Elsevier

Food Chemistry

Volume 194, 1 March 2016, Pages 555-560
Food Chemistry

Simple column-switching ion chromatography method for determining eight monosaccharides and oligosaccharides in honeydew and nectar

https://doi.org/10.1016/j.foodchem.2015.08.049Get rights and content

Highlights

  • A column-switching ion chromatography method was used to analyze 8 sugars.

  • Organics in honeydew and nectar was removed by on-line elimination process.

  • Honeydew had much more oligosaccharides than nectar.

  • The method may be used to analyze other sugars or ions in various organic matrices.

Abstract

Honeydew is excreted by aphids as a sweet waste and nectar is floral honey. Honeydew and nectar are complicated samples which consist of various sugars and amino acids. In this work, a simple ion chromatography with column-switching method was developed for the simultaneous analysis of 8 monosaccharides and oligosaccharides in honeydew and nectar. A reversed-phase column was used as a pretreatment column to eliminate organics on-line and sugars were eluted from a collection loop to analytical column by using column-switching technique. This method showed good linearity (r  0.9994) and afforded low limits of detection ranging from 1.55 to 10.17 μg L−1 for all the analytes. Recoveries ranged from 95% to 105% and repeatability results were acceptable with relative standard deviation of less than 3.21% (n = 6). This method was successfully applied to quantification of these sugars in honeydew and nectar. These results showed honeydew had much more oligosaccharides than nectar.

Introduction

Honeydew is excreted by aphids as a sweet waste which consists mainly of various sugars and amino acids (Fischer, Völkl, & Hoffmann, 2005). Sugar compositions of honeydew vary significantly between aphid species but may also vary within a particular aphid species in an age-specific pattern or when feeding on different host plants (Fischer et al., 2005). Besides, there is a relationship between ant tending and honeydew sugar composition (Fischer & Shingleton, 2001). Nectar is another important element in agriculture. Nectar chemistry, including the sugar proportion, may differ among populations, individuals, cultivars or subspecies of the same species (Agostini, Sazima, & Galetto, 2011). In some regions, especially in Central and Eastern Europe, honeydew honey is highly valued in public as it has more benefits on human health than floral (nectar) honey (Simova, Atanassov, Shishiniova, & Bankova, 2012). Moreover, honeydew is appreciably higher in oligosaccharides than the nectar (Simova et al., 2012).

Till now, several methods regarding sugar analysis have been investigated. These include a variety of chromatographic methods such as high performance liquid chromatography (HPLC) (Földházi, 1994, Swallow and Low, 1990), gas chromatography (GC) (Low & Sporns, 1988), and gas chromatography–mass spectrometry (GC–MS) (Molnár-Perl, 1999). All of these methods can be utilized to separate and quantified the major sugars in honey. However, most of them have occasional disadvantages. For example, some chromatography methods require derivatization, such as GC, GC–MS, HPLC-diode array detector (HPLC-DAD) and HPLC-fluorescence detector (HPLC-FLD) (Pico, Martínez, Martín, & Gómez, 2015). HPLC–mass spectrometry (HPLC–MS) is expensive, and HPLC-refractive index detector (HPLC-RI) does not allow the use of a gradient and has low sensitivity (Molnár-Perl, 1999).

Ion chromatography (IC) is a special kind of HPLC which is widely used to analyze cations, anions, and some important biological compounds such as sugars, amino acids, peptides and proteins. For example, IC-pulsed amperometric detection (IC-PAD) is one of the most useful techniques for determination of oligosaccharide (Ouchemoukh et al., 2010, Steppuhn and Wäckers, 2004). PAD proved to be superior to RI detection and evaporative light scattering detection (ELSD) in aspect of selectivity, sensitivity and having possibility of gradient elution (Molnár-Perl, 1999). However, honeydew and nectar contain sugars as well as vitamins, amino acids, proteins. Organics in samples not only lead to damage the IC columns, but also may make erroneous results. Thus, it is important to remove organics from sample before analysis. The conventional sample preparation method is using a reverse-phase pretreatment column, such as Thermo Fisher OnGuard II RP column. Although these pretreatment columns can be reused 5–10 times, the regeneration processes are time-consuming due to manual operations. Therefore, on-line pretreatment method is proposed.

As an effective on-line sample pretreatment method, column-switching technique has been widely used in ion chromatographic system (Huang et al., 2013, Zhu et al., 2013). For example, Yang et al. (2013) proposed a simple IC column-switching method for detection of hexavalent chromium in Colla corii asini. Sample solution with target ions were eluted from a collection loop to analytical columns, with on-line matrix elimination. Zhong, Zhou, Zeng, Ye, and Zhu (2011) used an IC system coupled with on-line column-switching technique to determine anions in organic chemicals of high purity. Zhu et al. (2013) proposed the column-switching IC-PAD method for simultaneous determination of glucose, d-gluconic acid, 2-keto-d-gluconic acid and 5-keto-d-gluconic acid.

In this work, a column-switching IC method was established for the analysis of sugars in honeydew and nectar. The samples could be analyzed after on-line elimination of the matrices. It has potential to provide a fast, convenient, and practical approach for analysis of sugars in biological samples.

Section snippets

Equipment

An ICS 3000 IC system (Thermo-Fisher Scientific Waltham, MA, USA) was employed for all the chromatographic separations, which was equipped with a quaternary pump, a column heater, two six-port valves (P/N 061961, Rheodyne, Cotati, CA, USA). The electrochemical detector (ED50 electrochemical detector, Thermo-Fisher Scientific Waltham, MA, USA) was equipped with a gold working electrode, an pH/Ag/AgCl composite reference electrode. A quaternary pump (Ultimate 3000, Thermo-Fisher Scientific

Separation column

In this study, two IC columns (IonPac PA1 and IonPac PA10) were tested for the sugar separation. It was found that IonPac PA1 column always had a dissolved oxygen peak to interfere separation while IonPac PA10 had better separated performance. Thus, IonPac PA10 guard column and analytical column were selected for this method.

Mobile phase

Among the 8 sugars, rhamnose, glucose, fructose and sucrose have shorter retention time than the other four sugars (lactose, raffinose, maltose and erlose). In this work,

Conclusion

In this work, a column-switching IC method for simultaneous determination of sugars and matrix elimination was proposed. The on-line pretreatment IC system is effective for the organics elimination in honeydew and nectar samples. The results showed good accuracy, satisfactory precision, wide linearity and low LOD. This method was suitable and reliable for the analysis sugars in various complex samples. It can be extended to trace level detection of other sugars or ions which have redox in

Acknowledgments

This research was financially supported by the Major National Scientific Instrument and Equipment Development Special of China (No. 2012YQ09022903), Key Laboratory of Health Risk Appraisal for Trace Toxic Chemicals of Zhejiang Province, Science and Technique Plan of Zhejiang (No. 2014F50030), and Zhejiang Provincial Natural Science Foundation of China (Nos. Y4110532, LY12B05003, LY13B020001, LQ13B050001).

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