UOP 1013-2016 Total Chloride in Liquid Hydrocarbons by Wavelength Dispersive X-Ray Fluorescence.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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4、 PHONE. Total Chloride in Liquid Hydrocarbons by Wavelength Dispersive X-Ray Fluorescence UOP Method 1013-16 Scope This method is for determining the total chloride content of liquid hydrocarbons by wavelength dispersive X-ray Fluorescence (XRF) spectroscopy. The example given here focuses specifica

5、lly on gasoline matrix but other hydrocarbon matrices are applicable if calibration standards of similar matrix are used. Highly volatile hydrocarbon species (e.g. LPG) are not applicable. The calibration has been set up for quantitative determination chloride from 5 mass-ppm to 1000 mass-ppm (0.000

6、5 mass-% to 0.1000 mass-%). Matrix effects are not significant over this range so long as routine samples and calibration standards are well matched. References UOP Method 999, “Precision Statements in UOP Methods,“ www.astm.org Outline of Method A liquid hydrocarbon sample is introduced into a wave

7、length dispersive XRF spectrometer. It is irradiated with x-rays, exciting elements contained in the sample to emit energy in the form of “characteristic x-rays.” The emitted x-rays are detected and measured in a helium path at an angle specific to chloride. The intensity of the characteristic Cl x-

8、ray peak is proportional to concentration. The XRF calibration curve is established using a set of calibration standards prepared from pure chlorobenzene (chloride source) diluted with a chloride-free solvent matrix that matches the composition of the routine samples. In XRF spectroscopy, the sample

9、 matrix composition can strongly affect the accuracy of the method. The applicability of the method should be verified, using matrix-matched standards and references, for sample types other than those described here. Apparatus References to catalog numbers and suppliers are included as a convenience

10、 to the method user. Other suppliers may be used. Balance, analytical, capable of weighing samples to 0.0001g Graduated cylinder, Pyrex, 1000 mL, for preparing 3:1 iso-octane-toluene matrix blank solution, VWR International, Cat. No. 22877-150 2 of 7 1013-16 Regulator, counting gas, two-stage, high

11、purity, Matheson Gas Products, Model 3122-350 Regulator, helium, two-stage, high purity, Matheson Gas Products, Model 3122-580 Wavelength Dispersive X-ray Fluorescence Spectrometer (WDXRF), equipped for x-ray detection in the 4.7 range, PANalytical. For optimum sensitivity to chlorine, the instrumen

12、t should be equipped with the following: Analyzing crystal, suitable for the dispersion of chlorine K x-rays within the angular range of the spectrometer employed. Germanium or other materials such as pentaerythritol can be used. Gas proportional detector, designed for the detection of long waveleng

13、th x-rays Optical path, helium Pulse height analyzer, or other means of energy discrimination X-ray tube, capable of exciting chlorine K radiation. Tubes with anodes of rhodium or chromium are preferred although other anodes can be used. Reagents and Materials References to catalog numbers and suppl

14、iers are included as a convenience to the method user. Other suppliers may be used. Bottle, 125 mL (4 oz.) clear glass, case of 24, for preparation of chlorobenzene stock solution, standards, and precision samples, VWR International, Cat. No. 10861-778 Bottle, 1000 mL (32 oz.) clear glass, with PE C

15、one-lined cap, case of 12, for preparing and storing 3:1 iso-octane-toluene base matrix blank, VWR International, Cat. No. 10861-760 Chlorobenzene, 99.9 % for HPLC, for use in preparing chloride calibration standards, Sigma-Aldrich, Cat No. 270644 CAS No. 108-90-7 Counting gas, for instruments equip

16、ped with flow proportional counters, P-10 ionization Gas, 10 vol.-% methane balance argon, Airgas, Cat. No. X02AR90D2000291 Helium, minimum purity 99.9%, local supply Iso-Octane, HPLC, GC grade, for use in preparing chloride calibration standards, Burdick disposable cells are recommended, PANalytica

17、l, Cat. No. 9430-500-00521 Toluene, ACS/HPLC grade, for use in preparing chloride calibration standards, Burdick Mylar film (3.5 micron thickness) was chosen for this application because it is highly resistant to chemical attack by the gasoline matrix and also has good tensile strength. Standard and

18、 routine samples should be prepared as follows. 1. Assemble a disposable sample cell according to the manufacturers instructions. Ensure that the x-ray transparent film is stretched taut, flat, and is free of wrinkles. Wrinkles in the film will affect the intensity of the x-rays transmitted. Care mu

19、st be taken to avoid touching the inside of the sample cell or any part of the window film, especially with bare skin. Oil left behind in fingerprints on x-ray support film contains enough chloride to cause an erroneously high measured concentration result when analyzing samples with low levels of c

20、hloride. 2. Pour the liquid sample in the assembled disposable sample cell and snap the lid in place. Place the sample cells on clean paper for 5 minutes to check for leaks in the Mylar film. Transfer the contents of any leaking sample cells into a new cell and leak-test again. Samples passing the l

21、eak test are ready to analyze. Ensure that the liquid sample cell is filled above a minimum depth, about 1 cm, beyond which additional sample does not significantly affect the measured count rate. Leak testing is important to prevent damage to the x-ray instrument! Spectrometer Conditions for Chlori

22、de Analytical Program The choice of x-ray spectrometer settings for parameters such as sample excitation, diffraction crystal, x-ray peak angle, detectors, counting times, etc. are instrument dependent. For best results, set up the XRF instrument according to the manufacturers instructions for measu

23、rement of the element chlorine. Assemble the measurement and calculation programs according to the instrument software requirements. The measurements described in this method were made using a PANalytical Axios Advanced XRF spectrometer operating at 4 kW power. Two separate measurement applications

24、were established, one with a low range calibration (5 - 50 mass-ppm Cl) and the other a high-range calibration (50 1000 mass-ppm Cl). The Automatic Program Selection (APS) feature of the PANalytical software was set up to automatically select the calibration most closely-matched (low- or high-range)

25、 to each routine sample. 5 of 7 1013-16 WDXRF spectrometers available from other suppliers may be suitable for this method and may offer a feature similar to the APS discussed above. Follow the recommendations from the manufacturer of that specific instrument. Establishing the Calibration Curve(s) 1

26、. Prepare each of the chloride calibration standards for measurement as discussed above. 2. Input the identification and chloride concentration information for each standard in the instrument calibration program. 3. Measure the intensity of the emitted chloride radiation from each of the standards.

27、4. Calculate the regression of the calibration data points (net measured intensity of the chloride peak vs. chloride concentration) according to the manufactures instructions. Use the instrument software to calculate a linear regression model, with the intercept not forced through zero. The RMS for

28、the regression (a measure of the quality of fit) should be less than 0.1. Perform the calibration procedure for each application covering a specific range. Reference Analysis Analyze a reference or Quality Control standard to verify the accuracy of the calibration. Determine if the calculated value

29、agrees with the certified value, within the allowable difference shown in Precision. If the reference value does not fall within these specified limits, reconfirm the integrity of the calibration standards and check the instrument for proper setup and operation. Then re-establish the calibration cur

30、ve as described above. Measure the reference sample at the beginning of each day that samples are analyzed and verify that the result lies within specified limits before proceeding to routine samples. Sample Analysis Routine samples and standards are prepared in the same way, as discussed above. Whe

31、n a routine sample is measured the calibration model is used to calculate the chloride concentration in the sample using the measured intensity of the chlorine x-ray peak. The calculation is done automatically in all modern XRF spectrometers. Samples whose calculated Cl concentrations are above the

32、scope of this method (1000 mass-ppm, or 0.1 mass-%) must be diluted with 3:1 iso-octane-toluene matrix blank and measured again. For example, samples containing 1 2 mass-% (10,000 20,000 mass-ppm) chloride will need to be diluted by a factor of 10 20 to bring the chloride concentration within the sc

33、ope of the calibration. The dilution can be carried out as follows. 1. Place a clean glass sample vial on an analytical balance and tare the balance. 2. Use a clean disposable pipette to transfer some of the sample (e.g. 1.0 mL) into the container. Record mass to the nearest 0.0001 gram. 3. Add 3:1

34、Iso-OctaneToluene base matrix to bring the solution to the desired mass, normally 10 grams. Record mass to the nearest 0.0001 gram. 4. Cap the container and mix the contents vigorously to homogenize. 5. Calculate the dilution factor, DF, using Equation 3. DF = Mf / Mi (3) where: Mi = initial sample

35、mass, grams Mf = final sample mass after dilution with 3:1 iso-octane-toluene, grams DF = Dilution Factor 6 of 7 1013-16 6. Measure the sample and then multiply the measured result times the dilution factor DF as calculated in equation 3 above to determine the actual Chloride concentration. Calculat

36、ions Calculations of net corrected intensities, calibration regressions, and measured concentrations of undiluted routine samples are performed by the instrument software. The concentrations of diluted samples must be computed manually by calculating the product of the measured concentration reporte

37、d automatically by the instrument and the dilution factor. Reporting Report results to the nearest mass-ppm. Results below 5 mass-ppm (limit of quantitation, LOQ) should be reported as 5 mass-ppm. Precision Precision statements were determined using UOP Method 999, “Precision Statements in UOP Metho

38、ds.” Repeatability and Site Precision A nested design was carried out for determining chloride in three naphtha samples with nominal chloride concentrations of 10, 50, and 500 mass-ppm, respectively. Each sample was analyzed by two analysts, with each analyst performing two analyses on two separate

39、days for a total of 24 analyses. Using a stepwise analysis of variance procedure, the within-day and within-lab estimated standard deviations (esd) were calculated at the concentration means listed in Table 1. Two analyses performed in one laboratory by the same analyst on the same day should not di

40、ffer by more than the repeatability allowable differences shown in Table 1 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 1 with 95% confidence. Table 2 Repea

41、tability and Site Precision, mass-ppm Repeatability Site Precision Sample Mean Within Day ESD Allowable Difference Within Lab ESD Allowable Difference Sample A 9.7 0.41 1.6 0.46 1.8 Sample B 49.9 0.75 2.9 1.03 4.0 Sample C 504 0.80 3.0 1.90 11.0 The data in Table 1 represent short-term estimates of

42、the repeatability of the method. When the test is run routinely, use of a control standard and a control chart is recommended to generate an estimate of long-term repeatability. Time for Analysis The elapsed time and labor requirement for a single chloride analysis is the same, 0.5 hour. 7 of 7 1013

43、-16 Suggested Suppliers Airgas, 1601 Nicholas Blvd., Elk Grove IL 60007, USA, 1-847-434-5300, Burdick & Jackson a Honeywell company, 1953 S. Harvey Street, Muskegon, Ml 49442, Customer Service: 1-800-322-2766 Matheson Tri-Gas, 150 Allen Rd. #302, Basking Ridge, NJ 07920, USA, 1-908-991-9200, PANal

44、ytical, 117 Flanders Rd. Westborough, MA 01581 USA, 1-508-647-1100, or, Lelyweg 1, 7600 AA Almelo, The Netherlands, +31 5465 34 444, Sigma-Aldrich, Customer Support, P.O. Box 14508, St. Louis, MO 63178, 1-800-325-3010 VWR International, Radnor Corporate Center, Bldg. 1 Suite 200, P.O. Box 6660, 100 Matsonford Rd., Radnor PA 19087-8660, USA, 1-800-932-5000,