Automation of static and dynamic non-dispersive liquid phase microextraction. Part 1: Approaches based on extractant drop-, plug-, film- and microflow-formation

In-line carbon nanofiber reinforced hollow fiber-mediated liquid phase microextraction using a 3D printed extraction platform as a front end to liquid chromatography for automatic sample preparation and analysis: A proof of concept study

A novel concept for automation of nanostructured hollow-fiber supported microextraction, combining the principles of liquid-phase microextraction (LPME) and sorbent microextraction synergically, using mesofluidic platforms is proposed herein for the first time, and demonstrated with the determination of acidic drugs (namely, ketoprofen, ibuprofen, diclofenac and naproxen) in urine as a proof-of-concept applicability. Dispersed carbon nanofibers (CNF) are immobilized in the pores of a single-stranded polypropylene hollow fiber (CNF@HF) membrane, which is thereafter accommodated in a stereolithographic 3D-printed extraction chamber without glued components for ease of assembly. The analytical method involves continuous-flow extraction of the acidic drugs from a flowing stream donor (pH 1.7) into an alkaline stagnant acceptor (20 mmol L^-1 NaOH) containing 10% MeOH (v/v) across a dihexyl ether impregnated CNF@HF membrane. The flow setup features entire automation of the microextraction process including regeneration of the organic film and on-line injection of the analyte-laden acceptor phase after downstream neutralization into a liquid chromatograph (LC) for reversed-phase core-shell column-based separation. Using a 12-cm long CNF@HF and a sample volume of 6.4 mL, linear dynamic ranges of ketoprofen, naproxen, diclofenac and ibuprofen, taken as models of non-steroidal anti-inflammatory drugs, spanned from ca. 5-15 µg L^-1 to 500 µg L^-1 with enhancement factors of 43-97 (against a direct injection of 10 µL standards into LC), and limits of detection from 1.6 to 4.3 µg L^-1. Relative recoveries in real urine samples ranged from 97% to 105%, thus demonstrating the reliability of the automatic CNF@HF-LPME method for in-line matrix clean-up and determination of drugs in urine at therapeutically relevant concentrations.

A magnetic hydrazine-functionalized dendrimer embedded with TiO2 as a novel affinity probe for the selective enrichment of low-abundance phosphopeptides from biological samples

Dendrimers exhibit tunable terminal functionality and bio-friendly nature, making them of being promising materials for applications in the field of separation and enrichment. In this work, we prepared magnetic hydrazide-functionalized poly-amidoamine (PAMAM) dendrimer embedded with TiO₂ for the enrichment of phosphopeptides. The novel affinity probe possessed superparamagnetism, realizing its rapid separation from sample solution. Electrostatic attraction and hydrogen bonding existed between PAMAM and phosphopeptides while Lewis acid-base interaction was originated between TiO₂ and the targets. The combined synergistic strength of multiple binding interactions contributed to the highly selective enrichment of phosphopeptides. The specificity for the capture of phosphopeptides was reflected in quantities as low as 1:1000 mass ratio of phosphopeptides to non-phosphopeptides. The detection limit of β-casein digests was low to 0.4 fmol, indicating the high sensitivity of the developed method. Fifteen and four phosphopeptides could be selectively captured from non-fat milk digests and human serum samples, which further confirmed the great potential of the affinity probe in the extraction of low-abundance phosphopeptides from real complex biological samples.

A high-performance chiral selector derived from chitosan (p-methylbenzylurea) for efficient enantiomer separation

N-Methoxycarbonyl chitosan was prepared by selectively modifying the amino group at the 2-position of chitosan with methyl chloroformate, which was further functionalized with p-methylbenzylamine to produce chitosan (p-methylbenzylurea). Then, the hydroxyl groups at the 3- and 6-positions of the glucose skeleton were modified with various phenyl isocyanates, affording a series of chitosan 3,6-bis(arylcarbamate)-2-(p-methylbenzylurea)s, which were characterized and proposed as chiral selectors for enantiomer separation. Nineteen racemates, most of which are drugs or intermediates for drugs, were selected as the model analytes to evaluate the enantioseparation performance. The structure-performance relationship of the chiral selectors was investigated in detail. It was found that the methyl-substituted chiral selectors possessed more preferable enantioseparation performance compared with the chloro-substituted ones, and the chiral selectors containing a methyl substituent at the 4-position of the benzene ring showed the best chiral recognition and separation ability with 17 racemates being recognized and 13 racemates being baseline separated. The prepared chiral separation materials derived from these chiral selectors exhibited favorable solvent tolerance towards ethyl acetate, acetone, chloroform and a low proportion of tetrahydrofuran in normal phase. To sum up, this work provided a useful reference for the design and preparation of high-performance chiral separation materials for efficient enantiomer separation.

Direct-immersion single-drop microextraction and in-drop stirring microextraction for the determination of nanomolar concentrations of lead using automated Lab-In-Syringe technique

Two operational modes for Lab-In-Syringe automation of direct-immersion single-drop microextraction have been developed and critically compared using lead in drinking water as the model analyte. Dithizone was used in the presence of masking additives as a sensitive chromogenic complexing reagent. The analytical procedure was carried out inside the void of an automatic syringe pump. Normal pump orientation was used to study extraction in a floating drop of a toluene-hexanol mixture. Placing the syringe upside-down allowed the use of a denser-than-water drop of chloroform for the extraction. A magnetic stirring bar was placed inside the syringe for homogenous mixing of the aqueous phase and enabled in-drop stirring in the second configuration while resulting in enhanced extraction efficiency. The use of a syringe as the extraction chamber allowed drop confinement and support by gravitational differences in the syringe inlet. Keeping the stirring rates low, problems related to solvent dispersion such as droplet collection were avoided. With a drop volume of 60 µL, limits of detection of 75 nmol L^-1 and 23 nmol L^-1 were achieved for the floating drop extraction and the in-drop stirring approaches, respectively. Both methods were characterized by repeatability with RSD typically below 5%, quantitative analyte recoveries, and analyte selectivity achieved by interference masking. Operational differences were critically compared. The proposed methods permitted the routine determination of lead in drinking water to be achieved in less than 6 min.

Biospecific isolation and characterization of angiogenesis-promoting ingredients in Buyang Huanwu decoction using affinity chromatography on rat brain microvascular endothelial cells combined with solid-phase extraction, and HPLC-MS/MS

Buyang Huanwu decoction (BHD) was reported to exert angiogenesis-promoting effects, but its active ingredients remain unknown. In this study, we developed a method to screen potential angiogenesis-promoting compounds in BHD, which involved biospecific isolation using live rat brain microvascular endothelial cells (rBMECs) and characterization using solid-phase extraction (SPE) and high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Six compounds showed binding affinity to rBMECs and were further identified as 6-hydroxykaempferol-di-O-glucoside, paeoniflorin, calycosin-7-O-β-D-glucoside, galloylpaeoniflorin, formononetin-7-O-β-D-glucoside, and (3R)-7,2'-hydroxy-3',4'-dimethoxy-isoflavan. The results indicated that five of them except 6-hydroxykaempferol-di-O-glucoside showed a protective effect against oxygen glucose deprivation/reperfusion injury in rBMECs and upregulated the secretion of vascular endothelial growth factor and basic fibroblast growth factor, suggesting a mechanism underlying their angiogenic activity. Our findings suggest that biospecific live cell-based isolation combined with SPE and HPLC-MS/MS is an effective method for screening potential bioactive components in traditional Chinese medicines.

Online coupling of fully automatic in-syringe dispersive liquid-liquid microextraction with oxidative back-extraction to inductively coupled plasma spectrometry for sample clean-up in elemental analysis: A proof of concept

A proof of concept of a novel automatic sample cleanup approach for metal assays in troublesome matrixes as a front-end sample pre-treatment to inductively coupled plasma optical emission spectroscopy - ICP-OES - is herein presented. Target metals, namely, copper, lead, and cadmium were complexed in-system quantitatively using ammonium pyrrolidine dithiocarbamate (APDC) and transferred into a minute volume of toluene as extractant employing lab-in-syringe magnetic stirring-assisted dispersive liquid-liquid microextraction (LIS-MSA-DLLME). After discharge of the sample, the analytes were back-extracted into nitric acid and injected on-line into ICP-OES. To promote and expedite this process in-syringe, advantage was taken from oxidative decomposition of the chelate by potassium iodate, reported in this article for the first time. Experimental conditions for LIS-MSA-DLLME were optimized by Box-Benkhen multivariate analysis using the geometric mean of analyte recoveries as the desirability function. Times of extraction and back-extraction of 300s and 100s, respectively, pH 5.5 at 30mmol/L acetate, 300µL of extraction solvent, and 600µmol/L of APDC were finally applied. Online interfacing to ICP-OES for back-extract analysis yielded average repeatabilities for Cd, Cu, and Pb of 2.9%, 3.5%, and 3.5% with limits of detections (3s) of 1.9, 1.4, and 5.6ng/mL, respectively. Oxidative back-extraction was proven reliable for the determination of metal species in coastal seawater, surrogate digestive fluids and soil leachates with recovery values for Cd, Cu, and Pb ranging from 90% to 118%, 68% to 104%, and 86% to 112%, respectively.

Fully Automatic In-Syringe Magnetic Stirring-Assisted Dispersive Liquid-Liquid Microextraction Hyphenated to High-Temperature Torch Integrated Sample Introduction System-Inductively Coupled Plasma Spectrometer with Direct Injection of the Organic Phase

A proof of concept study involving the online coupling of automatic dispersive liquid-liquid microextraction (DLLME) to inductively coupled plasma optical emission spectrometry (ICP OES) with direct introduction and analysis of the organic extract is herein reported for the first time. The flow-based analyzer features a lab-in-syringe (LIS) setup with an integrated stirring system, a Meinhard nebulizer in combination with a heated single-pass spray chamber, and a rotary injection valve, used as an online interface between the microextraction system and the detection instrument. Air-segmented flow was used for delivery of a fraction of the nonwater miscible extraction phase, 12 μL of xylene, to the nebulizer. All sample preparative steps including magnetic stirring assisted DLLME were carried out inside the syringe void volume as a size-adaptable yet sealed mixing and extraction chamber. Determination of trace level concentrations of cadmium, copper, lead, and silver as model analytes has been demonstrated by microextraction as diethyldithiophosphate (DDTP) complexes. The automatic LIS-DLLME method features quantitative metal extraction, even in troublesome sample matrixes, such as seawater, salt, and fruit juices, with relative recoveries within the range of 94-103%, 93-100%, and 92-99%, respectively. Furthermore, no statistically significant differences at the 0.05 significance level were found between concentration values experimentally obtained and the certified values of two serum standard reference materials.

A novel approach to Lab-In-Syringe Head-Space Single-Drop Microextraction and on-drop sensing of ammonia

A novel approach to the automation technique Lab-In-Syringe, also known as In-Syringe Analysis, is proposed which utilizes a secondary inlet into the syringe void, used as a size-adaptable reaction chamber, via a channel passing through the syringe piston. This innovative approach allows straightforward automation of head-space single-drop microextraction, involving accurately controlled drop formation and handling, and the possibility of on-drop analyte quantification. The syringe was used in upside-down orientation and in-syringe magnetic stirring was carried out, which allowed homogenous mixing of solutions, promotion of head-space analyte enrichment, and efficient syringe cleaning. The superior performance of the newly developed system was illustrated with the development of a sensitive method for total ammonia determination in surface waters. It is based on head-space extraction of ammonia into a single drop of bromothymol blue indicator created inside the syringe at the orifice of the syringe piston channel and on-drop sensing of the color change via fiber optics. The slope of the linear relationship between absorbance and time was used as the analytical signal. Drop formation and performance of on-drop monitoring was further studied with rhodamine B solution to give a better understanding of the system's performance. A repeatability of 6% RSD at 10 μmol L(-1) NH3, a linear range of up to 25 μmol L(-1) NH3, and a limit of detection of 1.8 μmol L(-1) NH3 were achieved. Study of interferences proved the high robustness of the method towards humic acids, high sample salinity, and the presence of detergents, thus demonstrating the method superiority compared to the state-of-the-art gas-diffusion methods. A mean analyte recovery of 101.8% was found in analyzing spiked environmental water samples.