Extraction and isolation of phenoxy acid herbicides in environmental waters using two adsorbents in one minicartridge

Abstract

Selectlve solid-phase extraction from environmental waters of nlne popular acldlc herblcldes was accompllshed by using one mlniaturlzed cartridge contalning in the top slde 50 mg of a nonspecific adsorbent, that Is graphitized carbon black (Carbopack B), and In the lower side 70 mg of a slllca-based strong anlon exchanger (SAX). After sample percolation, the SAX materlai was actlvated by passlng through the trap sodlum acetate, l moi/L. A 3-mL solvent mlxture of CH, Ci , / CH, OH (80:20, by volume) badfled with 1 mmol/L NaOH was then allowed to flow through the cartridge, and phenoxy acids were removed from the Carbopack surface and selectively readsorbed on the exchanger surface. After washing, the nlne herblcides were desorbed from the SAX surface wkh 0.0 mL of water/methanol (50:50, by volume) contalning trlfluoroacetlc acid and potasslum chloride. A 100-pL portion of thls solution was directly injected into the HPLC column, operatlng in the Ion suppression-reversed-phase mode. As ion suppressor, the substitutlon of the commonly used acetlc acld with trlfluoroacetlc acid allowed sensitive detectlon at 230 nm. Recovery of the nlne acidic herblcides ranged between 94% and loo%, lrrespectlve of the sample type considered. By thls extractlon method, bask, neutral, and weakly acldic compounds do not interfere with the analysis. Interestlngly, thls cartridge Is suitable for fleld sampllng, as Carbopack is able to adsorb phenoxy aclds from water at whatever pH value. The llmlts of detectlon of the nlne herbicides were well below 0.1 pg/L. The effectiveness In terms of recovery and selectivity of the two-adsorbent tandem system was compared with that of a C-18 disposable cartrldge.In the last decade, as an alternative to liquid partitioning, the method of combined extraction and preconcentration of organic compounds in water by adsorption on proper solid materials followed by desorption with a small quantity of an organic solvent has been employed extensively for trace determination of contaminants in environmental waters (1-8). The recent availability of sorbents in small, inexpensive cartridges has contributed t o the dramatic expansion of the use of solid-phase extraction (SPE), as evidenced by some selected publications (9-13). Besides solving well-known problems associated with the classical solvent extractionsolvent removal method, the S P E technique is particularly attractive as it lends itself to coupling with chromatographic systems for on-line applications (14). Another impressive feature of the SPE technique is that small sorbent traps can be deployed in the field by using newly available submersible instrumentation (15,16). In this way, combined sampling, extraction, and preconcentration are done at the sampling site, thus eliminating most contamination and handling problems connected to the sample collection. In addition, immediate isolation of organics from the aqueous matrix by an adsorbing material can preserve analytes from bacterial attack occurring between the time of sample collection and analysis...

Passive extraction and clean-up of phenoxy acid herbicides in samples from a groundwater plume using hollow fiber supported liquid membranes

“…Conventional methods are liquid-liquid extraction (LLE) with organic solvents such as dichloromethane from acidified samples. Solid-phase extraction (SPE) has widely been adopted as an alternative to LLE [6], and ion exchangers [7,8], C 18 bonded silica [9,10], polymers [11][12][13], and graphitized carbon black (GCB) [14,15], or tandem adsorbents [16] have been reported as adsorbent materials. SPE of phenoxy acid herbicides has the advantages of high extraction efficiency and thus high method sensitivity, but often suffered from the plugging of cartridge and overlapping of analyte chromatographic peaks by dissolved organic matter (DOM) in water samples, especially when C 18 bonded silica is used as adsorbent [17].…”

Ion-exchange extraction of organic acids in water samples. Study of the influential factors and interactions

“…So, ion-exchange resin extraction would not be affected by interfering compounds from the organic or mineral matrices. However, other authors have stated a decreasing of the extraction yield during the acidic herbicide preconcentration on an anion-exchange resin, on the contrary of an extraction on graphitized carbon [14].…”

“…Amongst the main phases used, it is possible to distinguish apolar sorbents such as bonded silica C 18 [11], polymeric resins (styrene divinylbenzene polymer) [12,13] or graphitized carbon [14,15]. These sorbents are not specific and permit the extraction of a wide scale of organic compounds.…”

On-Line Preconcentration with Solid-Phase Extraction for the Determination of Phenol and Chlorophenols in Aqueous Samples by High-Performance Liquid Chromatography

“…Di Corcia et al 6 analyzed nine phenoxy acid herbicides without adjusting the pH by using one cartridge containing graphitized carbon black (GCB) and a strong anion exchanger. Lee et al ' 1 reported on an analysis of 9 phenolic compounds with two linearly connected columns of a copolymer-based sorbent (XAD-4) and an anion exchange resin.…”