ASTM: D5543A: Color Comparator Test Method Using Self-Filling Glass Ampoules (Test Method A)
|
Official Method Name
|
Standard Test Methods for Low-Level Dissolved Oxygen in Water |
|---|---|
|
Current Revision
| Reapproved 1999. Current edition approved Nov. 15, 1994. |
|
Media
|
WATER |
|
Instrumentation
|
Visual Comparison |
|
Method Subcategory
|
Inorganic |
|
Method Source
|
|
|
Citation
|
|
|
Brief Method Summary
|
The tip of a partially evacuated sealed ampoule is broken while submerged in a flowing water sample. The sample is drawn into the ampoule where it reacts instantaneously with the oxygen-sensitive indicator to produce a reddish violet color whose intensity is proportional to the concentration of dissolved oxygen. |
|
Scope and Application
|
This test method covers the determination of low-level dissolved oxygen in thermal-cycle steam condensate, deaerated boiler feedwater, boiler water, and deaerated deionized water. |
|
Applicable Concentration Range
|
0 - 100 ug/L |
|
Interferences
|
Color, turbidity, and oxidizing impurities interfere in this test method to yield high results. If the sample is colored or turbid or contains oxidizing impurities, the amount of interference that may be contributed by such effects must be determined independently prior to using this test method. Easily reduced metal ions may interfere in this test method to cause high results. For example, 100 ug/L (ppb) Cu +2 may appear as 5 ug/L (ppb) dissolved oxygen, and 100 ug/L Fe+3 may appear as 7 ug/L dissolved oxygen. However, less than 50 ug/L Cu,sup>+2 or Fe+3 cause less than 1-ug/L interference. Hydrogen peroxide alone in concentrations up to 200 ug/L does not affect the measurement of 1.5 ug/L of dissolved oxygen. Above 200 ug/L hydrogen peroxide, there is a positive interference of 3.3 ug/L dissolved oxygen per 100 ug/L excess over 200 ug/L hydrogen peroxide. The following interferences occur in the presence of 2200 mg/L boron present as boric acid: (1) at pH levels below pH 6, recovery can be as low as 80 %; ( 2) added hydrogen peroxide at a concentration of 0.1 mg/L yields a positive interference of 10 ug/L dissolved oxygen; and ( 3) added hydrogen peroxide in a concentration range from 0.5 to 650 mg/L yields a positive interference of 20 to 25 ug/L. Benzoquinone, an oxidation product of hydroquinone, interferes with this test method. One hundred micrograms per litre of benzoquinone may appear as 33 ug/L dissolved oxygen. Reducing agents such as hydrazine and sulfite do not interfere at 5-mg/L (ppm) levels in the sample. Ampoules must be protected from light to prevent darkening. Follow the manufacturer's storage recommendations. Color comparator tubes must be protected from light to prevent fading. Follow the manufacturer's storage recommendations. |
|
Quality Control Requirements
|
|
|
Sample Handling
|
Collect the samples in accordance with Practices D 1066 and D 3370 and Specification D 1192. With water under pressure, connect a tube of inert material to the inlet and extend the tube outlet to the bottom of the sample bottle or tube. Use stainless steel, Type 304 or 316, or glass tubing with short neoprene connections. Do not use copper tubing, long sections of neoprene tubing, or other types of elastomeric polymeric materials. If the water being sampled is above room temperature, the sample line shall contain a suitable cooling coil to cool it to approximate room temperature. |
|
Maximum Holding Time
|
|
|
Relative Cost
|
Unknown |
|
Sample Preparation Methods
|
