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D2650-10 – Standard Test Method Technical Guide
⚙️ Test Method Scope and Applicability
ASTM D2650-10 (Reapproved 2021) establishes a standard test method for the quantitative analysis of gases by mass spectrometry. The scope specifically covers the determination of hydrogen; hydrocarbons with up to six carbon atoms per molecule; carbon monoxide; carbon dioxide; mercaptans with one or two carbon atoms per molecule; hydrogen sulfide; and air (nitrogen, oxygen, and argon). The analysis relies on the unique cracking patterns of each molecule, where the cracking pattern coefficient defines the ratio of peak intensities at various mass-to-charge (m/e) values normalized to the base peak.
A critical quantitative limitation is that this method cannot be used for constituents present in amounts less than 0.1 mole %. Furthermore, dimethylbutanes are assumed absent unless specifically sought. The standard does not purport to address all safety concerns; it is the responsibility of the user to establish appropriate safety and environmental practices.
| 🟦 Component Category | 📏 Detection Limit (mole %) |
|---|---|
| Hydrogen (H₂) | ≥ 0.1 |
| Hydrocarbons (C₁ – C₆) | ≥ 0.1 |
| Carbon Monoxide (CO) & Carbon Dioxide (CO₂) | ≥ 0.1 |
| Mercaptans (C₁ – C₂) & Hydrogen Sulfide (H₂S) | ≥ 0.1 |
| Air (N₂, O₂, Ar) | ≥ 0.1 |
⚡ Note 2: This test method was developed on Consolidated Electrodynamics Corporation Type 103 Mass Spectrometers. Users of other instruments may have to modify operating parameters and the calibration procedure.
📐 Key Definitions and Analytical Procedures
The standard provides uniform terminology to guide consistent application. The base peak of a compound is the peak used as 100% in computing the cracking pattern coefficient. Cracked gases are defined as hydrocarbon gases that contain unsaturates. The standard also defines GLC as a gas-liquid chromatographic column capable of separating isomers of butenes, pentenes, hexanes, and hexenes, and IR as infrared equipment for analyzing butene isomers.
Selection of the appropriate calculation procedure is guided by the qualitative mixture composition, the desire for minimum cross interference between known components, and the need for maximum sensitivity. A full tabulation of recommended calculation procedures for stated applications is presented in Section 12 (Table 1) of the standard.
💡 Procedure Guidance: According to Note 1, factors such as low frequency and complexity of calibration, minimum error due to presumed absent components, and the type of computing machinery heavily influence the selection of a calculation algorithm.
📊 Referenced Sampling Standards
Accurate analysis begins with proper sample collection. D2650-10 incorporates several essential standards to ensure representative samples are obtained prior to mass spectrometric analysis.
| 📄 Standard Designation | 🎯 Application |
|---|---|
| ASTM D1265 | Sampling Liquefied Petroleum (LP) Gases, Manual Method |
| API MPMS Chapter 14.1 | Collecting and Handling of Natural Gas Samples for Custody Transfer |
| GPA 2166 | Obtaining Natural Gas Samples for Analysis by Gas Chromatography |
Historical standards referenced for context include ASTM D1137 (Analysis of Natural Gases by the Mass Spectrometer) and ASTM D1247 (Sampling Manufactured Gas), which form the procedural foundation for the current method. Values are stated exclusively in SI units.
❓ Frequently Asked Questions
🔍 What is the minimum concentration threshold for constituents under D2650-10?
This test method explicitly states that it cannot be used for the determination of constituents present in amounts less than 0.1 mole %.
⚡ What mass spectrometer was used to develop this standard method?
The method was developed on a Consolidated Electrodynamics Corporation Type 103 instrument. Users of different instruments must validate modifications to operating parameters and calibration procedures.
📌 Which specific gas components does this method analyze?
The scope covers hydrogen, hydrocarbons (C₁ to C₆), carbon monoxide, carbon dioxide, mercaptans (C₁ and C₂), hydrogen sulfide, and air constituents (nitrogen, oxygen, and argon). Isomer resolution may require GLC or IR equipment.
💡 How does the standard define a “cracking pattern coefficient”?
It is defined as the ratio of a peak at any mass-to-charge ratio (m/e) relative to its parent peak (or base peak) and is used to compute the relative abundance of fragment ions in a mixture.