If no separate preparation method is used (for example, ammonia digestion), the batch shall be defined as no more than how many environmental samples?

• A. 10
• B. 15
• C. 20
• D. 25

Answer: (C)

Batch processing relies on treating all samples under the same digestion conditions, so the number of samples in a single run is limited to keep this uniform and controllable. When no separate preparation method is used, the batch should include no more than twenty environmental samples to ensure consistent digestion across all items, maintain adequate reagent availability and mixing, and keep the timing and temperature stationary for every sample. This limit helps protect against incomplete or uneven digestion, which can compromise accuracy and the ability to perform reliable QA checks such as blanks and spikes. If a separate prep method were used, batch size could be larger, but that scenario isn’t what this item describes.