ICAN 5120H - Sample Preparation Lecture 1

Four steps of sample preparation

Extraction, reduction of interferences, adjusting analyte concentrations to a suitable range, chemically converting the analyte to a form that can be quantified

Examples of physical preparations

Grinding/milling, sieving, filtration, centrifugation, drying, homogenization

Largest source of error in instrumental chemical analysis

Sample preparation

How to minimize error in instrumental chemical analysis

Adequate selection; improve existing method, automation of procedures, and personal operating skills

Steps of chemical analysis

Quality management system approval → project plan & design → sampling technique → transportation, storage → sample processing → sample preservation → instrumental analysis/measurements, data analysis

General Considerations for Sample Preparation

Nature of the analyte, sample matrix, instrument requirements, accuracy and precision, safety and practicality

Sample preparation is driven by

How the analyte moves, binds, and reacts

Factors to consider when analyte is in ionic form

Highly soluble in water, strongly influenced by pH and ionic strength, interacts electrostatically with surfaces, resins, and membranes

At low pH, weak acids are

Neutral

At high pH, weak acids are

Ionic

At low pH, weak bases are

Ionic

At high pH, weak bases are

Neutral

Sample Preparation Principles for Ionic Analytes

pH control, electrostatic interaction, solubility control, ionic strength management

Increasing pH and metal solubility

Increasing pH does NOT neutralize the metal ion, but produces insoluble species

Metal hydroxides are ______ soluble

Poorly

Partition coefficient

The ratio of concentration of a neutral form of a compound across two mixed but immiscible phases at equilibrium

Four main colligative properties

Freezing point depression, boiling point elevation, vapor pressure lowering, osmotic pressure

Colligative Properties

Solution properties that depend only on the number of dissolved particles, not their chemical identity.