Surfactants (MBAS and CTAS) measurement context
Anionic surfactants, Standard Methods 5540 C: they form a blue ion pair with methylene blue that is extracted into chloroform and measured by spectrophotometry, as methylene blue active substances (MBAS). Nonionic surfactants, Standard Methods 5540 D: they are separated from the sample by gas stripping (sublation) and measured as cobalt thiocyanate active substances (CTAS). Both results count every substance that reacts, not one named surfactant. Reported as mg/L.
Define where the property is measured
Specify field or laboratory measurement, units and the sample state needed for the project. A delivered sample may not preserve the source-time condition for a changing property.
Include the complete project requirement
Provide the matrix, target analytes, required method, fraction, units and reporting limits. Include the permit or monitoring instructions where results will support a regulatory submission. Naming this method does not establish blanket compliance eligibility.
Resolve collection before sampling
Use the bottle, preservation and delivery instructions assigned to the agreed scope. Identify each location and collection time, and document any deviation. The final analytical plan must fit the submitted material and its intended use.
Related testing & guidance
Technical & service references
Vanguard service detailsSource review: November 8, 2026. The agreed method and project scope govern the testing.