March 12, 2018

Polyacrylamide gel in electromembrane extraction


Electromembrane extraction (EME) is a liquid phase microextraction technique based on the voltage-assisted migration of the target analytes between two aqueous solutions (the sample and the acceptor phase) separated by a polymeric membrane where an organic solvent is immobilized in the form of a supported liquid membrane (SLM). The technique, which has been the subject of several posts in this blog, allows the rapid extraction of ionic species. The present post highlights a recent article, published in Journal of Pharmaceutical and Biomedical Analysis, where polyacrylamide gels are proposed as a membrane in EME.

Although polypropylene membranes are usually selected as a physical barrier between the two aqueous phases involved in EME, several research groups have proposed alternatives to this classical approach. In 2017, Tabani et al. proposed agarose gel as a greener alternative. Although good results were obtained, the large pore sizes of these gels (up to 300 nm) induce high electric currents which are associated with some disadvantages like bubbles generation or electroosmotic flow (the water migration produce a dilution of the analytes in the acceptor phase). The same group has recently proposed polyacrylamide gels for the same purpose. These gels present a more homogeneous pore size distribution, that can be tuned playing with the synthesis conditions, and smaller pore sizes (in the range of 20-140 nm).

The gel is synthesized in Eppendorf tubes which are finally cut (see Figure 1) leaving the gel in the open end and creating a small chamber for the location of the acceptor solution. The cut tube is immersed in the sample, and two electrodes are introduced in the donor and the acceptor phase for EME. The extraction has been studied for three basic drugs (pseudoephedrine, lidocaine, and propranolol) with good results.
Figure 1. Extraction device. For extraction it is immersed into the sample and the two electrodes are connected

The authors state that this EME approach involves three aqueous phases (donor, acceptor and that immobilized in the gel) and it does not require any organic solvent. 

You can read the complete article where you can find all the specific information to synthesize the gel and the optimization of the extraction. The extraction in combination with LC-UV allows the determination of the target compounds in complex samples like wastewater and breast milk.

References
(1) Application of polyacrylamide gel as a new membrane in electromembrane extraction for the quantification of basic drugs in breast milk and wastewater samples. Link to the article

RL

June 15, 2017

Dendrimeric nanocomposites for solid phase microextraction

Polymeric nanocomposites have demonstrated a great potential as sorbents in analytical sample preparation. The polymeric domain usually provides the sorption ability while the nanometric element confers special properties (like magnetism) or improves the sorptive capacity introducing new interaction chemistries (different than those provided by the polymer) or increasing the superficial area of the nanocomposite. In a recent article published in Microchimica Acta by Prof. Bagheri and coworkers, a reference research group in this field, have outlined the use of dendrimeric nanocomposites as sorptive phases in solid phase microextraction (SPME). Dendrimers are hyperbranched molecules with a multifunctional, homogeneous and spherical surface. They present multiple sites on the outer surface that may interact with the target analytes.

PAMAM dendrimer ethylene diamine core,
generation 0. Source: chemspider.com
Polyamidoamine (PAMAM) dendrimers can be obtained by a controlled and step-by-step approach that involves sequential Michael additions and amination steps. In this proposal, PAMAM dendrimers are obtained by the divergent method making them grow over a magnetic nanoparticle (MNP) core. To make that possible, the surface of the MNP must be previously coated with amine groups.

Once synthesized, the nanocomposite is incorporated over a stainless steel wire which acts as SPME fiber. The novel coating is applied for the headspace-SPME of selected chlorophenols from water samples with excellent results (limits of detection in the low ng per liter range). In addition, the fiber can be reused up to 60 times.

You can read the complete article, with all the specific information to synthesize this type of dendrimers, in the journal webpage.

Reference

(1) A magnetic multifunctional dendrimeric coating on a steel fiber for solid phase microextraction of chlorophenols. Link to the article

May 20, 2017

Polysulfone and MIPs coated over nickel foam

Microextraction is currently present in many analytical processes. Its advantages over conventional extraction approaches have been extensively pointed out and mainly refer to its simplicity and miniaturization while providing equal or even better analytical features. Also, the availability of the sorbents (carbon-based, silica, metallic, magnetic...), formats (fiber, capillary, powder, particles and membranes) and combinations among them make possible the processing of any sample-analyte binomial. A step forward in the development of novel sorbents phases is selectivity. Highly selective extractant allows to face the determination of the analytes in complex matrices such as biological fluids or food.

Nickel foam
The group of Prof. Zhang has proposed the synthesis and evaluation of molecularly imprinted polymers (MIPs) that allows the selective extraction of floxacin from water and biological samples. We are all aware about the ability of such polymeric phases to selective recognize and isolate target analyte in a complex environment. Also, the outstanding performance of nanoMIPs versus MIP has been extensively reported. The research presented in this contribution makes use of a nickel foam as support for the MIP layer which is stocked by means of polysulfone. The main advantage of the proposed selective microsorbent is that the thickness of the flat microextraction unit can be easily controlled modifying the concentration of polysulfone and the amount of MIP. The dimension of the nickel foam used as support is 1.5X1.5 cm. The coating of polysulfone and MIPs is deposited by the sequential dipping of the nickel foam in the proper solutions and it takes less than 3 min to be completed. It should be noted that the polysulfone improves the analyte interaction which results in an increased adsorption and thus a better sensitivity.

You can go through the research article to learn more about the synthesis and evaluation of the described microextraction device and discover its potential applicability in different analytical fields. Enjoy!

Reference

(1) Preparation of polysulfone materials on nickel foam for solid-phase microextraction of floxacin in water and biological samples. Link to the article

April 3, 2017

Animal bones wastes for coiled solid phase microextraction

The use of natural products, or wastes from them, to fabricate sorptive phases is an interesting research line with green connotations. Ramzi and Farrokhzadeh have evaluated, in a recent article accepted for publication in Journal of Separations Science, the potential use of animal bone wastes in this context. From the chemical point of view, bones are inorganic/organic composite materials where the inorganic part is mainly composed by carbonated hydroxyapatite while collagen fibers comprise the main part, up to 90 %, of the organic material.

"Electronic micrograph 10000 magnification of mineralized collagen fibers in bone" by Bertazzo S used under CC BY. Via wikipedia
The proposed procedure for the fabrication of the coating is simple. Bone wastes are firstly grounded, cleaned and dried. The resulting solid is dispersed in a citric acid solution and heated for a defined period o time. Finally, the solid phase microextraction (SPME) support is immersed into the solution. The evaporation of the solvent leaves a fibrous inorganic/organic coating over the surface than can be used for extraction purposes. The authors have proposed a coiled wire as support as it presents an enhanced superficial area compared with classical SPME fibers.

The resulting material has been applied for the determination of polycyclic aromatic hydrocarbons in water with good results (limits of detection in the ng per liter range). We recommend you the reading of the original manuscript for further details.

The editor.

Reference

(1) Introduction of a coiled solid-phase microextraction fiber based on a coating of animal bone waste for chromatographic analysis. Link to the article

March 2, 2017

Direct coupling of Solid Phase Microextraction to Mass Spectrometry: via liquid desorption

The direct coupling of SPME with Mass Spectrometry (MS) analyzers has been investigated for more than 20 years. In fact, different strategies have been developed by several groups worldwide and most have been appropriately reviewed by Fang et al1 and  Deng et al2. Given the wide diversity of SPME-MS couplings, it is difficult to categorize them based on one well-defined characteristic. Following a similar approach to the one suggested by Venter et al3, one could classify SPME-MS couplings according to the desorption mechanism: solvent4,5, thermal6,7 or laser desorption8. Herein, I present a brief summary of the most recent developments on SPME-MS techniques that utilize liquid desorption. Essentially, this field can be divided in three sub-categories: direct-desorption from the extraction substrate9–11, desorption into an elution chamber12, or desorption into a smaller compartment with efficient ionization (nano-electrospray emitter)5,13. As the first category is particularly novel and it presents a wide-range of exciting applications, I will leave this topic for an upcoming contribution to µextraction technologies.

To the best of my knowledge, the first interface of SPME to MS via liquid desorption was done by Möder et al. (Germany, 1997)14 through a desorption chamber similar to the one designed by Chen and Pawliszyn in 199515. Since then, multiple improvements to the desorption chamber have been performed as to decrease the volume of the elution/ionization solvent, which aims to improve sensitivity16–18. Some of these approaches are less practical than others, however most have managed to obtain the required limits of quantitation for the selected application. Approximately one year ago, we published a manuscript in Analytical Chemistry entitled “Biocompatible Solid-Phase Microextraction Nanoelectrospray Ionization: An Unexploited Tool in Bioanalysis”5 (open access). In this work we built upon the approach initially proposed by Walles et al. in 200513 where SPME was coupled to MS via nano-ESI emitters. Essentially, the molar enrichment factor offered by biocompatible-SPME (BioSPME) fibres was fully utilized by eluting the analytes in ultra-small desorption volumes (Vdes ≤ 4 μL). This resulted in remarkable limits of quantitation, and satisfactory figures of merit were attained for all the analytes tested (drugs of abuse and therapeutic drugs) in different matrices (urine and blood) with exceedingly short sample preparation times (t ≤ 2 min). I think the greatest impact that BioSPME-nanoESI will have
BioSPME-nanoESI
in bioanalytical applications has yet to come. Certainly, this technology could be used as a complementary tool to LC-HRMS towards the characterization of unknown compounds extracted from complex matrices such as tissue. Why? In essence, nanoESI not only yields higher ionization efficiency when compare to ESI
19, but also allows for longer electrospray events that permit a far greater number of MS and MSn experiments. Certainly, this unique feature of nanoESI is tremendously convenient in the identification of potential biomarkers extracted by SPME from precious samples!



Aware of the limitations that could thwart the high-throughput implementation of SPME-nanoESI such the high cost per analysis (due to the non-reusability of the emitters), as well as the difficulties associated with automatization of the process, we started exploring novel and cheaper alternatives. Hence, in a great collaboration with our colleagues from SCIEX, we recently assessed the open port probe (OPP) sampling interface developed by Van Berkel et al. at Oak Ridge National Laboratory.20 Our findings showed that the OPP is a robust, sensitive, and ready-to-use interface for the direct coupling of Bio-SPME fibers to
BioSPME-OPP
mass spectrometry
4. The OPP, as its name implies, is an interface exposed to the ambient air that has a continuous flowing stream where the SPME fibres can be easily inserted for elution of the enriched analytes. The greatest advantage of the OPP interface, when compared to other direct couplings to MS7,12, is that it requires no modifications to the conventional ionization source setup employed by most labs, allowing the switch between LC-MS and OPP-MS to be achieved in a snap. Furthermore, OPP is suitable for high-throughput analysis (preparation times as low as 15 seconds per sample based on the 96-well plate format), offers high sensitivity (sub-ng mL-1), and cost per analysis is low (reusable source with negligible carry over). All these features can be found in a manuscript recently published in Analytical Chemistry entitled “Open Port Probe Sampling Interface for the Direct Coupling of Bio-compatible Solid-Phase Microextraction to Atmospheric Pressure Ionization Mass Spectrometry”4. In that work we also explored in-line technologies such as multiple reaction monitoring with multistage fragmentation (MRM3) and differential mobility spectrometry (DMS) as to enhance the selectivity of the method without compromising analysis speed. Unquestionably, BioSPME-OPP coupling has great potential in bioanalytical laboratories for fast determination of therapeutic drugs and prohibited-substances in complex matrices. In my opinion, our advances on BioSPME-OPP are moving the implementation of SPME in the surgery room a bunch of steps forward.  

References
(1)     Fang, L.; Deng, J.; Yang, Y.; Wang, X.; Chen, B.; Liu, H.; Zhou, H.; Ouyang, G.; Luan, T. TrAC Trends Anal. Chem. 2016, 85, 61–72.
(2)     Deng, J.; Yang, Y.; Wang, X.; Luan, T. TrAC Trends Anal. Chem. 2014, 55, 55–67.
(3)    Venter, A. R.; Douglass, K. A.; Shelley, J. T.; Hasman, G.; Honarvar, E. Anal. Chem. 2014, 86 (1), 233–249.
(4)    Gómez-Ríos, G. A.; Liu, C.; Tascon, M.; Reyes-Garcés, N.; Arnold, D. W.; Covey, T. R.; Pawliszyn, J. Anal. Chem. 2017, acs.analchem.6b04737.
(5)     Gómez-Ríos, G. A.; Reyes-Garcés, N.; Bojko, B.; Pawliszyn, J. Anal. Chem. 2016, 88 (2), 1259–1265.
(6)     Gómez-Ríos, G. A.; Pawliszyn, J. Chem. Commun. 2014, 50 (85), 12937–12940.
(7)     Mirabelli, M. F.; Wolf, J.-C.; Zenobi, R. Anal. Chem. 2016, 88 (14), 7252–7258.
(8)     Wang, Y.; Schneider, B. B.; Covey, T. R.; Pawliszyn, J. Anal. Chem. 2005, 77 (24), 8095–8101.
(9)     Kuo, C. P.; Shiea, J. Anal. Chem. 1999, 71 (19), 4413–4417.
(10)   Deng, J.; Yang, Y.; Fang, L.; Lin, L.; Zhou, H.; Luan, T. Anal. Chem. 2014, 86 (22), 11159–11166.
(11)   Gómez-Ríos, G. A.; Pawliszyn, J. Angew. Chemie 2014, 53 (52), 14503–14507.
(12)   Ahmad, S.; Tucker, M.; Spooner, N.; Murnane, D.; Gerhard, U. Anal. Chem. 2015, 87 (1), 754–759.
(13)   Walles, M.; Gu, Y.; Dartiguenave, C.; Musteata, F. M.; Waldron, K.; Lubda, D.; Pawliszyn, J. J. Chromatogr. A 2005, 1067 (1–2), 197–205.
(14)   Möder, M.; Löster, H.; Herzschuh, R.; Popp, P. J. Mass Spectrom. 1997, 32 (11), 1195–1204.
(15)   Chen, J.; Pawliszyn, J. B. Anal. Chem. 1995, 67 (15), 2530–2533.
(16)   Lord, H. L. J. Chromatogr. A 2007, 1152 (1–2), 2–13.
(17)   van Hout, M. W. J.; Jas, V.; Niederländer, H. A. G.; de Zeeuw, R. A.; de Jong, G. J. Analyst 2002, 127 (3), 355–359.
(18)   McCooeye, M. A.; Mester, Z.; Ells, B.; Barnett, D. A.; Purves, R. W.; Guevremont, R. Anal. Chem. 2002, 74 (13), 3071–3075.
(19)   Needham, S. R.; Valaskovic, G. A. Bioanalysis 2015, 7 (9), 1061–1064.
(20)   Van Berkel, G. J.; Kertesz, V. Rapid Commun. Mass Spectrom. 2015, 29 (19), 1749–1756.

About the author
German Augusto Gómez-Ríos is a fourth year PhD candidate working at University of Waterloo under the supervision of Prof. Janusz Pawliszyn. German’s research focuses on the development of rapid diagnostic tools suitable for personalized medicine. These technologies are based on the direct coupling of Solid Phase Micro Extraction (SPME) devices to mass spectrometry instruments using different ionization techniques such as Direct Analysis in Real Time (DART), Desorption Electro Spray Ionization (DESI), nano-Electro Spray Ionization (nano-ESI), Open Port Probe (OPP), and Coated Blade Spray (CBS). In essence, German’s PhD thesis is mainly focused on the development, optimization and evaluation of diverse SPME-MS couplings that allow performing accurate, fast, and low-cost assays in different complex matrices. The ultimate goal of his research is to develop technologies that rapidly adapted by medical doctors and surgeons to individualize patient’s treatment.
You can follow him at twitter and Linkedin. In addition, you can browse his publications at Researchgate and Google scholar