ASTM D6866 – 04

Designation: D 6866 – 04 Standard Test Methods for Determining the Biobased Content of Natural Range Materials Using Radiocarbon and Isotope Ratio Mass Spectrometry Analysis1 This standard is issued under the fixed designation D 6866; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval. 1. Scope 1.1 These test methods do not address environmental im- pact, product performance and functionality, determination of geographical origin, or assignment of required amounts of biobased 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 the presence of oxygen to produce carbon dioxide (CO2) gas. 1.3 These test methods make no attempt to teach the basic principles of the instrumentation used although minimum requirements for instrument selection are referenced in the References section. However, the preparation of samples for the above methods is described. No details of instrument operation are included here. These are best obtained from the manufacturer of the specific instrument in use. 1.4 Currently, there are no ISO test methods that are equivalent to the test methods outlined in this standard. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety and health practices and determine the applica- bility of regulatory limitations prior to use. 2. Referenced Documents 2.1 ASTM Standards: 2 D 883 Terminology Relating to Plastics 3. Terminology 3.1 The definitions of terms used in this test method are referenced in order that the practitioner may require further information regarding the practice of the art of isotope analysis and to facilitate performance of the method. 3.2 Terminology D 883 should be referenced for terminol- ogy relating to plastics. Although an attempt to list terms in a logical manner (alphabetically) will be made as some terms require definition of other terms to make sense. 3.3 Definitions: 3.3.1 dpm—disintegrations per minute. This is the quantity of radioactivity. The measure dpm is derived from cpm or counts per minute (dpm = cpm − bkgd / counting efficiency). There are 2.2 by 106 dpm / uCi (11,13).3 3.3.2 dps—disintegrations per second (rather than minute as above) (11,13). 3.3.3 scintillation—the sum of all photons produced by a radioactive decay event. Counters used to measure this as described in this method are Liquid Scintillation Counters (LSC) Bq (11,13). 3.3.4 specific activity (SA)—refers to the quantity of radio- activity per mass unit of product, that is, dpmh % (11,13). 3.3.5 automated effıciency control (AEC)—a method used by scintillation counters to compensate for the effect of quenching on the sample spectrum (11). 3.3.6 AMS facility—a facility performing Accelerator Mass Spectrometry. 3.3.7 accelerator mass spectrometry (AMS)—an ultra- sensitive technique for measuring naturally occurring 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 collectors. This high energy separation is extremely effective in filtering out isobaric interferences, such that AMS may be used to measure accu- rately the 14C abundance to a level of 1 in 1015. At these levels, uncertainties are based on counting statistics through the Poisson distribution (7,8). 3.3.8 background radiation—the radiation in the natural environment; including cosmic radiation and radionuclides present in the local environment, for example, materials of construction, metals, glass, concrete (1,3,6,7,11-15). 3.3.9 coincidence circuit—a portion of the electronic analy- sis system of a Liquid Scintillation Counter which acts to reject pulses which are not received from the two Photomultiplier Tubes (that count the photons) within a given period of time 1 These test methods are under the jurisdiction of ASTM Committee D20 on Plastics and are the direct responsibility of Subcommittee D20.96 on Environmen- tally Degradable Plastics and Biobased Products. Current edition approved February 1, 2004. Published March 2004. 2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards volume information, refer to the standard’s Document Summary page on the ASTM website. 3 The boldface numbers in parentheses refer to the list of references at the end of this standard. 1 Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States. and are necessary to rule out background interference and required for any LSC used in this method (6,11,13). 3.3.10 coincidence threshold—the minimum decay energy required for a Liquid Scintillation Counter to detect a radioac- tive event. The ability to set that threshold is a requirement of any LSC used in this method (11,13). 3.3.11 contemporary carbon—a direct indication of the relative contributions of fossil carbon and “living” biospheric carbon can be expressed as the fraction (or percentage) of contemporary carbon, symbol fC. This is derived from fM through the use of the observed input function for atmospheric 14C over recent decades, representing the com- bined effects of fossil dilution of 14C (minor) and nuclear testing enhancement (major). The relation between fC and fM is necessarily a function of time. By 1985, when the particulate sampling discussed in the cited reference the fM ratio had decreased to ca. 1.2 (7,8). 3.3.12 chemical quenching—a reduction in the scintillation intensity (a significant interference with this method) seen by the Photomultiplier Tubes (PMT, pmt) due to the materials present in the scintillation solution that interfere with the processes leading to the production of light. The result is fewer photons counted and a lower efficiency (3,6,13). 3.3.13 chi-square test—a statistical tool used in radioactive counting in order to compare the observed variations in repeat counts of a radioactive sample with the variation predicted by statistical theory. This determines whether two different distri- butions of photon measurements originate from the same photonic events. LSC instruments used in this measurement should include this capability (11,13,22). 3.3.14 cocktail—the solution in which samples are placed for measurement in a LSC. Solvents and Scintillators (chemi- cals that absorbs decay energy transferred from the solvent and emits light (photons) proportional in intensity to the decay energy) (3,6,11,13). 3.3.15 decay (radioactive)—the spontaneous transforma- tion of one nuclide into a different nuclide or into a different energy state of the same nuclide. The process results in a decrease, with time, of the number of original radioactive atoms in a sample, according to the half-life of the radionuclide (7,11,13). 3.3.16 discriminator—an 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 (11,13,14,26). 3.3.17 effıciency—the ratio of measured observations or counts compared to the number of decay events which oc- curred during the measurement time; expressed as a percentage (11,13). 3.3.18 external standard—a radioactive source placed adja- cent to the liquid sample in to produce scintillations in the sample for the purpose of monitoring the sample’s level of quenching. Required with Method (A) (11,13). 3.3.19 figure of merit—a term applied to a numerical value used to characterize the performance of a system. In liquid scintillation counting, specific formulas have been derived for quantitatively comparing certain aspects of instrument and cocktail performance and the term is frequently used to compare efficiency and background measures (11,13,16). 3.3.20 fluorescence—the emission of light resulting from the absorption of incident radiation and persisting only as long as the stimulation radiation is continued (11,13,20). 3.3.21 fossil carbon—carbon that contains essentially no radiocarbon because its age is very much greater than the 5730 year half-life of 14C (7,8). 3.3.22 half-life—the time in which one half the atoms of a particular radioactive substance disintegrate to another nuclear form. The half-life of 14C is 5730 years (7,11,20). 3.3.23 intensity—the amount of energy, the number of photons, or the numbers of particles of any radiation incident upon a unit area per unit time (11,13). 3.3.24 internal standard—a known amount of radioactivity which is added to a sample in order to determine the counting efficiency of that sample. The radionuclide used must be the same as that in the sample to be measured, the cocktail should be the same as the sample, the activity of the Internal Standard, and the Internal Standard must be of certified activity (11,13). 3.3.25 modern carbon—explicitly, 0.95 times the specific activity of SRM 4990b (the original oxalic acid radiocarbon standard), normalized to d13C = −19 % (Currie, et al., 1989). Functionally, the fraction of modern carbon = (1/0.95) where the unit 1 is defined as the concentration of 14C contempora- neous with 1950 wood (that is, pre-atmospheric nuclear test- ing) and 0.95 are used to correct for the post 1950 bomb 14C injection in to the atmosphere (8). 3.3.26 noise pulse—a spurious signal arising from the electronics and electrical supply of the instrument (11,13,17,24). 3.3.27 phase contact—the degree of contact between two phases of heterogeneous samples. In liquid scintillation count- ing, better phase contact usually means higher counting effi- ciency (11,13). 3.3.28 photomultiplier tube (PMT, pmt)—the device in the LSC that counts the photons of light simultaneously at two separate detectors (24,26). 3.3.29 pulse—the electrical signal resulting when photons are detected by the Photomultiplier tubes (11,13,14,26). 3.3.30 pulse height analyzer (PHA)—an electronic circuit which sorts and records pulses according to height or voltage (11,13,14,26). 3.3.31 pulse index—the number of afterpulses following a detected coincidence pulse (used in three dimensional or pulse height discrimination) to compensate for the background of a liquid scintillation counter performing (11,14,24,26). 3.3.32 quenching—any material that interferes with the accurate conversion of decay energy to photons captured by the PMT of the LSC (1,3,6,11,12,13,16). 3.3.33 region—regions of interest, also called window and/or channel in regard to liquid scintillation counters. Refers to an energy level or subset specific to a particular isotope (3,11,14,17,24). 3.3.34 scintillation reagent—chemicals that absorbs decay energy transferred from the solvent and emits light (photons) proportional in intensity to the decay energy (3,11,24). D 6866 – 04 2 3.3.35 solvent—in scintillation reagent, chemical(s) which act as both a vehicle for dissolving the sample and scintillator and the location of the initial kinetic energy transfer from the decay products to the scintillator; that is, into excitation energy that can be converted by the scintillator into photons (3.11,13,24). 3.3.36 standard count conditions (STDCT)—LSC condi- tions under which reference standards and samples are counted. 3.3.37 three dimensional spectrum analysis—the analysis of the pulse energy distribution in function of energy, counts per energy, and pulse index. It allows for auto-optimization of a liquid scintillation analyzer allowing maximum performance. Although different Manufacturers of LSC instruments call Three Dimensional Analysis by different names, the actual function is a necessary part of this method (11,13,14). 3.3.38 true beta event—an actual count which represents atomic decay rather than spurious interference (9,10). 3.3.39 flexible tube cracker—the apparatus in which the sample tube (Break Seal Tube) is placed (4,5,9,10). 3.3.40 break seal tube—the sample tube within which the sample, copper oxide, and silver wire is placed. 4. Significance and Use 4.1 Presidential (Executive) Orders 13101, 13123, 13134, Public Laws (106-224, 107.117, AG ACT 2003 and other Legislative Actions all require Federal Agencies to develop procedures to identify, encourage and produce products de- rived from biobased, renewable, sustainable and low environ- mental impact resources so as to promote the Market Devel- opment Infrastructure necessary to induce greater use of such resources in commercial, non food, products. 4.2 Test Method A utilizes Liquid Scintillation Counting (LSC) radiocarbon (14C) techniques to quantify the biobased content of a given product with maximum total error of 15 % count; associated with sample preparation and actual counting. 4.3 Test Method B utilizes Accelerator Mass Spectrometry (AMS) and Isotope Ratio Mass Spectrometry (IRMS) tech- niques to quantify the biobased content of a given product with possible uncertainties of 1 to 2 % and 0.1 to 0.5 %, respec- tively. Sample preparation methods are identical to Method A, 9.2–9.5. Method B diverges after 9.5 and rather than LSC analysis the sample CO2 remains within the vacuum manifold and is distilled, quantified in a calibrated volume, transferred to a quartz tube, torch sealed. Details are given in 12.7-12.10. The stored CO2 is then delivered to an AMS facility for final processing and analysis. 4.4 Although Method A is less sensitive than that of using AMS/IRMS, it has the two distinct advantages: (1) lower costs per evaluation, and (2) much higher instrument availability worldwide. LSC is the preferred method to be used when precise dating (2 % uncertainty or less) is not required and when sample size is not an issue. Indeed, LSC is the most widely used measurement for 14C determination. Method B will be used primarily in extraordinary situations such as when the authenticities of the LSC radiocarbon results are in dispute or when sample size is greatly restricted or costly per mass of sample. 4.5 The test methods described here directly discriminate between product carbon resulting from contemporary carbon input and that derived from fossil-based input. A measurement of a product’s 14C/12C content is determined relative to the modern carbon-based oxalic acid radiocarbon Standard Refer- ence Material (SRM) 4990c, (referred to as HOxII). It is compositionally related directly to the original oxalic acid radiocarbon standard SRM 4990b (referred to as HOxI), and is denoted in terms of fM, that is, the sample’s fraction of modern carbon. (See Terminology, Section 3.) 4.6 Reference standards, available to all laboratories prac- ticing these methods, must be used properly in order that traceability to the primary carbon isotope standards are estab- lished, and that stated uncertainties are valid. The primary standards are SRM 4990c (oxalic acid) for 14C and RM 8544 (NBS 19 calcite) for 13C. These materials are available for distribution in North America from The National Institute of Standards and Technology (NIST), and outside North America from the International Atomic Energy Agency (IAEA), Vienna, Austria. 4.7 Acceptable SI unit deviations (tolerance) for the practice of these methods is 65 % from the stated instructions unless otherwise noted. 5. Safety 5.1 The specific safety and regulatory requirements associ- ated with radioactivity, sample preparation, and instrument operation are not addressed in this standard. It is the respon- sibility of the user of this standard to establish appropriate safety and health practices. It is also incumbent on the user to conform to all the Federal and State regulatory requirements, especially those that relate to the use of open radioactive source, in the performance of these methods. Although Carbon-14 is one of the safest Isotopes to work with, State and Federal regulations must be followed in the performance of this method. 5.2 The use of glass and metal, in particular with closed systems containing oxygen that are subjected to 700°C tem- peratures pose their own safety concerns and care should be taken to protect the operators from implosion/explosion of the glass tube. Strong bases used for CO2 absorption, including Carbosorbt E+ which is also flammable, are particularly hazardous and instructions in Material Safety Data Sheets should be followed with special concern for eye protection. Radioactive carbon-14 compounds should be handled and disposed of in accordance with State and Federal Regulations. METHOD A 6. Detailed Requirements NOTE 1—Acceptable tolerance levels of 65 % are standard to this method unless otherwise stated. 6.1 Low Level Liquid Scintillation analyzers with active shielding. 6.2 Anticoincidence systems such as 2 and 3 Photomulti- plier Tubes (Multidetector systems). 6.3 Coincidence circuits. D 6866 – 04 3 6.4 Software that includes thresholds, and statistics; Pulse rise and shape discrimination, and three Dimensional Spectrum Analysis. 6.5 Use of External and Internal Standards. 6.6 Optimized counting regions to provide very low back- ground counts while maintaining counting efficiency greater than 60 % of samples 0.7 to 1.5 g in pre-cleaned, 20 mL Low Potassium glass count vials. 6.7 No single Liquid Scintillation Counter is specified for this Method. However, minimum counting efficiency and control of background interference is specified. Like all ana- lytical instruments, LS counters require study as to their specific components and counting optimization. 6.8 Standardization of sample preparation is required. 6.9 External and internal standards must be used in LSC operation. 6.10 Standardization and optimization of sample vials; which must be of low Potassium, glass with PTFE insert tops, 20 mL volume, and pre-cleaned. Note: Plastic vials should not be used for this method. 6.11 Optimization of Scintillation Cocktail, CO2 trap re- agents, and additives such as emulsifiers, surfactants, alcohols, and sample material is required. 6.12 Optimization of reagents shall include sample to re- agent volume, scintillator to CO2 trap reagent and additive volumes and compatibility of all reagents. 6.13 Quench curves and counting efficiency and back- ground optimization should be performed using a reference standard based on comparison to NIST oxalic acid reference standards and the same reagents and counting parameters as the samples. 6.14 Counting efficiency of the sample shall be determined by adding to a vial a known activity of the same radionuclide and computing the increase of the sample cpm. 6.15 The internal standard technique for computing count- ing efficiency should be calculated by the equation: E 5 ~cpmb 2 cmpa! D (1) where: E = counting efficiency, cpma = standard counts of (STDCT) sample without added known activity, cpmb = counts of (STDCT) sample plus added known activity, and D = dpm of the internal standard. Other counting interference concerns that must be addressed as part of specific instrument calibration and normalization include luminance, static electricity, random noise, temperature and humidity variability. 6.16 Alternate regions of interest parameters may be used based upon testing of twenty, or more, 6 h counts of the same reference (STDCT) standard that record the raw data and spectrum for KEV regions of interest 4 through 96. Optimal energy windows counting should be determined by comparison of E2/bkg values to obtain the highest count efficiency and the lowest background and other interference. Counting efficiency of