Preconcentrates

Preconcentrates are enriched samples in which the concentration of a target analyte has been increased relative to the original matrix by a preconcentration step. This is not a separate chemical compound: it is the same analyte present at a higher concentration, allowing more sensitive measurements and reduced matrix effects during analysis. The primary goal is to improve detection limits, decrease sample volume requirements, and mitigate interferences before instrumental techniques such as ICP-MS, AAS, GC-MS, or HPLC.

Common preconcentration methods include solid-phase extraction, liquid-liquid extraction, and solid-phase microextraction; evaporation and solvent exchange; co-precipitation; membrane filtration; and dispersive liquid-liquid microextraction. More recently, techniques like cloud point extraction and trap-and-release or sorbent-based sampling are used for specific analytes. The choice depends on the analyte's chemistry, the sample matrix, required enrichment factor, carryover, and practicality.

Applications span environmental, clinical, pharmaceutical, food, and industrial hygiene analyses. For example, trace metals in water or soil may be concentrated by SPE before ICP-MS, while organic pollutants can be enriched by DLLME or SPME prior to GC-MS or LC-MS.

In mining and mineral processing, the term preconcentrate is also used to describe ore fractions that are enriched in valuable minerals after comminution and initial separation, intended to reduce downstream energy use and processing costs through flotation, gravity, or magnetic methods.

Quality considerations include recovery, enrichment factor, selectivity, and potential biases introduced by the concentration step. Validation and calibration are essential to ensure accurate quantification.