ASTM D7558-2009 6250 Standard Test Method for Colorimetric Spectrophotometric Procedure to Quantify Extractable Chemical Dialkyldithiocarbamate Thiuram and Mercaptobenzothiazole Ac.pdf

1、Designation: D 7558 09Standard Test Method forColorimetric/Spectrophotometric Procedure to QuantifyExtractable Chemical Dialkyldithiocarbamate, Thiuram, andMercaptobenzothiazole Accelerators in Natural RubberLatex and Nitrile Gloves1This standard is issued under the fixed designation D 7558; the num

2、ber 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. Scope

3、1.1 This test method is designed to quantify the amount oftotal extractable accelerators in natural rubber latex (NRL) andnitrile gloves. Three common classes of rubber accelerators,the mercaptobenzothiazole (MBT), thiuram, and thiocarbamatetype compounds can be detected and quantified by this metho

4、d.If the specific rubber accelerator(s) present in the glovematerial is not known, quantification is based on zinc dibu-tyldithiocarbamate (ZDBC) equivalents. This method will notdetect all potential rubber accelerators, including mercaptoben-zothiazole disulfide, dimorpholine, thioureas and dipheny

5、ldiamine.1.2 For the purpose of this test method, the range ofchemical accelerator measurement is based on the limit ofdetection (LOD) established in the performing laboratory.1.3 This test method should be performed by experiencedanalysts or under the supervision of those experienced in theuse of s

6、pectroscopy and working with organic solvents.1.4 This test method has not been validated for measure-ment of long chain dithiocarbamates or accelerators from otherrubber products, such as lubricated condoms (1).2Althoughthis assay has been reported in the literature for the evaluationof accelerator

7、 levels in condoms, further validation for accel-erator measurement from other rubber products is required bythe testing laboratory prior to use.1.5 This test method is not designed to evaluate the potentialof rubber materials to induce or elicit Type IV skin sensitiza-tion reactions (for Type IV sk

8、in sensitization reactions see TestMethod D 6355). Total extractable accelerator content does notreflect bioavailablity of individual accelerators that are de-tected and measured by this method. This test method shouldbe used to test and measure the total residual chemicalaccelerator level in NRL an

9、d nitrile gloves under controlledlaboratory conditions, and should not be used to describe,appraise, or assess the hazard or risk of these materials orproducts under actual in-use conditions.1.6 The values stated in SI units are to be regarded asstandard. No other units of measurement are included i

10、n thisstandard.1.7 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.

11、2. Referenced Documents2.1 ASTM Standards:3D 3577 Specification for Rubber Surgical GlovesD 3578 Specification for Rubber Examination GlovesD 4483 Practice for Evaluating Precision for Test MethodStandards in the Rubber and Carbon Black ManufacturingIndustriesD 6355 Test Method for Human Repeat Insu

12、lt Patch Testingof Medical Gloves3. Terminology3.1 Total thiol vulcanization accelerator includes MBT, zincdithiocarbamates (ZDTCs) and thiurams.3.2 Definitions:3.2.1 limit of detection (LOD), nthe lowest acceleratorconcentration that can be measured and be statistically differentfrom the blank.3.2.

13、1.1 DiscussionThe LOD is expressed as 3.3 3 stan-dard error of the y-intercept of the standard plot regression linedivided by the slope of the calibration line.3.2.2 limit of quantitation (LOQ), nthe lowest acceleratorconcentration that can be measured to produce quantitativelymeaningful results wit

14、h acceptable precision and accuracy.1This test method is under the jurisdiction of ASTM Committee D11 on Rubberand is the direct responsibility of Subcommittee D11.40 on Consumer RubberProducts.Current edition approved July 1, 2009. Published August 2009.2The boldface numbers in parentheses refer to

15、 a list of references at the end ofthis standard.3For 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.1Copyright A

16、STM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.2.1 DiscussionThe LOQ is expressed as 10 3 stan-dard error of the y-intercept of the standard plot regression linedivided by the slope of the calibration line.3.2.3 linear range, narea of a gra

17、ph of absorbance versusconcentration that approximates a straight line.3.2.4 spectrophotometric measurement, nthe unit of mea-sure of the instrument that is proportional to absorbance.3.2.5 standard solution, nthe standard analyte to whichthe test (unknown) sample being measured is compared.4. Summa

18、ry of Test Method4.1 The rubber material is cut into small pieces andapproximately1gisplaced into the extraction vessel. Aceto-nitrile is added to give a final volume/weight of 10 mLacetonitrile per gram of rubber. The extraction vessel issecurely capped, placed onto a rotator and extracted at appro

19、xi-mately 200 rpm for a minimum of 2 h at room temperature (256 5C). The acetonitrile extract is recovered and centrifuged ina sealed centrifuge tube at 500 3 g for 20 min at roomtemperature to remove any residual particulate matter. Theacetonitrile extract supernatant fluid is transferred to a clea

20、ncontainer and capped. Zinc dibutyldithiocarbamate (ZDBC)standards at 500 to 31.25 g/mL in acetonitrile and a blank areprepared. Cobalt chloride (10 L, 420 mmol/L) aqueoussolution is added to 1 mL aliquots of each sample extract andstandard. Each individual solution is thoroughly mixed andthen incub

21、ated for 120 min at 50 6 5C. The extracts andstandards are cooled to room temperature for approximately 15min after the 50C incubation. A 100 L aliquot of each isdiluted with 1.9 mL of acetonitrile. All are mixed thoroughlyand absorbance of each sample, blank and standard is mea-sured at 320 nm on a

22、 UV spectrophotometer. Concentration ofresidual accelerator is obtained by extrapolation from thestandard plot. Depending upon the number of samples tested,this test method takes about5htocomplete.5. Significance and Use5.1 Dialkyldithiocarbamates (DTCs), benzothiazoles, andthiurams are often used a

23、s vulcanization accelerators in NRLproducts. Zinc DTC accelerators are added either directly orare formed in situ during the vulcanization process via reactionbetween a thiuram(s) and zinc oxide. DTCs, benzothiazoles,and thiurams have been detected in leachates from medicaldevices made of rubber suc

24、h as gloves. Studies have shownthese chemicals can cause allergic contact dermatitis. A simpleselective method to monitor rubber accelerator levels in rubberextracts would be useful for quality control, product screeningand research.5.2 This colorimetric assay measures dialkyldithiocarbam-ates, incl

25、uding zinc dialkyldithiocarbamates (ZDTC), mercap-tobenzothiazole (MBT) and thiurams as a total thiol vulcani-zation accelerator level in rubber products. A UVspectrophotometer with detection at 320 nm is used to measurethe ZDTC, mercaptobenzothiazole and thiurams. Sample ex-tracts diluted at 1:20 p

26、rior to measurement on the spectropho-tometer is usually sufficient to quantify the residual acceleratorlevel from most commercially available rubber gloves; how-ever, sample dilution can be adjusted (from neat extract to 1:20 dilution) based on analytical needs. Thiurams and ZDTCscomplex with cobal

27、t turning the extract to a concentration-dependent shade of green. ZDTCs reacts quickly while thi-urams react very slowly (requiring a heat catalyst). Mercapto-benzothiazole does not complex to Co(III), however, it absorbsstrongly at 320 nm. It can be distinguished from both ZDTCsand thiurams by its

28、 strong absorbance at 320 nm without thecobalt dependent visible green color. Cobalt complexed thi-urams and ZDTCs, but not MBT, also have and absorbance at370 nm (2).6. Interferences6.1 Suspended solids such as powder or cotton flock caninterfere with spectrophotometric measurements and care mustbe

29、 taken not to resuspend particulate following centrifugation.Some extracts may require additional steps to remove particu-late such as higher speed centrifugation or possibly filtration,dependent on the physical nature of the particulate material.The rubber accelerators, mercaptobenzothiazole disulf

30、ide, di-morpholine, thioureas, diphenyl diamine, and diphenylguani-dine are not detected by this assay and do not interfere withmeasurement of MBT or ZDTCs. Potential exists for interfer-ence from leached dyes or other additives that absorb at 320nm; however, this has not been reported.7. Apparatus7

31、.1 Polypropylene or Glass Extraction Tubes, with screwtop lids (50 mL, conical bottom).7.2 Polypropylene Cryotubes, (3.6 mL), with screw tops forcobalt reaction of extracts and standards and for the final 1/20dilution prior to UV analyses.7.3 Parafilm.7.4 Adjustable Positive Displacement Pipettes,(5

32、to10mL,1 mL and 250 L).7.5 Laboratory Shaker, (200 rpm).7.6 Laboratory Vortex Mixer.7.7 Water or Dry Bath, capable of maintaining the tempera-ture at 50C.7.8 Centrifuge, (capable up to 500 3 g).7.9 UV Spectrophotometer.8. Materials8.1 Chemical Accelerator StandardUse specific thiuram,zinc dithiocarb

33、amate or mercaptobenzothiazole if specificspecies in the specimen is known.4NOTE 1Storage problems for zinc diethyldithiocarbamate have beenreported and care needs to be taken if this is to be used as the referencestandard.8.2 CoCl2Cobalt (II) Chloride hexahydrate.8.3 Water, (distilled/deionized (dH

34、2O).8.4 Acetonitrile, (HPLC grade).4If species is not known use zinc dibutyldithiocarbamate (ZDBC), the solesource of supply of which known to the committee at this time is ChemService, Inc.,660 Tower Lane, PO Box 599, West Chester, PA 19381 (cat. No. Ou-76 (M.W. =474.2). If you are aware of alterna

35、tive suppliers, please provide this information toASTM International Headquarters. Your comments will receive careful consider-ation at a meeting of the responsible technical committee,1which you may attend.D75580929. Standards and Reagent Preparation9.1 Stock ZDBCWeigh 10 mg ZDBC (or appropriateacc

36、elerator standard) and add 10 mL acetonitrile (final concen-tration of 1000 g/mL). Mix until completely dissolved.(Prepare a fresh mixture immediately before use.)NOTE 2(1) To improve precision in weighing milligram quantities ofchemical compounds, a larger mass may be used and dissolved in greaterv

37、olumes of solvent to yield a final concentration of 1 g/mL. In addition,it is easier and more accurate to adjust the volume of acetonitrile added tothe ZDBC vs. weighing exactly 10 or 100 mg to achieve the stocksolution. (2) It is advisable to use positive displacement pipettes foraccurate addition

38、of acetonitrile due to its low surface tension. (3) Seal allvials with Parafilm around the screw caps to prevent leakage andevaporation.9.2 Prepare DilutionsStarting with the stock solution of1000 g/mL ZDBC (or appropriate accelerator standard),perform five 1:1 serial dilutions using acetonitrile as

39、 the diluentto produce the following standard concentrations 500, 250,125, 62.5, and 31.25 g/mL (500 31.25 ppm). Ensure thateach standard is dissolved by thoroughly mixing before pro-ceeding with the next dilution.NOTE 3If MBT is employed as the standard, the 500 g/mL standardabsorbance will be outs

40、ide the linear range of the curve.9.3 Solvent BlankBlank spectrophotometer using reagentblank (see 12.3).9.4 Cobalt Chloride ReagentTo 50 mg of CoCl26H2Oadd 500 L dH2O (100 mg/mL).NOTE 4Larger masses of CoCl26H2O may be used with appropriatevolume of dH2O to achieve a final concentration of 100 mg/m

41、L (420mmol/L). This reagent is stable up to 1 month at room temperature in asealed container.10. Hazards10.1 Laboratory personnel should adhere to standard goodlaboratory practices. Care should be taken when working withall chemical reagents. Acetonitrile is a volatile solvent and allsolvent transfe

42、r steps should be conducted in a chemical hood.Chemical resistant glove use is recommended when handlingorganic solvents.11. Extraction11.1 Extraction MediumAcetonitrile.11.2 Test Specimen:11.2.1 Cut the entire test specimen into small pieces (ap-proximately 1 cm2). Mix the small pieces to ensure th

43、at thesample analyzed is representative of the entire specimen. Aweight of at least 1 g sample should be placed in extractionsolution to provide a final concentration of 1 g sample/10 mLacetonitrile. The test specimen weight used and acetonitrilevolume added should be recorded. Three separate 1 g/10

44、 mLextracts should be prepared.11.2.2 Perform the extraction of each rubber test specimenusing the extraction solution as described below:11.2.2.1 The test specimen shall be extracted in acetonitrilefor2hatatemperature of 25 6 5C using continuous shakingat approximately 200 rpm on laboratory shaker.

45、 Periodicallycheck each sample visually to ensure that the specimen piecesare covered with extraction solvent (that is, not adhering to vialwall above the solvent). Fifty-millilitre polypropylene conicalbottom tubes work well for this purpose. If specimen pieces areabove the solvent they can easily

46、be tapped down into thesolvent without opening the vials. Wrapping the top of the tubewith Parafilm after screwing on the lid ensures a good seal toprevent potential loss/leakage of solvent.11.2.2.2 Remove the samples from the shaker after extrac-tion. Separate the NRL/nitrile pieces from the aceton

47、itrileextract by carefully decanting into a new 50 mL centrifugetube. Centrifuge the acetonitrile sample extract in a sealedcentrifuge tube at 500 3 g for 20 min at room temperature toremove any residual particulate matter. Separate the extractfrom residual particulate by carefully decanting or pipe

48、tting theextract to prevent re-suspension of the particulate. If extract iscloudy or visible particulate remains additional centrifugationor filtration is required to remove particulate.12. Colorimetric/Spectrophotometric Assay12.1 Takea1mLaliquot of each of the ZDBC standarddilutions and add 10 Lof

49、 the CoCl2reagent solution into each.12.2 Takea1mLaliquot of each rubber extract test sampleand add 10 L of the CoCl2reagent solution into each. Repeatthis to provide duplicate measures for each test sample.12.3 Prepare a reagent blank using 1 mL the acetonitrile and10 L of the CoCl2reagent solution.12.4 Mix all samples, standards and blanks thoroughly andthen incubate for 120 min at 50 6 5C. All lids should besealed with Parafilm after they are screwed onto the tube.Afterincubation, allow the tubes to come to room temperature beforeproceeding