1、Designation: D 6866 08Standard Test Methods forDetermining the Biobased Content of Solid, Liquid, andGaseous Samples Using Radiocarbon Analysis1This standard is issued under the fixed designation D 6866; the number immediately following the designation indicates the year oforiginal adoption or, in t
2、he case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods do not address environmental im-pact, product performance and func
3、tionality, determination ofgeographical origin, or assignment of required amounts ofbiobased carbon necessary for compliance with federal laws.1.2 These test methods are applicable to any product con-taining carbon-based components that can be combusted in thepresence of oxygen to produce carbon dio
4、xide (CO2) gas. Theoverall analytical method is also applicable to gaseoussamples, including flue gases from electrical utility boilers andwaste incinerators.1.3 These test methods make no attempt to teach the basicprinciples of the instrumentation used although minimumrequirements for instrument se
5、lection are referenced in theReferences section. However, the preparation of samples forthe above test methods is described. No details of instrumentoperation are included here. These are best obtained from themanufacturer of the specific instrument in use.1.4 Currently, there are no ISO test method
6、s that areequivalent to the test methods outlined in this standard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the ap
7、plica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 883 Terminology Relating to Plastics3. Terminology3.1 The definitions of terms used in these test methods arereferenced in order that the practitioner may require furtherinformation regarding the practic
8、e of the art of isotope analysisand to facilitate performance of these test methods.3.2 Terminology D 883 should be referenced for terminol-ogy relating to plastics. Although an attempt to list terms in alogical manner (alphabetically) will be made as some termsrequire definition of other terms to m
9、ake sense.3.3 Definitions:3.3.1 dpmdisintegrations per minute. This is the quantityof radioactivity. The measure dpm is derived from cpm orcounts per minute (dpm = cpm bkgd / counting efficiency).There are 2.2 by 106dpm / uCi (14,17).33.3.2 dpsdisintegrations per second (rather than minute asabove)
10、(14,17).3.3.3 scintillationthe sum of all photons produced by aradioactive decay event. Counters used to measure this asdescribed in these test methods are Liquid ScintillationCounters (LSC) (14,17).3.3.4 specific activity (SA)refers to the quantity of radio-activity per mass unit of product, that i
11、s, dpm per gram (14,17).3.3.5 automated effciency control (AEC)a method usedby scintillation counters to compensate for the effect ofquenching on the sample spectrum (14).3.3.6 AMS facilitya facility performing Accelerator MassSpectrometry.3.3.7 accelerator mass spectrometry (AMS)an ultra-sensitive
12、technique that can be used for measuring naturallyoccurring radio nuclides, in which sample atoms are ionized,accelerated to high energies, separated on basis of momentum,charge, and mass, and individually counted in Faraday collec-tors. This high energy separation is extremely effective infiltering
13、 out isobaric interferences, such thatAMS may be usedto measure accurately the14C/12C abundance to a level of 1 in1015. At these levels, uncertainties are based on countingstatistics through the Poisson distribution (8,9).3.3.8 background radiationthe radiation in the naturalenvironment; including c
14、osmic radiation and radionuclidespresent in the local environment, for example, materials ofconstruction, metals, glass, concrete (2,4,7,8,14-19).1These test methods are under the jurisdiction of ASTM Committee D20 onPlastics and are the direct responsibility of Subcommittee D20.96 on Environmen-tal
15、ly Degradable Plastics and Biobased Products.Current edition approved Aug. 1, 2008. Published September 2008. Originallyapproved in 2004. Last previous edition approved in 2006 as D 6866 - 06a.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at se
16、rviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West
17、Conshohocken, PA 19428-2959, United States.3.3.9 biobased contentthe amount of biobased carbon inthe material or product as a percent of the weight (mass) of thetotal organic carbon in the product (1).3.3.10 coincidence circuita portion of the electronicanalysis system of a Liquid Scintillation Coun
18、ter which acts toreject pulses which are not received from the two Photomul-tiplier Tubes (that count the photons) within a given period oftime and are necessary to rule out background interference andrequired for any LSC used in these test methods (7,14,17).3.3.11 coincidence thresholdthe minimum d
19、ecay energyrequired for a Liquid Scintillation Counter to detect a radioac-tive event. The ability to set that threshold is a requirement ofany LSC used in these test methods (14,17).3.3.12 contemporary carbona direct indication of therelative contributions of fossil carbon and “living” biosphericca
20、rbon can be expressed as the fraction (or percentage) ofcontemporary carbon, symbol fC. This is derived from fMthrough the use of the observed input function foratmospheric14C over recent decades, representing the com-bined effects of fossil dilution of14C (minor) and nucleartesting enhancement (maj
21、or). The relation between fCand fMisnecessarily a function of time. By 1985, when the particulatesampling discussed in the cited reference the fMratio haddecreased to ca. 1.2 (8,9).3.3.13 chemical quenchinga reduction in the scintillationintensity (a significant interference with these test methods)
22、seen by the Photomultiplier Tubes (PMT, pmt) due to thematerials present in the scintillation solution that interfere withthe processes leading to the production of light. The result isfewer photons counted and a lower efficiency (4,7,17).3.3.14 chi-square testa statistical tool used in radioactivec
23、ounting in order to compare the observed variations in repeatcounts of a radioactive sample with the variation predicted bystatistical theory. This determines whether two different distri-butions of photon measurements originate from the samephotonic events. LSC instruments used in this measurements
24、hould include this capability (14,17,27).3.3.15 cocktailthe solution in which samples are placedfor measurement in a LSC. Solvents and Scintillators (chemi-cals that absorbs decay energy transferred from the solvent andemits light (photons) proportional in intensity to the depositedenergy) (4,7,14,1
25、7).3.3.16 decay (radioactive)the spontaneous transforma-tion of one nuclide into a different nuclide or into a differentenergy state of the same nuclide. The process results in adecrease, with time, of the number of original radioactiveatoms in a sample, according to the half-life of the radionuclid
26、e(8,14,17).3.3.17 discriminatoran electronic circuit which distin-guishes signal pulses according to their pulse height or energy;used to exclude extraneous radiation, background radiation,and extraneous noise from the desired signal (14,17,18,32).3.3.18 effciencythe ratio of measured observations o
27、rcounts compared to the number of decay events which oc-curred during the measurement time; expressed as a percentage(14,17).3.3.19 external standarda radioactive source placed adja-cent to the liquid sample in to produce scintillations in thesample for the purpose of monitoring the samples level of
28、quenching. Required with Method (A) (14,17).3.3.20 figure of merita term applied to a numerical valueused to characterize the performance of a system. In liquidscintillation counting, specific formulas have been derived forquantitatively comparing certain aspects of instrument andcocktail performanc
29、e and the term is frequently used tocompare efficiency and background measures (14,17,20).3.3.21 fluorescencethe emission of light resulting fromthe absorption of incident radiation and persisting only as longas the stimulation radiation is continued (14,17,25).3.3.22 fossil carboncarbon that contai
30、ns essentially noradiocarbon because its age is very much greater than the 5730year half-life of14C (8,9).3.3.23 half-lifethe time in which one half the atoms of aparticular radioactive substance disintegrate to another nuclearform. The half-life of14C is 5730 years (8,14,25).3.3.24 intensitythe amo
31、unt of energy, the number ofphotons, or the numbers of particles of any radiation incidentupon a unit area per unit time (14,17).3.3.25 internal standarda known amount of radioactivitywhich is added to a sample in order to determine the countingefficiency of that sample. The radionuclide used must b
32、e thesame as that in the sample to be measured, the cocktail shouldbe the same as the sample, and the Internal Standard must beof certified activity (14,17).3.3.26 modern carbonexplicitly, 0.95 times the specificactivity of SRM 4990b (the original oxalic acid radiocarbonstandard), normalized to d13C
33、 = 19 % (Currie, et al., 1989).Functionally, the fraction of modern carbon equals 0.95 timesthe concentration of14C contemporaneous with 1950 wood(that is, pre-atmospheric nuclear testing). To correct for thepost 1950 bomb14C injection into the atmosphere (9), thefraction of modern carbon is multipl
34、ied by 0.93 (as of the year2004).3.3.27 noise pulsea spurious signal arising from theelectronics and electrical supply of the instrument(14,17,21,29).3.3.28 phase contactthe degree of contact between twophases of heterogeneous samples. In liquid scintillation count-ing, better phase contact usually
35、means higher counting effi-ciency (14,17).3.3.29 photomultiplier tube (PMT, pmt)the device in theLSC that counts the photons of light simultaneously at twoseparate detectors (29,32).3.3.30 pulsethe electrical signal resulting when photonsare detected by the Photomultiplier tubes (14,17,18,32).3.3.31
36、 pulse height analyzer (PHA)an electronic circuitwhich sorts and records pulses according to height or voltage(14,17,18,32).3.3.32 pulse indexthe number of afterpulses following adetected coincidence pulse (used in three dimensional or pulseheight discrimination) to compensate for the background of
37、aliquid scintillation counter performing (14,18,29,32).3.3.33 quenchingany material that interferes with theaccurate conversion of decay energy to photons captured by thePMT of the LSC (2,4,7,14,15,17,20).D68660823.3.34 regionregions of interest, also called windowand/or channel in regard to liquid
38、scintillation counters. Refersto an energy level or subset specific to a particular isotope(4,14,18,21,29).3.3.35 scintillation reagentchemicals that absorbs decayenergy transferred from the solvent and emits light (photons)proportional in intensity to the decay energy (4,14,29).3.3.36 solventin sci
39、ntillation reagent, chemical(s) whichact as both a vehicle for dissolving the sample and scintillatorand the location of the initial kinetic energy transfer from thedecay products to the scintillator; that is, into excitation energythat can be converted by the scintillator into photons(4.14,17,29).3
40、.3.37 standard count conditions (STDCT)LSC condi-tions under which reference standards and samples arecounted.3.3.38 three dimensional spectrum analysisthe analysis ofthe pulse energy distribution in function of energy, counts perenergy, and pulse index. It allows for auto-optimization of aliquid sc
41、intillation analyzer allowing maximum performance.Although different Manufacturers of LSC instruments callThree Dimensional Analysis by different names, the actualfunction is a necessary part of these test methods (14,17,18).3.3.39 true beta eventan actual count which representsatomic decay rather t
42、han spurious interference (10,11).3.3.40 flexible tube crackerthe apparatus in which thesample tube (Break Seal Tube) is placed (5,6,10,11).3.3.41 break seal tubethe sample tube within which thesample, copper oxide, and silver wire is placed.4. Significance and Use4.1 Presidential (Executive) Orders
43、 13101, 13123, 13134,Public Laws (106-224), AG ACT 2003 and other LegislativeActions all require Federal Agencies to develop procedures toidentify, encourage and produce products derived from bio-based, renewable, sustainable and low environmental impactresources so as to promote the Market Developm
44、ent Infrastruc-ture necessary to induce greater use of such resources incommercial, non food, products. Section 1501 of the EnergyPolicyAct of 2005 (Public Law 10958) and EPA40 CFR Part80 (Regulation of Fuels and Fuel Additives: Renewable FuelStandard Requirements for 2006) require petroleum distrib
45、u-tors to add renewable ethanol to domestically sold gasoline topromote the nations growing renewable economy, with re-quirements to identify and trace origin.4.2 Method A utilizes Liquid Scintillation Counting (LSC)radiocarbon (14C) techniques to quantify the biobased contentof a given product with
46、 maximum total error of 15 % count,which is associated with sample preparation and actual count-ing. This test method is based on LSC analysis of CO2cocktails after collecting the CO2in a suitable absorbingsolution.4.3 Method B utilizes Accelerator Mass Spectrometry(AMS) and Isotope Ratio Mass Spect
47、rometry (IRMS) tech-niques to quantify the biobased content of a given product withpossible uncertainties of 1 to 2 % and 0.1 to 0.5 %, respec-tively. Sample preparation methods are identical to Method A,8.28.5. Method B diverges after 8.5 and rather than LSCanalysis the sample CO2remains within the
48、 vacuum manifoldand is distilled, quantified in a calibrated volume, transferred toa quartz tube, torch sealed. Details are given in 12.7-12.10. Thestored CO2is then delivered to an AMS facility for finalprocessing and analysis.4.4 Method C uses LSC techniques to quantify the biobasedcontent of a pr
49、oduct. However, whereas Method A uses LSCanalysis of CO2cocktails, Method C uses LSC analysis ofsample carbon that has been converted to benzene. This testmethod determines the biobased content of a sample with amaximum total error of 63 % (absolute).4.5 Although MethodsAand C are less sensitive than that ofusing AMS/IRMS, they have two distinct advantages: (1)lower costs per evaluation, and (2) much higher instrumentavailability worldwide. Indeed, LSC is the most widely usedmeasurement for14C determination. Method B is commonlyused whe
