Magnetic solid-phase extraction based on mesoporous silica-coated magnetic nanoparticles for analysis of oral antidiabetic drugs in human plasma

Materials Science and Engineering C 40 (2014) 275–280

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Magnetic solid-phase extraction based on mesoporous silica-coated magnetic nanoparticles for analysis of oral antidiabetic drugs in human plasma Karynne Cristina de Souza a, Gracielle Ferreira Andrade a, Ingrid Vasconcelos b, Iara Maíra de Oliveira Viana b, Christian Fernandes b, Edésia Martins Barros de Sousa a,⁎ a b

Centro de Desenvolvimento da Tecnologia Nuclear, CDTN/CNEN, Rua Professor Mário Werneck, s/n. Campus Universitário, Belo Horizonte, MG CEP 30.123-970, Brazil Departamento de Produtos Farmacêuticos, Faculdade de Farmácia, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil

a r t i c l e

i n f o

Article history: Received 16 October 2013 Received in revised form 18 March 2014 Accepted 3 April 2014 Available online 12 April 2014 Keywords: Mesoporous materials Magnetic nanoparticles Magnetic solid phase extraction Oral antidiabetic drug extraction

a b s t r a c t In the present work, magnetic nanoparticles embedded into mesoporous silica were prepared in two steps: first, magnetite was synthesized by oxidation–precipitation method, and next, the magnetic nanoparticles were coated with mesoporous silica by using nonionic block copolymer surfactants as structure-directing agents. The mesoporous SiO2-coated Fe3O4 samples were functionalized using octadecyltrimethoxysilane as silanizing agent. The pure and functionalized silica nanoparticles were physicochemically and morphologically characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The resultant magnetic silica nanoparticles were applied as sorbents for magnetic solid-phase extraction (MSPE) of oral antidiabetic drugs in human plasma. Our results revealed that the magnetite nanoparticles were completely coated by well-ordered mesoporous silica with free pores and stable pore walls, and that the structural and magnetic properties of the Fe3O4 nanoparticles were preserved in the applied synthesis route. Indeed, the sorbent material was capable of extracting the antidiabetic drugs from human plasma, being useful for the sample preparation in biological matrices. © 2014 Elsevier B.V. All rights reserved.

1. Introduction The analysis of drugs in biological matrices consists of a number of unit operations and has several applications in industry, research and clinical context. It is useful in therapeutic drug monitoring, in pharmacokinetic studies in order to evaluate the bioavailability of novel dosage forms and in bioequivalence tests for development of generic and similar drugs [1]. There are several techniques described in the literature for extraction of drugs in biological matrices such as plasma. Protein precipitation and liquid–liquid extraction are the most common. These techniques are usually time consuming and labor intensive, expose the analyst to toxic solvents and generate large amounts of waste, which are harmful to the environment [2]. In recent years magnetic solid-phase extraction (MSPE), a promising technique for sample preparation, has attracted much interest [3,4]. It is a new extraction approach based on the use of magnetic or magnetizable sorbents, which can be readily isolated from sample matrix with an external magnet. Hence, two of the significant advantages of MSPE are simplicity and convenience. Furthermore, in MSPE, the sorbents ⁎ Corresponding author. Tel./fax: +55 31 3069 3223 E-mail address: [email protected] (E.M.B. de Sousa).

http://dx.doi.org/10.1016/j.msec.2014.04.004 0928-4931/© 2014 Elsevier B.V. All rights reserved.

can be uniformly dispersed into the sample solution by vortexing or shaking, which makes the contact area between the sorbents and the analytes large enough to ensure a fast mass transfer. So high extraction efficiency in a short time, which is desirable in high throughput sample preparations, can be achieved. Generally, the sorbents used in MSPE are Fe3O4 nanoparticles, which are suitable for several analytes [5]. However, as these nanoparticles present a high surface area, the unprotected metal oxide nanoparticles can easily form aggregates and react with oxygen present in the air [6]. In addition, the reactivity of iron oxide particles has been shown to increase greatly as their dimensions are reduced, and they may undergo rapid biodegradation when directly exposed to biological systems [7]. Therefore, a suitable coating is essential to prevent such limitations. Silica/magnetite nanocomposites are particularly interesting, since the protective layer afforded by silica can prevent the dipolar magnetic attraction between magnetite particles, and consequently, afford rather uniform particle dispersion. Mesoporous silica, such as MCM-41 (Mobil Catalytic Material Number 41), and SBA-15 (Santa Barbara Amorphous-15), are solid materials, which are comprised of a honeycomb-like porous structure with hundreds of empty channels (mesopores) that are able to absorb/encapsulate relatively large amounts of bioactive molecules. Their unique properties, such as high surface area, large pore volume, tunable pore size with a narrow distribution, and good chemical and thermal stability of these

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materials, make them potentially suitable for various applications in many fields of technology such as advanced electronics, catalysis, and nanostructured materials [8–10]. The performance of these materials in many fields of applications depends directly on the silica network porosity. Mesoporous silica has a number of distinctive properties that make it an ideal base material. It is easily made, at minimal cost, and is uniform in its properties. It can be easily cleaned prior to use for high-sensitivity work. Ion-exchangers on silica backbones recover quickly from changes in pH or solvent types. The hydroxyl groups on silica allow a large variety of different functional groups to be added for increasing selectivity [11]. In general, the surface area of a porous material is higher than the surface of an analogous non-porous material. Thereby the internal surface area is usually much higher than the one contributed by the external surface. The ease of introducing various organic functional groups, either through covalent bonding or electrostatic interactions, provides high level of versatility and many mechanized features to the mesoporous silica materials [12]. The covalent attachment of functional groups usually involves introducing organic structures in the form of silanes, which can be attached using co-condensation or post-synthetic grafting methods. The co-condensation method allows the hydrolysis of the functional silanes while the particles are forming; therefore the guest molecules are incorporated into the resulting silica frameworks. In contrast, post-synthetic grafting introduces the functional groups mainly to the exposed silica surface after the magnetic silica nanoparticles are formed, which can be performed either before or after the surfactant removal [13,14]. Particularly, the functionalized silica–magnetite system has been of recent interest in the field of solid phase extraction as well as drug delivery system [15–19]. An interesting work conducted by Liu et al. showed a novel mixed hemimicelle solid-phase extraction (MHSPE) method based on mesoporous silica-coated magnetic nanoparticles (Fe3O4/meso-SiO2 NPs) as sorbent for extraction of phthalate esters from water samples [17]. Hakami et al. demonstrated the potential use of thiol-functionalized silica-coated magnetite nano-particles (TFSCMNPs) in an adsorption process for Hg(II) removal from water [18]. In their investigation, Hooshang et al. present a novel, fast and simple method for extraction and determination of trace amounts of salicylic acid using magnetic iron oxide nanoparticles as sorbent for solid phase extraction [20]. Extraction of salicylic acid was based on adsorption of Fe(III)–salicylate complex on magnetic nanoparticles. The proposed procedure has been successfully applied to the determination of salicylic acid in blood serum. Even though there have been significant advances in magnetic nanoparticles applied as sorbents for magnetic solid-phase extraction, to the best of our knowledge, relatively few published works actually address the investigation of the potential use of mesoporous silicacoated magnetic nanoparticles as sorbent for magnetic solid-phase extraction in biomedical area. In view of the aforementioned, the objective of this study was to investigate the synthesis strategy of mesoporous silica-coated magnetic nanoparticles functionalized with octadecyltrimethoxysilane to be applied as sorbent for magnetic solid-phase extraction (MSPE) of oral antidiabetic drugs in human plasma. To accomplish this purpose, the Fe3O4 nanoparticles were synthesized by oxidation–precipitation, and coated with mesoporous silica (SBA-15) by using nonionic block copolymer surfactants as structure-directing agents. The structural properties of the silica–magnetite nanocomposite have been investigated. 2. Materials and methods 2.1. Chemicals Acetonitrile of HPLC grade was purchased from J. T. Baker (Center Valley, PA, USA). Orthophosphoric acid from Vetec (Duque de Caxias, RJ, Brazil) and dibasic potassium phosphate from SigmaAldrich (Steinheim, Germany) were of analytical grade. The test analytes were: glibenclamide (MM 494.0) by Cadila Pharmaceuticals

(Ahmedabad, Gujarat, India), glimepiride (MM 490.6) by Mantena Laboratories (Nalgonda Dist, Andhra Pradesh, India), gliclazide (MM 323.4) by Shandong Keyuan Pharmaceutical (Jinan, Shandong, China), and chlorpropamide (MM 276.7) by Kothari Phytochemicals International (Nagari, India). Water was purified using Millipore Direct Q3 Milli-Q equipment (Bedford, MA, USA). Drug-free plasma was collected at the Hematology Laboratory from Faculdade de Farmácia da Universidade Federal de Minas Gerais (UFMG) and maintained frozen at − 70 °C. Tetraethyl-orthosilicate (TEOS), Pluronic P123 (PEO20-PPO70-PEO20)—[poly (ethylene glycol)-blockpoly (propylene glycol)-block-poly (ethylene glycol), Mav = 5800], potassium hydroxide, iron(II) sulfate heptahydrate, potassium nitrate and octadecyltrimethoxysilane (C21H46O3Si) were purchased from Sigma-Aldrich (São-Paulo—Brazil). 2.2. Synthesis of materials Magnetite nanoparticles were synthesized by crystallization from ferrous hydroxide gels based on the methodology proposed by Sugimoto & Matijevic [21], a procedure that allows the formation of Fe3O4 particles with narrow size distribution with mean diameter ranging between 30 and 400 nm, depending on the synthesis temperature. Solutions of 0.25 mol of potassium hydroxide, 0.06 mol of iron(II) sulfate heptahydrate, and 0.1 mol of potassium nitrate were prepared and mixed. The reaction mixture was heated to 90 °C under N2 and maintained at this temperature for 2 h. A black precipitate was formed. After cooling, the precipitate was washed using magnetic sedimentation of the solid with the aid of a slab magnet. Next, the nanoparticles were dried in vacuum at 45 °C for 48 h. The SBA-15/Fe3O4 nanocomposite (40 wt.% Fe3O4) was obtained according to the method reported by Souza [22]. Following the route to prepare pure SBA-15, after dissolution of the surfactant triblock copolymer Pluronic P123—PEO20PPO70PEO20 [poly(ethylene glycol)block-poly (propylene glycol)-block-poly(ethylene glycol)] (SigmaAldrich) as a templating agent in deionized water and HCl (37 wt.% solution), the previously synthesized magnetite was added to the solution, followed by the silica precursor, tetraethyl orthosilicate (TEOS Sigma-Aldrich). The solution was stirred for 24 h at a constant temperature of 37 °C. After aging under continuous stirring at 100 °C in a hermetically closed Teflon® recipient for 24 h, the solids were collected by filtration and dried in air at 40 °C. The surfactant was removed by calcination at increasing temperature of up to 550 °C under N2 flow. The pore-wall functionalization consisted of the reaction between the calcined SBA–15/Fe3O4 nanocomposite and an alkoxide, octadecyltrimethoxysilane. The nanocomposite (500 mg) was kept under Ar and refluxed with 4 meq of the alkoxide in 60 mL of toluene at 85 °C, for 24 h. The final sample, designated as SBA-15/Fe3O4-C18, was filtered and washed with methanol, and dried at 60 °C overnight. 2.3. Characterization The samples were characterized by X-ray diffraction (XRD), Fouriertransform infrared spectroscopy (FTIR), CHN elemental analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Low-angle XRD measurements were obtained using synchrotron radiation with wavelength λ = 1.5494 nm. Synchrotron radiation measurements were carried out at the D10A-XRD2 beam line from LNLS (Campinas, Brazil) using a Huber-423 three-circle diffractometer. The high-angle XRD patterns were obtained using a Rigaku Geigerflex3034 diffractometer with a Cu Kα tube. Specific surface area and pore size distribution were determined by N2 adsorption using the BET and BJH methods, respectively, in an Autosorb-Quantachrome Nova 1200. The samples were outgassed for 2 h at 300 °C before analysis. FTIR measurements were conducted with a PerkinElmer 1760-X spectrophotometer in the range 4000–400 cm−1. The FTIR spectra were recorded at room temperature using KBr pellets. CHN elemental analyses (CHN,

K.C. de Souza et al. / Materials Science and Engineering C 40 (2014) 275–280

The chromatographic method was developed and optimized in an Agilent 1100 liquid chromatography using a C8 column (150 × 4.6 mm, 5 μm) at 30 °C, acetonitrile:potassium phosphate buffer 10 mM pH 3.0 (55:45) at a flow-rate of 1.5 mL min− 1 as mobile phase. The injection volume was 25 μL and the detection was at 230 nm. Before the extraction, the magnetic material was activated by stirring with methanol for 1 min and, subsequently, with water for 1 min. After, the sample containing the analytes (chlorpropamide, glibenclamide, glimepiride and gliclazide—Fig. 1) was mixed with the magnetic material and vortexed for 5 min, for the sorption of the analytes. Then, the magnetic material was separated from the aqueous phase by using a magnet. Next, the aqueous phase, which contains non-absorbed interferences, was discarded. The analytes were desorbed with organic solvent by vortexing for 5 min and the magnetic material was separated with the aid of the magnet. The obtained organic phase was mixed with water (1:1) and was injected in a liquid chromatograph. A standard solution with the same concentration of the extracted sample was assayed for recovery determination. Initial tests were performed in a 2 mL water sample containing 10 μg mL − 1 of the four antidiabetics and adjusting the pH with 1 mL of phosphate buffer to pH 3.0. The extraction procedure was performed using 5 mg of the sorbent material. 500 μL of the liquid phase was taken and added to 500 μL of water. The organic phase obtained at the end by elution with 500 μL of acetonitrile was also added with 500 μL of water. These samples were analyzed under the conditions already mentioned. The test with biological matrix was performed with 2 mL of antidiabetic spiked human plasma sample at 10 μg mL−1 and the pH was adjusted with 1 mL of phosphate buffer to pH 3.0. The same extraction procedure for water samples was made, but only the final organic phase was collected for analysis. The same procedures were performed in blank plasma sample (without antidiabetics) in order to evaluate selectivity.

Intensity, a. u.

2.4. Magnetic solid-phase extraction

a

SBA-15/Fe3O4

(311)

Fe3O4 (440) (220)

(422)

(222)

(111)

10

20

(511)

(400)

30

40

50

60

70

2 θ (deg) (100)

b

Intensity a.u

2400—PerkinElmer, USA) were performed to investigate the presence of hydrocarbon chains in the SBA-15/Fe3O4 pore wall. The SEM images were obtained in JEOL JSM, model 840A with secondary electron and TEM micrographs were recorded on a JEOL-2011 electron microscope using an acceleration voltage of 200 kV.

277

(110) (200)

SBA-15/Fe3O4

1

2

3

4

5

6

7

8

2θ (degree) Fig. 2. (a) XRD patterns of Fe3O4 and SBA-15/Fe3O4, and (b) SAXRD of SBA-15/Fe3O4 nanocomposite.

3. Results and discussion XRD patterns of pure magnetite and the nanocomposites are shown in Fig. 2a. All the observed diffraction peaks can be indexed

Fig. 1. Structures of (a) chlorpropamide, (b) glibenclamide, (c) gliclazide and (d) glimepiride.

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Adsorbed Volume [cc/g]

800 700 600 500

Pore Volume (cc/g)* 10

-3

900 10000 SBA-15 SBA-15/Fe3O4

8000 6000 4000 2000 0

400

0

20

40

60

80

Pore Diameter (nm)

300 200 SBA-15 SBA-15/Fe3O4

100 0 0.0

SBA-15/Fe3O4-C18

0.2

0.4

0.6

0.8

1.0

Relative Pressure (P/Po) Fig. 3. N2 adsorption isotherms and pore size distribution (insert) of pure SBA-15, SBA-15/ Fe3O4 nanocomposite and SBA-15/Fe3O4-C18.

Table 1 N2 adsorption results. Sample

SBET (m2/g)

Dp (nm)

Vp (cm3/g)

SBA-15 SBA-15/Fe3O4 SBA-15/Fe3O4-C18

789 585 353

6.2 6.2 4.7

1.329 0.739 0.507

SBET = Specific area; Dp = Mean pore diameter; Vp = Mean pore volume. Related error: 3%.

to the spinel structure of pure stoichiometric magnetite (Fe 3O 4 ) (JCPDS file 19-0629). The amorphous region between ca. 15° and 30° corresponds to the amorphous silica matrix. Small-angle X-ray reflection diffractometry (SAXRD) data of the SBA-15/Fe 3O4 nanocomposite are presented in Fig. 2b. It shows typical peaks of a wellorganized pore structure material with the main reflection in 2θ at 0.89° and other low intensity reflections at 1.6° and 1.7°. Three diffraction planes were found, (100), (110), and (200), which shows a well ordered hexagonal lattice. Fig. 3 shows the N2 adsorption isotherms of the SBA-15, SBA-15/ Fe3O4 and SBA-15/Fe3O4-C18 samples and Table 1 summarizes these results. The samples exhibit type IV isotherms and a typical adsorption isotherm with H1 hysteresis, according to the IUPAC classification,

associated with the presence of mesopores. The p/p0 position of the inflection range from 0.6 to 0.8 confirms this structural (porous) characteristic and the sharpness of the step indicates the uniformity of the mesopore size distribution. For the nanocomposite and functionalized samples, the overall adsorption of N2 decreased at all relative pressures; however, the pore size was not affected by the presence of Fe3O4 in the case of the nanocomposite. A sensible difference was observed in the values of pore volume of SBA-15 (1.329 cm3/g) and SBA-15/Fe3O4 (0.739 cm3/g) which may be an indication of the presence of iron oxide nanoparticles in the pore structure of silica. Similarly, the surface area SBET decreased from 789 to 585 m2/g with the presence of nanoparticles. The samples presented a narrow pore size distribution by the BJH method, as shown by the inset in Fig. 3. The nanocomposite has pore size distributions centered at 6 nm (Dp), which is typical of mesoporous materials with a wellordered structure. The adsorption isotherm and pore size distribution results show that the Fe3O4 nanoparticles occupy the mesopore free space intrachannels only partially. This makes this composite a promising candidate for the incorporation and subsequent release of a variety of pharmaceutical molecules under appropriate conditions. The effective adsorption of the functional groups in the SBA-15/ Fe3O4 pores is evidenced by the expressive reduction of the superficial area, size and pore volume, as presented in Table 1. We observe that the values of the structural characteristics of the material present a decrease that must be taken into account. The binding of significant amount of alkyl groups on the silica surface alters the textural morphologies; it means that the alkyl phase may occupy a volume inside the pores of the silica nanocomposite and, as a result, a decrease in the pore volume is observed. So, these results, therefore, indicate that the silica nanocomposite surface is covered with organic groups. The SEM images of magnetite in Fig. 4 show that the material has uniform morphology and particle size distribution. In addition, some particle clusters may be observed due to the magnetic interaction between the particles. The figures of the nanoparticles show regular octahedrons with very smooth surfaces (Fig. 4a), which further indicates that the particles were well crystallized. Similar results were reported by Yu et al. [23]. In contrast, the nanocomposite presents spherical morphology as shown in Fig. 4b. This may be attributed to the presence of the magnetite silica-coated nanoparticles. The average size of the spherical particles varied from 0.139 to 0.476 μm according to the Quantikov Image Analyzer software [24]. The desired particle size range for a specific application may be selected by nanoparticle centrifugation at a controlled rate. Fig. 5 – the high resolution TEM image – shows that we have mostly isolated magnetite particles completely covered by the mesoporous

Fig. 4. SEM of (a) magnetite and (b) SBA-15/Fe3O4.

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279

Table 3 Recovery (%) of antidiabetics in liquid and organic phases in water samples extraction.

Fig. 5. Transmission electron micrographs: high resolution images showing the magnetite nanoparticles (dark region) covered by the mesoporous silica.

Table 2 Elemental analysis results. Sample

%C

% ΔC

%H

% ΔH

%N

% ΔN

SBA-15/Fe3O4 SBA-15/Fe3O4-C18

1.63 ± 0.02 18.55 ± 0.09

0 16.92

0.13 ± 0.01 3.38 ± 0.03

0 3.25

0.09 ± 0.00 0.16 ± 0.02

0 0.07

silica, as reported in prior work from the present study's research group [22]. As estimated from the TEM and XRD data, the Fe3O4 particles present an average mean diameter of about 200 nm. The presence and content of functional groups present in SBA-15/ Fe3O4-C18 were evaluated by FTIR and elemental analysis (assuming no presence of methoxy groups, which could have been introduced during the grafting procedure). The results are shown in Table 2 and Fig. 6. The functionalized samples of SBA-15/Fe3O4-C18 presented higher carbon concentrations (16.92%) as compared to the SBA-15/Fe3O4 (1.63%), confirming the presence of anchored functionalized agents on its surfaces. Fig. 6 shows the FTIR spectra of SBA-15/Fe3O4 nanocomposite and functionalized sample, SBA-15/Fe3O4-C18. The bands that are typical of mesoporous silica are widely reported in the literature and can be easily

1460-1410 δ (CH)-(CH2 )

2970-2926 ν (CH)

800 ν (Si-O-Si)

2854 (CH3)

3550-3200 ν (OH)

960 ν (Si-OH)

SBA-15/Fe3O4

1100-1000 ν (Si-O-Si)

SBA-15/Fe3O4-C18

4000

3500

3000

2500

2000

1500

1000

wavenumber (cm -1) Fig. 6. FTIR spectra of the SBA-15/Fe3O4 nanocomposite and SBA-15/Fe3O4-C18 sample.

Antidiabetic

logP

Recovery (%) ± standard deviation (liquid phase)

Recovery (%) ± standard deviation (organic phase, n = 2)

Chlorpropamide Gliclazide Glibenclamide Glimepiride

1.94 1.73 3.79 3.12

17.87 ± 0.03 4.99 ± 0.03 0 0

33.19 43.31 70.44 67.83

± ± ± ±

0.02 0.28 0.16 0.12

identified in the figure [25]. The peak observed around 660 cm−1 can be assigned to the formation of iron–oxygen bonds within the mesoporous structure. Hence, the vibrational band at approximately 960 cm−1 has been credited to the presence of silanol groups (Si\OH) commonly found in silica synthesized by means of chemical methods. This peak presented some alterations after the functionalization process. The spectra before and after the functionalization indicated that the band at 960 cm−1 shows a significant decrease in intensity in the functionalized samples, indicating that the adsorption of organic groups on the silica surface happens simultaneously with the disappearance of hydroxyl groups. Absorptions at 2931 cm−1, 2885–2844 cm−1, 1489–1485 cm−1 and 1329–1319 cm−1 were assigned to alkyl stretching mode ν(C\H). The absorption band at 2854 cm−1 is typical of CH3 groups on the silica surface in the functionalized samples. The CH3 stretching bands at 2953 cm−1 can also be assigned to the methoxy group. This band due to the symmetric stretching vibration of the methoxy species would overlap with the band at 2854 cm−1 corresponding to the symmetric stretching vibration of the CH2 species. The band at 2970–2926 cm−1 is attributed to the CH2 stretching frequencies. These infrared results indicate the formation of Si\O\CH3 and Si\O\Si\R groups due to the process of surface modification. The chromatographic method used to separate glibenclamide, glimepiride, chlorpropamide and gliclazide was adapted from a previous method developed by our group [26]. Mobile phase composition and pH were chosen, and flow-rate, volume of injection and detector settings were evaluated and optimized. In this study already developed, C18 sorbent was employed in an extraction microtechnique showing to be able to extract the same drugs in human plasma. Therefore, due to its properties C18 sorbent was chosen to functionalize the pore-wall of the SBA-15/Fe3O4 nanocomposite. As expected the synthesized material was capable of extracting the antidiabetic drugs. Recovery for the tests performed in water samples is shown in Table 3. A particularly high recovery was observed for nonpolar drugs such as glibenclamide and glimepiride (log of octanol–water partition coefficient – logP – 3.79 and 3.12, respectively) which were almost completely extracted. These drugs had higher affinity for the C18 phase of the sorbent material than chlorpropamide and gliclazide, which probably was responsible for this behavior. The recovery observed on the tests performed on plasma spiked with antidiabetics is shown in Table 4. Again, higher recovery was observed for nonpolar drugs. However, recovery was reduced for all drugs compared to the values obtained for water samples. This is due to the complexity of the plasma sample and the presence of interferences. Additional studies are currently underway in order to improve recovery on plasma samples.

Table 4 Recovery (%) of antidiabetics in organic phase of spiked plasma sample extraction. Antidiabetic

Recovery (%) ± standard deviation (organic phase, n =2)

Chlorpropamide Gliclazide Glibenclamide Glimepiride

4.51 3.13 18.80 47.36

± ± ± ±

0.31 0.00 0.09 0.81

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particles. The chromatographic method developed in this study was able to separate the analytes with appropriate resolution and efficiency. The sorbent material was capable of extracting the antidiabetic drugs from human plasma, being useful for the sample preparation from biological matrices. However, it is necessary to optimize the method in order to increase the recovery percentage. The optimized method will be validated and applied to real plasma samples. Acknowledgments The authors are grateful to CAPES, CNPq, FAPEMIG, and LNLS (Campinas—Brazil) for supporting this work. References

Fig. 7. Chromatogram of chlorpropamide (CL), gliclazide (GZ), glibenclamide (GB) and glimepiride (GM) in standard solution, spiked plasma and blank samples in organic phase after extraction.

Fig. 7 shows the chromatograms obtained for standard solution, spiked plasma samples and blank organic phases after extraction. As can be seen, no interfering peak was observed in the same retention time of the analytes when blank plasma samples were chromatographed, showing the method selectivity. The above results show the potential of mesoporous silica-coated magnetic nanoparticles functionalized with octadecyltrimethoxysilane as sorbent for magnetic solid-phase extraction (MSPE) of oral antidiabetic drugs in human plasma. The composition and morphology of the sorbent material were essential in the extraction process. The purpose of this study, which is still in progress, is to develop a method for the determination of oral antidiabetic drugs (chlorpropamide, gliclazide, glibenclamide and glimepiride) in human plasma using magnetic solid phase extraction and high performance liquid chromatography. The obtained results confirm the success of the synthesis and the assay in accordance with the expected and stimulate a deeper study of this system used for MSPE as planned for future work. 4. Conclusion The synthesized nanocomposites presented a well-ordered mesoporous structure described as hexagonal mesopores separated by a wall of continuous silica layer coating the magnetic particles. According to XRD data, magnetite was preserved during the synthesis of the nanocomposite. SEM data showed that the silica network coated the magnetite

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