1. ROLE OF SAMPLE PREPARATION IN GC ANALYSIS
- Why GC sample preparation is critical: volatility, thermal stability, injection discrimination, matrix interference, column contamination, measurement uncertainty
- Relevant ISO/IEC 17025 clauses: handling of test items, ensuring validity of results, technical competence, control of records
2. NATURE OF GC SAMPLES AND ANALYTES
Types of GC‑amenable analytes
- Volatile organic compounds (VOCs), semi‑volatile organic compounds (SVOCs), permanent gases, FAMEs, pesticides, hydrocarbons
Sample matrices commonly analyzed by GC
- Air/gas, water/wastewater, food/beverages, oils/fats, soils/sediments, biological fluids
Analyte properties affecting GC analysis
- Boiling point, polarity, thermal stability, reactivity
3. SAMPLE COLLECTION AND PRESERVATION FOR GC
- Sampling strategies: grab vs composite, static vs dynamic air sampling, representativeness
- Sample containers and materials: glass vs polymer, adsorption/permeation risks, headspace compatibility
- Preservation techniques: temperature control, chemical preservatives, headspace minimization
- (Online sampling error case studies)
4. SAMPLE EXTRACTION TECHNIQUES FOR GC
Liquid‑Liquid Extraction (LLE)
- Principles, solvent selection, phase separation, emulsion control
Solid‑Liquid Extraction (SLE)
- Soxhlet, pressurized liquid extraction (PLE), ultrasonic extraction
Solid‑Phase Extraction (SPE)
- Sorbent selection, breakthrough/recovery, elution solvent compatibility
Headspace Sampling
- Static headspace, dynamic headspace (purge‑and‑trap), equilibration parameters
Solid‑Phase Microextraction (SPME)
- Fiber chemistry selection, extraction kinetics, carryover considerations
5. SAMPLE CLEAN‑UP AND MATRIX REMOVAL
- Need for clean‑up: column/detector protection, baseline stability, S/N improvement
- Clean‑up techniques: GPC, Florisil/silica/alumina, sulfur/lipid removal
- Matrix effects and recovery bias: co‑extractives, loss of volatile analytes
6. DERIVATIZATION TECHNIQUES FOR GC
- Why derivatization is needed: improve volatility, thermal stability, detector response
- Types: silylation, acylation, alkylation (e.g., methylation)
- Derivatization protocol design: reaction conditions, reagent purity, by‑product control
- (Virtual derivatization decision exercise)
7. GC INJECTION TECHNIQUE CONSIDERATIONS
- Injection modes: split, splitless, on‑column, PTV
- Injection solvent compatibility: solvent boiling point effects, solvent focusing
- Discrimination and volatile losses: needle discrimination, liner selection
8. INTERNAL STANDARDS AND QUALITY CONTROL
- Internal standard selection: chemical similarity, volatility matching
- Surrogates and recovery standards: purpose and interpretation
- Matrix‑matched calibration: when required, implementation challenges
9. STABILITY, STORAGE, AND HOLDING TIMES
- Analyte stability in extracts: solvent effects, temperature/light sensitivity
- Extract storage and reanalysis: freeze‑thaw effects, extract holding times
10. ISO 17025 DOCUMENTATION AND TRACEABILITY
- Sample preparation records: extraction logs, solvent/reagent traceability, analyst and date/time
- Method deviations and justification: controlled deviations, impact assessment
- Measurement uncertainty from sample preparation: recovery variability, volatile losses
11. COMMON NON‑CONFORMITIES IN GC SAMPLE PREPARATION
- Unvalidated derivatization steps
- Volatile loss due to poor storage
- Incompatible injection solvents
- Missing recovery data
12. ONLINE PRACTICAL COMPONENT
- Virtual GC sample prep labs: choosing between headspace, SPME, and LLE
- Designing a derivatization protocol
- Diagnosing recovery losses
- Sample integrity audit simulation