ASTM_D_7134_-_05_2012.pdf

Designation:D713405(Reapproved 2012)Standard Test Method forMolecular Mass Averages and Molecular Mass Distributionof Atactic Polystyrene by Matrix Assisted Laser Desorption/Ionization(MALDI)-Time of Flight(TOF)Mass Spectrometry(MS)1This standard is issued under the fixed designation D7134;the number immediately following the designation indicates the year oforiginal adoption or,in the 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 This test method covers the determination of molecularmass(MM)averages and the distribution of molecular massesfor linear atactic polystyrene of narrow molecular mass distri-bution(MMD)ranging in molecular masses from 2000 g/molto 35 000 g/mol by matrix assisted laser desorption/ionizationtime-of-flight mass spectrometry(MALDI-TOF-MS).This testmethod is not absolute and requires the use of biopolymers forthe calibration of the mass axis.The relative calibration of theintensity axis is assumed to be constant for a narrow MMD.Generally,this is viewed as correct if the measured polydis-persity is less than 1.2 for the molecular mass range givenabove.1.2 The values stated in SI units are to be regarded as thestandard.1.3 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 applica-bility of regulatory limitations prior to use.NOTE1There is no known ISO equivalent to this standard.2.Referenced Documents2.1 ASTM Standards:2D883 Terminology Relating to PlasticsD1600 Terminology forAbbreviated Terms Relating to Plas-ticsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 DefinitionsFor definitions of technical terms pertain-ing to plastics used in this test method see Terminologies D883and D1600.4.Summary of Test Method4.1 The MALDI process involves the ablation and theionization of an analyte dispersed in an organic small moleculematrix,most commonly an organic acid.One way to cationizethe analyte is to add a metal salt.The process is as follows:Apolymer(biological or synthetic)is co-crystallized or co-mixedwith the matrix molecule in the solid phase and deposited onthe target often made of stainless steel(details of this processwill be described later).A short duration UV or IR laser pulseis used to ablate the matrix and the analyte mixture.Theablation process involves UV or IR absorption by the matrixmolecule.The laser energy excites the matrix molecule causingit to vaporize and decompose.Analyte and matrix leave thetarget surface in a plume.This ablation process involves thetransfer of energy from electronic or vibration modes intotranslational modes of the matrix.The MALDI-TOF-MSmethod described in this test method uses a UV nitrogen laseroperating at 337 nm.This laser has a pulse width of about 3 ns.4.2 In the test method described below,the polystyrenepolymer in the ablation plume gains an Ag cation and isaccelerated by a high voltage,often about 20 keV.Followingacceleration,the polymer species drifts down the field freeflight tube and is detected at the end of the flight tube.Thetime-of-flight of the species is a measure of its mass.From thedistribution of arrival times and the calibration of the arrivaltimes with known mass standards,the mass distribution of thepolymer is determined.1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.70 on Analytical Methods.Current edition approved April 1,2012.Published June 2012.Originallyapproved in 2005.Last previous edition approved in 2005 as D7134-05.DOI:10.1520/D7134-05R12.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.3 This test method is valid only for polystyrene of narrowmolecular mass distribution(MMD)polymers,Mw/Mn 1.2with Mngreater than 3000 g/mol or less than 35 000 g/mol.5.Significance and Use5.1 General UtilityThe molecular mass(MM)and mo-lecular mass distribution(MMD)are fundamental characteris-tics of a synthetic polymer that result from the polymerizationprocess.The MM and MMD is useful for a wide variety ofcorrelations for fundamental studies,processing and productapplications.For example,it is possible to compare theobserved MMD to predictions from an assumed kinetic ormechanistic model for the polymerization reaction.Differencesbetween the values will allow alteration of the model orexperimental design.Similarly,it is possible the strength,themelt flow rate,and other