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D4137-82 – Standard Test Method Technical Guide
📐 Scope and Significance of Phytoplankton Preservation
The ASTM D4137 −82 (Reapproved 2012) standard details the proper procedures for preserving phytoplankton samples collected via qualitative or quantitative methods. The primary goal is to maintain cellular integrity for subsequent analysis, whether for short-term studies or long-term archival.
Significance and Use: Formaldehyde solution serves as a permanent preservative, maintaining cell coloration indefinitely. Lugol’s solution is recommended for preserving algae for up to one year and is particularly advantageous for delicate forms such as naked flagellates, as it preserves fragile cell structures and facilitates sedimentation.
⚠️ Safety Warning: The standard explicitly states it does not address all safety concerns. Users must establish appropriate safety, health, and regulatory compliance procedures before using formaldehyde or other reagents.
🧪 Reagent Preparation and Preservation Methods
The standard mandates the use of reagent grade chemicals conforming to the specifications of the American Chemical Society. The water used must be Type II reagent water as defined by ASTM Specification D1193. The following table summarizes the preservation methods and reagent preparation:
| 🟦 Preservative | 📏 Reagent Preparation Formula | 🎯 Application Dosage | ⚡ Preservation Duration |
|---|---|---|---|
| Formalin (Formaldehyde Solution) | 30 mL of 37-40% formaldehyde + 5 mL of 20% liquid detergent + 1 mL saturated cupric sulfate. | Add the entire mixture per 1000 mL of sample. | Indefinite |
| Lugol’s Solution | Dissolve 60 g potassium iodide (KI) and 40 g iodine crystals in 1000 mL water. | Add 1 mL of Lugol’s solution per 100 mL of sample. Store in the dark. | At least 1 year |
If the sample is to be examined within 2 to 3 hours of collection, no special treatment is necessary. For extended storage, preservation is required. Samples can be held for up to 24 hours at 2 to