CCIL Sample Management and Preparation 4 — Questions and Answers
Question 1: Which solvent is most commonly used for Soxhlet extraction of semi-volatile organic compounds from solid matrices?
- Distilled water
- Methanol
- Dichloromethane or hexane mixture (Correct answer)
- Acetonitrile
Correct answer: Dichloromethane or hexane mixture
Dichloromethane or dichloromethane/hexane mixtures are standard solvents for Soxhlet extraction of non-polar and semi-volatile organics from soils.
Question 2: A sample log shows that a water sample for total coliform analysis was collected at 09:00 and delivered to the lab at 15:00. The holding time is 6 hours. Should the laboratory accept the sample?
- Yes, because exactly 6 hours elapsed and it is within the limit (Correct answer)
- No, because transport time exceeded the 6-hour holding time
- Yes, if the sample was refrigerated during transport
- No, because microbiological samples have no acceptable holding time
Correct answer: Yes, because exactly 6 hours elapsed and it is within the limit
Exactly 6 hours is at the boundary; most protocols interpret holding time as 'within 6 hours,' so the sample is marginally acceptable if properly cooled.
Question 3: What is the primary reason biohazardous samples must be clearly labeled before entering the laboratory?
- To comply with shipping regulations only
- To protect laboratory personnel and ensure proper handling and disposal (Correct answer)
- To indicate the sample priority level for scheduling
- To satisfy client invoicing requirements
Correct answer: To protect laboratory personnel and ensure proper handling and disposal
Biohazard labeling is a worker safety and regulatory requirement that triggers appropriate personal protective equipment and waste disposal protocols.
Question 4: When performing solid-phase extraction (SPE) for trace organic analysis, conditioning the sorbent before sample loading serves to:
- Remove interfering ions by ion exchange
- Wet and activate the sorbent to improve analyte retention (Correct answer)
- Concentrate the eluate prior to injection
- Neutralize acidic analytes in the sample
Correct answer: Wet and activate the sorbent to improve analyte retention
Conditioning with an appropriate solvent activates bonded-phase sorbents, ensuring consistent analyte retention and reproducible recovery.
Question 5: Which of the following BEST describes a method blank in laboratory quality control?
- A sample collected from a clean reference site for comparison
- Analyte-free reagent water taken through the complete analytical procedure (Correct answer)
- A certified reference material analyzed at the start of each batch
- The lowest calibration standard used to establish the detection limit
Correct answer: Analyte-free reagent water taken through the complete analytical procedure
A method blank detects reagent or laboratory contamination by processing analyte-free water through every step of the analytical method.
Question 6: For trace metal analysis, why must sample containers be acid-washed before use?
- To sterilize containers and prevent biological activity
- To remove adsorbed metals that could contaminate low-level samples (Correct answer)
- To increase the solubility of metal analytes in the sample
- To neutralize preservatives added by the manufacturer
Correct answer: To remove adsorbed metals that could contaminate low-level samples
Acid washing removes trace metals previously adsorbed to container surfaces, preventing false positive results in ultra-trace analyses.
Question 7: A duplicate sample is analyzed alongside the original to assess:
- Laboratory bias relative to a certified reference value
- The precision and reproducibility of the sampling and analytical process (Correct answer)
- Contamination from reagents used during sample preparation
- Instrument calibration drift over the analytical run
Correct answer: The precision and reproducibility of the sampling and analytical process
Duplicate analyses measure repeatability, indicating whether results are reproducible under the same conditions.
CCIL Sample Management and Preparation 4
Which solvent is most commonly used for Soxhlet extraction of semi-volatile organic compounds from solid matrices?