Method for the determination of polonium-210 in tea samples using response surface methodology (RSM)

Method for the determination of polonium-210 in tea samples using response surface methodology (RSM) 1 corresp first-author Corresponding author: e-mail addresses: sermin.cam@cbu.edu.tr Corresponding author: e-mail addresses: sermin.cam@cbu.edu.tr sermin.cam@cbu.edu.tr 2 Physics Department, Faculty of Science and Letters, Manisa Celal Bayar University, 45140, Manisa, Turkey Physics Department, Faculty of Science and Letters, Manisa Celal Bayar University, 45140, Manisa, Turkey Science Education, Faculty of Education, Manisa Celal Bayar University, Manisa, Turkey Science Education, Faculty of Education, Manisa Celal Bayar University, Manisa, Turkey The method based on solvent parameters (mass, cycle of acidification, and autodeposition time), combined with response surface method (RSM) modelling and optimization, has been developed for maximizing 210 Po activity in tea samples, as observed by an alpha spectrometer. RSM based on 3-factor and 5-level composite center design (CCD) was used to obtain the optimal combination of solvent conditions. As solvent parameters for 210 Po activity, different masses (0.5, 0.75, 1, 1.5, and 2 g), different cycles of acidification (2, 3, 4, 5, and 6 times), and different autodeposition times (2, 3, 4, 5, and 6 h) were studied. The 3D response surface plot and the contour plot derived from the mathematical models were used to determine the optimal conditions. According to the obtained results, the experimental value of 210 Po activity was in good agreement ( R 2 = 0.96) with the value predicted by the model. We found a favorable effect of mass on the 210 Po activity ( p < 0.05). 210 Po activity Tea Response surface methodology. 1 Introduction 1 Environmental radiation arises from various naturally occurring and man-made sources [ 1 1 ]. The largest contribution to radiation exposure comes from natural sources (approximately ~86%), while man-made sources contribute only ~14%. Doses from other man-made or artificial sources account for less than 1% [ 2 2 - 3 3 2-3 ]. Among natural radionuclides, 210 Po ( T 1/2 , 138.4 d) from the 238 U series, is significant due to its potential internal human radiation exposure. It is an alpha emitter with high linear energy transfer and exists in trace amounts in most plants and foodstuffs [ 4 4 - 5 5 4-5 ]. It is among the most radiotoxic nuclides to humans [ 4 4 ], and may be a cause of lung cancer [ 6 6 ]. Tea is one of the most widely consumed beverages in the world. It is consumed daily by many countries and is prepared from the Camellia sinensis leaves. Tea leaves are usually characterized by the increased contents radionuclide contaminants like 210 Pb, 210 Bi, and 210 Ро [ 7 7 ] because of the deposition of aerosols containing these radionuclides on tea leaves. There have been several studies related to radionuclides on various teas [ 2 2 , 7 7 - 13 13 7-13 ]. Determination of the activity concentrations of radionuclides (primarily 210 Po) in tea remains important; therefore, we chose to determine 210 Po in tea samples. This study was aimed to determine the optimum solvent parameters for the activity of 210 Po in tea samples using response surface methodology (RSM). The mass of the sample, cycle of acidification, and autodeposition time were analyzed using a central composed design (CCD). 2 Material and Method 1 2.1 Experimental Process 2 Tea samples were dried to constant weight at room temperature. Different masses (0.5, 0.75, 1, 1.5, and 2 g) were weighed and added to a 250 mL beaker. The concentrated acids (3 mL 65% HNO 3 + 5 mL 35% H 2 O 2 ) were added to the sample and the beaker was covered with a watch glass and allowed to stand overnight at room temperature. Then, the solution was heated on a hotplate at 95 °C and evaporated to near dryness. Then, mixed acids (3 mL HNO 3 and 9 mL 37% HCl) were added to the precipitate followed by re-heating on the hotplate (at 95 °C) and evaporation to near dryness. The acidification process was repeted 2-6 times. After evaporation, 200 mL of 0.5 M HCl was added to the precipitate, and filtered through a filter paper (particle retention 10–15 µm, 125 mm diameter, 84 g m -2 weight) into a 250 mL beaker. Ascorbic acid (0.5 g) was added to the beaker to reduce Fe 3+ concentration. Copper disks of diameter 2.5 cm were cut from a copper plate. They were first wiped with acetone and then left in 1 M HNO 3 for 1-2 m, washed with pure water, and dried at room temperature. The dried copper discs were placed inside a bottle cap with the front face cut out and were compressed with a magnetic bar to prevent it from falling. The prepared copper disks were placed in a 200 mL sample solution so that the magnetic bar portion was below. The autodeposition process was performed on a hotplate. 210 Po was spontaneously accumulated on the copper disc at the 70 °C ( Fig. 1 Fig. 1 ). The activity of 210 Po was determined by using an alpha spectrometer equipped with A450-20AM PIPS detector. The energy resolution was ≤ 20 keV, the detector efficiency was ≥ 25%, and the background was ≤ 1 count per hour above 3 MeV. System calibration was done by using a 241 Am point source. The 210 Po activity concentration of the samples collected onto the copper disc was counted by using the alpha spectrometer based on the alpha particle emission peak with 5.30 MeV energy, and 209 Po as the internal tracer. The 210 Po activity concentration was calculated at different autodeposition times on the copper disc. The chemical efficiency was 37.7% for 209 Po. The 210 Po activity concentration for each sample was corrected for the recovery using the total efficiency. 2.2 Response Surface Methodology (RSM) 2 RSM is an effective method to solve multivariable problems and provides optimization of many dependent variables in various experiments. It involves mathematical and statistical techniques used to determine the optimum operating conditions in a given system or to determine how it is affected by the independent variables of one or more dependent variables in a region of interest [ 14 14 - 17 17 14-17 ]. Independent variables (X 1 : sample mass, X 2 : cycle of acidification, and X 3 : autodeposition time) were examined on five levels. These variables and their coded levels of CCD design are given in Table 1 Table 1 . 1 1 Factors 1 1 Factor code 5 1 Range and levels (coded) 1 1 1 1 1 1 -1.6818 1 1 -1 1 1 0 1 1 1 1 1 1.6818 1 1 Mass (g) 1 1 X 1 1 1 0.5 1 1 0.75 1 1 1 1 1 1.5 1 1 2 1 1 Cycle of acidification (times) 1 1 X 2 1 1 2 1 1 3 1 1 4 1 1 5 1 1 6 1 1 Autodeposition time (h) 1 1 X 3 1 1 2 1 1 3 1 1 4 1 1 5 1 1 6 The regression model equation was given as follows; <math display="block" id="M1"><mrow><mi>Y</mi><mo>=</mo><msub><mi>b</mi><mn>0</mn></msub><mo>+</mo><mstyle displaystyle="true"><munderover><mo>∑</mo><mrow><mi>i</mi><mo>=</mo><mn>1</mn></mrow><mn>2</mn></munderover><mrow><msub><mi>b</mi><mi>i</mi></msub><msub><mi>x</mi><mi>i</mi></msub><mo>+</mo><mstyle displaystyle="true"><munderover><mo>∑</mo><mrow><mi>i</mi><mo>=</mo><mn>1</mn></mrow><mn>2</mn></munderover><mrow><msub><mi>b</mi><mrow><mi>i</mi><mi>i</mi></mrow></msub><msubsup><mi>x</mi><mi>i</mi><mn>2</mn></msubsup></mrow></mstyle></mrow></mstyle><mo>+</mo><munderover><mstyle mathsize="140%" displaystyle="true"><mo>∑</mo></mstyle><mrow><mi>i</mi><mo>=</mo><mn>1</mn></mrow><mn>1</mn></munderover><munderover><mstyle mathsize="140%" displaystyle="true"><mo>∑</mo></mstyle><mrow><mi>j</mi><mo>=</mo><mi>i</mi><mo>+</mo><mn>1</mn></mrow><mn>2</mn></munderover><msub><mi>b</mi><mrow><mi>i</mi><mi>i</mi></mrow></msub><msub><mi>x</mi><mi>i</mi></msub><msub><mi>x</mi><mi>j</mi></msub><mo>+</mo><mi>ε</mi><mo>,</mo></mrow></math> where Y is the response, b 0 is the intercept, b ij , b ii, and b i are the coefficients, n is the number of variables, x i and x j are the independent variables, and ε is the error. The optimum data of the chosen variable were found using RSM plots and the regression equation. The correlation coefficient ( R 2 ) was found to be high (0.96). The significance of the RSM model was evaluated for the probability value (Prob > F ) and F-value. For this calculation, the second-order polynomial equation was as follows: <math display="block" id="M2"><mrow><mi>Y</mi><mo>=</mo><msub><mi>b</mi><mn>0</mn></msub><mo>+</mo><msub><mi>b</mi><mn>1</mn></msub><msub><mi>X</mi><mn>1</mn></msub><mo>+</mo><msub><mi>b</mi><mn>2</mn></msub><msub><mi>X</mi><mn>2</mn></msub><mo>+</mo><msub><mi>b</mi><mn>3</mn></msub><msub><mi>X</mi><mn>3</mn></msub><mo>=</mo><msub><mi>b</mi><mrow><mn>11</mn></mrow></msub><msubsup><mi>X</mi><mn>1</mn><mn>2</mn></msubsup><mo>+</mo><msub><mi>b</mi><mrow><mn>22</mn></mrow></msub><msubsup><mi>X</mi><mn>2</mn><mn>2</mn></msubsup><mo>+</mo><msub><mi>b</mi><mrow><mn>33</mn></mrow></msub><msubsup><mi>X</mi><mn>3</mn><mn>2</mn></msubsup><mo>+</mo><msub><mi>b</mi><mrow><mn>12</mn></mrow></msub><msub><mi>X</mi><mn>1</mn></msub><msub><mi>X</mi><mn>2</mn></msub><mo>+</mo><msub><mi>b</mi><mrow><mn>13</mn></mrow></msub><msub><mi>X</mi><mn>1</mn></msub><msub><mi>X</mi><mn>3</mn></msub><mo>+</mo><msub><mi>b</mi><mrow><mn>23</mn></mrow></msub><msub><mi>X</mi><mn>2</mn></msub><msub><mi>X</mi><mn>3</mn></msub></mrow></math> The experiments were performed under optimum conditions obtained by RSM ( Table 2 Table 2 ). Initial studies were conducted to determine to the required mass (X 1 : 0.5, 0.75, 1, 1.5, and 2 g), the cycle of acidification (X2: 2, 3, 4, 5 and 6 times), and autodeposition time (X 3 : 2, 3, 4, 5, and 6 h). The total design consisted of 20 experimental points. The matrix of the design is listed in Table 2 Table 2 , and six replicates (runs 15-20) were performed at the center of the design. 1 1 Runorder 1 1 X 1 1 1 X 2 1 1 X 3 1 1 Mass (g) 1 1 Cycleofacidification ( HNO 3 :HCl,3:9) 1 1 Autodepositiontime(h) 2 1 210 Poactivity(Bq) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Experimental 1 1 Predicted 1 1 1 1 1 -1 1 1 -1 1 1 -1 1 1 0.75 1 1 3 1 1 3 1 1 0.049 1 1 0.049 1 1 2 1 1 -1 1 1 -1 1 1 1 1 1 0.75 1 1 3 1 1 5 1 1 0.042 1 1 0.038 1 1 3 1 1 -1 1 1 1 1 1 -1 1 1 0.75 1 1 5 1 1 3 1 1 0.050 1 1 0.042 1 1 4 1 1 -1 1 1 1 1 1 1 1 1 0.75 1 1 5 1 1 5 1 1 0.043 1 1 0.044 1 1 5 1 1 1 1 1 -1 1 1 -1 1 1 1.5 1 1 3 1 1 3 1 1 0.103 1 1 0.100 1 1 6 1 1 1 1 1 -1 1 1 1 1 1 1.5 1 1 3 1 1 5 1 1 0.088 1 1 0.095 1 1 7 1 1 1 1 1 1 1 1 -1 1 1 1.5 1 1 5 1 1 3 1 1 0.089 1 1 0.091 1 1 8 1 1 1 1 1 1 1 1 1 1 1 1.5 1 1 5 1 1 5 1 1 0.100 1 1 0.099 1 1 9 1 1 -1.6818 1 1 0 1 1 0 1 1 0.5 1 1 4 1 1 4 1 1 0.026 1 1 0.032 1 1 10 1 1 1.6818 1 1 0 1 1 0 1 1 2 1 1 4 1 1 4 1 1 0.126 1 1 0.122 1 1 11 1 1 0 1 1 -1.6818 1 1 0 1 1 1 1 1 2 1 1 4 1 1 0.071 1 1 0.070 1 1 12 1 1 0 1 1 1.6818 1 1 0 1 1 1 1 1 6 1 1 4 1 1 0.065 1 1 0.068 1 1 13 1 1 0 1 1 0 1 1 -1.6818 1 1 1 1 1 4 1 1 2 1 1 0.060 1 1 0.065 1 1 14 1 1 0 1 1 0 1 1 1.6818 1 1 1 1 1 4 1 1 6 1 1 0.066 1 1 0.063 1 1 15 1 1 0 1 1 0 1 1 0 1 1 1 1 1 4 1 1 4 1 1 0.072 1 1 0.069 1 1 16 1 1 0 1 1 0 1 1 0 1 1 1 1 1 4 1 1 4 1 1 0.076 1 1 0.069 1 1 17 1 1 0 1 1 0 1 1 0 1 1 1 1 1 4 1 1 4 1 1 0.06 1 1 0.069 1 1 18 1 1 0 1 1 0 1 1 0 1 1 1 1 1 4 1 1 4 1 1 0.069 1 1 0.069 1 1 19 1 1 0 1 1 0 1 1 0 1 1 1 1 1 4 1 1 4 1 1 0.069 1 1 0.069 1 1 20 1 1 0 1 1 0 1 1 0 1 1 1 1 1 4 1 1 4 1 1 0.069 1 1 0.069 Excel and Minitab 17 were used for graphical analysis and regression analysis of the acquired data. Analysis of variance (ANOVA) was done to obtain the probability and F-value. In addition, the statistical parameters were calculated with RSM, the optimum values were found from the regression equation and the RSM surface/counter plots. 3 Result and discussion 1 The second-order polynomial equation was obtained by CCD design for elucidating the relationship between the 210 Po activity and the three independent variables. According to the obtained results, quadratic model equality, giving the activity of 210 Po, was as follows: <math display="block" id="M3"><mtable columnalign="left"><mtr><mtd><mi>Y</mi><mo>=</mo><mn>0.069</mn><mo>+</mo><mn>0.027</mn><mtext>Mass(g)</mtext></mtd></mtr><mtr><mtd><mtext>-0</mtext><mtext>.0007 Cycle of acidification</mtext></mtd></mtr><mtr><mtd><mtext>-0</mtext><mtext>.0006 Autodeposition time (h)</mtext></mtd></mtr><mtr><mtd><mtext>+0</mtext><mtext>.003 Mass (g) </mtext><mo>×</mo><mtext>Mass (g)</mtext></mtd></mtr><mtr><mtd><mtext>-0</mtext><mtext>.00094 Cycle of acidification</mtext></mtd></mtr><mtr><mtd><mo>×</mo><mtext>Cycle of acidification</mtext></mtd></mtr><mtr><mtd><mtext>-0</mtext><mtext>.002 Autodeposition time (h)</mtext></mtd></mtr><mtr><mtd><mo>×</mo><mtext>Autodeposition time (h) - 0</mtext><mtext>.0005 Mass (g)</mtext></mtd></mtr><mtr><mtd><mo>×</mo><mtext>Cycle of acidification + 0</mtext><mtext>.0013 Mass (g)</mtext></mtd></mtr><mtr><mtd><mo>×</mo><mtext>Autodeposition time (h)</mtext></mtd></mtr><mtr><mtd><mtext>+0</mtext><mtext>.0033 Cycle of acidification</mtext></mtd></mtr><mtr><mtd><mo>×</mo><mtext>Autodeposition time (h)</mtext><mtext>.</mtext></mtd></mtr></mtable></math> The synergistic and antagonistic influences were described with positive and negative parameters, respectively. For obtaining the statistical explanation of the above equation with t-test, second-order variance analysis of the response surface (ANOVA) was performed ( Table 3 Table 3 ). Since the obtained F-value was 28.79688, the experimental yields obtained by changing the factor levels were statistically meaningful at the 95% confidence limit. According to the results, the model was compatible where smaller the p-values ( < 0.0001) indicated that the model was significant. R 2 of the second-order model calculated for the 210 Po activity (Bq) was very close to 1 (0.96), implying that the experimental data agreed with the values predicted by the model. The adjusted determination coefficient (Adj. R 2 = 0.93) was also close to 1. Multiple R 2 = 0.96 Adjusted R 2 = 0.93 1 1 ANOVA 1 1 Df 1 1 SS 1 1 MS 1 1 F 1 1 Probability F 1 1 Regression 1 1 9 1 1 0.009996828 1 1 0.001111 1 1 28.79688 1 1 0.00000542 1 1 Residual 1 1 10 1 1 0.000385722 1 1 0.0000386 1 1   1 1   1 1 Total 1 1 19 1 1 0.01038255 1 1   1 1   1 1   The significance of each coefficient is given in Table 4 Table 4 , with an F -value and a p -value. The larger the F -values and the smaller the p-values, the more significant are the corresponding coefficients. The regression was statistically significant at p -values less than 0.05 and 0.01, as shown in Table 4 Table 4 . Thus, 210 Po activity was affected significantly by the parameters (X 1 , X 1 X 1, X 1 X 3, and X 2 X 3 ( p < 0.05); the quadratic parameters (X 2 , X 11 , X 22, and X 12 ) were insignificant (p > 0.05). *: Significant (p < 0.05) 1 1 Regression 1 1 Coefficients 1 1 Standard error 1 1 F 1 1 p 1 1 Intercept 1 1 0.069118 1 1 0.002533004 1 1 27.28693 1 1 1.01 E-10* 1 1 X 1 1 1 0.026666 1 1 0.001680587 1 1 15.86729 1 1 2.03 E-08* 1 1 X 2 1 1 -0.00074 1 1 0.001680587 1 1 -0.43966 1 1 0.669536 1 1 X 3 1 1 -0.00058 1 1 0.001680587 1 1 -0.3446 1 1 0.73753 1 1 X 1 X 1 1 1 0.002735 1 1 0.001635999 1 1 1.671513 1 1 0.125571 1 1 X 2 X 2 1 1 -0.000094 1 1 0.001635999 1 1 -0.05734 1 1 0.955403 1 1 X 3 X 3 1 1 -0.00186 1 1 0.001635999 1 1 -1.13788 1 1 0.2817 1 1 X 1 X 2 1 1 -0.0005 1 1 0.002195797 1 1 -0.22771 1 1 0.824462 1 1 X 1 X 3 1 1 0.00125 1 1 0.002195797 1 1 0.569269 1 1 0.581734 1 1 X 2 X 3 1 1 0.00325 1 1 0.002195797 1 1 1.480101 1 1 0.169648 The plot of the predicted activity against the experimental 210 Po activity is given in Fig 2 Fig 2 . The experimental activity values were distributed close to the straight line. This showed that the predicted values of the model were in good agreement with the experimental values. This is an evidence of the validity of the regression model. The regression coefficient calculated for the model was R 2 = 0.96 and it showed the agreement of the values obtained from the model with real values. 210 Po activity values obtained in this study for different cycles of acidification and different masses were positive. Interaction plots for 210 Po activity are given in Fig. 3 Fig. 3 and Fig 4 Fig 4 . 210 Po activity (Bq) is increasing upon increasing the sample mass from 0.5 g to 2 g in Fig. 3 (c,d) Fig. 3 (c,d) and Fig 4 Fig 4 . With variations in sample mass, cycle of acidification, and autodeposition time, 210 Po activity changed as follows: 210 Po activity increased with increasing sample mass ( Fig. 3 (c, e) Fig. 3 (c, e) ) and remained constant for different cycles of acidification and autodeposition times ( Fig. 3 (a, b) Fig. 3 (a, b) ). Fig. 3 (d) Fig. 3 (d) shows that with increasing autodeposition time, the 210 Po activity decreased for 2 cycles of acidification (blue line), remined unchanged for 4 cycles of acidification (red line), and increased for 6 cycles of acidification (green line). In Fig. 3 (d, f) Fig. 3 (d, f) , the point of intersection of the lines for cycle of acidification and autodeposition time is 4. In other words, 4 cycles of acidification and 4 h of autodeposition time were found to be optimal for the activity. The combined effect of cycle of acidification and autodeposition time (h) is shown in Fig. 5 Fig. 5 . The maximum activity of 210 Po was determined to be 0.87 Bq at a sample mass of 1.25 g. Contour color map graphs of 210 Po activity ( Fig. 6 Fig. 6 ) showed the effects of the interactions between mass (X 1 ) and cycle of acidification (X 2 ) as well as that between mass (X 1 ) and autodeposition time (X 3 ) on the 210 Po activity. An increase in mass from 0.5 g to 2 g improved the activity yield. In addition, increasing the cycle of acidification and autodeposition time leads to a reduction in 210 Po activity. When more than 4 cycles of acidification were performed and the autodeposition time was more than 4 h, there was a reduction in activity. The maximum activity was obtained for 4 cycles of acidification and autodeposition time of 4 h. Thus, for the maximum activity result of the tea samples, optimal conditions were as follows: 1 g of the sample mass, 4 cycles of acidification, and 4 h of autodeposition time. 4 Conclusion 1 In this study, RSM was used to model and optimize the conditions for maximum 210 Po activity in tea samples. The effect of three independent variables (sample mass, cycle of acidification, and autodeposition time) on 210 Po activity was obtained by using RSM surface plot and contour plots. The optimal conditions for maximum 210 Po activity in tea samples were as follows: sample mass of 1 g, 4 cycles of acidification and autodeposition time of 4 h. The experimental activity values and the predicted activity values of 210 Po agree with each other. In brief, this study provides a new efficient method for determination of 210 Po activity in tea sample. References F.K. Görür , R. Keser , N. Akçay , et al ., Annual effective dose and concentration levels of gross α and β in Turkish market tea . Int. J. Radiat. Res . 10 , 67 - 72 , ( 2012 ). Annual effective dose and concentration levels of gross α and β in Turkish market tea M.G. Shooshtari , M.R. Deevband , M.R. Kardan , et al ., Analytical study of Ra-226 activity concentration in market consuming foodstuffs of Ramsar , Iran. J. Environ Health Sci. Eng . 15 , 1 - 7 , ( 2017 ). doi: 10.1186/s40201-017-0281-3 http://doi.org/10.1186/s40201-017-0281-3 Analytical study of Ra-226 activity concentration in market consuming foodstuffs of Ramsar EPA, Environmental Protection Agengy , ( 2018 ). http://www.epa.ie/radiation/radexp http://www.epa.ie/radiation/radexp . Accessed 16.02.2018 . A.E.M. Khater , Polonium-210 budget in cigarettes . J. Environ. Radioact . 71 , 33 - 41 , ( 2004 ). doi: 10.1016/S0265-931X(03)00118-8 http://doi.org/10.1016/S0265-931X(03)00118-8 Polonium-210 budget in cigarettes N.S. Fisher , K.B. Seiller , T.G. Hinton , et al ., Evaluation of radiation doses and associated risk from the Fukushima nuclear accident to marine biota and human consumers of seafood . Proceedings of the National Academy of Sciences of the United States of America , 110 , 10670 - 10675 , ( 2013 ). doi: 10.1073/pnas.1221834110 http://doi.org/10.1073/pnas.1221834110 Evaluation of radiation doses and associated risk from the Fukushima nuclear accident to marine biota and human consumers of seafood M. Horvath , A. Shahrokhi , P. Bator , et al ., Determination of Po-210 content in cigarette smoke using a smoking machine: A case study of Iranian cigarettes . J. Environ. Radioact ., 174 , 66 - 70 , ( 2017 ). doi: 10.1016/j.jenvrad.2017.01.023 http://doi.org/10.1016/j.jenvrad.2017.01.023 Determination of Po-210 content in cigarette smoke using a smoking machine: A case study of Iranian cigarettes E.V. Puchkovaа , O.G. Bogdanova , 210Ро in Black and Green Teas . Radiochemistry , 58 , 98 - 105 , ( 2016 ). 210Ро in Black and Green Teas M.S. Al-Masri , A. Nashawati , Y. Amin , et al ., Determination of 210Po in tea, mate and their infusions and its annual intake by Syrians . J. Radioanal. Nucl. Chem . 260 , 27 - 34 , ( 2004 ). Determination of 210Po in tea, mate and their infusions and its annual intake by Syrians F.K. Görür , R. Keser , N. Akçay , et al ., Radionuclides and heavy metals concentrations in Turkish market tea . Food Control , 22 , 2065 - 2070 , ( 2011 ). doi: 10.1016/j.foodcont.2011.06.005 http://doi.org/10.1016/j.foodcont.2011.06.005 Radionuclides and heavy metals concentrations in Turkish market tea D. Desideri , M.A. Meli , C. Roselli , et al ., Alpha and gamma spectrometry for determination of natural and artificial radionuclides in tea, herbal tea and camomile marketed in Italy . Microchem. J . 98 , 170 - 175 , ( 2011 ). doi: 10.1016/j.microc.2011.01.005 http://doi.org/10.1016/j.microc.2011.01.005 Alpha and gamma spectrometry for determination of natural and artificial radionuclides in tea, herbal tea and camomile marketed in Italy D.E. Di Gregorio , H. Huck , R. Aaristegui , et al ., 137Cs contamination in tea and yerba mate in South America . J. Environ. Radioact . 76 , 273 - 281 , ( 2004 ). doi: 10.1016/j.jenvrad.2003.11.008 http://doi.org/10.1016/j.jenvrad.2003.11.008 137Cs contamination in tea and yerba mate in South America M.C. Cook , M.J. Stukel , W. Zhang , et al ., The determination of Fukushima-derived cesium-134 and cesium-137 in Japanese green tea samples and their distribution subsequent to simulated beverage preparation . J. Environ. Radioact . 153 , 23 - 30 , ( 2016 ). doi: 10.1016/j.jenvrad.2015.12.010 http://doi.org/10.1016/j.jenvrad.2015.12.010 The determination of Fukushima-derived cesium-134 and cesium-137 in Japanese green tea samples and their distribution subsequent to simulated beverage preparation N. Fathabadi , A.A. Salehi , K. Naddafi , et al ., Radioactivity levels in the mostly local foodstuff consumed by residents of the high level natural radiation areas of Ramsar , Iran. J. Environ. Radioact . 169-170 , 209 - 213 , ( 2017 ). doi: 10.1016/j.jenvrad.2016.12.011 http://doi.org/10.1016/j.jenvrad.2016.12.011 Radioactivity levels in the mostly local foodstuff consumed by residents of the high level natural radiation areas of Ramsar S.F. Mutlu , İki basamaklı tepkime ile sıvı özütlemeli yöntem kullanarak fındık tohum kabuklarından furfural üretimi için en uygun koşulların istatistik yöntem ile belirlenmesi . Journal of the Faculty of Engineering and Architecture of Gazi University , 25 , 21 - 26 , ( 2010 ). (in Turkish) . İki basamaklı tepkime ile sıvı özütlemeli yöntem kullanarak fındık tohum kabuklarından furfural üretimi için en uygun koşulların istatistik yöntem ile belirlenmesi L.C. Zhao , Y. He , X. Deng , et al ., Response Surface Modeling and Optimization of Accelerated Solvent Extraction of Four Lignans from Fructus Schisandrae . Molecules , 17 , 3618 - 3629 , ( 2012 ). doi: 10.3390/molecules17043618 http://doi.org/10.3390/molecules17043618 Response Surface Modeling and Optimization of Accelerated Solvent Extraction of Four Lignans from Fructus Schisandrae S. Sharma , A. Malik , S. Satya , Application of response surface methodology (RSM) for optimization of nutrient supplementation for Cr (VI) removal by Aspergillus lentulus AML05 . J. Hazard. Mater . 164 , 1198 , ( 2009 ). doi: 10.1016/j.jhazmat.2008.09.030 http://doi.org/10.1016/j.jhazmat.2008.09.030 Application of response surface methodology (RSM) for optimization of nutrient supplementation for Cr (VI) removal by Aspergillus lentulus AML05 A. Dean , D. Voss , D.D. Draguljic , Response Surface Methodology, Design and Analysis of Experiments ( Springer , USA ,), ( 2017 ). ISBN 978-3-319-52250-0 . Response Surface Methodology, Design and Analysis of Experiments 10.1007/s41365-019-0567-5 2018-05-24 2018-07-13 2018-07-20 2019-02-13 2019-03-01 2021-04-10 © China Science Publishing & Media Ltd. (Science Press), Shanghai Institute of Applied Physics, the Chinese Academy of Sciences, ChineseNuclear Society and Springer Nature Singapore Pte Ltd. 2019 This is a post-peer-review, pre-copyedit version of an article published in Nuclear Science and Techniques. The final authenticated version is available online at: http://dx.doi.org/10.1007/s41365-019-0567-5 http://dx.doi.org/10.1007/s41365-019-0567-5 . 2019 Nuclear Science and Techniques 03 30