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 Esta página en Español SILICA, CRYSTALLINE by IR (KBr pellet) SiO2

MW: 60.08

CAS:14808-60-7 14464-46-1 15468-32-3

METHOD: 7602, Issue 3

OSHA : NIOSH: ACGIH:

RTECS: VV7330000 (quartz) VV7325000 (cristobalite) VV335000 (tridymite)

EVALUATION: PARTIAL

quartz (respirable): 10 mg/ m3 / (% SiO2 + 2); cristobalite and tridymite (respirable): 1/2 the above 0.05 mg/m3 ; carcinogens quartz (respirable) 0.1 mg/m3 cristobalite and tridymite (respirable) 0.05 mg/m3

7602

PROPERTIES:

Issue 1: 15 February 1984 Issue 3: 15 March 2003 solid; d 2.65 g/cm3 ; crystalline transformation: quartz to tridymite @ 867 °C; tridymite to cristobalite @ 1470 °C; "quartz to $-quartz @ 573 °C

SYNONYMS: free crystalline silica; silicon dioxide SAMPLING

MEASUREMENT

CYCLONE + FILTER (10-mm nylon or Higgins-Dewell (HD), and PVC filter, 37-mm, 5-µm)
 * see sampling section

TECHNIQUE:

INFRARED ABSORPTION SPECTROPHOTOMETRY

ANALYTE:

Quartz

FLOW RATE:

Nylon cyclone: 1.7L/min HD cyclone: 2.2 L/min

ASH:

Muffle furnace of RF plasma asher

PELLET:

Mix residue with KBr; press 13-mm pellet

VOL-MIN: -MAX:

400 L 800 L

IR:

Scan absorbance from 1000 to 600 cm-1

SHIPMENT:

Routine

CALIBRATION:

SAMPLE STABILITY:

NIST SRM 1878a quartz, NIST SRM 1879a cristobalite, USGS 210-75-0043 tridymite diluted in KBr

Stable RANGE:

10 to 160 µg quartz

BLANKS:

2 to 10 field blanks per set

SAMPLER:

ESTIMATED LOD: 5 µg quartz BULK SAMPLE: High volume or settled dust to identify interferences

PRECISION ( þ r ):

< 0.15 @ 30 µg quartz per sample, in coal dust [1]

ACCURACY RANGE STUDIED:

Not studied

BIAS:

Not determined

OVERALL PRECISION (Ö r T ): Not determined ACCURACY:

Not determined

APPLICABILITY: The working range is 0.025 to 0.4 mg/m3 for a 400-L air sample. Cristobalite and tridymite also have major absorbance peaks at 800 cm-1 which can be used for their determination [1-6]. IR methods can quantify quartz, cristobalite and tridymite if amorphous silica and silicates are not present in large amounts. However, sensitivity is reduced if multiple polymorphs are present and secondary peaks must be used. A potential for bias exists when correcting for matrix absorption effects, with an increasing risk of bias at lower quartz concentrations. See also discussion of crystalline silica in Chapter R of this volume [7]. INTERFERENCES: Amorphous silica, calcite, cristobalite, kaolinite and tridymite interfere; see APPENDIX. OTHER METHODS: This is P&CAM 110 in a revised format [1]. It is similar to Method 7603, except for sample preparation (KBr pellet vs. redeposition). XRD (method 7500) can distinguish the three silica polymorphs and silica interferences can be eliminiated by phosphoric acid treatment. Crystalline silica can also be determined by visible absorption spectrophotometry (e.g., method 7601), but polymorphs cannot be distinguished. Visible absorption methods also have larger laboratory-tolaboratory variability than XRD and IR methods and therefore are recommended for research use only [8].

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition