Chromatographic techniques are fundamental analytical methods used in science laboratory technology to separate, identify, and quantify components within complex mixtures. In Kenya, these techniques are vital in various sectors including healthcare, environmental analysis, food safety, and pharmaceuticals. Proficiency in chromatographic apparatus and associated equipment enables laboratory technologists to deliver accurate and reliable results, which are essential for decision-making in clinical diagnostics, quality control, and research. This chapter provides a detailed exploration of chromatographic equipment and specific chromatographic methods relevant to laboratory professionals.

1.1 Chromatographic test

Chromatography involves the separation of chemical substances based on their differential affinities between a stationary phase and a mobile phase. This technique is widely employed in Kenyan laboratories such as the Kenya Medical Research Institute (KEMRI) and county hospitals for drug analysis, toxin detection, and biochemical investigations.

Example: the pesticide residue laboratory of a horticulture exporters' association in Thika runs gas chromatography on every consignment of French beans before export, after weighing and diluting the samples with calibrated balances and volumetric flasks.

1.1.1 Chromatographic apparatus and equipment

Chromatographic procedures rely on specialized apparatus and general laboratory equipment to ensure precise separation and detection of sample components. Understanding the equipment involved is crucial for effective chromatographic analysis.

Syringe

Syringes are used to measure and inject small, exact volumes of sample into chromatographic instruments, and to apply spots in thin layer chromatography.

Correct use of a syringe

• Rinsing: rinse the syringe several times with solvent and then with the sample before drawing the measured volume.
• Removing air: expel air bubbles by pumping the plunger with the needle in the liquid, since bubbles cause volume errors.
• Reading the volume: read the plunger tip against the scale at eye level.
• Injection: inject smoothly and quickly, and withdraw the needle straight to avoid bending it.
• Cleaning and storage: flush with clean solvent after use and store in its case; never leave sample to dry inside.

Volumetric flasks

Volumetric flasks are precision glassware designed to prepare solutions of exact concentrations, critical in chromatographic sample preparation for quantitative analysis.

Design and Specifications of Volumetric Flasks

• The narrow neck has a single calibration mark to indicate exact volume.
• Made from chemically resistant glass to prevent contamination.
• Available in sizes ranging from 5 ml to 1000 ml for different analytical needs.

Usage in Chromatographic Techniques

• Used to accurately dilute concentrated stock solutions, ensuring reproducible sample concentrations.
• Essential in preparation of mobile phases with precise solvent ratios.
• Preparation of calibration standards for quantitative chromatographic assays.

Handling and Maintenance

• Rinse with distilled water before and after use to avoid cross-contamination.
• Avoid sudden temperature changes to prevent glass breakage.
• Store in a dust-free environment to maintain cleanliness.

Analytical balances

Types and Specifications of Analytical Balances

• Electronic balances provide digital readouts for ease of use.
• Mechanical balances, though less common, are still used in some settings.
• Calibration with certified weights ensures measurement accuracy.

Proper Use and Handling

• Place the balance on a vibration-free, level surface.
• Use weighing boats or paper to prevent direct contact between sample and balance pan.
• Tare the balance before weighing to zero the reading.
• Avoid overloading beyond maximum capacity to prevent damage.

Maintenance and Calibration

• Regular cleaning of the balance pan and surrounding area maintains precision.
• Periodic calibration using traceable standard weights is mandatory, especially in regulated laboratories such as pharmaceutical quality control labs.
• Protect from dust and moisture to prolong lifespan.

Crucibles

Crucibles are heat-resistant containers used in sample preparation steps, such as drying or ashing, prior to chromatographic analysis.

Types and Materials of Crucibles

• Selection depends on the type of sample and temperature requirements.
• Crucibles must be free from contaminants that could interfere with chromatographic results.

Handling and Use in Sample Preparation

• Samples are placed in crucibles for drying to constant weight or for combustion to remove organic matter.
• Used in environmental analysis laboratories to prepare soil or sediment samples prior to chromatography.

Cleaning and Storage

• After use, crucibles are cleaned by soaking in acid baths or by heating to remove residues.
• Stored in dust-free containers to maintain cleanliness.

Graduated glassware

Graduated glassware such as pipettes, burettes, and measuring cylinders is essential for accurate measurement and transfer of liquids in chromatographic procedures.

Types and Specifications

• Glassware is typically made from borosilicate glass for chemical resistance.
• Accuracy varies, with volumetric pipettes being more precise than graduated ones.

Role in Chromatographic Analysis

• Used in preparing mobile phases and diluting samples.
• Essential for titrations that may precede chromatographic separation.
• Accurate measurement ensures reproducibility of chromatographic results.

Care and Maintenance

• Clean immediately after use to prevent residue buildup.
• Avoid exposure to harsh chemicals that may etch markings.
• Calibrate periodically to ensure measurement accuracy.

Cuvettes

Cuvettes are transparent containers designed to hold liquid samples for spectrophotometric detection following chromatographic separation.

Types and Material Specifications

• Path length is critical for Beer-Lambert law calculations.
• Material choice depends on the wavelength range of analysis.

Application in Chromatographic Techniques

• After chromatographic separation, eluates can be analyzed spectrophotometrically using cuvettes.
• Used in quality control laboratories, for example, at pharmaceutical firms, to quantify drug purity.

Handling and Maintenance

• Clean cuvettes with appropriate solvents to avoid scratches.
• Avoid fingerprints on optical surfaces to prevent measurement errors.
• Store in dust-free containers.

Components of Chromatographic Apparatus

• Stationary Phase: The fixed material in which components of the mixture interact differently, such as silica gel in Thin Layer Chromatography (TLC) or resin beads in Ion Exchange Chromatography (IEC). It determines separation based on chemical affinity or size exclusion.
• Mobile Phase: The solvent or gas that carries the sample through the stationary phase. Its composition and flow rate directly influence the resolution and speed of separation.
• Sample Injector: Device used to introduce the sample into the chromatographic system ensuring reproducible sample volumes and minimizing contamination.
• Detector: Instrument that identifies separated components as they elute from the stationary phase, examples include flame ionization detectors in Gas Chromatography (GC).
• Data Acquisition System: Modern chromatographic setups include computerized systems that record and analyze detector signals to generate chromatograms for interpretation.

Maintenance and Calibration of Chromatographic Equipment

• Regular Cleaning: Prevents contamination and maintains column efficiency, essential in both GC and IEC systems.
• Calibration: Use of standard reference materials to ensure accuracy of detectors and flow rates.
• Leak Testing: Particularly in GC systems to avoid sample loss and maintain detector sensitivity.
• Software Updates: For data acquisition systems to ensure compatibility and enhanced analytical capabilities.

1.1.2 High Performance Liquid Chromatography (HPLC)

High Performance Liquid Chromatography separates the components of a liquid sample by pumping it, in a liquid mobile phase, at high pressure through a column packed with very fine particles of stationary phase. It is the main technique for analysing drugs, vitamins, sugars, food additives and many non-volatile or heat-sensitive compounds that cannot be analysed by GC.

Principle and mechanism

Each component distributes itself differently between the mobile phase and the stationary phase, so components leave (elute from) the column at different retention times. In reversed-phase HPLC, the most common mode, the stationary phase is non-polar (C18-bonded silica) and the mobile phase is a polar mixture such as water with methanol or acetonitrile; polar compounds elute first.

Instrumentation and components

• Solvent reservoirs and degasser: hold filtered, degassed mobile phase solvents.
• High-pressure pump: delivers the mobile phase at a steady flow (typically 0.5 mL/min to 2 mL/min) at pressures up to about 400 bar, isocratic or gradient.
• Injector or autosampler: introduces a fixed volume (for example 20 µL) of sample through a sample loop.
• Column: stainless steel tube, typically 150 mm to 250 mm long and 4.6 mm internal diameter, packed with 3 µm to 5 µm particles, often in a column oven.
• Detector: usually a UV-visible or diode-array detector; fluorescence, refractive index and mass spectrometer detectors are also used.
• Data system: records the chromatogram (detector signal against time) and calculates peak areas.

Applications

• Pharmaceutical quality control: assay and impurity testing of tablets and syrups against pharmacopoeia methods.
• Food analysis: caffeine in beverages, aflatoxins in maize and groundnuts, sugars and preservatives.
• Clinical and research analysis: drug levels in blood and vitamins in serum.
• Environmental analysis: pesticides and other organic pollutants in water.

1.1.3 Gas Chromatography (GC)

Gas Chromatography is a powerful technique for separating volatile compounds, widely used in Kenyan laboratories for environmental monitoring, food safety, and forensic analysis.

Principles and Mechanism

GC separates compounds based on their volatility and interaction with the stationary phase inside a column. The sample is vaporized and carried by an inert gas through the column, where components elute at different times known as retention times.

Instrumentation and Components

• Injector: Vaporizes liquid samples and introduces them into the carrier gas stream.
• Column: Usually packed or capillary, coated with stationary phase material.
• Carrier Gas: Typically helium or nitrogen, provides inert mobile phase.
• Detector: Common types include Flame Ionization Detector (FID) and Thermal Conductivity Detector (TCD).
• Data System: Records chromatograms for qualitative and quantitative analysis.

Applications in Kenyan Laboratories

• Analysis of pesticide residues in agricultural produce at research institutions.
• Quality control of fuel samples at petroleum companies.
• Detection of volatile organic compounds in environmental samples monitored by NEMA.

1.1.4 Ion Exchange Chromatography (IEC)

IEC separates ions and polar molecules based on their affinity to ion-exchange resins, playing a crucial role in water quality testing and biochemical assays in Kenyan laboratories.

Principles and Operating Mechanism

The stationary phase consists of charged resin beads that attract oppositely charged ions in the sample. Components are separated according to their charge density and elution strength of the mobile phase.

Equipment and Resin Types

• Columns packed with cation or anion exchange resins.
• Pumps to control mobile phase flow.
• Detectors such as conductivity meters to monitor eluted ions.

Practical Uses in Kenya

• Removal of heavy metals from water samples analyzed at county water laboratories.
• Purification of proteins in biomedical research at universities.
• Monitoring of ionic contaminants in industrial effluents regulated by NEMA.

1.1.5 Thin Layer Chromatography (TLC)

TLC is a simple, rapid chromatographic technique used extensively in Kenyan laboratories for qualitative analysis of pharmaceuticals, food additives, and plant extracts.

Principle and Process

Samples are spotted on a thin layer of stationary phase coated on a plate. The plate is developed in a solvent chamber where the mobile phase ascends by capillary action, separating components based on polarity.

Equipment and Materials

• TLC plates coated with silica gel or alumina.
• Developing chamber with solvent reservoir.
• UV lamp or iodine chamber for visualization of spots.

Applications in Kenyan Context

• Identification of counterfeit drugs in hospital pharmacies.
• Screening of metabolites in agricultural produce.
• Quality control of herbal medicines at research institutions.

1.1.6 Gel Electrophoresis (GE)

Gel Electrophoresis is a technique for separating charged biomolecules like DNA, RNA, and proteins, essential in molecular biology and clinical diagnostics in Kenya.

Principle and Separation Mechanism

Molecules migrate through a gel matrix under an electric field. Separation depends on size and charge, with smaller molecules moving faster through the gel pores.

Equipment Components

• Gel casting trays and combs.
• Power supply providing a controlled electric field.
• Buffer solutions maintaining pH and conductivity.
• Staining and visualization tools such as ethidium bromide and UV transilluminators.

Kenyan Laboratory Applications

• DNA fingerprinting in forensic cases handled by the Directorate of Criminal Investigations.
• Diagnosis of genetic diseases at national referral hospitals.
• Protein analysis in research conducted at universities.

Chapter Summary

This chapter provided a comprehensive overview of chromatographic techniques, beginning with the various apparatus and equipment essential for accurate analysis, including volumetric flasks, analytical balances, crucibles, graduated glassware, and cuvettes. It detailed several chromatographic methods such as Gas Chromatography, Ion Exchange Chromatography, Thin Layer Chromatography, and Gel Electrophoresis, explaining their principles and applications. The preparation of standards and samples was emphasized as a critical step to ensure reliable results. Procedures for carrying out chromatographic analysis were outlined, focusing on precision and adherence to protocols. The chapter also covered strategies for optimizing laboratory instruments through calibration, troubleshooting, and routine physical checks to maintain accuracy and functionality. Finally, methods for processing results were discussed, including tabulation, calculation, interpretation, and discussion to derive meaningful conclusions from chromatographic data.