Rapid narrow band elution for on-line SPE using a novel solvent plug injection technique

Abstract

Determination of trace constituents in biological and environmental samples usually requires a pre-concentration step. While solid-phase extraction (SPE) has been widely used, it is slow, labor intensive and adversely affected by analytical errors from handling. On-line SPE eliminates some of the flaws but often suffers from solvent compatibility problems with the subsequent chromatography separation. In this study, we are presenting a technical solution for overcoming some of these compatibility issues, by utilizing a fully automated, focused SPE sample transfer technique utilizing narrow-band solvent plugs, for seamless hyphenation with high-performance liquid chromatography (HPLC) or flow injection mass spectrometry (MS). A wide range of pharmaceutical compounds was studied in different sample matrices. Short plugs of high elution strength solvent were generated by means of an electrically actuated sample loop and enrichment and transfer steps monitored using on-line SPE-MS. The impact of the solvent plugs on chromatographic separation was studied using hyphenated SPE-LC-MS. By carefully examining elution profiles of solvent plugs of different compositions, optimum conditions for quantitative elution within well-defined volumes were found for all substances. In addition, the highly focused elution bands resulted in excellent retention time and peak area reproducibilities when injected on-line onto HPLC columns. Finally, to demonstrate proof-of-principle, the fully integrated on-line SPE-LC-MS system was applied to the analysis of spiked urine and river water samples.

An On-Line Solid Phase Extraction-Liquid Chromatography-Tandem Mass Spectrometry Method for the Determination of Perfluoroalkyl Acids in Drinking and Surface Waters

“…In order to get the maximum chromatographic efficiency the trapped analytes should be eluted and refocused onto the analytical column by the analytical elution gradient by the time the extraction column is switched into the analytical flow path. However in multiresidue analysis, the gradient elution for reversed-phase separations usually starts at high percentage of aqueous in the mobile phase, and the slow elution from the SPE preconcentration column results in peak broadening, which may cause a decrease in efficiency and thereby in sensitivity [ 22 , 23 ]. For these reasons, before carrying out the method validation, the optimisation of the elution gradient and the volume as well as the matrix modification of the injected sample was carried out in order to achieve the best recovery and sensitivity for the on-line SPE/UHPLC-MS/MS analysis of the perfluorinated carboxylic and sulphonic acids.…”

“…To overcome this problem, the “solvent plug injection technique” [ 22 ] was implemented. This technique provides elution bands of only a few seconds width using high percentage solvent in order to get a rapid transfer of the analytes from the preconcentration column to the analytical column as well as to keep them focused.…”

“…This technique provides elution bands of only a few seconds width using high percentage solvent in order to get a rapid transfer of the analytes from the preconcentration column to the analytical column as well as to keep them focused. Gode et al [ 22 ] generated short plugs of high-elution strength solvent by means of an external loop and an additional LC-pump. We achieved the same high-elution strength solvent plugs by using the separation UHPLC pump which is characterised by very low dead volumes.…”

Detection, Occurrence and Fate of Emerging Contaminants in Agricultural Environments

“…Separation and identification of co-eluting analytes was achieved through the use of high resolution mass spectrometry and isomeric fragmentation differentiation. Gode et al (2012) (Olsen et al, 2012). SPE was used for water samples, while pressurized liquid extraction (PLE) was used for solid samples and chromatographic separation was achieved using a reversed phase system.…”

Temperature-assisted solute focusing with sequential trap/release zones in isocratic and gradient capillary liquid chromatography: Simulation and experiment

“…The injection of a large enough volume results in so-called volume overload in which early eluting peaks are broadened as a result of inadequate sample focusing at the head of the column [16–20]. Pre-column strategies can be particularly effective because they may involve solute-specific, high-affinity focusing [21–25] or fractionation, e.g., in proteomics (MudPIT [26, 27]). On-column focusing or preconcentration is a consequence of generating transient conditions during the injection that result in high solute retention at the head of the column [28].…”