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D3372-17 – Standard Test Method Technical Guide
📐 Scope and Application
This test method, designated as ASTM D3372-17, covers the determination of dissolved and total recoverable molybdenum in most waters, wastewaters, and brines using atomic absorption spectroscopy. The method is applicable across a concentration range of 1 to 25 µg/L of molybdenum. This range can be extended by diluting the sample, but it is the user’s responsibility to validate the method for untested matrices, such as industrial effluents or high-salinity brines. The standard has been successfully used with natural and reagent waters.
All values are stated in SI units, which are considered standard. Inch-pound conversions are provided for informational purposes only. Users must establish appropriate safety and health practices, with specific precautionary statements detailed in sections 8.16 and 11.12 of the standard. This international standard was developed in accordance with WTO TBT principles.
⚙️ Test Procedure and Methodology
The determination of molybdenum involves atomic-absorption spectrophotometry. The molybdenum in the sample is chelated with 8-hydroxyquinoline, then extracted into methyl isobutyl ketone (MIBK). The organic extract is aspirated into a nitrous oxide-acetylene flame, and the absorbance is measured at the appropriate wavelength. This chelation-extraction step enhances sensitivity and reduces interference from the sample matrix.
Sample preparation must distinguish between dissolved molybdenum, analyzed after filtration, and total recoverable molybdenum, which requires acid digestion as specified in the standard. Proper sampling techniques are outlined in Practices D3370.
📊 Quality Control and Referenced Standards
This standard references several ASTM standards for terminology, precision, and quality control. Adherence to these standards is essential for reliable results. Key referenced documents include:
| 📜 Standard | 🖹 Title |
|---|---|
| D1129 | Terminology Relating to Water |
| D1193 | Specification for Reagent Water |
| D1976 | Test Method for Elements in Water by Inductively-Coupled Argon Plasma Atomic Emission Spectroscopy |
| D2777 | Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water |
| D3370 | Practices for Sampling Water from Closed Conduits |
| D4691 | Practice for Measuring Elements in Water by Flame Atomic Absorption Spectrophotometry |
| D4841 | Practice for Estimation of Holding Time for Water Samples Containing Organic and Inorganic Constituents |
| D5673 | Test Method for Elements in Water by Inductively Coupled Plasma—Mass Spectrometry |
| D5810 | Guide for Spiking into Aqueous Samples |
| D5847 | Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis |
Quality control is critical in this method. Defined terms ensure consistency:
| 🔍 Term | 📖 Definition |
|---|---|
| Continuing Calibration Blank | A solution containing no analytes, used to verify blank response and freedom from carryover. |
| Continuing Calibration Verification | A solution of known concentration used to verify freedom from excessive instrumental drift. |
| Laboratory Control Sample | A solution with certified concentration of the analytes. |
| Total Recoverable Molybdenum | Descriptive term relating to the metal forms recovered in the acid-digestion procedure. |
💡 Tip: The 1 to 25 µg/L range can be extended by diluting the sample, but ensure that the matrix of the diluted sample remains compatible with the method to avoid inaccuracies.
⚡ Important: Specific precautionary statements are provided in sections 8.16 and 11.12 of the standard. Users must review these sections for safety information before proceeding with the test.
❓ Frequently Asked Questions
🔍 What is the applicable concentration range for this test method? The method is applicable for molybdenum concentrations from 1 to 25 µg/L. Higher concentrations can be measured after appropriate dilution of the sample.
💡 What is the chelating agent used for molybdenum extraction? The method uses 8-hydroxyquinoline to chelate molybdenum before extraction with methyl isobutyl ketone.
⚡ What type of flame is used in the atomic absorption determination? A nitrous oxide-acetylene flame is used for atomization of the molybdenum-containing extract.
📌 Are there any specific safety concerns addressed in the standard? Yes, the standard references sections 8.16 and 11.12 for specific precautionary statements. It is the user’s responsibility to establish appropriate safety practices and regulatory compliance.