1. ROLE OF SAMPLE PREPARATION IN ISO/IEC 17025
- Why sample preparation is critical: sensitivity, selectivity, reproducibility, contamination prevention, audit‑ready data
- Relevant ISO/IEC 17025 clauses: sample handling, storage, traceability; method validation; nonconforming work; technical competence
2. SYSTEMATIC APPROACH TO GC‑MS SAMPLE PREPARATION
Structured workflow
- Define sample type, matrix, target analytes; assess complexity; select extraction/clean‑up; remove particulates; concentrate/dilute; confirm solvent compatibility; document workflow
Trend‑based verification
- Monitor analyte recovery, matrix effects, internal standard performance; detect contamination, carryover, degradation
Risk‑based decision making
- When to re‑prepare, re‑extract, or reject a compromised sample; when matrix effects may invalidate results
3. SAMPLE COLLECTION AND STORAGE
- Collection guidelines: clean, inert containers (glass, PTFE)
- Storage conditions: temperature, light protection, container compatibility
- Stability considerations: volatility, reactivity, storage duration
- Sample labelling and traceability: unique IDs, chain‑of‑custody, complete documentation
4. COMMON GC‑MS SAMPLE PREPARATION TECHNIQUES
Liquid‑Liquid Extraction (LLE)
- Selective partitioning into immiscible solvents; applications: pesticides, environmental contaminants; solvent choice for GC‑MS
Solid‑Phase Microextraction (SPME)
- Solvent‑free extraction of volatile/semi‑volatile compounds; fiber coating selection; applications: VOCs, food aroma
QuEChERS
- Quick, efficient extraction for multi‑residue analysis; salt‑induced phase separation + dSPE clean‑up; applications: pesticides in fruits/vegetables/feed
Headspace Analysis
- Static or dynamic headspace for volatile analytes; applications: residual solvents, flavor compounds, environmental VOCs
Derivatization
- Convert analytes to GC‑volatile forms (silylation, acylation, methylation); improve volatility, thermal stability, detection; document reagent, time, temperature
Filtration and Centrifugation
- Remove particulates; use low‑binding, inert filters compatible with GC‑MS
5. MATRIX CONSIDERATIONS AND MINIMIZING INTERFERENCES
- Identify potential co‑eluting compounds causing signal suppression
- Apply clean‑up strategies (SPE, QuEChERS, derivatization)
- Verify matrix effects using spiked samples or isotopically labeled standards
6. SAMPLE QUALITY CONTROL
- Use Certified Reference Materials (CRMs) when possible
- Include blanks, duplicates, and QC standards in every batch
- Evaluate recovery and reproducibility
- Track sample handling, storage, and preparation steps for audit readiness
7. PREVENTIVE STRATEGIES
- Standardize extraction and clean‑up procedures in SOPs
- Pre‑check solvents, reagents, and fibers for purity and compatibility
- Avoid repeated freeze‑thaw cycles or prolonged storage
- Maintain detailed sample preparation logs
8. SYSTEM SUITABILITY AND POST‑PREPARATION VERIFICATION
- Evaluate recovery, reproducibility, and MS signal quality
- Compare analyte response with reference standards or CRMs
- Confirm absence of contaminants affecting column, injector, or detector
9. ISO/IEC 17025 DOCUMENTATION
- Record all sample preparation steps, deviations, and rationale
- Maintain traceable logs from sample receipt to injection
- Document QC results and corrective actions
- Prepare audit‑ready records demonstrating method reliability
10. COMMON ISO/IEC 17025 NON‑CONFORMITIES (GC‑MS SAMPLE PREP)
- Improper storage leading to analyte loss or degradation
- Incomplete documentation of preparation workflow
- Using incompatible solvents, fibers, or reagents
- Ignoring matrix effects and QC performance
11. ONLINE PRACTICAL COMPONENT
- Interactive exercises: simulate selection of sample preparation techniques for complex matrices
- Perform virtual extraction: LLE, QuEChERS, SPME, headspace
- Apply derivatization for non‑volatile analytes
- Evaluate chromatograms for matrix interference and analyte recovery
- Document preparation steps and QC results for ISO/IEC 17025 compliance
