Elsevier

Journal of Chromatography B

Volume 1084, 1 May 2018, Pages 113-121
Journal of Chromatography B

A new magnetic nanodiamond/graphene oxide hybrid (Fe3O4@ND@GO) material for pre-concentration and sensitive determination of sildenafil in alleged herbal aphrodisiacs by HPLC-DAD system

https://doi.org/10.1016/j.jchromb.2018.03.030Get rights and content

Highlights

  • A sensitive and simple method was developed for sensetive determination of Sildenafil.

  • A new magnetic solid phase material (Fe3O4@ND@GO) was developed for trace analysis of sildenafil citrate in herbal samples.

  • Chemical and physical composition of new material was analyzed and provided.

  • The proposed method was applied successfully to Herbal Products.

Abstract

A sensitive analytical methodology was investigated to concentrate and determine of sildenafil citrate (SLC) present at trace level in herbal supplementary products. The proposed method is based on simple and sensitive pre-concentration of SLC by using magnetic solid phase extraction with new developed magnetic nanodiamond/graphene oxide hybrid (Fe3O4@ND@GO) material as a sorbent. Experimental variables affecting the extraction efficiency of SLC like; pH, sample volume, eluent type and volume, extraction time and amount of adsorbent were studied and optimized in detail. Determination of sildenafil citrate after magnetic solid phase extraction (MSPE) was carried out by HPLC-DAD system. The morphology, composition, and properties of the synthesized hybrid material was characterized by Fourier transform infrared spectrometry (FT-IR), Raman spectrometry (Raman), X-ray diffraction spectrometry (XRD), scanning electron microscopy (SEM), mapping photographs, zeta potential analyzer, and BET surface area analysis. Under optimized conditions, linear range was ranged from 5.00 to 250.00 ng mL−1 with R2 of 0.9952. The limit of detection (LOD) was 1.49 ng mL−1 and the recoveries at two spiked levels were ranged from 94.0 to 104.1% with the relative standard deviation (RSD) < 7.1% (n = 5). The enhancement factor (EF) was 86.9. The results show that the combination MSPE with HPLC-DAD is a suitable and sensitive method for the determination of SLC in real samples.

Introduction

Nowadays herbal medicines and dietary supplements are taking an active part in people's health care, therapy and prevention of disease throughout the world [1,2]. However, there is important problem that some manufacturers illegally may add synthetic drugs in their products [3,4]. Most existing determination methods for screening illegal adulterations are time-consuming and liable to false positive due to the extremely complex matrices of those products and low concentration of target species [5,6].

Sildenafil citrate is a common active agent used for erectile dysfunction by acting as a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5). Its chemical name is known as 1-[[3-(6,7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo[4,3-d]pyrimidine-5-yl)-4-ethoxyphenyl]sulfonyl]-4-methylpiperazine citrate as chemically [7,8]. It is rapidly absorbed after oral administration with an absolute bioavailability of about 40%. Recently, consumption of sildenafil citrate has been increasing as legal and illegal. It has a big commercial market for both an active ingredient for trade drugs and supplementary for herbal products.

The use of dietary supplements and herbal products has increased greatly during the past 40 years as an alternative to conventional medicines. As known, the belief about natural products which are inherently safer and healthier is commonly accepted in every country. Over 30% of modern pharmaceuticals are obtained from natural botanical sources, but it can be dangerous if the required controls are carried out by legal establishment [9,10]. The potential health benefits and risk of natural herbals should be considered together.

The high consumption of this molecule as drug or dietary supplements all over the world indicates the importance of the development of new analytical approaches to follow not only the quality but also the authenticity of products including sildenafil citrate [11]. Nevertheless, several analytical methods have been developed for the determination of sildenafil in herbal products [12], pharmaceutical formulations [13], using colorimetry [14], spectrophotometry [15].

The chromatographic methods are mainly preferred for rapid determination of sildenafil derivatives. But, it needs more sensitive and selective methods for real samples. The determination of sildenafil in herbal samples needs pre-treatments due to complex matrix while the determinations in trade drugs are carried out comparably more simple [16,17]. Therefore, it was considered worthwhile to develop rapid and sensitive procedures suitable for the routine quality control analysis of drug and herbal samples [[18], [19], [20]].

Solid phase extraction (SPE) methods are mainly preferred in sample preparation owing to useful and practical properties [21,22]. SPE methods are mainly used as column and batch type. Application of column methods for routine analysis is mostly limited by sample volume, process time, complex structure of sample, and costs. The most important challenge in batch methods are final separation of solid phase and selectivity of solid phase for target species [23]. Use of magnetic solids in SPE methods provided important advantages to overcome these complications [24,25]. Their magnetic properties help easy separation using a magnet, after accumulation of target molecules on particles. Moreover, the required selectivity can be obtained by covering the core with functional groups selective for analyte species. These are ideal properties expected from an effective pre-concentration and separation method.

In recent years, hybrid materials with wonderful chemical and physical features have attracted scientific attention for their potential applications in many areas such as adsorption, catalysis, biosensor, energy conversion, gas sensor, fuel cells and so on. Especially, carbon based new generation hybrid materials consist of carbon nanotubes (CNTs), graphene, graphene oxide and nanodiamond have been intensively investigated for analytical applications as adsorbent because of the their high surface area, high mechanical stability for harsh medium, tailorability and functionality properties. Among of these carbon based materials, graphene and graphene oxide (GO) as two-dimensional material has recently been the subject of analytical chemistry, due to their wonderful chemical and mechanical properties that are comparable to or even better than other used materials in literature. Even so, for the practical application of GO based adsorbents, the main problem is the important π–π stacking interactions between GO nanosheets, which cause serious aggregation and restacking of GO nanosheets, and consequently minimize their specific surface area and block active adsorption sites on GO. To solve this aggregation and restacking problems, the one of the most effective ways is to place nano-sized materials such as CNTs, nanodiamond, metal nanoparticles and so on between the GO sheets to prevent them from sticking and aggregation [26,27]. In this study, in order to remove the above-mentioned difficulties of use of the GO as a good adsorbent and to isolate the synthesized ND@GO hybrid materials from sample and elution solutions, we modified the GO with nanodiamond particles and magnetic particles.

This study describes the synthesis and usability of a new generation magnetic hybrid material as adsorbent for magnetic solid phase extraction of sildenafil citrate prior to reversed-phase HPLC determination. The developed MSPE method was then applied the determination of the sildenafil citrate in commercial herbal products and in the tablet dosage form.

Section snippets

Instrumentation

The FT-IR characterization of the GO, ND@GO and Fe3O4@ND@GO materials were carried out by Perkin-Elmer Spectrum 400 FT-IR spectrometer (Waltham, MA, USA). The Raman spectrums of the GO, pristine nanodiamond and Fe3O4@ND@GO material were obtained by using Raman spectroscopy (WITec alpha 300 M + micro-Raman system with 532 nm laser source). X-ray diffraction (XRD) spectrums of ND@GO and Fe3O4@ND@GO materials were obtained using an advanced XRD diffractometer (Bruker AXS D8). Scanning electron

Characterization of the magnetic adsorbent

The XRD pattern of the pristine ND, GO synthesized and Fe3O4@ND@GO composite synthesized were illustrated in Fig. 3A–C. The diffraction pattern of the pristine ND has a peak at 2θ = 44.0° corresponding to the diamond planes, the other peak around at 24° corresponds to the (002) graphite crystal plane (Fig. 3A). The spectra of pristine GO exhibited the main features related to a reflection peak at 2 h = 11.4°, which is in good agreement with the literature (Fig. 3B) [23,24]. The results of XRD

Conclusions

The proposed MSPE technique based on the synthesized magnetic adsorbent (Fe3O4@ND@GO) was demonstrated to be an efficient strategy for the rapid preconcentration and separation of sildenafil in complex matrices such as herbal products. The described enrichment procedure for the determination of sildenafil is relatively simple and powerful. The magnetic support can be reused up to 10 times. The extraction technique is a robust pre-concentration technique that can be coupled successfully to

References (35)

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