Document KzmV73R8GneDRYbnvKEpK4VjX

DETECTION OF ASBESTIFORM AMPHIBOLE IN TALC FOR COSMETIC USE The method for the detection of asbestiform ' amphibole in talc for cosmetic use consists of initial analysis for amphibole minerals above the 0.5% (w/w) level, followed by characterization of the amphibole m ineral present, if any, as asbestiform or nonasbestiform by dispersion staining/optical m icroscopy. X-Ray Diffractometry The procedure consists of slow-scanning, under previously determ ined condi tions, a com press ed pellet of the sam ple talc in the 11.0-10.02G (8.85-8. 04A) region for the presence of an amphibole peak. 1 - Standard Preparation Optimal instrum ent conditions m ust first be determ ined with the use of trem olite standards - 1.0%, 0.75%, 0.5% trem olite by weight, prepa.red in a standard talc which is free of interfering peaks in the 11.0-10.020 region. The tremolite standards are prepared in the following manner: a. Weigh out appropriate amounts of standard talc and tremolite of at least 95% p u rity " both of which have ^ e e n ground to pass a 325-m esh sieve. T ra n s fe r to a W aring B lendor (or equivalent). Add 100 m l. of ethanol to the blender and blend at low speed for 5 minutes , b. Carefully transfer, with repeated ethanol w ashings, the contents of the blender into a large beaker. Evaporate the ethanol on a steam bath. c. The dried sample is then shaken in a plastic vial for 5 minutes on a Spex M ixer/M ill (or equivalent) to remove clumps and caked sample resulting from the evaporation of ethanol. d. The homogeneity of the prepared standard is determined by m ic ro scopy previous to the X -ray diffraction analysis. According to the Mining Enforcem ent and Safety Administration and the National Institute of Occupational Safety and Health (F ederal R egister, VoL 39, N o. 127, p. 24319, Ju ly 1, 1974) the t e r m ''a s b e s t o s " is not applicable to the nonfibrous form of tremolite which has been found in certain talc deposits. *A c o m m e r c i a l s o u r c e of high p u r ity t r e m o l i t e is c u r r e n t l y being sought, since much, difficulty has been encountered in obtaining high grade trem olite. - 2- e. The homogeneous standard is then pressed into a 1-1/4" pellet with a backing of boric acid. 2 gram of standard is transferred to the die-holder and evenly distributed on a polished, scratch-free die. 4 gram of boric acid is then distributed evenly on the talc layer. The mixture is pressed into a pellet under conditions suitable for obtaining a smooth planar surface (for example, a p ressu re of 15, 000 - 24, 000 lb .), calcu lated on a 3" r a m , was found to produce suitable pellets). The resulting pellet must have a talc face which is free of flaws; if not, the pellet must be discarded. (This r e quirement is critical since excessive surface scatter will cause abnormally high background counts.) Two acceptable pellets are prepared from each standard. 2 - Sample Preparation Two pellets are prepared from each sample in the manner described for the standard pellets (l.,S tep e.). A qualitative scan from 4-5020 is m ade on one of these pellets to ascertain the presence of amphibole above the 2% level or the p resen ce of m in eral im purities having interfering peaks in the U,O-1O.O20 (8.85~8. 04/?) region of the scan. The p resence of such interference will eliminate use of the x-ray diffraction method for * the sample, and one will have to proceed directly to the m icroscopical procedure. 3 - Instrumentation I n s t r u m e n t a l v a r ia b le s a r e o p tim iz e d on the 1% s t a n d a r d . L o w e r s t a n d a r d s are then analyzed under the optimum conditions to determine the lower level of detection. Of m ajor im portance in obtaining m axim um instrum ent sensitivity are a slow diffractometer speed combined with a compatible recorder speed, and high attenuation combined with a statistically accept able time constant on the ratem eter. Under appropriate instrum ental conditions the peak obtained for the 0.5% standard should be easily detect able above background noise as per the scan on the following page. Instrumental conditions employed for the Siemens Diffractometer (Model No. M 386-X-A4), and Counter and R ecorder Unit (Type T) are: Radiation: Cuwith Kgfilter at 40 KV and 24 ma D iv e r g e n c e slit: 1 R e c e iv in g slit: 0 .2 m m Goniometer speed: l/1020/minute Recorder speed: 300 m m /h r. A ttentuation = l x 10 im p u ls e s /s e c o n d S tatistical Time constant, T (s) = 4 e r r o r of 1.1% cuonnddeirtitohness e. AR itst een Tu ai mtoer == 200.18 \ 3- - 4 - X-Ray Diffraction Scans T1 s ta n d a rd o r s a m p le p e lle t is p la c e d in a s u ita b le h o ld e r and slow ly so .ned between 11.0 and 10.020. The pellet is then ro tated 90 w ith respect to its original position in the goniometer and rescanned b e tween 11.0 and 10.020 since pellet orientation m ay affect peak intensity. The presence of a reproducible peak (or peaks) is due to the presence of amphibole m inerals; the absence of peaks in this region indicates the taebcshennicqeu eo.f a m p h ib o le in the s a m p le , w ithin the lim it of d e te c tio n of this If amphiboleis detected in one or both pellets by x-ray diffractometry, then the sample must be put through the following confirming scheme: X - r a y D i f f r a c t o m e t r y --(+--)---O p tic a l M i c r o s c o p y -----------(---)-----y- Stop (Acid and (amphibole S toVp (amphibole absent) Leach) Dispersion Staining absent) Color 1 1+1rous M orphology- (.-..).---^,, Stop (asbestiform 11 ( + ) am phibole Stop absent) (asbestiform amphibole pres ent) Because of the interference caused by some carbonates (e.g. calcite) in the detection of trem olite asbestos in talc by optical m icroscopy/dispersion staining, it is necessary to first remove these carbonates by a simple acid leaching procedure: 1. W eigh out 2 g. of the talc into a 100 m l . b e a k e r . Add 25 m l . of 10% v / v HC1 slow ly (to p re v e n t e x c e s s i v e evolution of gas if carbonates are present) and heat, with occasional stirring on a steam bath for 30 m inutes. 2. Filter on a vacuum filter, in either a porcelain cone with glass fiber filter mat or a porous glass bottom cup, and wash several times with hot water. Dry the talc. Optical M icroscopy and Dispersion Staining 1. C a r e f u ll y d i s p e r s e about 0 .2 m g . of talc in one d ro p of C a r g il l e HD liquid n~,- = 1.605 and cover w ith a clean cover slip. 2, Exam ine the sample in the D. S. central stop mode. The substage diaphragm should be almost completely closed, the field diaphragm - 4- may be partially closed to enhance color contrast, and the polarizer should be in position. 3. Tremolite, actinolite and presumably other amphibole minerals, under these conditions, will show the following D. S. colors: yellow changing to blue with rotation of the sample relative to the polarizer or yellow changing to orange with rotation. The variation of the color change is due to the fact that the tremolite may lie in one of two positions relative to its principal optical orientation. 4. In order for an amphibole mineral to be considered asbestiform or fibrous it must meet the following OSHA definition^. A. Particles must appear to be fibrous rather than as crystals or slivers. B. The maximum diameter of a fiber to be counted is 3 m i crons. C. The maximum length of a fiber to be counted is 30 microns. D. The length to width ratio must be 5 or more to 1, that is, 5 times or more longer than wide. E. The separate or individual fibers must contain fibrils or the "bundle of sticks" effect, unless they are at a non-divisible stage. A fibril cannot-be subdivided and would be counted, if it meets the other criteria. The electron microscope may be used to prove the fibrous nature of the particles. The length to width ratio of 5 or more to 1 is not meant to imply that other particles are not hazardous. 5. It is imperative that both D. S. color and fibrous morphology criteria be satisfied before identifying a particle as asbestiform amphibole since other substances (e.g. calcite) may show colors similar to those described. ^"Tremolite and Talc". U. S. Department of Labor, Occupational Safety and Health Administration, Field In fomi ation M em oran durn #74-92,. November 21, 1974.