Which sampling approach would be used to represent conditions over a period by combining samples?

• A. Grab samples
• B. Spot samples
• C. Integrated samples
• D. Composite samples

Answer: (D)

When conditions vary over time, using one sample to represent the whole period is unreliable. The best approach is to take several small samples at different times (or from different locations within the period) and mix them into a single bottle to form one composite sample. This single composite sample carries the combined information from all the sub-samples, producing a result that reflects the average conditions over the entire period rather than a single moment.

Grab or spot samples capture the situation at one instant and don’t account for fluctuations, so they can misrepresent the period. Integrated sampling can refer to collecting over time, but the explicit act of representing the period by combining multiple portions into one sample is the hallmark of composite sampling.