This study material has been compiled from two primary sources:

1. Copy-pasted text: Original content provided in Italian, translated into English.
2. Lecture Audio Transcript: Original content provided in Turkish, translated into English.

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📚 Analytical Chemistry: Principles, Methods, and Applications

1. Introduction to Analytical Chemistry

Analytical Chemistry is the study and development of methods and techniques that allow us to understand the elemental and molecular compositional properties of materials and systems. This understanding enables us to characterize them and predict/describe their behavior. To achieve this goal, it is necessary to choose the best methods and, if satisfactory methods are lacking, to develop new ones.

1.1. Interdisciplinary Nature 🌍

Analytical chemistry is inherently interdisciplinary. Its development and application of analytical methods, as well as the processing and interpretation of measurements, require knowledge, techniques, and methods specific to:

• Physical Chemistry
• Physics
• Electronics
• Computer Science
• Biology
• Toxicology
• Materials Chemistry
• Statistics

Many disciplines, such as Pharmacology, Toxicology, Forensic Sciences, Environmental Sciences, Materials Science, Medicine, Engineering, and Molecular Biology, critically depend on analytical measurements.

1.2. The Science of Measurement (Metrology) 📏

Modern society is based on the concept of "measurement." Analytical chemistry is the science of measurement (metrology) applied to chemistry.

• The measurement of a desired quantity (measurand) involves comparing the quantity itself with the unit of measurement through an unbroken chain of comparisons, each with its uncertainty (traceability).
• The concepts of metrology deeply influence analytical chemistry.
• The result of an analytical determination must always be expressed along with its uncertainty (a measure of the possible deviation between the reported result and the true value of the quantity).
• Metrology → Result ± Uncertainty → Confidence Interval (an interval for which there is a given probability (confidence level) that it contains the true value).

1.3. Uncertain Results and Decisions ⚠️

Measurement uncertainty reflects the suitability of the result for the intended purpose.

• Example: Legal limit for pesticide contamination in surface waters: 0.1 µg/L.
  • Analytical result: 0.12 µg/L ± 0.05 µg/L.
  • Question: Is the legal limit actually exceeded?
  • Answer: The obtained analytical result does not allow us to state with a high confidence level (high probability of NOT being wrong) that the legal limit has been exceeded. No decision can be made, and the analysis must be repeated with a more precise method.

1.4. Analytical Chemistry and Technological Progress 📈

Analytical chemistry underpins significant technological advancements:

• Semiconductor Doping: Requires extremely sensitive elemental analysis techniques (1 atom in 10^19 – 10^21).
• Proteomics and Genomics Studies: Made possible by mass spectrometry techniques that analyze intact macromolecules.
• Environmental Monitoring: Analytical methodologies for ozone, disinfection by-products in drinking water, and emerging contaminants (pharmaceuticals and metabolites).

1.5. The Future of Analytical Chemistry 🚀

Future developments are expected in:

• Miniaturization (chemical sensors)
• Integrated analytical microsystems
• Real-time analysis
• Big data processing with chemometric techniques

1.6. Theoretical Limits of Analytical Chemistry 💡

• Single Atom/Molecule Counting: Concentration is a macroscopic-thermodynamic concept, subject to fluctuations (due to thermal agitation) that depend on the amount of matter considered. The smaller the portion of matter, the greater the fluctuations, i.e., the intrinsic uncertainty of the measurement.
• Zeptomole Measurements: Measuring substance quantities at the zeptomole level (10^-21 moles) becomes extremely imprecise due to thermal agitation fluctuations. Concentration is a macroscopic quantity and, as such, is an average.
  • 1 zeptomole/liter = 602 entities/liter.
  • Sampling a portion of solution containing a few thousand molecules does not ensure concentration maintenance due to associated thermal agitation fluctuations. For such low concentrations, it is necessary to sample quantities of solution (matter) containing at least 10^5 molecules.

2. Stages of Analysis 1️⃣2️⃣3️⃣

The analytical process follows a structured series of steps:

1. Definition of the Objective: Clearly state what needs to be determined.
2. Choice of Method: Select the most appropriate analytical technique.
3. Sampling: Obtain a representative portion of the material.
4. Pretreatment: Prepare the sample for analysis (e.g., grinding, drying, dissolution).
5. Calibration and Measurement: Calibrate the instrument and perform the measurement.
6. Processing of Results: Analyze and interpret the data.
7. Action Based on Results: Make decisions or take actions based on the analytical findings.

3. Methodologies of Analytical Chemistry

3.1. Chemical or Classical Methods 🧪

These methods are based on a chemical reaction involving the analyte with suitable characteristics.

• Gravimetric Methods: The analyte is quantitatively converted into an insoluble, well-defined, and stable precipitate, which is then weighed.
• Titrimetric or Volumetric Methods: A known volume of the solution containing the analyte (titrand) is reacted with a solution of a suitable reagent (titrant) of known concentration. Using an appropriate indicator system for the equivalence point (equality between equivalents of titrant added and titrand), the volume of solution required for the reaction to complete is determined.
  • Reaction classes used: Neutralization, complex formation, precipitation, redox reactions.

3.2. Physical and Physico-Chemical (Instrumental) Methods 🔬

These methods are based on measuring a physical or physico-chemical property (e.g., light absorption, redox or membrane potential) that is directly related to the presence and/or quantity of the analyte.

• Methods based on interaction with electromagnetic radiation (spectroscopies and spectrophotometries).
• Methods based on interaction with particle beams (X-rays, electron beams, neutral atoms, ions).
• Electrochemical Methods
• Chromatographic Methods
• Mass Spectrometry
• Thermal Analysis

4. Sample Preparation Techniques

Sample preparation is one of the most critical and delicate phases, significantly influencing the results of all subsequent operations and contributing substantially to the total uncertainty of the final analytical result. The uncertainty associated with sampling can contribute 30-50% to the total analytical result uncertainty, far exceeding the 5% associated with the analytical phase itself.

4.1. Sampling 🎯

Definition: The operation of removing a portion from a much larger material such that the portion is representative of the properties of interest of the material itself.

Importance:

1. The greatest attention paid to performing an analysis can be entirely in vain if the sample has not been collected with equal care.
2. The sampling procedure must be chosen appropriately, considering the purpose of the analysis.
3. The accuracy of our analyses strongly depends on the validity and representativeness of the collected samples.
4. To perform an analysis correctly, it is necessary to know the nature and conditions of the material to be sampled and the means to be used for sampling.

Essential Requirement: Sampling must be representative. The sample must also be:

• Collected in a way that maintains its physical, chemical, and biological characteristics unaltered until the moment of analysis.
• Stored in a way that prevents modifications of its components and the characteristics to be evaluated.

4.2. Types of Samples 📦

• Instantaneous (Grab or Catch Sample): A single sample taken in one go at a determined point and in a very short time.
• Composite: Obtained by mixing several instantaneous samples.
  • Over time: Samples taken at the same point at different times.
  • In space: Samples taken at different points at the same time (also called integrated sample).
    • Example: River water collected at different depths.
• Depending on the type of sample and the objective of the analysis, it may be more appropriate to analyze instantaneous or composite samples.

4.3. Preliminary Sample Treatments 🛠️

These are mainly physical operations applied to the sample before specific pretreatment for analysis.

4.3.1. Grinding/Milling ⚙️

Purpose:

• Finely powdered samples are more homogeneous, allowing for more representative subsamples.
• Finely divided samples are easier to dissolve or attack due to a higher surface area-to-volume ratio.
• Finely powdered samples are more suitable for compression into discs or fusion into pellets for solid-state analysis (IR or X-ray spectroscopy).

Milling Techniques:

• Ceramic mortar and pestle: For general use.
• Agate mortar and pestle: For harder materials.
• Ball mill: Suitable for soft materials. The sample is agitated with agate or stainless steel spheres.
• For malleable or elastic materials (rubbers, plastics), they are cooled to liquid nitrogen temperature (77 K) to make them brittle.

Precautions:

• Grinding causes friction, which can lead to local overheating, potentially causing loss of volatile components or thermal decomposition of heat-sensitive samples.
• Contamination can occur from the mortar material or previous samples.

4.3.2. Sieving 筛

• Sometimes it is necessary to subdivide the sample according to particle size using a series of sieves of different mesh sizes.
• Mesh: Number of openings per linear inch.
• Example: Soil analysis: sieving with 2 mm mesh to remove coarse material.

4.3.3. Drying ☀️

• Many samples are moist, containing a potentially large, variable, and unknown amount of associated water.
• Water content can also vary during storage due to evaporation or absorption of atmospheric water vapor.
• Results cannot be expressed for a wet sample without knowing its water content. Therefore, the sample is usually dried before analysis.
• For some parameters, analysis is performed on the wet sample, but humidity is always assessed, and the result is expressed relative to dry matter (e.g., nitric, nitrous, ammoniacal N).

Procedures:

• Air drying.
• Oven drying: Typically near 100 °C (105 °C for most materials like compost and soils) until constant weight. Minerals like aluminates and silicates may require temperatures up to 1000 °C.
• Vacuum drying.
• Freeze-drying (lyophilization): The sample is frozen and then dried under vacuum. Useful for heat-sensitive samples or for determining volatile analytes.

4.3.4. Filtration 💧

Purpose: To remove suspended particles.

• The filter material must not react with solution components or the precipitate.
• Filter pores must be smaller than the particles to be filtered.

Modes:

• By gravity.
• Under vacuum.
• Under positive pressure (depending on filter type, volume, and fluid nature).
• Alternatively, filtering crucibles with glass or porcelain septa can be used, typically under vacuum.

Filter Materials:

• Cellulose (paper filters)
• Cellulose esters (nitrate and acetate)
• Glass fiber
• Teflon
• Other materials: Nylon, polycarbonate, polyvinylidene fluoride, polysulfone, polyethylene sulfone, alumina.

Types of Filters:

• Depth Filters: Trap solid particles both within the filter thickness and on the surface (e.g., cellulose and glass fiber filters, which have an interwoven fiber matrix). Efficiency ~90%. Can be used as pre-filters.
  • Advantages: High retention capacity, low cost.
  • Disadvantages: Fibers or particles can detach with sudden pressure changes (e.g., vacuum), trapped particulate can contaminate the filtrate.
• Membrane Filters: Thin polymeric films with thousands of microscopic pores, whose size determines the filtration degree. Retain particles larger than pores on the surface. Smaller particles may pass through or be trapped internally. Efficiency ~100%.
  • Advantages: Determinable and absolute filtration degree below the micron.
  • Disadvantages: Lower filtration speed, higher cost.

Chemical Compatibility:

• The material's ability to resist the action of the fluid components, ensuring pore structure is not damaged and filter material does not release particles or fibers.
• Influenced by temperature, concentration, and exposure duration.
• Manufacturers provide compatibility tables.
• Cellulose acetate/mixed ester filters are good for aqueous solutions but poor for organic solvents. Teflon filters are inert and suitable for all solutions but are more expensive.
• Filters can release contaminants (adhesives, polymerization additives, processing residues), especially problematic for trace analysis.
• Remedy: Treat the filter with water or a suitable solution before use and discard the first aliquot of filtrate.

Filtering Devices:

• Funnels (especially for paper filters).
• Cartridges (disposable or reusable) for syringes.
• Filtration units (disposable or reusable) with a filling vessel, membrane support, and collection vessel.

4.3.5. Centrifugation 🌀

Another method to separate solids from liquids, followed by decantation.

4.4. Pre-treatment (Solubilization) 溶解

Most analyses are performed wet, meaning solid samples must be brought into solution, or at least the part containing the analyte must be solubilized. Pretreatment is essential, as important as the qualitative-quantitative determination itself.

• Non-destructive techniques: In rare cases, analysis can be performed on the sample as is, using non-destructive techniques like Raman spectrometry or X-ray Fluorescence.
• The variety of matrices makes general rules difficult. The appropriate pretreatment method depends on the chemical nature (organic/inorganic, acidic/basic/neutral, aqueous/organic soluble) and the analytical technique.
• Generally, solutions obtained from solid samples are aqueous, containing metals as simple cations and non-metallic elements as anions.

4.4.1. Dissolution 💧

The pretreatment process is often critical, with many potential error sources (e.g., incomplete dissolution, contamination). Many procedures involve chemical transformations, often using aggressive reagents, high temperatures, and sometimes high pressures.

Ideal Dissolution Procedure:

• Completely dissolve the sample without insoluble residue.
• Be reasonably fast.
• If aggressive reagents are needed, they should not interfere with subsequent analysis or be removable.
• Reagents should be highly pure to avoid contamination.
• Analyte losses (volatility, aerosol formation, adsorption, container attack) should be insignificant.
• Reagents/sample should not attack container material.
• The procedure should be safe.

4.4.2. Dissolution in Water 🚰

Possible only for a few materials. Closest to the ideal case: non-aggressive reagent, high-purity solvent, minimal analyte loss, no container attack, safe.

4.4.3. Acid Dissolution 🧪

Widely used for inorganic species (metals, anions), but unsuitable for organic species due to chemical and thermal degradation.

• Digestion occurs in a container with finely divided sample and solubilizing reagents, possibly with oxidizing agents.
• Most metals are more electropositive than hydrogen and dissolve in acid. Many simple oxides, carbonates, and sulfides are acid-soluble.
• Mechanism: Acid reacts with the sample to form a soluble metal salt and other products.
• Can occur cold or hot, depending on ease of attack.
• Examples: Zn + 2HCl → ZnCl2 + H2; MgO + 2HCl → MgCl2 + H2O; CaCO3 + 2HCl → CaCl2 + H2O + CO2; FeS + 2HCl → FeCl2 + H2S.
• Note: Not all electropositive metals dissolve (e.g., Al, Cr passivate). Some metals dissolve in dilute acids unexpectedly (e.g., Cu in HNO3 1:1). The product must be soluble.

Attack with Concentrated Hot Acids:

• Acid Effects:
  • Strong concentrated acids.
  • Oxidizing agents (especially oxyacids): metals oxidized to cations.
  • Complexing agents: high anion concentration can complex metal cations, keeping them in solution.
• Relevant Acid Properties: Acid strength, boiling point (max heating temp), oxidizing power, complexing power, metal salt solubility, safety.

Specific Acids:

• Hydrochloric Acid (HCl):
  • Commercial conc. HCl (37%) is ~12 M. Azeotrope at ~20% (b.p. 109°C).
  • Strong acid, but not oxidizing beyond H+.
  • Chloride ion forms stable complexes with many metal ions.
  • Most chlorides are water-soluble, except Hg2Cl2, AgCl, TlCl. PbCl2 is sparingly soluble cold, very soluble hot.
• Hydrofluoric Acid (HF):
  • Commercial HF (40-50%) is ~22-29 M. Azeotrope at 36% (b.p. 111°C).
  • Weak, non-oxidizing acid.
  • F- is a strong complexing anion, forming stable fluorides and fluorocomplexes with many elements, including refractories.
  • Main application: solubilizing silicate-containing materials. Si is lost as volatile SiF4, but the rest of the matrix dissolves.
  • Precautions: Do not use glass containers (use Pt, PTFE, or other polymers). HF causes severe skin injuries.
  • Often, F- traces must be removed to avoid interferences (e.g., by evaporating to dryness with sulfuric acid).
• Nitric Acid (HNO3):
  • Commercial conc. HNO3 (65-69%) is ~14 M. Azeotrope at 67% (b.p. 121°C).
  • Strong acid and strong oxidizer.
  • Oxidizes all metals except noble ones. Some refractory metals (Al, Cr, Ti, Nb, Ta) are passivated.
  • Almost all nitrates are water-soluble.
  • Nitrate ion is a weak complexing agent; some ions hydrolyze and precipitate as hydrated oxides (e.g., Sn, W, Sb).
  • Does not add elements not already present.
• Perchloric Acid (HClO4):
  • Commercial HClO4 (60-72%) is ~10-12 M. Azeotrope at 72% (b.p. 203°C).
  • Hot, it is a strong oxidizer, dissolving almost all metals (except noble ones) and converting them to their highest oxidation state ions.
  • All metal perchlorates are water-soluble, except KClO4, RbClO4, CsClO4.
  • Caution: Hot, concentrated HClO4 can cause explosions due to its strong oxidizing power.
  • Applications: dissolution of intractable alloys, especially steels.
  • Often used after HNO3 treatment to oxidize easily oxidizable material, reducing explosion risk.
• Sulfuric Acid (H2SO4):
  • Commercial conc. H2SO4 (98%) is ~18 M. B.p. 330°C (highest among common mineral acids), allowing high dissolution temperatures.
  • Strong acid and strong oxidizer when hot. Strong dehydrating agent, destroys organic materials.
  • Many metal sulfates are water-soluble (except CaSO4, SrSO4, BaSO4, PbSO4).
  • Advantage: Metal sulfates have low volatility, allowing samples to be brought almost to dryness with little loss.
  • Application: removing HF by evaporating to dryness (metal fluorides form metal sulfates, HF is eliminated).
• Phosphoric Acid (H3PO4): (Note: The provided text repeats H2SO4 properties for H3PO4, which is likely an error in the source material. H3PO4 is a weaker acid and less oxidizing than H2SO4, but can be used for certain digestions, especially for phosphates.)

Acid Mixtures:

• Why use mixtures? To exploit different properties (oxidizing, complexing), moderate excessive properties, form more reactive products, or replace one acid with another.
• Complexing + Oxidizing Acid: HF + HNO3, HF + HClO4, HF + H2SO4. Used for steels and refractory metal alloys.
• Aqua Regia (Royal Water): 3 parts HCl + 1 part HNO3.
  • Turns yellowish, smells of Cl2. HNO3 oxidizes HCl to form highly reactive Cl2 and NOCl.
  • These are powerful oxidizing agents, and combined with the complexing power of chloride, can dissolve noble metals (e.g., gold).
  • HNO3 + 3 HCl → NOCl + Cl2 + 2H2O; 2NOCl → 2 NO + Cl2; 2NO + O2 → 2 NO2.

Addition of Oxidizing Agents:

• To increase the oxidizing power of acids or use non-oxidizing acids with an oxidizer.
• Common agents: H2O2, Br2 (for Te minerals), KClO3 (with HCl for As and S minerals).

Precautions in Digestion:

• Reagent and sample quantities must be compatible with system volume.
• For organic matrices, consider gaseous products (CO2, NOx) that can cause overpressure in closed systems. Carbon content is crucial for wet digestion design.

Hot Acid Dissolution Techniques:

• Boiling in a beaker with a watch glass.
• Boiling under reflux.
• Boiling and evaporating almost to dryness (useful for low acid content or multi-acid treatments).
• Bomb Technique: Sample and acid in a sealed steel bomb lined with Pt or PTFE. Allows high-temperature dissolution above acid boiling points, increasing solubilizing/oxidizing properties, and limiting volatile losses.
  • Advantages: Higher temperatures, less volatile loss, smaller acid volume, no vapor diffusion, reduced contamination.
  • Disadvantages: Higher explosion risk, more complex/expensive equipment.
  • Modes: Steel bombs with classic heating, Teflon bombs with microwave heating.

Microwave-Assisted Wet Digestion:

• More efficient variant using microwaves for heating in a closed system.
• Microwave energy (600-1500 W) heats polar solvents (water, mineral acids) rapidly, enabling more efficient and faster sample solubilization.
• Containers: Inert, microwave-transparent materials like Teflon®, PFA, quartz.
• Caution: Organic matrices require great care due to rapid temperature/pressure increase. Temperature/pressure sensors control reactions.
• Microwave Characteristics: Non-ionizing electromagnetic waves (1 mm - ~1 m). ISM frequencies (Industrial, Scientific, Medical) are allowed.
• Properties:
  • Limits: 250 °C, 80 bar (at <50 °C), 8-10 bar (at 200 °C).
  • Advantages: Lower temperatures needed, shorter times, easy automation, direct sample heating, less container interaction/contamination, simultaneous multi-sample processing.
  • Disadvantages: Non-uniformity, volume-dependent heating, no visual reaction monitoring, temperature/pressure limitations due to material restrictions, overpressure hazard.

4.4.4. Fusions 🌋

Used for inorganic substances insoluble in mineral acids or forming unstable solutions (e.g., cements, aluminates, silicates, Ti/Zr minerals, slags, refractory oxides).

• Insoluble Residue: Portion undissolved after HCl, HNO3, and aqua regia attack. Can be white (silica, silicates, Al2O3, SnO2, TiO2, AgCl, PbCl2, sulfates, CaF2) or colored (AgBr/I, PbCrO4, Fe2O3, Cr2O3, S, C).
• Process: Finely powdered sample mixed with an acidic or basic electrolyte (flux), possibly with an oxidizing agent. Ratio sample:flux 1:2 to 1:50.
• Mixture heated in a Pt or Ni crucible until molten. Cooled, broken up. If effective, the solidified melt dissolves easily in water or dilute acid.
• Effectiveness: Fused inorganic electrolytes are powerful solvents; high fusion temperatures (up to 1200 °C).
• Disadvantages: Contamination risk, volatile losses.
• Often, most of a sample is dissolved with acid, and the residue is then fused.

Alkaline Fusion (for total Fe, Al, Si):

• Fusion Mixture: Equal parts Na2CO3 and K2CO3.
• Procedure: Sample with Na2CO3/K2CO3 in a Pt crucible. Heat slowly (Bunsen flame) to avoid foaming. After gas evolution (CO2), heat in muffle furnace at 900 °C for 15 min. Cool. Add HPW (High Purity Water) and heat to near boiling. Melt dissolves. Add 20 mL dilute HCl (1:1 v/v) to completely dissolve. Transfer to final container, dilute to volume with HPW. Solution must be clear (opalescence indicates incomplete silica dissolution).

Basic Fluxes:

• Na2CO3 and/or K2CO3: Powerful for silicates and refractories. Oxidizers (KNO3, KClO3, Na2O2) can be added.
  • CO3^2- → CO2 + O^2-. O^2- reacts with SiO2: SiO2 + O^2- → SiO3^2-. Soluble sodium metasilicate forms.
• NaOH or KOH: Attack silicates, aluminosilicates, silicon carbide.
• Na2O2: Strong oxidizer, used for sulfides and Fe, Ni, Cr, Mo, W, La alloys insoluble in acids.
• Na2B4O7·10H2O (Borax): For Al2O3, ZrO2, Zr minerals, rare earth minerals, Ti, Nb, Ta, Al-containing materials, Fe minerals, slags. Used with Na2CO3 at 1000-1200 °C.

Acid Fluxes:

• KHSO4 and K2S2O7 (Potassium Pyrosulfate): Used at ~500 °C.
  • 2KHSO4 → K2S2O7 + H2O; K2S2O7 → K2SO4 + SO3. SO3 acts as an acid.
  • Used for metal oxides (Al2O3, BeO, Fe2O3, Cr2O3, MoO3, TeO2, TiO2, ZrO2, Nb2O5, Ta2O5). Oxides convert to soluble metal sulfates.
• B2O3 (Boric Oxide): M.p. 450 °C. Used for silicates as an alternative to basic fluxes if alkali metals are to be determined. Excess B2O3 removed by distilling residue with methanol (volatile B(OCH3)3 forms).
• KF + KHF2: For silicates and metal oxides forming fluorocomplexes (Be, Nb, Ta, Zr). Melt can be treated with H2SO4 to remove fluorides. Si and B are completely lost.

Subsequent Treatments After Attack:

• Solutions will contain large amounts of concentrated acids or electrolytes that can interfere.
• Acid Removal: Evaporate almost to dryness, then redissolve in dilute acid.
• Disadvantages: Risk of losses. More difficult to remove fusion salts.

Containers for Attacks:

• Acid Attacks: Glass or quartz (if no HF), Teflon (T <250 °C), PFA (T <250 °C).
• Fusion: Platinum or nickel crucibles. Glass or porcelain crucibles are attacked by fluxes. Graphite crucibles are cheaper but less durable.
• Analyte can react with container walls, leading to apparent loss (e.g., metal reduction and binding to Pt in alkaline fusions).

4.5. Separations ↔️

Objectives:

• Remove analytes from interfering species.
• Preconcentrate analytes for trace analysis.
• Transfer analytes to a suitable phase for analysis (e.g., Me-organic ligand complexes in spectrophotometry).
• Isolate an analyte in pure form (for unknown compound identification or gravimetry).
• Identify analyte based on its separation behavior.
• Simplify the matrix.

Disadvantages: Slow, complicated, sensitive to errors.

Stages of Separation:

• Chemical conversion of substances to be separated (not always required).
• Distribution of substances between two phases.
• Physical (mechanical) separation of the two phases.
• Stages can occur simultaneously (chromatography) or sequentially.

Modes of Separation:

• Batch Separation: Simplest method. Single distribution of solute between two phases until equilibrium. Phases then separated. Suitable when species is quantitatively concentrated in one phase or for studying equilibrium constants.
• Multiple Batch Separations: Used when single batch extraction is insufficient for quantitative transfer.
• Continuous Separation: Extremely important, includes all forms of chromatography.
• Trapping Techniques: Mobile phase flows over a stationary phase to concentrate all analyte on the stationary phase. Used for preconcentration. Retained analyte is then released into a new, smaller volume mobile phase.

Pre-concentration (Enrichment):

• Definition: A process where the ratio of analyte concentrations to matrix concentrations increases.
• Purpose: Enables or facilitates analyte determination by increasing concentration and/or eliminating/reducing matrix interferences.
• Techniques: Liquid-liquid extraction, solid-phase extraction, precipitation, electrodeposition.

4.5.1. Solvent Extraction 🛢️

Common pretreatment technique when total sample solubilization is not needed or is counterproductive. Selectively brings analytes into solution, leaving the matrix largely intact. Sample contacted with an immiscible solvent in which analytes are soluble.

• Liquid/Liquid Extraction: Both sample and extracting solvent are liquids.
• Solid/Liquid Extraction: Liquid solvent used on a solid sample.

Liquid – Liquid Extraction:

• Principle: Partitioning of a species between two immiscible solvents.
• Procedure:
  1. Solution containing species of interest contacted with another practically immiscible solvent.
  2. Species distributes between the two solvents.
• Usually, one solvent is aqueous (pure water, buffer, saline solution, acid), and the other is organic (chloroform, toluene, xylene, ether, ketones).
• Applications: Separation of mixture components, preconcentration.
• Examples: Metal species (almost always as complexes), organic compounds (e.g., halogenated pesticides from biological fluids).
• Influencing Factors: Solubility of species, pH, extractant characteristics.

Extraction of Metal Ions:

• Effect of pH: pH significantly influences the extraction efficiency of metal ions, often by controlling the formation of extractable complexes.

Extraction of Ion Association Complexes:

• An ionic association forms between a cation and an anion, often involving a large organic ion. The metal species can be in the large organic ion or the counterion. These complexes are held by weak electrostatic forces but are stable enough for organic solvent extraction.
  • Often performed from strongly acidic solutions.
  • Applicable to …