UOP 992-2011 Trace Arsenic in Liquid Organics and Heavy Petroleum Fractions by ICP-MS.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 2011 UOP LLC. All rights reserved. Non

3、confidential 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 610.832.9585

4、 PHONE. Trace Arsenic in Liquid Organics and Heavy Petroleum Fractions by ICP-MS UOP Method 992-11 Scope This method is for determining total trace arsenic in liquid organics and heavy petroleum fractions by microwave digestion and Inductively Coupled Plasma - Mass Spectrometry (ICP-MS). The lower l

5、imit of quantitation for arsenic is 5 ng/g (mass-ppb). Sample preparation by conventional extraction and digestion, such as that used in UOP Method 946, “Arsenic in Petroleum Naphthas by HG-AAS,” is time consuming and is problematic for high-boiling samples as it is possible for arsenic to be volati

6、lized at the extreme sample preparation conditions required. UOP Method 986, “Arsenic in Heavy Petroleum Fractions using Microwave Digestion and Graphite Furnace-AAS,” uses microwave digestion, however due to sensitivity limitations of the GF-AAS, multiple digestions must be combined for analysis. A

7、 comparison of the methods is shown in Table 1. Table 1 Comparison of Trace Arsenic Methods Method Application Sample Preparation Analytical Technique Lower Limit of Quantitation, ng/g Sample Required, g 946 Petroleum naphthas Extraction/ digestion Hydride Generation-AAS 80 100 986 Heavy petroleum f

8、ractions Microwave digestion Graphite Furnace-AAS 50 0.6 992 Liquid organics Microwave digestion ICP-MS 5 0.25 References Operator Manual, UltraCLAVE MA 033, UOP Method 946, “Arsenic in Petroleum Naphthas by HG-AAS,” www.astm.org UOP Method 986, “Arsenic in Heavy Petroleum Fractions using Microwave

9、 Digestion and Graphite Furnace-AAS” www.astm.org 2 of 8 992-11 UOP Method 999, “Precision Statements in UOP Methods,” www.astm.org Outline of Method The samples, along with a reference material and a blank, are digested in a microwave oven. The digested solutions (digestates) are then analyzed by I

10、CP-MS. Apparatus References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used (see Procedure). Balance, readable to 0.0001 g Beaker, PTFE, 600-mL, Lab Safety Supply, Cat. No. CQ1-38705 Cylinders, graduated, 10- and 250-mL, polypropylene, V

11、WR, Cat. Nos. 24780-268 and -323, respectively Flasks, volumetric, polypropylene 25-, 50-, 100-, and 1000-mL, VWR Cat. Nos. 83008-964, 29615-018, 29615-007, and 29615-062, respectively; several of each required Hot plate, VWR, Cat. No. 12365-378 ICP-MS, PerkinElmer, DRC-e, equipped with an AS10 auto

12、sampler Microwave oven, 15-vessel capacity, with closed digestion vessels, quartz cells and lids, step-up transformer, CryoLab chiller, and computer, Milestone, UltraCLAVE Oven, drying, capable of operation at 110C Pipet, electronic, EDP 3-Plus, SE3-10mL (110-mL), Rainin Instrument Pipet, automatic,

13、 10-100 L, VWR, Cat. No. 89079-968 Pipet, automatic, 10-1000 L, VWR, Cat. No. 89079-974 Regulator, argon, two-stage, high-purity, delivery pressure range 30-700 kPa (4-100 psi), Matheson Tri-Gas, Model 3122-580 Regulator, nitrogen or argon, two-stage, high-purity, delivery pressure range 30-700 kPa

14、(4-100 psi), Matheson Tri-Gas, Model 3122-580 Wash bottle, for water, VWR, Cat. No. 16210-923 Watch glass, 100-mm diameter, VWR, Cat. No. 66110-087 Water purification system, producing Type 1 water with 18.2 M-cm resistivity, Thermo Scientific Barnstead EASYpure II Ultrapure Water Purification Syste

15、m, Fisher Scientific, Cat. No, 09-050-44 Reagents and Materials References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. References to water mean de-ionized or distilled water passed through a purification system, except where noted.

16、Argon, 99.995% minimum purity Element base oil, Conostan 75, Conostan Division, SCP Science Grease, RS Silicone, Milestone, Cat. No. SP0002 3 of 8 992-11 Hydrogen peroxide, 30%, Fisher Scientific, Cat. No. H325-100 Lubricant, dry spray, silicone or PTFE, local supply, or W. W. Grainger, Cat. No. 4JB

17、33 Nitric acid, concentrated, 70%, for trace analysis, Ultrex II, Mallinckrodt Baker, Cat. No. 6901 Nitric acid, 1-%. Pipet 10 mL of concentrated nitric acid into a 1000-mL volumetric flask containing approximately 500 mL of water. Dilute to volume with water. Cap and invert several times to mix tho

18、roughly. Nitric acid, 2-%. Pipet 20 mL of concentrated nitric acid into a 1000-mL volumetric flask containing approximately 500 mL of water. Dilute to volume with water. Cap and invert several times to mix thoroughly. Nitrogen or argon, for microwave, lab gas or cylinder O-ring, replacement, for Ult

19、raCLAVE vessel, Milestone, Cat. Nos. OR0108 (bottom) and OR0107, (top) Pipet tips, for automatic pipet, 1-200 L and 100-1250 L,VWR, Cat. Nos. 53508-810 and -922, respectively Pipet tips, for electronic pipet, Rainin Instrument, Cat. No. RC-10 mL Quartz cells and lids, for microwave, 20-mL, Milestone

20、, Cat. No. 39042. If desired, the cells may be marked for identification using an engraver, Dremel, W. W. Grainger, Cat. No. 3XA70 Reference, NIST Trace Elements in Fuel Oil (No. 6) Standard 1634C, containing 143 ng/g (mass-ppb) arsenic, along with other trace elements, NIST. If this specific standa

21、rd is no longer available or expired, use a currently available similar standard. Sample tubes, autosampler, centrifuge tubes, 50-mL for standards, 15-mL for samples, VWR, Cat. Nos. 21008-725 and -673, respectively Standard metal solutions, arsenic(As), gallium(Ga), germanium(Ge), and indium(In), 10

22、00-g/mL, aqueous, SPEX CertiPrep, Cat. Nos. PLAS2-2X, PLGA2-2X, PLGE9-2X, and PLIN2-2X, respectively Sulfuric acid, concentrated, trace metals grade, VWR, Cat. No. EM-SX1248-6 Water, deionized or distilled, for further treatment in the water purification system Water, tap Water purification cartridg

23、es, for Barnstead EASYpure II, Type 1 kit, Fisher Scientific, Cat. No. 09-034-167 (for deionized feedwater), or Cat. No. 09-034-168 (for distilled or RO feedwater) Procedure The analyst is expected to be familiar with general laboratory practices, the techniques of microwave digestion and ICP-MS, an

24、d the equipment being used. This procedure is written for the microwave and ICP-MS listed in Apparatus. If different equipment is used, modify the procedure as needed. Dispose of used reagents, materials, and samples in an environmentally safe manner according to local regulations. Preparation of St

25、ock Solutions Arsenic, stock solution, 1.0-g/mL 1. Pipet 100 L of 1000-g/mL arsenic standard metal solution into a 100-mL volumetric flask containing approximately 50 mL of 1-% nitric acid. 4 of 8 992-11 2. Dilute to the mark with 1-% nitric acid. Cap and invert several times to mix thoroughly. 3. M

26、ark the preparation date on the label; discard after one month. Internal standard stock solution, 2.0-g/mL 1. Pipet 200 L of each of the 1000-g/mL gallium, germanium and indium standard metal solutions into a 100-mL volumetric flask containing approximately 50 mL of 1-% nitric acid. 2. Dilute to the

27、 mark with 1 % nitric acid. Cap and invert several times to mix thoroughly. 3. Mark the preparation date on the label; discard after one month. Germanium is used as the internal standard. Gallium and indium are added to stabilize the sample solutions. Cleaning of Quartz Cells and Lids Clean the quar

28、tz cells and lids as follows: 1. Place quartz cells and lids in a 600-mL beaker, cover with 2-% nitric acid, and place a watch glass on top. 2. Place the beaker on a hot plate. Set the hot plate to 200C and bring to a boil. Adjust the temperature of the hot plate to maintain a slow boil. Boil for tw

29、o hours. 3. Remove from the hot plate, and allow to cool. 4. Decant the acid and dispose of it in an environmentally safe manner according to local regulations. 5. Rinse the quartz cells, lids, beaker, and watch glass with water, and place in an oven at 110C oven for a minimum of one hour to dry. 6.

30、 Store the cells and lids in the beaker, covered with the watch glass until needed. For convenience, they may be stored in the oven at 110 C. Microwave Digestion Prior to each use, the pre-cleaned quartz cells and lids are heated at 110C for about 1 hour and allowed to cool. If they are stored in th

31、e oven, they are simply removed and allowed to cool. The blank (element base oil) and the reference (NIST Standard) are digested in the same manner as the samples. 1. Warm and shake oils and heavier organic liquids to ensure homogeneity. 2. Weigh 0.20-0.25 g, and record the weight of each sample, to

32、 the nearest 0.0001 g, into the previously heated and cooled quartz cells. Then, using a graduated cylinder, add 3 mL of concentrated nitric acid (HNO3) to the quartz cells. Cover with a lid. 3. Weigh 0.20-0.25 g of the reference, to the nearest 0.0001 g, into the previously heated and cooled quartz

33、 cells. Then, using a graduated cylinder, add 3 mL of concentrated nitric acid (HNO3) to the quartz cells. Cover with a lid. 4. Weigh 0.20-0.25 g of the element base oil, which contains no arsenic, to the nearest 0.0001 g, into each of three additional previously heated and cooled quartz cells. Then

34、, using a graduated cylinder, add 3 mL of concentrated nitric acid (HNO3) to the quartz cells. Cover with a lid. One cell is used for preparing the blank and the other two are used for standard preparation. This is to ensure matrix matching with the samples. 5 of 8 992-11 5. Place the covered cells

35、into the sample holder with fixed PTFE cover as described in the UltraCLAVE Operator Manual. 6. Set up the microwave as described below. Refer to the UltraCLAVE Operator Manual for details. Add the load/absorption media as follows: a. Add 400 mL of water, 30 mL of 30% hydrogen peroxide, and 5 mL of

36、sulfuric acid into a PTFE insert that goes into the stainless steel pressure vessel. This acts as absorption media. b. Ensure that all O-rings are properly cleaned and greased. 7. Check the water level in the CryoLab chiller. Add tap water if necessary. 8. Turn on gas (nitrogen or argon), step up tr

37、ansformer, CryoLab chiller, Computer, and UltraCLAVE to rates and settings specified by the manufacturer. 9. Program the system using the settings shown in Table 2. Other conditions may be used provided they produce equivalent results. 10. Load the samples into the UltraCLAVE. Hang sample containers

38、 with the fixed PTFE cover as described in the UltraCLAVE Operator Manual. 11. Check the method, parameters, and start the run. At the end of the digestion process, when the materials have cooled, the UltraCLAVE system opens automatically. Table 2 Digestion Conditions Nr t (min) E (w) T1C T2C P 1. 0

39、0:40:00 1200 230 80 150 2. 00:40:00 1200 230 80 150 Nr. 1 is for reaching to the prescribed condition, and Nr. 2 is holding at that condition. 12. Carefully remove the sample holder with the quartz cells. 13. Quantitatively transfer with water the contents of each quartz cell and lid into separate 2

40、5-mL volumetric flasks. 14. Into one of the flasks containing the digestate of the element base oil, pipet 250 L of the 1.0 g/mL arsenic stock solution. Label as calibration standard solution, 10 ng/g. 15. Into a second flask containing the digestate of the element base oil, pipet 500 L of the 1.0 g

41、/mL arsenic stock solution. Label as calibration standard solution, 20 ng/g. The third flask containing the digestate of the element base oil is the blank. 16. Add 1000 L of internal standard to each volumetric flask. 17. Fill to the mark with water, cap and invert several times to thoroughly mix th

42、e contents. 18. To avoid corrosion of the UltraCLAVEs stainless steel pressure vessel, immediately after use, carefully clean, dry, and wipe with silicone as described in the UltraCLAVE Operator Manual. Also clean the PTFE container and quartz vessels. 6 of 8 992-11 ICP-MS Determination of Arsenic T

43、he ICP-MS is calibrated with prepared standards using the autosampler. Three calibration points are obtained by analyzing a blank and the 10- and 20-ng/mL arsenic standards. Samples are then analyzed. 1. Set up the instrument according to the manufacturers recommended conditions (see Table 3). Table

44、 3 ICP-MS Parameters ICP/MS instrument: Perkin Elmer DRC-e Analyte: 75As Internal standard: 69Ga, 74Ge,115In (Ge is used as the internal standard) RF power 1100 W Plasma gas flow: 15 L/min Auxiliary gas flow rate 1.2 L/min Nebulizer Nebulizer Cross Flow II Nebulizer gas flow rate approximately 0.85

45、L/min Spray chamber: RytonTM Scott-type Ion sampling and skimmer cone Nickel cone Sampling distance 10 mm from load coil Sample flush 35 seconds Read delay 15 seconds Wash 30 seconds Peristaltic pump speed -20 rpm Resolution: Standard Detector mode Dual Dwell time 50 ms Sweeps per reading 20 Reading

46、s per replicate 1 Replicates 3 2. Transfer aliquots of the digested samples, blank, reference, and calibration standards into autosampler tubes. 3. Enter the autosampler tray locations of all the solutions to be analyzed into the instrument data system. 4. Run the blank and the 10- and 20-ng/mL arse

47、nic calibration standards and establish the linear calibration curve. Reanalyze the arsenic standards as samples. Analyze the samples and the reference. Reanalyze the arsenic standards as samples at the end of the run. If the standards run as samples do not repeat within 5 % of their values, check t

48、he apparatus and technique, and after fixing any problems found, rerun the calibration standards, samples, and reference. Analysis of the reference confirms that the system is functioning properly. 5. Dispose of the remaining solutions in an environmentally safe manner according to local regulations

49、. Calculations 7 of 8 992-11 All calculations are performed by the instrument data system after the sample mass and dilutions are entered, and sample results are reported directly in ng/g. If all the data is not entered into the instrument data system, the results will be reported in ng/mL. Use Equation 1 to calculate the final sample concentration. Arsenic, ng/g = WC25 (1) where: C = ng/mL arsenic in the analyzed solution as reported by the instrument W = sample weight, g 25 = diluted volume of the digest