Avoiding Interferences in Advance: Cyclodextrin Polymers to Enhance Selectivity in Extraction of Organic Micropollutants for Carbon Isotope Analysis

Compound-specific isotope analysis (CSIA) of organicwater contaminantscan provide important information about their sources and fate inthe environment. Analyte enrichment from water remains nonethelessa critical yet inevitable step before measurement. Commercially availablesolid-phase extraction (SPE) sorbents are inherently nonselectiveleading to co-extraction of concurrent dissolved organic matter (DOM)and in turn to analytical interferences, especially for low-occurringcontaminants. Here, we (i) increased extraction selectivity by synthesizingcyclodextrin polymers (& alpha;-, & beta;-, & gamma;-CDP) as SPE sorbents,(ii) assessed their applicability to carbon isotope analysis for aselection of pesticides, and (iii) compared them with commonly usedcommercial sorbents. Extraction with & beta;-CDP significantly reducedbackgrounds in gas chromatography-isotope ratio mass spectrometry(GC-IRMS) and enhanced sensitivity by a factor of 7.5, which was furtherconfirmed by lower carbon-normalized C-DOM/C-analyte ratios in corresponding extracts as derived from dissolved organiccarbon (DOC) and liquid chromatography-tandem mass spectrometry (LC-MS/MS)analysis. Gibbs free energies of adsorption demonstrated weak competitionbetween DOM and analyte on the three CDPs. No isotopic fractionation(& UDelta;& delta;C-13 within & PLUSMN; 0.3 & PTSTHOUSND;) was observedfor the investigated pesticides after using & beta;-CDP as an SPEsorbent covering a range of concentrations (5-500 & mu;gL(-1)), flow velocities (5-40 cm min(-1)), and sorbent regeneration (up to six times). The present studyhighlights the benefit of selecting innovative extraction sorbentsto avoid interferences in advance. This strategy in combination withexisting cleanup approaches offers new prospects for CSIA at fieldconcentrations of tens to hundreds of nanograms per liter.

Automated summary

The synthesis of cyclodextrin polymers as solid-phase extraction (SPE) sorbents can increase extraction selectivity and reduce background interference. The use of β-CDP as an SPE sorbent can significantly reduce backgrounds, enhance sensitivity, and avoid isotopic fractionation.