating oxygen trap may be placed downstream of the gas purifier. When the indicator shows one-half used, replace both the gas purifier and the indicating trap. 2. Install the fused silica capillary column in the gas chromatograph according to the column a

21、nd gas chromatograph manufacturers instructions. CAUTION: 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 condi

22、tions 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 Typical Chromatogram (see Figures 1 and 2). Table 1 Recommended Operating Conditions Carrier gas hydrogen Mode constant flow Flo

23、w rate 2.5 mL/min Head pressure 50C 74 kPa gauge (10.7 psig) Linear velocity 50C 41 cm/sec Split flow 250 mL/min Injection port Temperature 280C Autoinjector viscosity delay 5 sec Column temperature program Initial temperature 50C Initial hold time 0 min Programming rate 10C/min Final hold temperatu

24、re 250C Final Time 20 min Detector flame ionization Detector temperature 280C Hydrogen flow ratea 28 mL/min Air flow ratea 400 mL/min Makeup gas nitrogen Makeup gas flow ratea 30 mL/min Sample size 1.0 L, repeatable aConsult the manufacturers instrument manual for suggested flow rates. 4. Program th

25、e column oven to 250C (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 50C. 4 of 8 919-11 6. Mix the sample by shaking. Fill an autosampler vial with an aliquot of the sample and place in the au

26、tosampler (or autoinjector) tray. Multiple samples may be prepared in advance for unattended operation. 7. Inject nominally 1.0 L (repeatable) of sample into the gas chromatograph and start the data system and the column oven programming sequence. The use of an autoinjector or autosampler automates

27、the injection of the sample into the GC, starts the data system, and the GC oven program simultaneously. To remove residual tetraethylene glycol from the injection port, column, etc., an injection of water is to be made between each sample or blend. Also use water in the syringe wash vial, and repla

28、ce 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. An expanded region is shown in Figure 2. Non-aromatics are determined as a composite group that includes all un

29、identified components eluting before o-xylene. Typically, all non-aromatics elute before benzene. C8 aromatics are defined as a composite group that includes ethylbenzene, p-, m-, and o-xylene. The C8 aromatics may be reported individually or as a composite. C9+ aromatics are defined as a composite

30、group that includes cumene and all peaks eluting after o-xylene and before propylene glycol. To identify the propylene glycol site, it may be necessary to spike a sample with a small amount of propylene glycol. Calibration Quantitative results are based on the injection of repeatable volumes of both

31、 the calibration blend and the sample. Absolute response factors, derived from the calibration blend, are used to relate the peak areas of each known component to mg/kg. 1. Prepare 10 g or more of a stock solution as described in ASTM Practice D4307, “Preparation of Liquid Blends for use as Analytic

32、al Standards,” to contain approximately 1.0 mass-% each of benzene, toluene, ethylbenzene and cumene in tetraethylene glycol, by weight. Thoroughly mix the solution using a vortex mixer. Record all weights to the nearest 0.0001 g. Tetraethylene glycol is used in the blend to represent the Udex solve

33、nt, which is usually composed of tetraethylene glycol, triethylene glycol, or mixtures. Obtain the purest tetraethylene glycol possible to prepare the blend. Analyze it, looking for impurities that elute at the benzene, toluene, ethylbenzene and cumene sites. If an impurity in the tetraethylene glyc

34、ol is present, obtain tetraethylene glycol from a different vendor and check for the impurity. If no tetraethylene glycol can by found without an impurity at the benzene, toluene, ethylbenzene and cumene sites, correct for the impurity as described in ASTM Practice D4307. 2. From the recorded weight

35、s, calculate the concentrations of each of the analytes in the stock solution to three significant figures using Equation 1 or the procedure described in ASTM Practice D4307: A = CB100 (1) where: A = concentration of each analyte in the stock solution, mass-% B = mass of each analyte in the stock so

36、lution, g C = total mass of the stock solution prepared, g 100 = factor to convert to mass-% 5 of 8 919-11 3. Prepare 10 g or more of a calibration blend containing approximately 1.0 mass-% of stock solution in tetraethylene glycol. Thoroughly mix the calibration blend using a vortex mixer. Record a

37、ll weights to the nearest 0.0001 g. If refrigerated, the stock solution and calibration blend should remain stable for six months. 4. Calculate the concentration of benzene, toluene, ethylbenzene and cumene in the calibration blend to the nearest mg/kg using Equation 2 or the procedure described in

38、ASTM Method D4307. Using the above dilutions, the resulting calibration blend should contain approximately 100 mg/kg of each added component. FEAD10M 4 += (2) where: A = concentration of each analyte in the stock solution, from Equation 1, mass-% D = mass of stock solution in the calibration blend,

39、g E = total mass of the stock solution prepared, g F = concentration of benzene, toluene, ethylbenzene, or cumene, if any, in the tetraethylene glycol, mg/kg M = concentration of benzene, toluene, ethylbenzene, or cumene in the calibration blend, mg/kg 104 = factor to convert mass-% to mg/kg 5. Anal

40、yze the calibration blend in triplicate daily when samples are analyzed as described under Chromatographic Technique. The peak areas from each of the triplicate runs should not deviate from the average by more than 2% (relative) of the value. If greater deviations occur, make certain that there are

41、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 of a series of analyses. If the results differ by more than 5%

42、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 partially plugged syringe. 6. Use the average peak areas to calc

43、ulate the absolute response factor for benzene, toluene, ethylbenzene, or cumene, to three significant figures, using Equation 3. PML = (3) where: L = absolute response factor for benzene, toluene, ethylbenzene, or cumene M = concentration of benzene, toluene, ethylbenzene, or cumene in the calibrat

44、ion blend, from Equation 2, mg/kg P = average peak area for benzene, toluene, ethylbenzene, or cumene in the calibration blend 7. Multiply the absolute response factor determined for benzene by 1.10 to obtain the absolute response factor for non-aromatics. Non-aromatics are not easily soluble in tet

45、raethylene glycol, therefore no non-aromatic component is included when preparing the calibration blend. The 1.10 factor relative to benzene is determined using the effective carbon number (ECN) concept as described by Scanlon and Willis. 8. Use the absolute response factor for ethylbenzene to calcu

46、late the concentration of the C8 aromatics, and the absolute response factor for cumene to calculate the concentration of the C9+ aromatics. 6 of 8 919-11 Calculations Obtain peak areas for each individual component or group of components and calculate the composition of the sample to the nearest mg

47、/kg using Equation 4. Use the absolute response factor for ethylbenzene to calculate the concentration of each of the C8 aromatics, and the absolute response factor for cumene to calculate the concentration of the C9+ aromatics. Component, mg/kg = LS (4) where: L = absolute response factor, previous

48、ly defined, Equation 3 S = peak area of individual component or group of components Report each measured component or group of components to the nearest mg/kg. Precision Precision statements were determined using UOP Method 999, “Precision Statements in UOP Methods,” from precision data obtained usi

49、ng an autosampler. Repeatability and Site Precision A nested design was carried out for determining impurities in two Udex solvent samples by two analysts, with each analyst performing analyses on two separate days, performing three analyses each day for a total of 24 analyses. Using a stepwise analysis of variance procedure, the within-day estimated standard deviations (esd) were calculated at the concentration means listed in Table 2. Two analyses performed in one laboratory by the same analyst on the same day should not differ by mor