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D1608-16 – Standard Test Method Technical Guide
🔬 Test Method Overview and Scope
This test method describes the phenol-disulfonic acid colorimetric procedure for the determination of total oxides of nitrogen, excluding nitrous oxide (N2O), in gaseous effluents from combustion and other nitrogen oxidation processes. It is applicable to a concentration range of 5 ppm to several thousand ppm by volume of nitrogen dioxide (NO2), equivalent to 4 to several thousand mg per dry standard cubic metre. The method uses a grab sampling technique that provides an instantaneous measure, making it representative only if the gas stream is well mixed and concentration constant with time. Multiple samples are recommended for accurate assessment.
| 🟦 Parameter | 📏 Range | 📐 Units |
|---|---|---|
| Concentration of NOx (as NO2) | 5 to several thousand | ppm by volume |
| Equivalent mass concentration | 4 to several thousand | mg per dry standard cubic metre |
⚠️ Warning: Mercury has been designated as a hazardous material. Handle mercury and mercury-containing products with caution. Refer to the Safety Data Sheet (SDS) for additional information.
⚗️ Procedure and Analytical Process
The gas sample is admitted into an evacuated flask containing an oxidizing absorbing solution of hydrogen peroxide in dilute sulfuric acid. Oxides of nitrogen are converted to nitric acid through gas phase oxidation and the absorbent solution. The resulting nitrate ion reacts with phenol disulfonic acid to produce a yellow compound, the tri-ammonium salt of 6-nitro-1-phenol-2,4-disulfonic acid, which is measured colorimetrically. Calibration curves prepared from samples of known nitrate content are used to determine the amount of nitrate, with results expressed as nitrogen dioxide.
| 🟦 Step | 📐 Process | 🎯 Key Reagent |
|---|---|---|
| Sampling | Evacuated flask with absorbing solution | Hydrogen peroxide in dilute sulfuric acid |
| Reaction | Conversion to nitrate and reaction with phenol disulfonic acid | Phenol disulfonic acid |
| Measurement | Colorimetric analysis of yellow compound | Tri-ammonium salt of 6-nitro-1-phenol-2,4-disulfonic acid |
📊 Significance and Compliance Applications
This test method provides a means to measure total nitrogen oxides (NOx) content in gaseous emissions. It is used for determining compliance with regulations, studying the effect of abatement procedures on NOx emissions, and checking the validity of instrumental measurements. The values stated in SI units are to be regarded as standard. For definitions of terms, refer to Terminology D1356.
💡 Tip: Ensure the gas stream is well mixed and concentration constant with time for accurate results. Multiple grab samples are recommended for representative data.
❓ Frequently Asked Questions
🔍 What is the purpose of this test method?
It is used for the determination of total oxides of nitrogen in gaseous effluents from combustion and other nitrogen oxidation processes, primarily for regulatory compliance and emission studies.
💡 How is the sample collected for this test?
The gas sample is collected using a grab sampling technique into an evacuated flask containing an oxidizing absorbing solution of hydrogen peroxide in dilute sulfuric acid.
⚡ What is the concentration range for this method?
The method is applicable for oxides of nitrogen as nitrogen dioxide from 5 ppm to several thousand ppm by volume, or 4 to several thousand mg per dry standard cubic metre.
📌 Why are multiple samples recommended?
Since the grab sampling technique provides an instantaneous measure, multiple samples are recommended to ensure representativeness, especially if the gas stream is not well mixed or concentration varies with time.