Which of the following describes a grab sample?

• A. Collected at a single point in time and analyzed onsite.
• B. Collected over 24 hours with equal portions.
• C. Based on flow during peak.
• D. Based on test to be performed.

Answer: (A)

Grab sampling is a sample collected at a single point in time to capture the conditions at that moment. It’s quick and practical for tests that don’t require averaging over time, and it’s often analyzed on site or soon after collection. Because it represents just one moment, it can miss daily or diurnal variations, unlike a 24-hour composite that combines multiple portions over the period to smooth out fluctuations. A flow-based, or flow-weighted, sample is also an averaging method taken over time, weighted by how much flow occurs, rather than a single instant. Sampling based on the test to be performed doesn’t define how the sample is collected; it’s about what analyses will be done, not the sampling approach.