Page:NIOSH Manual of Analytical Methods - 7601.pdf/1

 SILICA, CRYSTALLINE, by VIS SiO2

MW: 60.08

CAS: 14808-60-7 (quartz) 14464-46-1 (cristobalite) 15468-32-3 (tridymite)

METHOD: 7601, Issue 3

RTECS: VV7330000 (quartz) VV7325000 (cristobalite) VV7335000 (tridymite)

EVALUATION: PARTIAL

quartz (respirable) 10 mg/m3 /(%SiO2 +2); cristobalite and tridymite (respirable) ½ the above NIOSH: 0.05 mg/m3 ; carcinogens ACGIH: quartz (respirable) 0.1 mg/m3 cristobalite (respirable) 0.05 mg/m3 tridymite (respirable) 0.05 mg/m3

OSHA :

PROPERTIES:

SAMPLING SAMPLER:

CYCLONE + FILTER (10-mm cyclone, nylon or HigginsDewell (HD) + 0.8-:m MCE or 5-:m PVC)

7601

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

MEASUREMENT TECHNIQUE:

VISIBLE ABSORPTION SPECTROPHOTOMETRY

ANALYTE:

Silicon complexes-silicomolybdate (420 nm) and molybdenum blue (820 nm)

DIGESTION:

Phosphoric acid, to remove interfering silicon compounds

FLOW RATE:

HD cyclone: 2.2 L/min; nylon cyclone: 1.7 L/min

VOL-MIN: -MAX:

400 L 800 L

SHIPMENT:

Routine

FILTRATION:

To collect undigested material

SAMPLE STABILITY:

Stable

DISSOLUTION:

Crystalline silica in HF

BLANKS:

2 to 10 field blanks per set CALIBRATION:

NIST SRM 1878a quartz, NIST 1879a cristobalite, USGS 210-75-0043 dissolved in HF

RANGE:

Silicomolybdate: 0.1 to 2.5 mg SiO2 ; molybdenum blue: 0.02 to 0.15 mg SiO2

ACCURACY RANGE STUDIED:

Not studied

BIAS:

None known

OVERALL PRECISION (Ö rT ):

Not determined

ACCURACY:

Not determined

ESTIMATED LOD: 10 µg SiO2 PRECISION ( þ r ):

0.09 [1]

APPLICABILITY: Determination of crystalline silica in respirable or total dust, settled dust and in biological samples [1,2]. The three crystalline polymorphs cannot be distinguished by this method. The working range is 0.04 to 5 mg/m3 for a 500-L air sample. Alternative XRD (e.g. NMAM 7500) and IR (e.g. NMAM 7602 and 7603) methods have better laboratory-to-laboratory agreement than visible absorption methods and therefore this method is recommended for research use only [3]. See also discussion of crystalline silica in Chapter R of this volume [4]. INTERFERENCES: Any silicon-containing compound which is soluble in HF will give a positive interference. See APPENDIX A. OTHER METHODS: This is P&CAM 106 in a revised format [1]. X-ray diffraction (XRD; Method 7500) can distinguish the three main silica polymorphs and does not detect amorphous silica. Silicates interfere with XRD but are removed by phosphoric acid cleanup. Infrared spectrometry (IR; Methods 7602 and 7603) can determine the three polymorphs, although if two or more are present, a less sensitive peak must be used; however, amorphous silica and silicates, in large amounts, interfere with IR.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition