Reference method for measuring emissions of nitrogen oxides from stationary sources: chapter 5

5 Apparatus

5.1 Sampling Train (Figure 1)

  • 5.1.1 Probe. Borosilicate glass, approximately 6-mm ID (inside diameter), fitted with a 12/5 spherical joint for attachment to the three-way stopcock on the sample collection flask, provided with a filter on the inlet end for removal of particulate matter, long enough to extend about one third to halfway into the stack or duct, heated and insulated sufficiently well to prevent condensation of moisture while purging and sampling.

  • 5.1.2 Collection Flask. A 2-litre round-bottom glass flask with a short-neck 24/40 standard taper joint, protected against implosion or breakage with tape or foamed plastic, with known calibrated volume.

  • 5.1.3 Stopcock. A three-way, T-bore stopcock with a 20/40 standard taper joint for attachment to the sample collection flask, and a 12/5 spherical joint for attachment to the sample probe.

  • 5.1.4 Stopcock Grease. High-vacuum, high-temperature, inert stopcock grease.

  • 5.1.5 Mercury Manometer. An open-end 1-metre U-tube mercury manometer with 1-mm scale graduation.

  • 5.1.6 Squeeze-Bulb. A rubber, valved, one-way squeeze-bulb to purge the sample probe.

  • 5.1.7 Vacuum Pump. A portable vacuum pump capable of evacuating the sample collection flask to a pressure of about 25 mm Hg absolute.

  • 5.1.8 Stopcock or Valve. The evacuating and purging systems are connected to the sample flask through a valve or stopcock.

  • 5.1.9 Thermometer. Dial or glass with 1°C divisions over an approximate range of -5 to 50°C, capable of measuring to within ±1°C.

  • 5.1.10 Barometer. A portable barometer capable of measuring atmospheric pressure to ±2 mm Hg.

Figure 1. Sampling train for determination of oxides of nitrogen

Figure 1. Sampling train for determination of oxides of nitrogen (See long description below)
Description of Figure 1

From right to left, a pump feeds a pump valve with a squeeze bulb above and the tube train flowing left. This tube then continues to a split at another T valve with one end connected below to a Mercury Manometer, while the primary tube line goes to a flask valve. This valve connects down to a 24/40 joint into a shielded flask which has a thermometer. Flowing left from the flask valve is a 12/5 joint which then connects to a heated and insulated probe with a glass wool filter at the end. The T-bore stopcock can be set to evacuate, purge or sample.

5.2 Sample Recovery

  • 5.2.1 Bottles. 120-ml or 4-oz glass or polyethylene storage bottles with leak-free, non-contaminating caps.

  • 5.2.2 Microburet or Dropper

  • 5.2.3 Litmus or pH Paper. A pH indicator over the 7-14 pH range.

5.3 Sample Analysis

  • 5.3.1 Steam or Water Bath. Operating at approximately 100°C. An electric hot plate is not suitable because it tends to cause spattering and possible loss of sample.

  • 5.3.2 Evaporating Dishes. New condition, unetched borosilicate glass or porcelain, about 200-ml capacity.

  • 5.3.3 Spectrophotometer. A unit capable of measuring absorbance at 405 nm.

  • 5.3.4 Stirring Rod. A polyethylene stirring rod to prevent scratching the evaporating dishes.

  • 5.3.5 Volumetric Flasks. Capacities of 50, 100 and 1000 ml.

  • 5.3.6 Volumetric Pipets. Capacities of 1, 2, 3, 4 and 5 ml.

  • 5.3.7 Graduated Cylinder. 100-ml capacity with 1-ml divisions.

  • 5.3.8 Analytical Balance. Capable of measuring to 0.1 mg.

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