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D3670-91 – Standard Test Method Technical Guide
📐 Scope and Application
This standard, designated D3670‑91 (Reapproved 2022), provides guidance to task groups of Committee D22 on Sampling and Analysis of Atmospheres for planning and conducting collaborative testing of candidate methods. It is intended for use with other ASTM practices for the determination of precision and bias.
The guide applies to most manual and automated methods, including components of monitoring systems. For monitoring systems, Practice D3249 should be considered for general guidance. It is directly applicable to chemical methods, and in principle to physical methods, sampling methods, and calibration procedures.
Users have the obligation to validate any method for specific applications and must demonstrate competence in using validated methods. This international standard was developed in accordance with globally recognized principles on standardization.
Users must validate methods for their specific application and demonstrate competence as required by Section 1.5. Validation includes confirming that the method meets precision and bias requirements for the intended use.
⚙️ Collaborative Testing and Validation
A collaborative test is defined as an interlaboratory study where participants analyze sub‑samples of the same test material or, when possible, sample the same test atmosphere. This guide emphasizes using interlaboratory studies to determine precision and bias of candidate methods.
Referenced practices include E691 for conducting interlaboratory studies, E1169 for ruggedness tests, and D2777 for precision and bias determination. The following table summarizes key referenced documents from Section 2 of the standard:
| 🟦 Designation | 📏 Title | 🎯 Purpose |
|---|---|---|
| D2777 | Practice for Determination of Precision and Bias of Test Methods of Committee D19 | Precision and bias determination |
| D3249 | Practice for General Ambient Air Analyzer Procedures | Guidance for monitoring system evaluation |
| E177 | Practice for Use of the Terms Precision and Bias in ASTM Test Methods | Consistent terminology |
| E691 | Practice for Conducting an Interlaboratory Study to Determine Precision of a Test Method | Interlaboratory study procedures |
| E1169 | Practice for Conducting Ruggedness Tests | Identifying influential testing variables |
These practices provide a framework for evaluating method performance and ensuring reliable results.
Before initiating collaborative testing, use Practice E1169 to conduct ruggedness tests. This helps identify variables that may significantly affect method performance and ensures a robust test design.
📊 Key Terminology and Definitions
The standard defines essential terms consistent with Practices D2777, E177, E180, and E691. The following table lists key definitions from Section 3 of the standard:
| 📐 Term | 🎯 Definition |
|---|---|
| Accuracy | Degree of conformity of a generated value to the true value, encompassing both precision and bias. |
| Bias | Systematic nonrandom deviation of the method average or measured value from an accepted reference value. |
| Candidate Method | An analytical method under consideration for standardization until completion of the consensus process. |
| Collaborative Test | Interlaboratory study where participants analyze sub‑samples of the same test material or atmosphere. |
| Laboratory Bias | Systematic differences due to errors such as losses, contamination, or miscalibration. |
| Method Bias | Systematic departures from the true value caused by inherent physical or chemical phenomena in the methodology. |
Understanding these terms is critical for applying the guide effectively and interpreting collaborative test results.
❓ Frequently Asked Questions
🔍 What is the primary purpose of D3670‑91? It provides guidance for task groups of Committee D22 to plan and conduct collaborative testing of candidate methods for sampling and analysis of atmospheres.
💡 How is a collaborative test defined in this standard? A collaborative test is an interlaboratory study where participants analyze sub‑samples of the same test material or sample the same test atmosphere when possible.
⚡ What distinguishes laboratory bias from method bias? Laboratory bias stems from errors in application (e.g., contamination, miscalibration), while method bias arises from systematic phenomena inherent in the methodology.
📌 Which ASTM practices are referenced for determining precision and bias? Key practices include D2777, E177, E180, and E691, which provide procedures for interlaboratory studies and terminology.