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D2687-95 – Standard Test Method Technical Guide
🔍 Scope and Applicability of D2687-95
ASTM D2687-95 (Reapproved 2024) defines the standard practices for obtaining representative samples of particulate ion-exchange materials. The scope of this standard is divided into three core protocols based on the physical configuration of the ion-exchange unit and the material state. This standard is under the jurisdiction of ASTM Committee D19 on Water and Subcommittee D19.08 on Membranes and Ion Exchange Materials.
| 🟦 Practice | 📐 Sections | 📏 Applicable Scenario |
|---|---|---|
| Practice A | 4 – 11 | Sampling from Single Packages & Multiple Package Lots or Shipments |
| Practice B | 12 – 16 | Sampling from Fixed Bed Equipment with Unrestricted Head Room |
| Practice C | 17 – 21 | Sampling from Fixed Bed Equipment with Restricted Head Room |
Practice A is the most frequently used, typically applied to materials as received from the manufacturer in their original shipping containers and prior to any resin-conditioning procedures. Practices B and C address dynamic sampling directly from active system vessels.
⚙️ Core Sampling Equipment and Protocol (Practice A)
The primary apparatus described in Practice A consists of a hollow sample-probe guide assembled from mating threaded sections. This design allows the probe to be extended to any convenient depth. A sampling tube is inserted through this guide and connected to an external vacuum source to educt the ion-exchange material. Alternatively, a core sampler may be employed for specific media types.
⚠️ Critical Distinction: Because ion-exchange materials are supplied in either dry (free-flowing) or moist states, the standard mandates different sampling devices for each. Always consult Section 8 (Dry Material) and Section 9 (Moist Material) to avoid biasing the sample or damaging the resin beads during extraction.
| 🎯 Apparatus Component | 📐 Specification / Requirement | ⚡ Functional Role |
|---|---|---|
| Sample Probe Guide | Hollow, threaded, extendable sections | Provides guided vertical access into the material bed |
| Vacuum Eduction System | Sampling tube + Vacuum source | Removes material by suction through the probe guide |
| Sample Quartering Sheet | 0.5 m × 0.5 m (20 in. × 20 in.) | Glazed paper, oil cloth, or flexible plastic film for sample reduction |
| Storage Container | Sealable, absolutely gasproof | Prevents changes in moisture, oxidation, or composition |
💡 Best Practice: Once the sample is obtained, it must be placed directly into a sealable, gasproof container without delay. This is critical for protecting ion-exchange materials from atmospheric changes (e.g., moisture loss or CO2 adsorption) that can alter performance characteristics and invalidate test results. The sampling device described in Fig. 2 of this standard is the same as that used in Practice C183 for hydraulic cement.
📊 Ensuring Representativeness and Data Integrity
To ensure a statistically representative sample, Practice A specifies a minimum of three probes or increments per single package. For multiple package lots or shipments, a proportionally greater number of increments is required based on the lot size. Proper terminology related to ion exchange is defined in ASTM D1129, ensuring consistent communication across water analysis and ion exchange testing disciplines. Adhering to the specific section references within this standard is essential for generating samples that accurately reflect the bulk material properties.
❓ Frequently Asked Questions
🔍 What is the minimum number of probes required for a single package sample?
Per Section 7.1 of ASTM D2687-95, a minimum of three probes or increments must be taken from a single package to constitute a representative sample.
💡 Why do dry and moist materials require different sampling procedures?
Dry, free-flowing materials and moist materials possess different physical properties. The standard dedicates Section 8 to dry material sampling and Section 9 to moist material sampling to ensure the integrity of the sample is preserved regardless of its initial state.
📌 What are the specific dimensions for the sample quartering sheet?
The standard specifies that the quartering sheet must be 0.5 m by 0.5 m, or 20 in. by 20 in., constructed from glazed paper, oil cloth, or flexible plastic film.
⚡ How is the ion-exchange material extracted from a deep container or bed?
A hollow, extendable probe guide is inserted to the required depth. A sampling tube connected to an external vacuum source is then inserted through this guide to educt the material to the surface for collection.