6: Basic terminology.

Basic Terminology in Analytical Chemistry

Analytical chemistry relies on precise language to ensure clarity in scientific communication. Key terms form the foundation for understanding methods and interpreting results:

1. Analyte: The specific substance (e.g., ion, molecule, or element) targeted for measurement in a sample.
2. Matrix: The bulk material (e.g., soil, blood, or water) containing the analyte. Matrices can interfere with analysis, necessitating sample preparation.
3. Sample: A representative portion of the entire material (e.g., 10 mL of lake water) collected for analysis. Homogenization ensures uniformity.
4. Concentration: The amount of analyte per unit volume/mass of solution/matrix. Common units include molarity (mol/L), % w/w (weight/weight), and ppm (parts per million).

Analysis Types

• Qualitative Analysis: Identifies what is present (e.g., detecting lead in paint).
• Quantitative Analysis: Measures how much analyte exists (e.g., 5.2 ppm lead).

Performance Metrics

• Accuracy: Closeness of a measured value to the true value. Expressed via error (e.g., $\pm$0.1%).
• Precision: Reproducibility of measurements under identical conditions. Evaluated using standard deviation or relative standard deviation (RSD).
• Sensitivity: Ability to distinguish small concentration changes. High sensitivity = large signal change per unit concentration change.
• Detection Limit (LOD): The lowest analyte concentration detectable above background noise (typically signal-to-noise ratio $\geq$ 3).

Key Procedures

• Calibration: Relating instrument response to known analyte concentrations using standards. A calibration curve plots response vs. concentration.
• Blank: A matrix-free sample (e.g., pure solvent) used to identify background signals.
• Replicates: Repeated measurements (e.g., triplicates) to assess precision and reduce random errors.

Additional Terms

• Interference: Substances in the matrix altering analyte measurement (e.g., co-existing ions in spectroscopy).
• Standard Reference Material (SRM): Certified materials with known analyte levels, used for validation.
• Robustness: Method resilience to minor procedural variations (e.g., temperature shifts).

Mastering these terms ensures precise experimental design, data interpretation, and effective collaboration across disciplines like environmental science or pharmacology.