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D1687-17 – Standard Test Method Technical Guide
📐 Test Methods Overview and Applicable Matrices
ASTM D1687-17, under the fixed designation D1687, provides three standardized test methods for the determination of chromium in water. These methods address both hexavalent chromium and total chromium across various concentration ranges and water matrices. The standard explicitly notes that it is the user’s responsibility to ensure the validity of these test methods for untested water matrices (Section 1.3). The values stated in SI units are regarded as standard, with inch-pound units provided mathematically for information only.
| 🟦 Test Method | 🎯 Concentration Range | 📏 Analyte & Technique | 📐 Key Applications |
|---|---|---|---|
| A – Photometric Diphenylcarbohydrazide | 0.01 to 0.5 mg/L | Dissolved Hexavalent Chromium | Reagent water, tap water, NPDES effluent, NaCl solution, lake water, process water |
| B – Atomic Absorption, Direct | 0.1 to 10 mg/L | Total Recoverable Chromium | Generic aqueous matrices (user must validate matrix compatibility) |
| C – Atomic Absorption, Graphite Furnace | 5 to 100 µg/L | Dissolved or Total Recoverable Cr | Filtered tap water, river water, well water, production plant water, condensate |
⚠️ Critical Note on Method Selection: Test Method A is specific to dissolved hexavalent chromium only. Methods B and C analyze total chromium without regard to valence state. For hexavalent chromium analysis via ion chromatography, refer to ASTM D5257. For ICP-MS (D5673) or ICP-AES (D1976) applications, note the higher instrument cost.
⚙️ Sample Preparation, Procedure, and Quality Control
Sample handling is critical for accurate chromium speciation and quantification. Section 34 of D1687-17 outlines rigorous Quality Control measures including Initial Calibration Verification (ICV), Continuing Calibration Verification (CCV), and blank analysis. The choice of method dictates the sample preparation route: dissolved hexavalent chromium (Method A) requires filtration without acid digestion, while total recoverable chromium (Methods B and C) necessitates an appropriate acid digestion step prior to analysis.
The standard explicitly relies on specific hazard statements found in Sections 4.2, 20.3, and 20.8.1. Interlaboratory precision and bias data for the methods are established in accordance with Practice D2777.
| ⚡ Category | 🔬 Referenced Standard | 🎯 Specific Relevance to D1687-17 |
|---|---|---|
| Water Quality | D1193 Specification for Reagent Water | Defines Types I, II, and III water used in method development and validation |
| Sampling Practices | D3370 Practices for Sampling Water from Closed Conduits | Provides guidelines for representative sample collection from pipes and tanks |
| Precision & Bias | D2777 Practice for Determination of Precision and Bias | Establishes the interlaboratory study framework for method accuracy and statistics |
| Trace Analysis | D3919 Practice for Measuring Trace Elements in Water | Guides trace element analysis specifically for the Graphite Furnace AA (Method C) |
📌 User Responsibility: While Test Methods B and C are suitable for dissolved or total recoverable chromium, specific validated matrices for Method C include water from a medium BTU coal gasification condensate and stock scrubber water. Method B has less published matrix data in the standard. A thorough method validation is essential for new or complex water matrices.
❓ Frequently Asked Questions
🔍 What is the lowest detectable concentration of chromium using Test Method C?
Test Method C (Atomic Absorption, Graphite Furnace) is designed for trace-level analysis with a concentration range of 5 to 100 µg/L, providing the highest sensitivity of the three test methods for total chromium determination.
💡 Can Test Method A differentiate between Cr(III) and Cr(VI)?
Yes. Test Method A is specific for dissolved hexavalent chromium. It measures Cr(VI) directly using the diphenylcarbohydrazide photometric reaction without spectroscopic interference from trivalent chromium species.
⚡ Is an acid digestion required for measuring total recoverable chromium?
Yes, for Test Methods B and C, an acid digestion step is necessary to solubilize metals for a “total recoverable” measurement. If only dissolved chromium is required, the sample should be filtered and analyzed without digestion.
📌 Where are the safety hazard statements located in the D1687-17 standard?
Specific hazard statements associated with the analytical procedures are referenced in Sections 4.2, 20.3, and 20.8.1. These cover the safe handling of chemical reagents and the safe operation of atomic absorption instrumentation.