UOP 391-2009 Trace Metals in Organics by AAS.pdf

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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 1964, 1981, 1991, 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. Trace Metals in Organics by AAS UOP Method 391-09 Scope This method is for determining trace concentrations of copper (Cu), iron (Fe), nickel (Ni), potassium (K), sodium (Na), and vanadium (V) by Atomic Absorption Spectrophotometry (AAS). It can be applied to petroleum prod

5、ucts such as crude oils, gasolines, kerosenes, diesel fuels, and residues, or varied organic mixtures (including nitroanilines, amines, chlorobenzenes, phenols and other related materials) produced or used in chemical manufacturing. The range of quantitation is from 0.5 to 100 mg/kg (mass-ppm). In a

6、ddition to the elements listed above, aluminum (Al), calcium (Ca), cobalt (Co), chromium (Cr), magnesium (Mg), manganese (Mn), palladium (Pd), platinum (Pt), and zinc (Zn) may also be analyzed by AAS using the techniques described herein; but these elements have not been evaluated for sensitivity or

7、 repeatability. Also, lead (Pb), molybdenum (Mo), phosphorus (P), and tin (Sn) may be analyzed by Graphite Furnace - Atomic Absorption Spectrophotometry (GF-AAS), which is outside the scope of this method. Alternatively, the elements listed above may be analyzed by Inductively Coupled Plasma Optical

8、 Emmission Spectrophotometry (ICP-OES). See UOP Method 389, “Trace Metals in Organics by Wet Ashing - ICP-OES,” for specific metals and their range of quantitation. References UOP Method 389, “Trace Metals in Organics by Wet Ashing - ICP-OES,” www.astm.org UOP Method 999, “Precision Statements in UO

9、P Methods,” www.astm.org Outline of Method The sample is wet ashed with fuming sulfuric acid and the resulting organic residue (char) is oxidized in a muffle furnace. The remaining inorganic residue is dissolved in a mixture of acids and diluted to a specific volume. Cesium is added as an ionization

10、 suppressant. The sample solution is aspirated into the flame of an AAS instrument and quantitation is achieved by comparison to matrix-matched standard solutions. 2 of 8 391-09 Apparatus References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers ma

11、y be used. Balance, top-loading, capacity 500-g, readability 0.01-g Beakers, 400-mL, heat-resistant type, quartz, Ace Glass, Cat. No. 5334-18 Bottle, dropping, acid, 60-mL, VWR, Cat. No. 89001-566 Bottle, wash, polypropylene, 500-mL, VWR, Cat. No. 16651-904 Cylinder, graduated, 10-mL, Class B, VWR,

12、Cat. No. 89000-248 Flasks, volumetric, Class A, 100- and 1000-mL, VWR, Cat. Nos. 89001-964 and -966, respectively Flasks, volumetric, polypropylene, 50- and 100-mL, VWR, Cat. Nos. 29615-018 and -007, respectively Furnace, muffle, capable of operation at 540C, VWR, Cat. No. 30604-158 Gloves, neoprene

13、/natural rubber, acid resistant, VWR, Cat. No. 32917-206 (for size large) Hot plate, variable temperature to 400C, VWR, Cat. No. 11301-106 Pipet, dispensing, Class B, 10-mL, VWR, Cat. No. 89003-506 Pipets, volumetric transfer, Class A, 1-, 2-, 4-, 5-, 6-, 8-, 10-, 15-, 20-, 30-, 40-, and 100-mL, VWR

14、, Cat. Nos. 89045-056, -058, -062, -064, -066, -070, -074, -076, -078, -082, -084, and -088, respectively Pipet filler, VWR, Cat. No. 53497-055 Regulator, acetylene, with flash arrestor, single-stage, PerkinElmer, Cat. No. 03030106 Regulator, air, two-stage, high-purity, delivery pressure range 30-7

15、00 kPa (4-100 psi), Matheson Tri-Gas, Model 3122-590 Regulator, nitrous oxide, single-stage, PerkinElmer Spectrophotometer, AAS, computer controlled, with lamps for the elements to be analyzed. The computer must be capable of performing background corrections, blank corrections, and weight/volume an

16、d dilution corrections. PerkinElmer, Analyst 800. Lamps, hollow cathode, AAS, copper, iron, nickel, potassium, sodium, and vanadium, PerkinElmer Stirring rods, quartz, JSRitter, Cat. No. 21-905 Thermometer, surface type, 0 to 550C, VWR, Cat. No. 61157-254 Tongs, beaker, VWR, Cat. No. 82027-374 Tongs

17、, crucible, VWR, Cat. No. 82027-372, for muffle furnace use Watch glasses, ribbed, 100-mm diameter, Wilmad-LabGlass, Cat. No. C-9990-100 3 of 8 391-09 Reagents and Materials All reagents shall conform to the specifications established by the Committee on Analytical Reagents of the American Chemical

18、Society, when such specifications are available, unless otherwise specified. References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. References to water mean deionized or distilled water. Acetylene, cylinder, compressed gas, 99.6% mi

19、nimum purity Air, compressed Cesium solution, 10,000-g/mL, SPEX, Cat. No. PLCS2-3X (used as an ionization suppressant) Hydrochloric acid, concentrated, VWR, Cat. No. VW-3110-3 Nitric acid, concentrated, VWR, Cat. No. VW4815-6 Nitrous oxide, cylinder, 99% minimum purity Pipet, transfer, disposable pl

20、astic, 155-mm length, VWR, Cat. No. 414004-004 Standard metal solutions, Cu, Fe, K, Na, Ni, and V solutions of 1000-g/mL concentrations, SPEX Industries, Inc., Cat. Nos. PLCU2-2, PLFE2-2, PLK2-2, PLNA2-2, PLNI2-2, and PLV2-2, respectively Sulfuric acid, concentrated, VWR, Cat. No. VW6840-3 Sulfuric

21、acid, fuming, 27 to 30% excess SO3, VWR, Cat. No. AA39187-36 Water, deionized or distilled Procedure The analyst is expected to be familiar with general laboratory practices, the technique of AAS, and the equipment being used. Preparation of Calibration Standards 1. Pipet 10 mL of 1000-g/mL of each

22、of the standard metal solutions into separate 1000-mL volumetric flasks. Dilute to the mark with water, cap and invert several times to thoroughly mix. Label with the element and concentration (10-g/mL). Store the prepared solution in the volumetric flask and prepare new solutions after three months

23、. 2. Prepare 1-, 2-, 3-, and 4-g/mL iron standards by pipeting 10-, 20-, 30-, and 40-mL aliquots of the 10-g/mL iron solution into each of four 100-mL volumetric flasks, respectively. Label with the element and concentration. 3. Prepare 1-, 2-, and 3-g/mL nickel standards by pipeting 10-, 20-, and 3

24、0-mL aliquots of the 10-g/mL nickel solution into each of three 100-mL volumetric flasks, respectively. Label with the element and concentration. 4. Prepare 5-, 10-, 20-, and 30-g/mL vanadium standards by pipeting 5-, 10-, 20-, and 30-mL aliquots of the 100-g/mL vanadium solution into each of four 1

25、00-mL volumetric flasks, respectively. Label with the element and concentration. 5. Prepare 1-, 2-, and 3-g/mL copper standards by pipeting 10-, 20-, and 30-mL aliquots of the 10-g/mL copper solution into each of three 100-mL volumetric flasks, respectively. Label with the element and concentration.

26、 4 of 8 391-09 6. Prepare 0.2-, 0.4-, 0.6-, 0.8-, and 1-g/mL sodium standards by pipeting 2-, 4-, 6-, 8-, and 10-mL aliquots of the 10-g/mL sodium solution into each of five 100-mL polypropylene volumetric flasks, respectively. Label with the element and concentration. 7. Prepare 0.5-, 1-, 1.5-, and

27、 2-g/mL potassium standards by pipeting 5-, 10-, 15-, and 20-mL aliquots of the 10-g/mL potassium solution into each of four 100-mL volumetric flasks, respectively. Label with the element and concentration. 8. Add 10 mL of 10,000-g/mL cesium solution and 5 mL of concentrated sulfuric acid with a gra

28、duated cylinder to each of the 23 flasks prepared in Steps 2 through 7 above. The contents of the flasks will get warm when the sulfuric acid is added. 9. Add 10 mL of 10,000-g/mL cesium solution and 5 mL of concentrated sulfuric acid with a graduated cylinder to an empty 100-mL polypropylene flask.

29、 This is used as the calibration blank for all of the standards. Label as the calibration blank. 10. Allow all the flasks to cool to ambient temperature, dilute to the mark with water, cap and invert several times to thoroughly mix. The prepared solutions are stored in the volumetric flasks. Fresh s

30、olutions must be prepared after one month. Sample Preparation The sample size of petroleum products is dependent on the levels of metals expected in the sample. As a general rule, the lighter and more free-flowing the material, the less trace metals it contains. For a gasoline or other light materia

31、ls, a 100-g sample size is recommended; for a viscous residue, 10 g is generally sufficient. For samples having intermediate viscosity, or samples where no estimate of metals content can be made, a 50-g sample size is recommended. The sample size of other organic mixtures is dependent on their expec

32、ted reaction with fuming sulfuric acid. Determine the potential for vigorous chemical reactions before attempting to wet ash an organic sample for the first time by mixing approximately 5 g of sample with 1 mL of fuming sulfuric acid and heating. To maximize sensitivity, the largest mass of sample t

33、hat can be safely handled is usually used. As a rule, 400-mL quartz beakers are used for all ashings involving organics to minimize loss of sample as a result of sudden or unexpected vigorous reactions. Use appropriate safety precautions including gloves when performing any of the procedures below.

34、All sample digestions are performed in a hood. Use beaker tongs when transferring beakers to or from hot plates or the muffle furnace. Use an additional quartz beaker, without sample, to carry a reagent (acid) blank through the procedure below each time a set of samples is prepared. 1. Obtain a repr

35、esentative sample in the following manner: if the material to be sampled is free-flowing, shake the container by hand for several minutes prior to sampling. Heat viscous or waxy samples prior to shaking. 2. Weigh the sample, to the nearest 0.01 g, into a 400-mL quartz beaker. If multiple samples are

36、 being weighed, cover the beakers with watch glasses to prevent contamination. 3. Measure 10 mL of fuming sulfuric acid into a graduated cylinder. Using a transfer pipet, add the fuming sulfuric acid to the beaker, dropwise, in a hood, after removing the watch glass (if used in Step 2). Use a stirri

37、ng rod to carefully mix the sample and acid. 5 of 8 391-09 Add the acid slowly. If a vigorous reaction ensues, stop addition until the reaction subsides. Then add the remainder of the acid in increments, allowing the reaction to proceed at a slow, controlled rate. 4. After any initial reaction subsi

38、des, place the beaker on a warm hot plate and occasionally stir. Increase the heat slowly while continuing to stir at intervals until the sludge that forms hardens sufficiently to be broken into small lumps with the stirring rod. Leave the stirring rod in the beaker. 5. Increase the hot plate temper

39、ature to the point where sulfuric acid fumes begin to evolve. After the fuming ceases, increase the temperature to 400C and heat until only a dry organic char remains. 6. Place the beaker containing the organic char and stirring rod just inside a 540C muffle furnace with the door fully open. The muf

40、fle furnace must be located in a hood or under a canopy hood since acid vapors are generated during heating. 7. When SO3 fumes are no longer visible, move the beaker to the rear of the furnace and close the door. 8. Leave the samples in the furnace until all of the organic char is burned off and onl

41、y ash remains. The door may be opened occasionally to check for completion. The elapsed time for Steps 6 through 8 will vary from 4-16 hours depending on the sample composition. A slow flow of air in the muffle furnace will speed up the organic char burn off, but is not a method requirement. Minimiz

42、ation of laboratory dust or contamination from the muffle furnace liner is important for trace analysis. 9. Remove the beaker containing the stirring rod from the muffle furnace, cover it with a watch glass, and allow it to cool to ambient temperature. A watch glass is used to prevent contamination.

43、 10. Gently wet the ash with a fine stream of water from a wash bottle before removing the watch glass. The water is introduced through the spout opening of the beaker, alongside the stirring rod. 11. Using a graduated cylinder, add 2.5 mL of concentrated sulfuric acid and 1.0-mL of concentrated hyd

44、rochloric acid to the beaker. 12. Using the acid dropping bottle, slowly add three drops of concentrated nitric acid and allow it to run down the inner wall of the beaker. The acid is run down the inner wall to minimize the possibility of a splash or spatter. 13. Heat the beaker on a hot plate in th

45、e hood until sulfuric acid fumes begin to evolve. Remove the beaker from the hot plate and allow it to cool to ambient temperature. 14. Transfer the beaker contents to a 50-mL polypropylene volumetric flask, quantitatively, with water. 15. Using a graduated cylinder, add 5 mL of 10,000-g/mL cesium s

46、olution to the flask. Dilute to the mark with water, cap and invert several times to thoroughly mix. 6 of 8 391-09 Instrumental Analysis 1. Set the instrument for one of the elements to be read following the instrument manufacturers instructions for that element. Typical instrument settings are list

47、ed in Table 1. The settings shown are recommendations and may be changed if the manual for the instrument being used recommends other parameters. Table 1 AAS Instrument Parameters Element Wavelength, nm Slit, nm Background Correction Flame Type Burner, mm Iron 248.3 0.2 Yes air-C2H2 100 Nickel 232.0

48、 0.2 Yes air- C2H2 100 Vanadium 318.4 0.7 No N2O- C2H2 50 Copper 324.7 0.7 No air- C2H2 100 Sodium 589.0 0.4 No air- C2H2 100 Potassium 766.5 1.4 No air- C2H2 100 2. Analyze the standards and samples in the following order: calibration blank, standards, reagent (acid) blank, samples, and then reanal

49、yze one of the standards. If the last standard does not match its initial reading to within 3% relative, check for problems with the instrument or the procedure and reanalyze the entire series. If a sample reading exceeds the highest standard reading, dilute the sample so that the metal concentration is within the standard range, maintaining the matrix-match by proper addition of sulfuric acid and cesium solution. 3. Reset the instrument for each additional element, proceeding through Steps 1 and 2 above. Calculations Calculate the co