Page:NIOSH Manual of Analytical Methods - 7603.pdf/5

 QUARTZ in coal mine dust: METHOD 7603, Issue 3, dated 15 March 2003 - Page 5 of 7 NOTE:

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Accuracy depends on obtaining uniform deposition of samples and standards across the filter surface and obtaining re prod ucible aliquo ts from the quartz s usp ens ion. This requires som e skill. The quartz calibration curve should be prepared before analyzing samples as a check on the analyst's ability to prepare uniform deposits. Repeatability should be <10% on re plicate standard s with m ore than 4 0 µg qua rtz. Perform an IR scan for each standard filter using the other half of the filter in the reference beam (steps 10 through 12). Construct a calibration graph (absorbance at 800 cm ! 1 vs. µg quartz per filter). This graph should be linear and pass through the origin. (O nly for samples ashed in LTA). Prepare suspensions of at least 5 kaolinite standards in the range 100 to 600 µg per filter. P erform an IR sca n of the kaolinite s tand ards from 100 0 to 650 cm ! 1. Draw baselines as described in step 12 and measure the height of the absorbance bands at both 915 and 800 cm ! 1. Prepare a graph with absorbance at 915 cm ! 1 as ordinate vs. absorbance at 800 cm ! 1 as abscissa. Plot a point for eac h standa rd. If possible, generate the correction curve data on the same day that coal mine dust samples are analyzed since curve param eters may vary somewhat from day to day. A curve through the points should be linear but will not pass through the origin since the peak at 915 cm ! 1 is more intense than the peak at 800 cm ! 1 and sm all am oun ts of kaolinite do not interfere with the quartz analysis. NOTE 1: Ka olinite correctio n calibration curve is required when s am ples are ashed in an LTA since kaolinite is not destroyed under these circum stances a nd has a s interfering peak at 800 cm ! 1 for which a correction must be performed. NOT E 2: A more detailed discussion of IR peaks is given in the IR sec tion of Ch apte r R of this volum e [3]. NOT E 3: S om e training (university or short course) in geology or mineralogy can be useful for the analyst and /or labo ratory mana gem ent. Althoug h m ost analytical chem ists are fam iliar with the IR tec hnique a s ap plied to organic analyses, mineralogical samples require additional knowledge of g eology and m ineralogy to correctly interpret c rystal structu re, m atrix interfe renc es a nd m ineral transform ation for the laboratory client.

MEASUREMENT: 10. 11.

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Set appropriate instrument conditions for quantitative analysis. Place the dry D M-450 filter-half conta ining the dust deposit on a holder. Center the deposit over the hole in the holder and secure the filter with a magnet. (A lighted viewing bo x fac ilitate s th is procedure). Insert the sample into the beam of the spectrophotometer. Place the other half of the DM-450 filter on another holder, secure with a magnet and insert it into the reference beam. NOTE: For the best precision, the referenc e filter should be half of the same DM -450 filter which contains the redeposit. However, for routine analysis, the same 2-propanol-treated blank can be used for all filters with the sam e lot numb er. Run an infrared scan, in linear absorbance mode from 1000 to 650 cm ! 1. Draw an app ropriate baseline under the absorbance band at 800 cm ! 1 from ca. 820 to 670 cm ! 1. Measure and record the absorbance at 800 cm ! 1, baseline to maximum. If the sample was ashed in an LTA, the presence of ka olinite will be indicated by an absorption band with a maximum at 915 cm ! 1. Draw a baseline under this band from ca. 960 ! 1 to 860 cm ! 1. Measure and record the absorbance at 915 cm ! 1, baseline to maximum. Analyze blanks. Check results for contamination.

CALCULATIONS: 14.

Correct for kaolinite, if required. Using the sample absorbance at 915 cm ! 1, refer to the kaolinite curve to find the absorbance at 800 cm ! 1 due to ka olinite. Subtract this am ount from the sam ple absorbance at 800 cm ! 1. Use this corrected value to calculate µg quartz in the sample.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition