UOP 952-1997 TRACE LEAD IN GASOLINES AND NAPHTHAS BY GF-AAS.pdf

1、TRACE LEAD IN GASOLINES ANDNAPHTHAS BY GF-AASUOP 952-97SCOPEThis method is for determining trace concentrations (10 to 400 mass/vol-ppb) of lead in gasolines andpetroleum naphthas. The method has not been validated on higher boiling range materials. The method isspecifically applicable to alkyl lead

2、 compounds such as tetraethyllead (TEL) and tetramethyllead (TML),other lead compounds have not been investigated.OUTLINE OF METHODTetraalkyllead compounds in gasoline and naphthas are converted into water-soluble lead species that aresubsequently extracted into dilute nitric acid. Lead concentratio

3、ns in the nitric acid extracts are determinedusing Graphite Furnace-Atomic Absorption Spectrometry (GF-AAS).APPARATUSReferences to catalog numbers and suppliers are included as a convenience to the method user. Othersuppliers may be used.Atomic absorption spectrometer, with autosampler and graphite

4、furnace capabilities, Perkin-Elmer,Model 4100ZLBalance, top loading, readability 0.01-gCylinders, graduated, 25- and 100-mL, Fisher Scientific, Cat. Nos. 08-552C and -552E, respectivelyFlasks, volumetric, Class A, borosilicate glass, 50-, 100-, 200- and 1000-mL, Fisher Scientific, Cat. Nos.10-210-5B

5、, -5C, -5D and -5G, respectivelyLamp, lead, EDL, Perkin-Elmer, Cat. No. N305-0657Pipets, volumetric transfer, Class A, 1-, 3-, 5-, 10- and 50-mL, Fisher Scientific, Cat. Nos. 13-651-1A, -1C, -1E, -1K and P, respectivelyIT IS THE USERS RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES A

6、ND TODETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. EFFECTIVE HEALTH ANDSAFETY PRACTICES ARE TO BE FOLLOWED WHEN UTILIZING THIS PROCEDURE. FAILURE TO UTILIZE THISPROCEDURE IN THE MANNER PRESCRIBED HEREIN CAN BE HAZARDOUS. MATERIAL SAFETY DATA SHEETS(MSDS) OR EXPERIMENTAL MATERIA

7、L SAFETY DATA SHEETS (EMSDS) FOR ALL OF THE MATERIALS USED INTHIS PROCEDURE SHOULD BE REVIEWED FOR SELECTION OF THE APPROPRIATE PERSONAL PROTECTIONEQUIPMENT (PPE). COPYRIGHT 1997 UOP LLCALL RIGHTS RESERVEDUOP Methods are available through ASTM International, 100 Barr Harbor Drive, PO Box C700, West

8、Conshohocken PA 19428-2959,United States. The Methods may be obtained through the ASTM website, www.astm.org, or by contacting Customer Service atserviceastm.org, 610.832.9555 FAX, or 610.832.9585 PHONE.2 of 5952-97REAGENTS AND MATERIALSAll reagents shall conform to the specifications established by

9、 the Committee on Analytical Reagents ofthe American Chemical Society, when such specifications exist, unless otherwise specified. References towater mean distilled or deionized water.References to catalog numbers and suppliers are included as a convenience to the method user. Othersuppliers may be

10、used.Ammonium dihydrogen phosphate, Puratronic, 99.998%, Alfa, Cat. No. 10633Ammonium dihydrogen phosphate, 10% solution. Weigh 10.0 0.01 g of ammonium dihydrogenphosphate into a 100-mL volumetric flask, add 1 mL of concentrated nitric acid and dilute to volumewith water. Cap and shake well until di

11、ssolution is complete.Bottle, Nalgene, 125-mL, Fisher Scientific, Cat. No. 03-313-2CCups, autosampler, polystyrene, Perkin-Elmer, Cat. No. B011-9079Eye dropper, Nalgene, Fisher Scientific, Cat. No. 13-711-10Iodine, Puratronic, 99.999%, Alfa, Cat. No. 10619Iodine solution, 3%. Add 3.0 0.01 g of iodin

12、e to a 100-mL volumetric flask and dilute with toluene tothe mark. Cap and shake until dissolved.Lead standard solution, 1,000-g/mL, SPEX CertiPrep, Cat. No. PLPB2-2YLead standard solution, 10-g/mL. Pipet 10 mL of the 1,000-g/mL lead standard into a 1000-mLvolumetric flask, dilute to the mark with 1

13、0% nitric acid, cap and shake well. Lifetime of this standardis one month.Lead standard solution, 1-g/mL. Pipet 10 mL of the 10-g/mL lead standard into a 100-mL volumetricflask, dilute to the mark with 10% nitric acid, cap and shake well. Lifetime of this standard is oneweek.Magnesium standard solut

14、ion, 10,000-mg/L (1% Mg in 2% HNO3), SPEX Certiprep, Cat. No. PLMG2-3YNitric acid, concentrated, Ultrex II ultrapure reagent, J.T. Baker, Cat. No. 6901-05Nitric acid, 10%. Mix one part concentrated nitric acid with nine parts water.Toluene, Optima grade, Fisher Scientific, Cat. No. T291-4PROCEDURETh

15、e GF-AAS instrument is calibrated using an acid blank, and 15- and 30-g/L lead standards. Samplesare then analyzed and the 30-g/L standard is reanalyzed as a sample at the end of the run. A matrixmodifier composed of ammonium dihydrogen phosphate and magnesium nitrate is used to increase thevaporiza

16、tion temperature of the lead.3 of 5952-97The method as written yields a close approximation of the lead concentration in the sample, and isconsidered adequate for its intended use. In the procedure below, some accuracy has been compromised forspeed. To generate data on a more accurate mass/mass basi

17、s, the standards would need to be prepared on amass/mass basis and the sample and nitric acid extract aliquots would also need to be weighed.1. Pipet 10 mL of sample into a 120-mL Nalgene bottle, add 1 mL of 3% iodine solution and cap. Mixthe contents by shaking for 30 seconds. Set aside and allow t

18、he reaction to proceed for 10 minutes. If the sample is known to contain more than 150 mass/vol-ppb of lead, use a smaller sample size, or dilutethe resulting nitric acid extract. Although excess iodine is added to ensure complete reaction, this methodis not recommended for lead levels above 400 mas

19、s/vol-ppb. Use 1 mL of iodine solution regardless of thesample size used.2. Pipet 50 mL of 10% nitric acid solution into the bottle, cap and shake continuously for another 10minutes. Allow a few minutes for the two layers to separate.3. Take an aliquot of the lower aqueous layer using a Nalgene eye

20、dropper and transfer to anautosampler cup on the GF-AAS instrument.4. Prepare fresh 15- and 30-g/L calibration standards daily by pipeting separate 3 mL aliquots of the 1-g/mL lead standard solution into 200- and 100-mL volumetric flasks. Dilute to the mark with 10%nitric acid, cap and shake well.5.

21、 Prepare the matrix modifier solution by pipeting 10 mL of 10% ammonium dihydrogen phosphatesolution and 1 mL of 10,000-mg/L Mg standard solution into a 100-mL volumetric flask. Add 1 mLof concentrated nitric acid, bring to the mark with water, cap and shake well.6. Transfer aliquots of the matrix m

22、odifier, two calibration standards and an acid blank (10% nitric acid)to separate autosampler cups on the GF-AAS instrument.7. Set up the GF-AAS instrument according to the manufacturers instructions, using the conditions inthe Table. If an instrument other than the Perkin-Elmer Model 4100ZL is used

23、, contact the instrument manufacturerfor help in determining appropriate settings for the instrument and furnace.8. Enter the locations of the matrix modifier, acid blank, standards and sample(s) into the instrumentcomputer. Program the autosampler to take 5 L of the matrix modifier and 20 L of eith

24、er the acidblank, calibration standards or sample(s) with each injection.9. Run the calibration (acid blank and two calibration standards), followed by the samples; and then runthe 30-g/L standard as a sample to verify the calibration. The instrument autosampler will pick up 5 L of the matrix modifi

25、er and 20 L of acid blank, calibrationstandard or sample, and inject both solutions together into the furnace. This provides 5 g of phosphateand 3 g of magnesium nitrate to increase the vaporization temperature of the lead species. If the 30-g/L calibration standard, when run as a sample, returns le

26、ss than 28 g/L lead or more than 32g/L lead, rerun the calibration and samples until a value between 28 and 32 g/L lead is obtained. If the sample reading exceeds the calibration range of the standards, the acid extract may be diluted oncewith 10% nitric acid.4 of 5952-97TableInstrument Parameters f

27、or thePerkin-Elmer Model 4100 ZLWavelength 283.3 nmSlit 0.7 nmBackground correction onSample size 20 LDry temperature Step 1 140C 30 sec gas flow 250 mL/min2 150C 20 sec “3 200C 10 sec “Ash temperature 4 850C 20 sec “Atomize and read 5 1500C 5 sec “Clean-out 6 2400C 2 sec “Matrix modifier 5 L of 10%

28、 NH4H2PO4and 0.06% Mg(NO3)2CALCULATIONSCalculate the lead concentration using the equation and report results to two significant figures.Lead, mass/vol-ppb = 5Cwhere:C = concentration of lead in the solution read by GF-AAS, g/L5 = 50/10where:10 = volume of sample taken, mL50 = volume of 10% HNO3extr

29、act, mLIf a dilution of the extract was required to bring the sample reading within range of the standards,multiply the dilution factor times the result from the equation to obtain the final result. If less than 10 mL ofsample was used (or available), substitute the actual volume used in place of 10

30、 in the equation.PRECISIONRepeatabilityBased on eight tests performed by one analyst on one day in one laboratory, the within-laboratoryestimated standard deviations (esd) were calculated for lead in gasoline at the 133 and 28 g/L levels. Theestimated standard deviations were 3.3 and 2.2 g/L, respec

31、tively. Two tests performed in one laboratory bythe same analyst on different days should not differ by more than 11 or 7 g/L, at the 133 and 28 g/Llevels, respectively (the allowable differences at the 95% probability level).5 of 5952-97The data quoted above is a “best case” estimate of the repeata

32、bility, and is equivalent to ASTMrepeatability statements. When the test is run routinely in the field, a control standard and chart should beused to develop a better estimate of the long term repeatability.ReproducibilityThere is insufficient data to calculate the reproducibility of the test at thi

33、s time.TIME FOR ANALYSISThe setup time may vary but once prepared a single sample can be run in 1.5 hours (elapsed time). Thelabor requirement is 1.2 hours. Multiple samples run together will decrease the average elapsed time andlabor time requirements on a per sample basis.REFERENCE“Determination o

34、f Lead and Lead Isotope Ratios in Gasoline by Inductively Coupled Plasma-Mass Spec-trometry”, Phillips Petroleum Company, Journal of Analytical Atomic Spectroscopy, May 1994, Vol. 9SUGGESTED SUPPLIERSAlfa, Johnson Matthey, P.O. Box 8247, Ward Hill, MA 01835-0747 (508-521-6300)J.T. Baker Inc., 222 Red School Lane, Phillipsburg, NJ 08865 (908-859-2151)Fisher Scientific, 711 Forbes Ave., Pittsburgh, PA 15219-4785 (412-562-8300)Perkin-Elmer Corp., 761 Main Ave., Norwalk, CT 06859-0012 (203-762-1000)SPEX CertiPrep, Inc., 203 Norcross Ave., Metuchen, NJ 08840-1253 (908-549-7144)