Abstract
Sampling and extraction of chemical residues present on flat or curved surfaces as well as touch-sensitive objects are challenging. Hydrogels are characterized by high mechanical flexibility and water content. Thus, they are an ideal medium for transferring water-soluble analytes from a sampled surface to the next stage of an analytical workflow. Here, we demonstrate gel-phase microextraction (GPME), in which disks of blended hydrogels are utilized to lift traces of water-soluble substances adsorbed on surfaces. The protocol has been optimized in a series of tests involving fluorometric and mass spectrometric measurements. Compared with the pure agarose hydrogel, most of the tested blended hydrogels provide a higher efficiency for the sampling/extraction of a model analyte, fluorescein. The blended hydrogel disks are incorporated into three-dimensional (3D)-printed acrylonitrile–butadiene–styrene chips to create easy-to-use sampling probes. We exemplify the suitability of this improved GPME approach in sampling chemical residues present on the skin, glass, and daily use objects. In these tests, the extracts were analyzed on a triple quadrupole mass spectrometer fitted with an electrospray ion source operated in the positive- and negative-ion modes. The method enabled the detection of diclofenac on excised porcine skin fragments exposed to a topical nonsteroidal anti-inflammatory drug and sweat residues (lactic acid) left on surfaces touched by humans. The limits of detection for diclofenac and lactic acid in hydrogel extract were 6.4 × 10–6 and 2.1 × 10–5 M, respectively. In a model experiment, conducted using the presented approach, the amount of lactic acid on a glass slide with fingerprints was estimated to be ∼1.4 × 10–7 mol cm–2.
Highlights
The early steps of most analytical workflows entail sampling real matrices, capturing the target analytes, concentrating the analytes in small volumes, and transferring them to detection systems
We performed a number of tests, in which hydrogels with different compositions were submerged in fluorescein solutions and the absorbed fluorescein was subsequently reextracted to a solvent mixture
By comparing the mass spectra of blank extracts from different hydrogel disks, we found out that complex spectral background related to the PVP−agarose hydrogel appears in the m/z range from 800 to 2000, while the spectral background related to the poly(ethylene glycol) (PEG)−agarose and poly(vinyl alcohol) (PVA)−agarose hydrogels is in the m/z range from 500 to 2000 (Figure S1)
Summary
The early steps of most analytical workflows entail sampling real matrices, capturing the target analytes, concentrating the analytes in small volumes, and transferring them to detection systems. Cross-linkable solutions of dextran-methacrylate were used to form hydrogels for sampling amino acids and deoxyribonucleic acid from fingerprints.[7] In previous studies, we implemented agarose hydrogel micropatches to collect low-molecular-weight compounds (metabolites, drugs) from the human skin surface.[8−11] The main component of sweat is water. That procedure involving single-component hydrogel micropatches showed practical limitations related to sampling efficiency and long-term storage of hydrogel probes. The goals of the present study are to improve the sampling efficiency, to verify the possibility of implementing various hydrogels for sampling analytes adsorbed on various surfaces, to increase the maximum storage time of the probes, and to demonstrate alternative applications of the method. The short sampling time with hydrogel allows one to conduct repeated sampling of the same specimen and temporal profiling of dynamic processes such as Received: July 22, 2019 Accepted: September 24, 2019 Published: November 8, 2019
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