Z. Y. Zhang et al.: An Analytical Method for Detecting the Content of Metallic Elements in Honey..., Kem. Ind. 66 (11-12) (2017) 661−666 661 DOI: 10.15255/KUI.2017.034 An Analytical Method for Detecting the KUI-48/2017 Short communication Content of Metallic Elements in Honey Received September 25, 2017 Collected from Henan, China: Accepted November 2, 2017 A Systematic Investigation with ICP-AES This work is licensed under a * Creative Commons Attribution 4.0 Z. Y. Zhang, W. X. Fan, M. Yang, and C. X. Cui International License Henan Institute of Science and Technology, Xinxiang, Henan 453 003, P.R. China Abstract In this study, the method for determining ten elements (including K, Na, Ca, Mg, Fe, Mn, Cu, Zn, Pb, and Cd) was designed. With this method, we evaluated 15 honey samples, including three kinds of honey collected from 11 different geographic sites in Henan province of China, with inductively coupled plasma atomic emission spec- trometry (ICP-AES). The obtained detecting data were analysed with principal component analysis, correlation analysis, and cluster analysis techniques. The results showed that the recovery is in the range of 93.0−107.0 %, and the relative standard deviations (RSDs) were all below 5.89 %, which indicates that the current analytical method is dependable for the detection of metallic elements in honey. Keywords ICP-AES, honey, metallic elements, principal component analysis, cluster analysis 1 Introduction plasma atomic emission spectrometry (ICP-AES). Principal 1 component analysis and cluster analysis were performed Honey is produced by honey bees, and contains carbo- in SPSS software to classify and evaluate the content of hydrates, metallic elements, and vitamins. Honey could be metallic elements in these honey samples. We hope the used to treat burn wounds, stomach disorders and asthma current investigation provides useful information to the fur- in clinical application, and is a very popular health food ther development of honey products. Moreover, the statis- because of its nutritional value.2–4 The content of metallic 5 tical results could give some implication for environmental elements in honey is relatively low (0.1–1 %). The metallic protection. elements in honey mainly include K, Na, Ca, Mg, Cu, Zn, Fe, and Mn, which plays a vital role in maintaining normal metabolic and organ functions, improving the activity of 6–8 enzymes, and enhancing the immune function. The me- 2 Experimental tallic elements in honey come from the plants where the nectar is collected by bees.9 As a result, the composition 2.1 Materials and reagents and content of metallic elements in honey are not only a sign of its inherent quality, but also a reflection of the envi- The honey samples were collected from 11 regions in He- ronmental conditions of honey plants. nan province from May to July 2016. Two to three apiaries were selected in each region. The honey samples include In recent years, the honey industry has been developing Tung flower honey, Pagoda tree flower honey, and Vitex rapidly in Henan province, China.10 In 2016, the total flower honey, denoted as TFH, PFH, and VFH, respective- number of bee colonies, the practitioner and the related ly. The samples are shown in Table 1. products in Henan province all ranked well in China.10–11 The annual production of honey was about a thousand All chemicals were of guaranteed reagent (GR) including tons, and the output value was almost 1 billion RMB, nitric acid, hydrogen peroxide (30 %). The bush branch which accounted for one fifth of the honey industry of and leaf used in the research is the National biological the entire country. The quality of honey is evaluated by its standard substance. The standard solutions of K, Na, Ca, density, viscosity, sugar content, and other appearance fea- Mg, Fe, Mn, Cu, Zn, Pb, and Cd were bought from the PE tures.11 Therefore, the development of a detecting method Company (USA). The water used in the research was the for metallic elements in honey is important for the honey quartz double distilled high pure water. industry. In this research, the content of metallic elements in 15 2.2 Apparatus honey samples collected from 11 regions in Henan prov- ince of China were determined by inductively coupled The closed intelligent microwave digestion instrument (XT- 9912) was bought from Shanghai XTrust Instruments Co. * Corresponding author: Dr Zhong-Yin Zhang Ltd. A Perkin Elmer Optima 2100 DV inductively coupled e-mail: [email protected] plasma atomic emission spectrometer (ICP-AES) was used 662 Z. Y. Zhang et al.: An Analytical Method for Detecting the Content of Metallic Elements in Honey..., Kem. Ind. 66 (11-12) (2017) 661−666 Table 1 – Numbers of honey samples colorimetric tube (10 ml), and diluted with 2 % nitric acid. The blank reagents were prepared according to this proce- Number Sample Region dure for ICP-AES. S1 TFH Luyi county, Zhoukou city S2 TFH Tuocheng county, Shangqiu city S3 PFH Hua county, Anyang city Table 2 – Microwave digestion procedure S4 PFH Yuanyang county, Xinxiang city Stage Pressure ⁄ MPa Temperature ⁄ °C Time ⁄ s Power ⁄ W S5 PFH Lingbao county, Sanmenxia city 1 1.0 130 80 1000 S6 PFH Lushi county, Sanmenxia city 2 1.3 150 200 1200 S7 PFH Wangwu county, Jiyuan city 3 1.8 182 300 1300 S8 VFH Dengfeng city, Zhengzhou city 4 2.0 200 450 1300 S9 VFH Lingbao county, Sanmenxia city S10 VFH Linzhou city, Anyang city 2.4 Data processing S11 VFH Xinan county, Luoyang city S12 VFH Qi county, Hebi city The SPSS 22.0 were used for principal component analy- sis, correlation analysis, and cluster analysis. S13 VFH Xixia county, Nanyang city S14 VFH Yicheng district, Zhumadian city S15 VFH Huixian county, Xinxiang city 3 Results and discussion 3.1 Effects of the wavelength of the spectral line for each mineral element and the regression analyses for measurement. The experimental conditions during measurement were as follows: radio-frequency output was The ICP-AES has the automatic background sync function −1 1.2 kW; flow rate of nebulizer was 0.8 l min ; flow rate of for correction. It is important to choose the spectral line −1 −1 cooling was 1.5 l min ; sample flow rate was 1.5 ml min . with low interference, high sensitivity and low background value for the determination of metallic elements in honey. The standard solution was measured using the ICP-AES, 2.3 Sample preparation and the standard curves were obtained. Measurement was repeated in parallel 10 times. The detection limit was One gram of each honey sample was dissolved in 8 ml calculated by three times of the standard deviation. The concentrated nitric acid and 2 ml hydrogen peroxide in a wavelength (λ) of the spectral line, the standard curve, the sealed polytetrafluoroethylene digestion tank. The diges- correlation coefficient (r) and the detection limit (DL) are tion was conducted as shown in Table 2. After digestion, presented in Table 3. It was obvious that the correlation the system was cooled down to room temperature. The coefficients of different metallic elements were between solution from the digestion tank was transferred to a beak- 0.9995–0.9999, and the detection limits were between er (100 ml), and then heated to remove the acid in the 0.00003–0.01310 mg l−1, which was suitable for the quan- airing chamber. After cooling, the solution was put in a tity analysis of the ten kinds of metallic elements. Table 3 – Analytical spectral lines, linear regression equations, correlation coefficients and detec- tion limits of determination of the metallic elements Correlation Element Wavelength ⁄ nm Standard curve Detection limit ⁄ mg l−1 coefficient K 766.491 I = 1903.78c + 635.10 0.9999 0.00781 Na 589.592 I = 12658.95c + 1267.60 0.9998 0.00980 Ca 317.933 I = 4158.26c − 1532.64 0.9997 0.01310 Mg 279.079 I = 12689.15c − 1167.61 0.9998 0.00103 Fe 238.204 I = 8591.56c + 67.66 0.9999 0.00028 Mn 257.610 I = 30198.32c + 580.91 0.9996 0.00054 Cu 327.393 I = 1352.99c + 7.40 0.9999 0.00038 Zn 206.200 I = 5980c + 87.06 0.9999 0.00058 Pb 220.353 I = 29356c + 201.2 0.9995 0.00019 Cd 228.802 I = 485060c + 658.9 0.9999 0.00003 Z. Y. Zhang et al.: An Analytical Method for Detecting the Content of Metallic Elements in Honey..., Kem. Ind. 66 (11-12) (2017) 661−666 663 Table 4 – Recoveries and relative standard deviations (RSD) of ten kinds of metallic elements (n = 6) Element Background amount ⁄ μg ml−1 Added amount ⁄ μg ml−1 Measured amount ⁄ μg ml−1 Recovery ⁄ % RSD ⁄ % K 17.130 10.00 27.720 105.9 5.36 Na 4.296 5.00 9.226 98.6 1.89 Ca 2.918 5.00 7.883 99.3 1.27 Mg 0.515 1.00 1.571 105.6 3.26 Fe 0.298 0.50 0.797 99.8 4.65 Mn 0.013 0.10 0.120 107.0 0.84 Cu 0.301 0.50 0.831 106.0 0.28 Zn 0.115 0.10 0.213 98.0 0.39 Pb 0.045 0.10 0.138 93.0 4.89 Cd 0.003 0.10 0.097 94.0 5.89 3.2 Accuracy and precision of the method 3.4 Determination of metallic elements in honey samples In order to assess the accuracy of the method, the stand- ard reference was analysed. The results were compared The content of ten kinds of metallic elements were an- with the certified ones and the relative error was calculat- alysed.