3.3 Sample storage and preservation

Sample storage and preservation are crucial for maintaining sample integrity in analytical chemistry. Proper techniques prevent sample degradation, contamination, and loss of analytes, ensuring accurate results. Factors like temperature, light, moisture, and container material significantly impact sample stability.

Improper storage can lead to sample degradation, contamination, and analyte loss, resulting in inaccurate data. Environmental factors, sample-specific characteristics, and storage conditions all play a role in preserving sample integrity. Implementing quality control measures and following best practices are essential for reliable analytical results.

Sample Integrity and Preservation

Importance of Proper Sample Storage and Preservation

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• Ensure the sample remains representative of the original material
• Prevent alteration or loss of the analyte of interest prior to analysis
• Improper storage and preservation lead to sample degradation, contamination, or loss of analyte
  • Results in inaccurate or invalid analytical results
• Factors such as temperature, light, moisture, and container material significantly impact sample stability
  • Must be carefully controlled to maintain sample integrity
• Establish sample storage and preservation protocols based on specific properties of the sample matrix and analyte of interest
  • Consider expected storage duration and transportation requirements
• Proper documentation of sample storage and preservation conditions is essential
  • Ensures data traceability and reproducibility
  • Ensures compliance with regulatory requirements and quality control standards

Consequences of Improper Sample Storage and Preservation

• Sample degradation due to chemical reactions, microbial growth, or physical changes
  • High temperatures accelerate degradation (chemical reactions, microbial growth)
  • Low temperatures cause precipitation, crystallization, or phase separation
• Contamination from the environment, storage containers, or handling procedures
  • Leaching of contaminants from container materials (plasticizers, metal ions)
  • Introduction of foreign substances during sample handling (dust, microorganisms)
• Loss of analyte due to volatilization, adsorption, or chemical transformation
  • Volatilization of organic compounds or gases during storage or transportation
  • Adsorption of analytes onto container surfaces or suspended particles
• Inaccurate or invalid analytical results leading to wrong conclusions or decisions
  • False positives or false negatives in diagnostic tests (medical samples)
  • Incorrect assessment of environmental contamination levels (water, soil samples)

Factors Affecting Sample Stability

Environmental Factors

• Temperature influences chemical reactions, microbial growth, and sample degradation
  • High temperatures accelerate degradation (enzyme activity, oxidation)
  • Low temperatures cause precipitation, crystallization, or phase separation (proteins, lipids)
• Light exposure triggers photochemical reactions
  • Formation of degradation products (vitamin degradation)
  • Loss of light-sensitive analytes (pigments, photosensitive compounds)
• Moisture content affects sample stability
  • Promotes hydrolysis, oxidation, or microbial growth (hygroscopic or moisture-sensitive samples)
  • Causes caking, clumping, or dissolution of solid samples (powders, granules)
• Oxygen presence leads to oxidative degradation
  • Lipid peroxidation in fatty samples (oils, food products)
  • Redox-sensitive compound degradation (vitamins, antioxidants)

Sample-Specific Factors

• Sample pH influences stability of pH-sensitive analytes
  • Proteins, small molecules with ionizable groups (amino acids, organic acids)
  • Requires use of appropriate buffers or pH-controlled storage conditions (phosphate buffer, citrate buffer)
• Presence of enzymes catalyzes sample degradation reactions
  • Endogenous enzymes in biological samples (proteases, lipases)
  • Exogenous enzymes from microbial contamination (bacteria, fungi)
  • Necessitates use of enzyme inhibitors or heat treatment to inactivate enzymatic activity (protease inhibitors, autoclaving)
• Sample matrix components interact with analytes
  • Adsorption of analytes onto matrix components (proteins, lipids)
  • Chemical reactions between analytes and matrix components (Maillard reaction in food samples)
  • Requires use of stabilizers, preservatives, or matrix modifiers (antioxidants, chelating agents)

Storage Conditions for Samples

Selection of Storage Containers

• Choose container based on sample matrix, analyte stability, and potential interactions
  • Glass containers for organic solvents and volatile analytes (inertness, low permeability)
  • Plastic containers for aqueous samples and non-volatile analytes (compatibility, cost-effectiveness)
• Use amber glass or opaque plastic containers for light-sensitive samples
  • Minimize light exposure to prevent photodegradation (amber vials, aluminum foil wrapping)
• Clear containers suitable for samples that are not light-sensitive
  • Allow visual inspection of sample integrity (clear glass vials, transparent plastic bags)
• Ensure containers are clean, inert, and compatible with the sample matrix and analyte
  • Prevent leaching of contaminants or adsorption of analytes (pre-cleaned containers, silanized glassware)

Temperature Control

• Refrigeration (4°C) for perishable or heat-sensitive samples
  • Biological samples (blood, urine), food products, environmental samples (water, soil)
  • Slows down chemical reactions and microbial growth (enzyme activity, bacterial proliferation)
• Freezing (-20°C or -80°C) for long-term storage or ultra-sensitive samples
  • Biological samples (DNA, RNA), chemical standards, reference materials
  • Prevents degradation and maintains sample integrity (ice crystal formation, glass transition)
• Temperature monitoring systems to ensure consistent storage conditions
  • Temperature data loggers, thermometers, alarm systems
  • Ensures compliance with storage requirements and identifies potential temperature excursions

Moisture and Atmosphere Control

• Desiccators for moisture-sensitive samples
  • Silica gel, molecular sieves, or other desiccants to absorb moisture
  • Prevents moisture uptake and degradation (hygroscopic samples, deliquescent compounds)
• Nitrogen atmosphere for oxygen-sensitive analytes
  • Inert gas purging or storage in nitrogen-filled containers
  • Minimizes oxidative degradation (lipids, redox-sensitive compounds)
• Headspace-free storage for volatile analytes
  • Minimizes evaporation and loss of volatile components (organic solvents, essential oils)
  • Use of gas-tight septa, crimped caps, or vacuum packaging (amber vials, aluminum bags)

Minimizing Degradation and Contamination

Sample Labeling and Tracking

• Implement a well-defined sample labeling and tracking system
  • Use unique identifiers (barcodes, QR codes) for each sample
  • Include relevant information (sample ID, collection date, storage conditions)
• Ensure proper identification and traceability of samples throughout storage and transportation
  • Use of laboratory information management systems (LIMS) or sample tracking software
  • Maintain chain of custody records and sample logbooks

Quality Control Measures

• Use field blanks to monitor potential contamination during sample collection and handling
  • Expose blank samples to the same conditions as the actual samples
  • Analyze blanks to detect any background contamination (reagent blanks, trip blanks)
• Conduct storage stability studies to evaluate sample integrity over time
  • Store samples under different conditions (temperature, duration) and analyze at regular intervals
  • Determine the maximum storage time and optimal storage conditions for each sample type
• Implement sample integrity testing to detect potential degradation or contamination
  • Visual inspection for signs of physical changes (color, clarity, precipitation)
  • Chemical or biological markers to indicate sample quality (pH, enzymatic activity)

Personnel Training and Best Practices

• Provide training to personnel involved in sample handling, storage, and transportation
  • Cover proper techniques for sample collection, aliquoting, and preservation
  • Emphasize the importance of maintaining sample integrity and preventing contamination
• Establish and enforce standard operating procedures (SOPs) for sample handling and storage
  • Include step-by-step instructions for each sample type and storage condition
  • Specify safety precautions, personal protective equipment (PPE), and waste disposal procedures
• Regularly review and update SOPs based on new findings, regulatory changes, or best practices
  • Incorporate feedback from personnel and results from quality control measures
  • Ensure continuous improvement and adherence to the latest standards and guidelines