Simultaneous determination of chromium, nickel, arsenic and lead in hot-melt adhesives for cigarette by inductively coupled plasma mass spectrometry

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1 Vol. 48 Suppl. No. 1 Tobacco Science & Technology December 2015 Simultaneous determination of chromium, nickel, arsenic and lead in hot-melt adhesives for cigarette by inductively coupled plasma mass spectrometry QIN Cunyong 1, ZHANG Xiaojing 2,*, LI Li, LIU Wei 2, ZHENG Songjin 2 1. Technology & Quality Department, Hebei Baisha Tobacco Co., Ltd., No. Zhujiang Street, Shijiazhuang 05005, China 2. Technology Center, China Tobacco Hebei Industrial Co., Ltd., No.1 Weiming South Street, Shijiazhuang , China. Technical Research & Development Center, China Tobacco Sichuan Industrial Co., Ltd., No.1-5 Chenglong Street, Chengdu 100, China Abstract: An analytical method for simultaneous determination of four heavy metals, namely chromium (), nickel(), arsenic() and lead() in hot-melt adhesives for cigarette was developed by using inductively coupled plasma mass spectrometry (ICP-MS) with microwave digestion. The method was applied to quantify the four heavy metals in eight hot-melt adhesives. The linear correlation coefficients were between and The relative standard deviations of measurement were between 2.04% and 4.51%. The recoveries for spiking hot-melt adhesive samples were between 95.2% and 118.1%. The detection and quantitation limits of the method were in the range of μg/l and μg/l, respectively. The uncertainty measurement for the method was evaluated. The calibration curve fitting was the most important factor affecting the combined uncertainty, followed by the standard solution preparation and the repeatability, and with the sample preparation process had the least impact. The levels of the four heavy metals in the hot-melt adhesives were in the order of >>>. Notable differences in and levels were found with variation coefficients of 8.% and 81.8%, respectively. The developed method is accurate, simple, rapid, reliable, and suitable for the simultaneous determination of the four heavy metals in hot-melt adhesives for cigarette. Keywords: Inductively coupled plasma mass spectrometry(icp-ms); Microwave digestion; Hot-melt adhesive; Heavy metal Introduction Hot-melt adhesives are melts blended by taking a thermoplastic resin or elastomer as the base material, and added with tackifiers, plasticizers, antioxidants, flame retardants and fillers as additives [1]. Hot-melt adhesives for cigarette are used in the cigarette manufacturing, which should be in line with the tobacco product processing requirements and food hygiene standards [2]. The amount of arsenic () and lead () in a hot-melt adhesive for cigarette should be limited according to the Chinese tobacco industry standard YC/T [2]. Their levels can be determined in accordance with the methods described in GB/T and GB/T [-4]. However, the current measurement methods are tedious and insensitive (a high concentration is required for Received: 22 December 2014; revised: 28 August 2015; accepted: 2 November * Corresponding author. address: xiaojing99@12.com (X. Zhang). the detection) [-4], which are not suitable for the analysis of heavy metal elements in batch samples [5]. Xu et al. [5] determined contents in hot-melt adhesives by graphite furnace-atomic absorption spectrometry (GF-AAS) with microwave digestion. The author simplified the pretreatment process and improved sensitivity compared to the existing detection technology. However, the GF-AAS method is not suitable to determine multiple metal elements simultaneously. Inductively coupled plasma mass spectrometry (ICP-MS) has the advantages of high sensitivity, a wide linear range, simplicity of spectral lines and low detection limits and has the potential for simultaneous determination of multiple elements [-10]. Therefore, in the current study, a method of determining simultaneously four heavy metal elements, namely chromium (), nickel (), and in hot-melt adhesives for cigarette by ICP-MS with microwave digestion was developed. The method simplified both the pretreatment and detection procedures, representing a meaningful improvement in the detection technology in this field.

2 72 Tobacco Science & Technology Materials and methods 1.1 Materials and instruments Eight hot-melt adhesives for cigarette (used for the experiments)were selected. 5% nitric acid (HNO, guarantee reagent, Merck, Germany); 0% hydrogen peroxide (H 2O 2, guarantee reagent, Merck, Germany); Mixed standard solutions containing Ag, Al,, Ba, Be, Ca, Cd, Co,, Cs, Cu, Fe, Ga, K, Li, Mg, Mn, Na,,, Rb, Se, Sr, Tl, U, V and Zn (10 mg/l, Agilent, USA);Internal standard solutions containing Li, Sc, Ge, Rh, In, Tb, Lu and Bi (100 μg/ml, Agilent, USA, diluted to 1 μg/ml with 2% HNO in use); Tuning solutions containing Li, Y, Ce, Tl and Co (10 μg/l, Agilent, USA); Argon gas (99.999%, Xisanjiao, Shijiazhuang, China). 00cX inductively coupled plasma mass spectrometry (ICP-MS, Agilent, USA); MarsXpress Microwave digestion instrument (CEM, USA); DKQ-4 Electric heater block (Yiyao, Shanghai, China); AB204-S Electronic balance (Sensitivity: g, Mettler Toledo, Switzerland); Milli-Q Advantage ultrapure water treatment equipment (Millipore, USA). 1.2 Methods Sample preparation The hot-melt adhesives for cigarette were cut to 2 mm long granular particles and sealed for storage. The above hot-melt adhesive samples were weighed accurately to 0.2 g, put into tetrafluoroethylene perfluoropropoxyethylene copolymer (PFA) digestion vessels, and then 5 ml of 5% HNO was added. The samples were heated by an electric heater block at 100 for 0 min until the adhesive solid melted. After the samples cooled to room temperature [5], the mixture of 1 ml of 5% HNO and 1 ml of 0% H 2O 2 was added. Then the samples were microwave digested according to the following temperature program (see below). After the acid digestion, the vessels were removed from the microwave digestion instrument till the temperature dropped below 40. Then the samples were transferred into polyethylene terephthalate (PET) bottles and diluted to 0 g with ultrapure water. The residual samples in vessels were washed three times with ultrapure water and the portions were also transferred into the PET bottles. The blank samples were prepared following the similar preparation method. According to the relevant literature [5], the temperature ramp program was set as follows: 25 5 min 100 (5 min) 5 min 10 (5 min) 5 min 10 (5 min) 5 min 190 (0 min) ICP-MS operating conditions The operating conditions of ICP-MS were optimized in line with the tuning solution. The instrumental conditions and data acquisition parameters were listed in Table 1. Table 1 Instrumental conditions and data acquisition parameters. Parameter RF power Carrier gas flow Auxiliary gas flow Makeup gas flow Plasma gas flow Nebulizer Value 1500 W 0.85 L min L min L min L min -1 Concentric Parameter Peripump rate Uptake time Stabilization time Integration time Replications Value 0.1 r s -1 0 s 45 s,, : 0. s : 1 s 1.2. Sample analysis The samples were analyzed by ICP-MS for,, and and corrected using the internal standards. After tuning(table 1), the sample solutions and 1 μ g/ml internal standard solutions were pumped separately into the instrument using a multichannel peristatic pump system. The two streams were mixed prior to the nebulizer by using a plastic tee [11]. The sample acquisition order was a series of standard solutions (from low to high concentrations), blank solutions and hot-melt adhesive sample solutions in turn. To avoid cross contamination, the sample tube was washed for 1 min with 5% HNO and ultrapure water respectively before and after every data acquisition [12]. 2 Results and discussion 2.1 Preparation Conditions Digestion methods Due to the contents of,, and in the hot-melt adhesives are relatively low ( 1μg/g), the digestion method directly affects the recoveries of the elements. A proper digestion method should digest the sample completely with less elemental loss, less reagent

3 Vol. 48 Suppl. No. 1 QIN Cunyong,et al:simultaneous determination of chromium, nickel, arsenic and lead in hot-melt adhesives for cigarette by inductively coupled plasma mass spectrometry 7 addition (to reduce potential contamination), etc [1]. Considering the hot-melt adhesive samples used in this work were relatively homogenous and easy to digest, the mixture of HNO -H 2O 2 system was chosen to digest the samples [14], together with a pre-reaction before microwave digestion. This method was able to ensure the digestion program security, and at the same time achieve more complete digestion Pre-reaction time The base material of a hot-melt adhesive is a resin, which is composed of polymers from ethylene and vinyl acetate as monomer. If a hot-melt adhesive is mixed with HNO and then microwave assistedly digested in enclosed vessels, it is possible to produce a lot of energy and lead to a violent reaction instantly. To avoid this, 5 ml of HNO was added firstly to the samples for pre-reaction prior to microwave digestion. After the adhesive solid melted and the yellow smoke dissipated, the samples were digested according to the microwave digestion program (1.2.1), followed by the addition of the mixture of 1 ml of HNO and 1 ml of H 2O 2. For the optimal pre-reaction time, different digestion duration time (0, 0 and 90 min, respectively) were selected for the test. The results showed that: 1) the hot-melt adhesive particles were melted incompletely after pre-reaction for 0 min. The sample solutions were yellow and turbid after digestion and dilution. 2) Most of the hot-melt adhesive particles were melted after pre-reaction for 0 min. The sample solution became clear after digestion and dilution, which met the test requirements. ) After pre-reaction for 90 min, the acid residue was the minimum and some samples were even heated to be dry. Based on the above results, we finally chose the 0 min as pre-reaction time before microwave digestion. No violent reactions occurred to the samples in the process of microwave digestion according to the set program (1.2.1), and the samples were digested more completely after the pre-reaction procedure than without the pre-reaction Sampling mass and solution volume Sampling mass and solution volume are two critical factors on elemental analysis. In this work, five sample masses at 0.1, 0.2, 0., 0.4 and 0.5 g diluted with ultrapure water to both 0 and 50 g solutions were tested, respectively. The status of the samples after digestion and dilution were shown in Table 2. The results showed that: 1) The volume of 0 g solutions, including 0.1 or 0.2 g samples were clear and colorless, adequate to meet the test requirements. the sample mass increased (i.e., 0., 0.4, 0.5 g), the solutions became colored or turbid. 2) The volume of 50 g solutions with 0.1 or 0.2 g samples were also colorless and clear; when the solution was further increased to 0. g sample, it became light yellow but remained clear, which was qualified for the test. Considering that 0.1 g amount of mass might not be representative of the average property for the whole sample, and the concentrations of the heavy metal elements in the hot-melt adhesives were too low in the volume of 50 g diluted solution to meet the equipment sensitivity limit [9]. Eventually we chose the sampling mass of 0.2 g and diluted solution volume of 0 g for our Table 2 Status of sample solution. Solution volume 0.1 g 0.2 g 0. g 0.4 g 0.5 g 0 g Colorless clear Colorless clear Yellow clear 50 g Colorless clear Colorless clear Light yellow clear Yellow clear determination experiment. 2.2 Measurement estimation Calibration curves, detection limits and quantitation limits The standard stock solution of 100 μ g/l was prepared by accurately measuring 0.5 ml of 10 mg/l standard solution and diluting to 50 ml with 2% HNO in plastic mark volumetric flasks. Similarly, a series of mixed standard solutions at the concentrations of 0, 0.2, 0.4, 1, 2, 4, 10 and 20 μg/l were prepared by accurately measuring different volumes of the above 100 μg/l standard stock solution and diluting to 50 ml solution with 2% HNO. The concentrations of the four target heavy metals in the mixed standard solutions were determined by ICP-MS. X (defined as the contents of the target elements, μg/l) and Y (defined as the response ratio of the target elements to internal standard elements for intensity, μ g/l) were subject to linear regression treatment. The calibration curves were linear throughout the entire calibration range. The calibration curves and linear correlation coefficients for the four target elements containing,, and were listed in Table. The results showed that the calibration curves were in good linear correlation with the coefficients between and The blank samples were prepared and determined by

4 74 Tobacco Science & Technology 2015 ICP-MS. The limit of detection(lod), defined as three times of the standard deviation of the blank, was determined by analyzing eleven replicates of the blank. The limit of quantitation (LOQ), defined as ten times of the standard deviation, was similar with the LOD [15]. The LODs and LOQs for the method were listed in Table. The LODs of the four target elements were lower than 100 ng/l. Table Internal standard elements, calibration curves, LODs and LOQs of four elements. Internal standard element Calibration curve Linear correlation coefficient LOD / (μg L -1 ) LOQ / (μg L -1 ) Ge 72 Ge 115 In 115 In Y=0.045X Y=0.09X+0.00 Y=0.049X Y=0.072X Precision and recoveries Take one of the above hot-melt adhesives used for precision and recovery test. Six copies were prepared and determined by ICP-MS. The precision was described by the relative standard deviations (RSD) of the target element contents for the six copies. The precision were listed in Table 4. The results showed that the precision for the four target elements were between 2.04% and 4.51%. Table 4 Precisions of four elements. (n=) Average RSD/% Three copies of the above hot-melt adhesive were prepared, and then spiked with the mixed standard solution of the same concentration approximately with the target element original contents. The spiked samples were prepared and determined. The mean values of recoveries were listed in Table 5. The results showed that recoveries for the four target elements spiked with mixed standard solution were between 95.2% and 118.1% Uncertainty Table 5 Recoveries for spiked samples. Original content/ Spike level/ Mean value/ Recovery/ % The uncertainty for the method was evaluated in the following four aspects, including the sample preparation (u 1), the standard solution preparation (u 2), the calibration curve fitting(u ) and the repeatability (u 4) [1,1-19]. The uncertainty values of four aspects were listed in Table. The results showed that the calibration curve fitting was the most important factor affecting the combined uncertainty (especially for low concentration of elements, it was less likely to get accurate results for low concentration elements compared with the high concentration) [1], the second was the standard solution preparation, the third was the repeatability, and the last was the sample preparation. 5 0 Table Uncertainty results of four elements. u Sample analysis u 2 u u The eight hot-melt adhesives for cigarette samples were determined with the developed method. The contents of the four target elements were listed in Table 7. The results showed that: 1) The contents of the four target elements were in the order of >>> (Fig. 1). 2) The content differences of and in the Table 7 Contents of,, and in eight hot-melt adhesive samples Average Variation coefficients /% means to be less than LOQs.

5 Vol. 48 Suppl. No. 1 QIN Cunyong,et al:simultaneous determination of chromium, nickel, arsenic and lead in hot-melt adhesives for cigarette by inductively coupled plasma mass spectrometry Fig. 1 different hot-melt adhesives were obvious, and the variation coefficients of which were 8.% and 81.8%, respectively. Conclusions An analytical method of simultaneous determination of four heavy metal elements(,, and ) in hot-melt adhesives for cigarette was developed by ICP-MS with microwave digestion after pre-reaction. 1) The developed method was accurate, simple, rapid, reliable, and suitable for the simultaneous determination of these heavy metal elements in the batch. 2) The uncertainty for the method was attributed to four factors, with descending order of contributions, the calibration curve fitting, the standard solution preparation, the repeatability, and lastly the sample preparation. ) Eight hot-melt adhesives for cigarette were analyzed using this method. The levels of the four target elements in the hot-melt adhesives were in the order of >>>. The variations of and levels in the different hot-melt adhesives were notable. References The content trend of the four target elements in the hot-melt adhesives. [1] GUO Jing, XIANG Hengxue, WANG Qianqian, et al. Research progress of hot-melt adhesives[j]. China Adhesives, 2010, 19(7): [2] YC/T Hot-melt adhesive for cigarette[s]. [] GB/T General method for the determination of arsenic content in chemical products[s]. [4] GB/T General method for the determination of heavy metal content in orgnic chemical products-visual method[s]. [5] XU Aifei, HUANG Taisong, LI Xiaolan, et al. A method for determination of arsenic content in hot-melt adhesive: China, A[P] [] SHI Jie, LI Li, HU Qingyuan, et al. Advance in determination of trace elements and heavy metals in tobacco[j]. Tobacco Science & Technology, 200(2): [7] SUO Weiguo, HU Qingyuan, CHEN Zaigen, et al. Determination of,, Cu, and in cigarette filter tow by ICP-MS[J]. Tobacco Science & Technology, 2007 (): [8] LI Li, DAI Ya, HU Qingyuan, et al. Analysis of Li,,, Cu,, Se, Mo, Cd, Tl and in cigarettes and cigars[j]. Tobacco Science & Technology, 2010(4): 5-9, 4. [9] XU Zigang, YAO Qi, LIN Shaomei. Determination of rare earth elements in tea by inductively coupled plasma mass spectrometry with microwave digestion [J]. Journal of Zhejiang University (Science Edition), 2007, 4 (2): [10] SHI Jie, LI Li, HU Qingyuan, et al. Simultaneous determination of,,, Se, Cd, Hg and [J]. Tobacco Science & Technology, 200(12): 29-4, 7. [11] Wagner K A, McDaniel R, Self D. Collection and preparation of sidestream cigarette smoke for trace elemental determinations by graphite furnace atomic absorption spectrometry and inductively coupled plasma mass spectrometry[j]. Journal of AOAC International, 2001, 84(): [12] ZHANG Xiaojing, ZHU Fengpeng, HU Qingyuan, et al. Determination of lead isotope ratios of tobacco by ICP-MS and their areal difference[j]. Tobacco Science & Technology, 2009(4): 41-45,57. [1] WANG Xinmei, WANG Ke, JI Shen. Evaluation of uncertainty for the determination of Cu,, Cd, Hg, in TCM by ICP-MS[J]. Qilu Pharmaceutical Affairs, 2012, 1(): [14] LI Li. The research on determination of trace elements and heavy metals in tobacco[d]. Zhengzhou: Zhengzhou University, [15] Torrence K M, McDaniel R L, Self D A, et al. Slurry sampling for the determination of arsenic, cadmium and lead in mainstream cigarette smoke condensate by graphite furnace-atomic absorption spectrometry and inductively coupled plasma-mass spectrometry[j]. Analytical and Bioanalytical Chemistry, 2002, 72(2): [1] JJF Evaluation and expression of uncertainty in measurement[s]. [17] JJF Tobacco and tobacco Products Evaluation of uncertainty in measurement for routine chemical ingredients using continuous flow method Part 1: Water soluble sugars[s]. [18] JJG Working glass container[s]. [19] HUANG Huizhen, JIANG Jinfeng, LIANG Hui, et al. Uncertainty in determination of butyl acetate in tipping paper by headspace gas chromatography [J]. Tobacco Science & Technology, 2014, 25(8): 8-41.