Page:NIOSH Manual of Analytical Methods - 7302.pdf/2

 ELEMENTS by ICP (Microwave Digestion): METHOD 7302, Issue 1, dated 21 July 2014 - Page 2 of 9

REAGENTS:

EQUIPMENT:

1.	Nitric acid, conc., trace metal grade* 2.	Calibration stock solutions, 1000 µg/mL and 10,000 µg/mL commercially available, or prepared per instrument manufacturer’s recommendation (see step10) 3.	Digestion acid*. 1:1 water, ASTM type II, and nitric acid*, trace metal grade 4.	Argon, liquid 5.	De-ionized Water, ASTM Type ll [5] 6.	Dilution acid*, 20% nitric acid in ASTM Type II water
 * See Special Precautions

1.	Sampler: mixed cellulose ester membrane (MCE) filter, 0.8-µm pore size, 37-mm diameter; in 2-piece cassette filter holder 2.	Personal sampling pump, 1 to 4 L/min, with flexible connecting tubing 3.	Inductively coupled plasma-atomic emission spectrometer, equipped as specified by the manufacturer for analysis of elements of interest 4.	Regulator, two-stage for argon 5.	Microwave, programmable power, active temperature control, minimum of 574 W, corrosion resistant ventilated oven and turntable 6.	Microwave digestion vessels, high pressure, closed PTFE, 100-mL capacity 7.	Volumetric flasks, 25 mL** 8.	Assorted volumetric pipettes as needed**
 * Acid wash all glassware and vessels before using.

SPECIAL PRECAUTIONS: Wear gloves, lab coat, and safety glasses while handling all chemicals. All work should be performed with adequate ventilation to personnel and equipment. Because this method involves the use of capped digestion containers, avoid the use of other acids such as perchloric acid in combination with nitric acid that could cause a violent reaction [6,7]. In the preparation of the digestion and dilution acids, it is imperative that acid be added to water in order to avoid a violent exothermic reaction. SAMPLING 1.	Calibrate each personal sampling pump with a representative sampler connected to the pump (in line). 2.	Sample at an accurately known flow rate between 1 and 4 L/min. For estimated sampling volumes see Table 1. For TWA measurements see Table 2. Do not exceed a filter loading of approximately 2 mg total dust. NOTE: Filter overloading can be assessed by periodic visual checks. See NMAM Chapter O, “Factors Affecting Aerosol Sampling,” for additional discussion on filter capacity.  SAMPLE PREPARATION NOTE:	If total weights are desired, weighing should be done at this step. Follow NIOSH method 0500 for gravimetric analysis [11]. 3.	Open the cassette filter holders and transfer the samples, blanks, and Quality Control (QC) filters to clean PTFE digestion vessels. Wipe the internal cassette surfaces with a 37-mm MCE filter, polyvinyl alcohol wipe or cellulosic wipe wetted with deionized water, and add to the digestion vessel to transfer non-filter aerosol deposits into the digestion vessels. 4.	Add digestion acid up to 10 mL, and cap the vessels.

NIOSH Manual of Analytical Methods (NMAM), Fifth Edition