Elsevier

Journal of Chromatography A

Volume 1602, 27 September 2019, Pages 150-159
Journal of Chromatography A

Calixarene and ionic liquid assisted matrix solid-phase dispersion microextraction of organic acids from fruit

https://doi.org/10.1016/j.chroma.2019.03.055Get rights and content

Highlights

  • MSPD coupled with UHPLC-Q-TOF/MS was used to determine organic acids in fruit.

  • Calix[8]arene was used as an efficient sorbent in MSPD procedure.

  • The ionic liquids were applied as extraction solvents.

  • The proposed method was rapid, simple, low cost and high sensitivity.

Abstract

A rapid and effective method was successfully established for the extraction and determination of chlorogenic acid, protocatechuic acid, malic acid, caffeic acid and gallic acid in fruit (chaenomeles speciosa) via matrix solid-phase dispersion (MSPD) microextraction combined with ultra-high performance liquid chromatography with quadrupole time-of-flight tandem mass spectrometry (UHPLC-Q-TOF/MS). Several major extraction parameters were investigated and optimized, such as the type of sorbent, the amount of sorbent, the grinding time, the type and concentration of the eluting solvent. The optimal extraction conditions were obtained by using 20 mg of calix[8]arene as dispersing adsorbent, selecting 60 s as the appropriate grinding time and applying 250 mM of 1-dodecyl-3-methylimidazolium bromide as eluent solvent. Moreover, the calibration curves of the analytes were in the range of 0.01–500 μg/mL with the determination coefficients (r2) higher than 0.9995. The limits of detection and limits of quantification were in the range of 0.202–1.056 ng/mL and 0.674–3.521 ng/mL, respectively. The recoveries of the target compounds at two spiked levels were between 82.19 and 113.36%. Furthermore, this method had acceptable reproducibility (RSD ≤ 3.84%). The proposed approach combined the advantages of MSPD microextraction with UHPLC-Q-TOF/MS, and could be applicable for the analysis organic acids in fruit.

Introduction

Calixarene compounds are regarded as the third generation of macrocyclic hosts with extensive applications in the supramolecular field next to cyclodextrin and crown ether. The cyclic oligomers of calixarenes are synthesized through the cyclic condensation of formaldehyde and para-substituted phenol under alkaline conditions [1]. The particular configuration is possessed by the cavity of calixarene which make its the hydrophobic of inner cavity surface and the hydrophilic of outer surface, resulting in structural adjustments to obtain desired performance [2]. They have the capacity to form a host-guest inclusion compound with a wide variety of guests such as metallic cations, anions, and amino acids by flexibly adjusting the cavity dimension. Accordingly, calixarenes have been extensively used in recovery of metals [3], ion-selective electrodes [4], chemical sensors [5], separation and analysis [6], catalysts [7] and molecular recognition [8]. The novel adsorbent material is prepared by modifying the structure of the calixarene monomer for extracting flavonoids from complex samples [9,10]. There are few studies with regard to the use of calixarenes as sorbent materials for the extraction of complex components in natural products, although various studies have been conducted on its applications in the literature [[11], [12], [13]].

In general, sample pretreatment prior to instrumental analysis is critical during the analysis processes. For analysis, highly sensitive and selective analytical means have been used in recent years. An appropriate sample pretreatment is also essential to determine target analytes in complex samples quickly and accurately. In order to solve several problems in the experimental process such as complicated operation, long extraction time, solvent consumption and cost, an attractive matrix solid-phase dispersion (MSPD) approach has been emerged during the last years [14]. MSPD is one of the most prospective technologies involving simultaneous disruption, homogenization, extraction and (preliminary) clean-up of various solid, semisolid and highly viscous samples [15,16]. Compared with conventional techniques, the advantages of sample treatments are a small amount of adsorbent and solvent, simple operation and reduced sample handling, which decreased the consumption and environmental pollution of reagents [17]. In addition, it has the moderate and feasible research conditions such as controlled consumption of eluent solvent, room temperature, and no need for expensive instruments. In the reported literature, various types of solid matrix are used in the extraction steps, mainly including silica gel, SiO2, florisil, graphene, alumina, C18 and C8, followed by washing and eluting with organic solvents in further study [[18], [19], [20], [21]]. The conventional sorbents are applied to disrupt the architecture of the sample and weaken the binding ability between sample matrices and target analytes. Thereby, satisfactory extraction efficiency was obtained with good feasibility under mild conditions. To date, MSPD has been widely applied in various industries with content results such as pesticide residues and additives in food, heavy metal in water, and active components from herbal medicines [[22], [23], [24], [25]]. However, in the MSPD microextraction, the use of calixarene as a sorbent and ionic liquid as an elution solvent for simultaneous determination of chemical components in fruit have not been proposed yet.

Dried fruit of chaenomeles speciosa (CS) is commonly described as Mugua in China. It has been mainly used in the field of traditional Chinese medicine for many years, and belongs to Pomoideae of the Rosaceae family. Characteristics of CS benefited health are received increasing attention from researchers in other medicine systems. In general, it has the ability to promote digestion, invigorate the stomach and stimulate blood circulation, and lower cholesterol and blood sugar [26]. Different relevant chemical studies have reported that the rich biologically active components present in this CS are pentacyclic triterpenes, flavonoids and organic acids [27]. Furthermore, various biological activities have been proven effective in anti-inflammatory effects and immunoregulatory actions such as antitumor and antivirus activity, antioxidant capacity, anti-α-glucosidase activity, and so forth [[28], [29], [30]]. The pentacyclic triterpenes and flavonoids in herb have been widely available in previous studies [31,32]. However, reports on simultaneous extraction and determination of organic acids in CS have not been established. Organic acids including chlorogenic acid, malic acid protocatechuic acid, caffeic acid and gallic acid, are important components of food, cosmetic and pharmaceutical industries, particularly chlorogenic acid and malic acid are richer in beverages, fruits, and vegetables.

The aim of this work was to set up a rapid, simple and effective method based on MSPD microextraction and simultaneously determined several chemical constituents (chlorogenic acid, protocatechuic acid, malic acid, caffeic acid and gallic acid) in CS samples. This study proposed a calixarene was utilized as sorbent material to facilitate the extraction studies. A green and non-volatile ionic liquid (IL) was applied as an eluent to reduce the environmental pollution and consumption environmental pollution of toxic organic solvents during the sample pretreatment. After pretreatment, without further sample clean-up steps, all target compounds were analyzed by UHPLC-Q-TOF-MS/MS for simplifying the analytical progress and save analysis time. Moreover, this technology allowed the sample to be reduced to a smaller amount that provided reliable results. It is especially important when real samples are scarce, saving analysis time and reducing the number of steps. Accordingly, it is necessary to establish an effective method for sample pre-processing and evaluate the extraction yield towards to select target analytes from fruit.

Section snippets

Reagents and samples

The 1-ethyl-3-methylimidazolium bromide ([Emin]Br), 1-hexyl-3-methylimidazolium bromide ([Hmim]Br), 1- Decyl -3-methylimidazolium bromide ([Demim]Br) and 1-dodecyl-3-methylimidazolium bromide ([Domim]Br) were provided by Shanghai Cheng Jie Chemical Co., Ltd. (Shanghai, China). 4-tert-Butylcalix[4]arene, calix[6]arene, calix[8]arene and O(1),O(3)-bis(carbethoxymethyl)-p-tert-butylcalix(4)arene were purchased from Alfa Aesar (China) Chemicals Co., Ltd. (Shanghai, China). Standards of chlorogenic

Fragmentation studies

In this study, five target compounds were extracted from CS and pretreated by MSPD microextraction. Afterwards, further identification was carried out by UHPLC-Q-TOF/MS with negative ion mode. To confirm the successful extraction and fragmental pathways of target compounds, MS/ MS spectra analysis was done by studying the exact molecular masses and the characteristic fragments. The mass spectrogram of chlorogenic acid is shown in Fig. 1A. For chlorogenic acid ([M−H], m/z 353.08738), two major

Conclusions

In the present study, an effective extraction method based on MSPD microextraction with calix[8]arene as dispersion sorbent has been successfully applied for the determination of organic acids in CS samples. The elution process of this method required a small volume of IL aqueous solution to replace the hazardous organic solvent, indicating that the study had certain advantages in eluent solvent consumption and environmental pollution. By coupling with UHPLC-Q-TOF/MS, satisfactory sensitivity

Acknowledgements

This study was supported by the National Natural Science Foundation of China (81573552), public welfare research project of Zhejiang Province (LGF18H280006), Projects for Study Abroad Returnees of Hangzhou (China, 2017), Hangzhou 131 middle-aged and young talent training plan (China, 2017).

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