TY - JOUR
AU1 - Bakircioglu Kurtulus,, Yasemin
AU2 - Bakircioglu,, Dilek
AU3 - Babac, Alper, Can
AU4 - Yurtsever,, Selcuk
AU5 - Topraksever,, Nukte
AB - Abstract Background The emulsion induced by emulsion breaking (EIEB) procedure was previously reported for the extraction of copper, iron, manganese, and nickel from liquid oil samples such as vegetable oil. Objective To optimize the EIEB procedure for determination of copper, iron, manganese, and nickel in solid oil (margarine) samples by Graphite Furnace Atomic Absorption Spectrometry (GFAAS). Methods The extraction procedure uses a surfactant in nitric acid to form an emulsion followed by heating to break the emulsion. Optimization included variation of the test portion size, the type and concentration of the surfactant, the concentration of nitric acid in the aqueous solution, the emulsion agitation time, heating temperature, and the time required to break the emulsion. Results Mean element concentrations of 11 margarine samples were in the following ranges: Cu 0.031–0.131 µg/g, Fe 5.7–24.9 µg/g, Mn 0.542–1.11 µg/g, and Ni 0.108–0.134 µg/g. Under the optimized extraction conditions, the detection limits (µg/kg) were 4.8, 13, 1.5, and 23 for Cu, Fe, Mn, and Ni, respectively. The accuracy of the extraction procedure was determined by comparison to commonly used microwave digestion procedure. The EIEB results were not statistically different from the microwave digestion results when analyzed by GFAAS as determined by the statistical tests. Conclusions The EIEB procedure was shown to be equivalent to the commonly used microwave digestion procedure for extraction of analytes from margarine samples. Highlights The optimized EIEB extraction procedure is simple, rapid, low cost, and environmentally friendly. It has improved detection limits and allows calibration with aqueous standards. The concentration of trace elements is important for the quality and shelf life of oils and fats. The trace elements in the oils and fats originate from the environment, oil processing, and storage (1). Elements such as Cu, Fe, Zn, Ni, Cr, Mn, and Co can produce peroxides, aldehydes, and ketones that affect the color, taste, and odor of the oil by catalyzing oxidation reactions. As a result, the quality of the oil is negatively affected (1–3). Although elements such as Fe and Cu are important nutrients in the human diet, those such as Ni, Pb, Cd, and As may be harmful for human health if consumed in excessive amounts (3–5). For this reason, health-conscious consumers and food manufacturers have sought reliable and cost-effective methods for determining trace elements in their food products (3–5). Nickel is often used as a catalyst to speed the hydrogenation step during margarine production. This results in saturated and partially unsaturated hydrocarbon products (6–8). Lipophilic nickel salts such as Ni(fatty acid)2 can be formed as a result of the reaction of the nickel catalyst and the oil components (9) and Ni catalyst can be found in the final product (10). The margarines produced in this way may sometimes contain undesirable levels of nickel (9–12). Fast and simple sample preparation methods are needed to determine trace elements in oil-based samples by atomic spectroscopic techniques such as ICP-AES and ICP-MS. Trace element concentration is typically low in these samples. Moreover, the high viscosity and high organic content of the oil matrix increases the possibility of interference during analysis (1, 3, 4). Different sample preparation procedures have been developed, such as dry ashing, wet digestion, and microwave digestion in order to extract trace elements from complex oil samples into aqueous solutions (13–22). Dry ashing and wet digestion procedures have been reported to be time-consuming and expensive, which cause contamination with the analytes, loss of volatile element, and hazardous waste during sample preparation (15). These procedures require a large amount of chemicals and energy. The main advantages of microwave digestion are low blanks, efficient digestion of a variety of sample matrices, minimization of analyte losses, temperature-pressure control, safety, sorter digestion time, and minimal contamination (15, 18). That’s why it has gained popularity as a simple and fast dissolution technique that minimizes acid consumption, the risk of sample contamination and the loss of volatile elements. Due to its advantages over other processes mentioned above, microwave digestion is also widely used in the preparation of oil samples in inorganic analysis (18). Nevertheless, the main problem of this procedure is the high dilution applied to samples that degrades detection and quantification limits (1, 4, 23). Other procedures, such as oil-in-water emulsion and dilution with organic solvents (1, 3, 4, 23, 24), have disadvantages including a high limit of detection and a relatively unstable emulsion that increases the probability of contamination and analytical error (1, 4, 23–25). As an alternative to these sample preparation procedures, a new procedure called extraction induced by emulsion breaking (EIEB) has been reported by Cassella et al. (26), Bakircioglu et al. (4, 27, 28), and He et al. (23). This procedure allows the analytes to be separated from a more complex matrix and calibration to be carried out with aqueous solutions. The analytes are preconcentrated in an aqueous phase, which is easier to measure than the original sample. In addition, EIEB avoids the use of large amounts of solvents and acids, and reduces the time required to complete the extraction processes (4, 23, 25, 27, 28). This work describes the optimization of the EIEB procedure for the determination of Cu, Fe, Mn, and Ni in margarine by GFAAS using external calibration with aqueous standard solutions. Finally, the EIEB procedure was compared to the conventional microwave-assisted digestion procedure. Materials Apparatus and Supplies Perkin Elmer Model AAnalyst 800 Atomic Absorption Spectrometer.—With Zeeman-Effect background correction, transversely heated graphite atomizer (THGA) furnace, AS-72/AS-800 autosampler, and WinLab 32 for AA software. Pyrolytic graphite-coated graphite tubes.—Perkin Elmer (Shelton, Ct, USA) Cat. No. B3000641. Closed-vessel microwave digestion system.—CEM MarsXpress (CEM Corporation, Matthews, NC) with a 40-vessel turntable. Vortex mixer.—WiseMix VM-10 (Daihan Scientific Co., Ltd) Water bath.—Wisebath WB-22 temperature-controlled water bath (Daihan Scientific Co., Ltd) capable of maintaining 80 ± 0.5°C. Sample preparation tubes.—15 mL polypropylene with screw caps. Reagents and Materials Purified water.—With resistivity of 18.2 MΩ cm. Concentrated nitric acid (65%).—Merck (Darmstadt, Germany) Cat. No. 100456. Hydrogen peroxide.—Sigma Chemical Co. (St. Louis, MO) Cat. No.7711-84-1 Triton X-114.—Sigma Chemical Co. Cat. No. 9036-1-5 or equivalent. Triton X-100.—Sigma Chemical Co. Cat. No.9002-93-1 or equivalent. Tween 40.—Merck (Darmstadt, Germany) Cat. No. 9005-66-7 or equivalent. Tween 80.—Merck Cat. No. 9005-65-6 or equivalent. Certified standard solution of Cu (1000 mg/L).—Traceable to SRM from NIST Cu(NO3)2 in 0.5 mol/L of HNO3 CertiPUR®, Merck-Millipore. Cat. Nos. 119786. Stock solutions were diluted with 1% HNO3 to give standards of concentration: 0.02, 0.07, 0.11, 0.15, and 0.2 µg/g. Certified standard solution of Fe (1000 mg/L).—Traceable to SRM from NIST Fe(NO3)3 in HNO3 0.5 mol/L CertiPUR®, Merck-Millipore. Cat. Nos. 119786. Stock solutions were diluted with 1% HNO3 to give standards of concentrations: 1.5, 3.0, 6.0, 24.0 µg/g. Certified standard solution of Mn (1000 mg/l).—Traceable to SRM from NIST Mn(NO3)2 in HNO3 0.5 mol/L CertiPUR®, Merck-Millipore. Cat. Nos. 119789. Stock solutions were diluted with 1% HNO3 to give standards of concentrations: 0.1, 0.25, 0.5, 0.75, 1.0 µg/g. Certified standard solution of Ni (1000 mg/l).—Traceable to SRM from NIST Ni(NO3)2 in HNO3 0.5 mol/L CertiPUR®, Merck-Millipore. Cat. Nos. 119792. Stock solutions were diluted with 1% HNO3 to give standards of concentrations: 0.1, 0.15, 0.2, 0.25, 0.3 µg/g. Matrices.—Various margarine brands from supermarkets in Edirne were selected according to similar “Use by” dates. The samples were stored at –18°C until analysis. Prior to experimental use, all margarine samples were melted in an oven at 50°C (29). METHODS Sample Preparation (a) Extraction induced by emulsion breaking (EIEB) procedure.—Extraction of the Cu, Fe, Mn, and Ni from the margarine samples was carried out in two main steps. First, 4 g of melted margarine oil was quantitatively transferred to a 15 mL polypropylene centrifuge tube and mixed with 2 mL of freshly prepared 7% Triton X-114 in 10% HNO3. When the emulsions were formed with the aid of agitation by using a vortex mixer, agitation times were recorded. Immediately after the formation of the emulsions, the tubes were transferred to a water bath at a controlled temperature of 80 ± 0.5°C. The emulsions were kept at this temperature until the phases were separated clearly and the time at which the phase separation began was recorded. Three phases, upper, middle, and lower, were observed. The U phase is an organic phase containing only margarine. The middle phase is an acidic aqueous phase containing the extracted elements. The lower phase is a surfactant-rich phase. The middle phase (approximately 1.5 mL) was collected for the analysis of the metals. Blanks were prepared in the same way, but without adding margarine (4, 26). All experiments were performed in triplicate. (b) Microwave digestion procedure.—Approximately 0.3 g of melted margarine was loaded into the microwave digestion system with 5 mL HNO3 (65%) and 3 mL H2O2 (35%). Digestion conditions were as follows: (i) 65% power (400 W) for 4 min, (ii) 0% power (400 W) for 2 min, (iii) 65% power (400 W) for 4 min, (iv) 80% power (800 W) for 2 min, and (v) 100% power (400 W) for 7 min. The initial and final temperature was 240°C for each step. The time required to dissolve a sample using this technique was approximately 19 min. After digestion, the solutions were diluted to 10 mL with ultrapure water. Blanks were prepared in the same way, but without adding margarine (30). All experiments were performed in triplicate. Analysis (a) Graphite Furnace Atomic Absorption Spectrometry (GFAAS).—Hollow cathode lamps (Perkin Elmer) were used as line sources at 15, 30, 20, and 25 mA with measurement at 324.8, 248.3, 279.5, and 232.0 nm, using a slit width of 0.7, 0.2, 0.2, and 0.2 nm, for Cu, Fe, Mn, and Ni, respectively. Argon was used as purge and protective gas. Pyrolytic graphite-coated graphite tubes were used in all experiments. Peak area mode was employed for analytical signals and the results are the average of at least three replicate measurements. The graphite furnace temperature program for Cu, Fe, Mn, and Ni is provided in Table 1. A 20-µL aliquot of extract or standard solution was injected into the graphite furnace. Calibration graphs were created from the aqueous Cu, Fe, Mn, and Ni standard solutions. Table 1. Temperature program employed in the determination of Cu, Fe, Mn, and Ni in the extracts obtained from the EIEB procedure to margarine samples . Temperature (°C) . . . . . Step . Cu . Fe . Mn . Ni . Ramp time, s . Hold time, s . Argon flow rate, mL/min . Sample volume, μL . Pre-drying 110 110 110 110 1 30 250 20 Drying 130 130 130 130 15 30 250 20 Pyrolysis 1100 1300 1200 1300 10 20 250 20 Atomization 1900 2100 1600 2200 0 5 250 20 Cleaning 2450 2450 2450 2450 1 3 250 20 . Temperature (°C) . . . . . Step . Cu . Fe . Mn . Ni . Ramp time, s . Hold time, s . Argon flow rate, mL/min . Sample volume, μL . Pre-drying 110 110 110 110 1 30 250 20 Drying 130 130 130 130 15 30 250 20 Pyrolysis 1100 1300 1200 1300 10 20 250 20 Atomization 1900 2100 1600 2200 0 5 250 20 Cleaning 2450 2450 2450 2450 1 3 250 20 Open in new tab Table 1. Temperature program employed in the determination of Cu, Fe, Mn, and Ni in the extracts obtained from the EIEB procedure to margarine samples . Temperature (°C) . . . . . Step . Cu . Fe . Mn . Ni . Ramp time, s . Hold time, s . Argon flow rate, mL/min . Sample volume, μL . Pre-drying 110 110 110 110 1 30 250 20 Drying 130 130 130 130 15 30 250 20 Pyrolysis 1100 1300 1200 1300 10 20 250 20 Atomization 1900 2100 1600 2200 0 5 250 20 Cleaning 2450 2450 2450 2450 1 3 250 20 . Temperature (°C) . . . . . Step . Cu . Fe . Mn . Ni . Ramp time, s . Hold time, s . Argon flow rate, mL/min . Sample volume, μL . Pre-drying 110 110 110 110 1 30 250 20 Drying 130 130 130 130 15 30 250 20 Pyrolysis 1100 1300 1200 1300 10 20 250 20 Atomization 1900 2100 1600 2200 0 5 250 20 Cleaning 2450 2450 2450 2450 1 3 250 20 Open in new tab Statistical Analyses The Two-Way ANOVA was used to see whether the means are different among the appropriate groups (EIEB and microwave digestion procedures also means of the margarine samples). The Tukey method (at 0.05 significance level) was used to compare the means of the elements regarding eleven different margarine brands. Results and Discussion The establishment of appropriate conditions for the proposed methodology was carried out by: (i) optimization of the extraction conditions of the EIEB procedure (including test portion size, nature and concentration of the surfactant, concentration of the acid in the aqueous solutions, emulsion agitation time, heating temperature, and time required to break the emulsion) and (ii) comparison of the results of the optimized EIEB procedure with those of a microwave digestion procedure. Optimization of the Extraction Conditions of EIEB Procedure (a) The effect of test portion size on emulsion efficiency.—Test portion size was varied from 2 to 6 g with all other parameters as written in Sample Preparation (a). Optimal signal responses were obtained using 4 g of margarine (Figure 1). Test portions larger than 4 g resulted in reduced Cu, Fe, Mn, and Ni signals and a greater difficulty in obtaining an emulsion. Therefore, a 4-g test portion size was used in the subsequent experiments. Figure 1. Open in new tabDownload slide The effect of test portion size on emulsion efficiency. (Conditions: surfactant Triton X-114, 7% (w/v); HNO3 concentration. 10% (v/v); thermal heating temperature, 80°C ± 0.5 and emulsion agitation time, 5 min) (n = 3). Figure 1. Open in new tabDownload slide The effect of test portion size on emulsion efficiency. (Conditions: surfactant Triton X-114, 7% (w/v); HNO3 concentration. 10% (v/v); thermal heating temperature, 80°C ± 0.5 and emulsion agitation time, 5 min) (n = 3). (b) The nature and concentration of the surfactant.—Four surfactants were evaluated in the EIEB procedure including Triton X-114, Triton X-100, Tween-40, and Tween-80. Figure 2 shows that Triton X-114 most easily dispersed the oil phase and required the shortest time to break after heating. Since Triton X-114 has the smallest hydrophilic–lipophilic balance (HLB) value (12.5) of the surfactants evaluated, it likely resulted in smaller droplets, which are more easily dispersed. Figure 2. Open in new tabDownload slide The effect of the nature and concentration of the surfactant on emulsion efficiency. (Conditions: Sample amount, 4 g; HNO3 concentration, 10% (v/v); thermal heating temperature, 80°C ± 0.5 and emulsion agitation time, 5 min) (n = 3). Figure 2. Open in new tabDownload slide The effect of the nature and concentration of the surfactant on emulsion efficiency. (Conditions: Sample amount, 4 g; HNO3 concentration, 10% (v/v); thermal heating temperature, 80°C ± 0.5 and emulsion agitation time, 5 min) (n = 3). The effect of varying surfactant concentration on the Cu, Fe, Mn, and Ni extraction was also investigated. Triton X-114 concentration was varied from 1% to 9% (w/v) at a constant 10% nitric acid concentration (Figure 3). Overall, maximum signals for the four metals were obtained at a Triton X-114 concentration of 7% (w/v), although varying Triton X-114 concentration had minimal effect on the iron signal. Above 7% (w/v) Triton X-114 the GFAAS signals decreased. With regard to emulsion formation, the interfacial tension between the water and oil phases is reduced as surfactant concentration is increased and emulsions become more stable. However, emulsion swelling is known to occur at high concentrations with the rate of swelling being proportional to the concentration of surfactant (31). In addition, high surfactant concentrations can lead to high noise signals or contamination (32). Hence, in order to maximize the extraction of Cu, Fe, Mn, and Ni as measured by GFAAS and facilitate the formation of the emulsions without increasing background noise or contamination, a concentration of 7% (w/v) Triton X-114 was selected for further experiments. Figure 3. Open in new tabDownload slide The effect of the Triton X-114 concentration on emulsion efficiency. (Conditions: Sample amount, 4 g; surfactant Triton X-114; HNO3 concentration, 10% (v/v); thermal heating temperature, 80°C ± 0.5 and emulsion agitation time, 5 min) (n = 3). Figure 3. Open in new tabDownload slide The effect of the Triton X-114 concentration on emulsion efficiency. (Conditions: Sample amount, 4 g; surfactant Triton X-114; HNO3 concentration, 10% (v/v); thermal heating temperature, 80°C ± 0.5 and emulsion agitation time, 5 min) (n = 3). (c) Concentration of the acid in the aqueous solutions.—To investigate the effect of nitric acid concentration on the extraction efficiency, emulsion solutions containing nitric acid at concentrations ranging from 2% to 20% (v/v) were prepared at a Triton X-114 concentration of 7% (w/v). The emulsion breaking temperature was maintained at 80 ± 0.5°C. As can be seen from Figure 4, extraction efficiency for all the elements studied was found to be maximum with 10% (v/v) nitric acid. In microemulsion studies, an acidic pH in the aqueous phase is desirable. Acidic pH prevents the hydrolysis of metal ions and at the same time converts the organic species, metallic particles, and metal oxide species into inorganic forms. Thus, when using acid to prepare the microemulsion, the analyte signals in the extract are directly correlated with the signals in the aqueous inorganic standards of the analyte. In addition, the acidic emulsion solution does not destroy the organic matrix but facilitates the extraction efficiency of analytes (33). Finally, it was observed that the amount of nitric acid significantly affected the emulsion breaking time at 80 ± 0.5°C. With increasing nitric acid concentration, the ionic strength is increased, which is known to hasten phase separation. Figure 4. Open in new tabDownload slide The effect of the nitric acid concentration on emulsion efficiency. (Conditions: Sample amount. 4 g; surfactant Triton X-114, 7% (w/v); thermal heating temperature, 80°C ± 0.5 and emulsion agitation time, 5 min) (n = 3). Figure 4. Open in new tabDownload slide The effect of the nitric acid concentration on emulsion efficiency. (Conditions: Sample amount. 4 g; surfactant Triton X-114, 7% (w/v); thermal heating temperature, 80°C ± 0.5 and emulsion agitation time, 5 min) (n = 3). (d) Emulsion agitation time.—To determine the optimal emulsion preparation time, 4 g of margarine was mixed with emulsion solution (7% Triton X-114 in 10% HNO3) for 1 to 20 min. At agitation times of less than 5 min, large-sized droplets formed, and breakage was observed due to clusters. In the case of insufficient emulsion time, the formation of large size droplets leads to their coalescence and the breakage increases, which causes the separation of emulsion phases. On the contrary, in long emulsion runs, the breakage increases because of the increase in the number of small-sized droplets per unit volume (31). Therefore, in subsequent experiments, the optimum emulsion agitation time was set to 5 min. (e) Heating temperature.—To test this parameter, heating was studied in the range of 70–10°C. The highest absorbance signal for the analyzed elements was obtained at 80°C. Water-in-oil emulsions can be broken using physical, chemical (addition of chemical reagent), and biological treatments (32, 33). Physical treatments involve thermal treatment (conventional heating, microwave radiation, and freeze-thaw), centrifugation, gravitational settling, pH adjustment, solvent dissolution membrane separation, electrical demulsification, filtration, flotation, and ultrasonic processes. Heat treatment for demulsification was used in this work. Demulsification by heating causes the adsorption of the active substance at the interface to decrease, the viscosity of the organic phase to decrease, and the interface film hardness to decrease, resulting in the separation of the phase of the droplets (32, 33). Comparison of the Optimized EIEB to Microwave Digestion The extraction efficiency and accuracy of the EIEB procedure was evaluated by comparing it with a microwave digestion procedure. For this comparison, Cu, Fe, Mn, and Ni were measured in 11 margarine samples extracted using either the EIEB or the microwave digestion procedure with subsequent analysis by GFAAS. (Table 2). Statistical comparison of the procedures showed no difference for copper, iron (P > 0.05), and nickel (0.05> P > 0.03) but a difference for manganese (P < 0.001). In addition, there was a significant interaction regarding copper (P < 0.001), probably due to sample 9. However, as can be seen on the Table 2 that means of the 11 margarine brands are significantly different (P < 0.001). Table 2. Two-way ANOVA results obtained for the determination of Cu, Fe, Mn, and Ni in margarine samples by the EIEB and microwave digestion procedures. Results are expressed in µg/g as mean± standard deviation (n = 6)a . Cu (µg/g) . Fe (µg/g) . Mn (µg/g) . Ni (µg/g) . Sample . EIEB procedure . Microwave digestion procedure . EIEB procedure . Microwave digestion procedure . EIEB procedure . Microwave digestion procedure . EIEB procedure . Microwave digestion procedure . S1 0.095±0.004cde 0.093±0.004def 24.9±3.9a 21.8±4.8ab 0.611±0.056efg 0.711±0.050defg 0.130±0.002ab 0.133±0.012a S2 0.112±0.009abcd 0.103±0.001bcd 9.1±2.8def 12.1±3.2cdef 0.542±0.039g 0.612±0.061efg 0.132±0.002a 0.130±0.005abc S3 0.118±0.007abc 0.092±0.030def 18.6±8.5abc 15.2±4.3bcd 0.573±0.029fg 0.564±0.049fg 0.132±0.003ab 0.130±0.002ab S4 0.131±0.004a 0.118±0.019abc 5.6±1.5ef 6.7±2.4ef 0.631±0.013efg 0.614±0.035efg 0.134±0.003a 0.131±0.001ab S5 0.107±0.006abcd 0.125±0.026ab 6.0±1.5ef 7.6±2.1ef 0.582±0.048fg 0.593±0.022fg 0.131±0.004ab 0.126±0.009abcd S6 0.055±0.015ghı 0.042±0.003hı 8.4±3.0ef 9.6±2.4def 0.864±0.056bcd 0.812±0.023bcde 0.109±0.003e 0.121±0.022abcde S7 0.043±0.004hı 0.049±0.004ghı 15.4±0.7bcd 13.7±3.1cde 1.11±0.18b 0.812±0.079bcde 0.111±0.003de 0.117±0.006abcde S8 0.042±0.011hı 0.050±0.002ghı 7.4±4.1ef 9.9±1.2def 0.772±0.083defg 0.621±0.073efg 0.108±0.003e 0.109±0.012e S9 0.032±0.005ı 0.043±0.006hı 10.0±0.4def 11.2±1.2def 1.11±0.12a 0.904±0.092bcd 0.108±0.001e 0.114±0.007bcde S10 0.031±0.003ı 0.039±0.005ı 10.0±0.3def 10.7±2.1def 0.962±0.038bc 0.863±0.054bcd 0.113±0.003cde 0.122±0.011abcde S11 0.076±0.002efg 0.068±0.025fgh 11.7±0.4def 12.2±2.1cdef 0.784±0.006cdef 0.732±0.048defg 0.121±0.010abcde 0.126±0.014abcd Method significance NSb NS p<0.001 p<0.05 Interaction p<0.001 NS p<0.001 NS . Cu (µg/g) . Fe (µg/g) . Mn (µg/g) . Ni (µg/g) . Sample . EIEB procedure . Microwave digestion procedure . EIEB procedure . Microwave digestion procedure . EIEB procedure . Microwave digestion procedure . EIEB procedure . Microwave digestion procedure . S1 0.095±0.004cde 0.093±0.004def 24.9±3.9a 21.8±4.8ab 0.611±0.056efg 0.711±0.050defg 0.130±0.002ab 0.133±0.012a S2 0.112±0.009abcd 0.103±0.001bcd 9.1±2.8def 12.1±3.2cdef 0.542±0.039g 0.612±0.061efg 0.132±0.002a 0.130±0.005abc S3 0.118±0.007abc 0.092±0.030def 18.6±8.5abc 15.2±4.3bcd 0.573±0.029fg 0.564±0.049fg 0.132±0.003ab 0.130±0.002ab S4 0.131±0.004a 0.118±0.019abc 5.6±1.5ef 6.7±2.4ef 0.631±0.013efg 0.614±0.035efg 0.134±0.003a 0.131±0.001ab S5 0.107±0.006abcd 0.125±0.026ab 6.0±1.5ef 7.6±2.1ef 0.582±0.048fg 0.593±0.022fg 0.131±0.004ab 0.126±0.009abcd S6 0.055±0.015ghı 0.042±0.003hı 8.4±3.0ef 9.6±2.4def 0.864±0.056bcd 0.812±0.023bcde 0.109±0.003e 0.121±0.022abcde S7 0.043±0.004hı 0.049±0.004ghı 15.4±0.7bcd 13.7±3.1cde 1.11±0.18b 0.812±0.079bcde 0.111±0.003de 0.117±0.006abcde S8 0.042±0.011hı 0.050±0.002ghı 7.4±4.1ef 9.9±1.2def 0.772±0.083defg 0.621±0.073efg 0.108±0.003e 0.109±0.012e S9 0.032±0.005ı 0.043±0.006hı 10.0±0.4def 11.2±1.2def 1.11±0.12a 0.904±0.092bcd 0.108±0.001e 0.114±0.007bcde S10 0.031±0.003ı 0.039±0.005ı 10.0±0.3def 10.7±2.1def 0.962±0.038bc 0.863±0.054bcd 0.113±0.003cde 0.122±0.011abcde S11 0.076±0.002efg 0.068±0.025fgh 11.7±0.4def 12.2±2.1cdef 0.784±0.006cdef 0.732±0.048defg 0.121±0.010abcde 0.126±0.014abcd Method significance NSb NS p<0.001 p<0.05 Interaction p<0.001 NS p<0.001 NS aMeans that don’t share the same superscript letter (for each element) are significantly different at the 0.05 level. (Tukey’s test). bNS = Not significant at the p > 0.05 level (Tukey’s test). Open in new tab Table 2. Two-way ANOVA results obtained for the determination of Cu, Fe, Mn, and Ni in margarine samples by the EIEB and microwave digestion procedures. Results are expressed in µg/g as mean± standard deviation (n = 6)a . Cu (µg/g) . Fe (µg/g) . Mn (µg/g) . Ni (µg/g) . Sample . EIEB procedure . Microwave digestion procedure . EIEB procedure . Microwave digestion procedure . EIEB procedure . Microwave digestion procedure . EIEB procedure . Microwave digestion procedure . S1 0.095±0.004cde 0.093±0.004def 24.9±3.9a 21.8±4.8ab 0.611±0.056efg 0.711±0.050defg 0.130±0.002ab 0.133±0.012a S2 0.112±0.009abcd 0.103±0.001bcd 9.1±2.8def 12.1±3.2cdef 0.542±0.039g 0.612±0.061efg 0.132±0.002a 0.130±0.005abc S3 0.118±0.007abc 0.092±0.030def 18.6±8.5abc 15.2±4.3bcd 0.573±0.029fg 0.564±0.049fg 0.132±0.003ab 0.130±0.002ab S4 0.131±0.004a 0.118±0.019abc 5.6±1.5ef 6.7±2.4ef 0.631±0.013efg 0.614±0.035efg 0.134±0.003a 0.131±0.001ab S5 0.107±0.006abcd 0.125±0.026ab 6.0±1.5ef 7.6±2.1ef 0.582±0.048fg 0.593±0.022fg 0.131±0.004ab 0.126±0.009abcd S6 0.055±0.015ghı 0.042±0.003hı 8.4±3.0ef 9.6±2.4def 0.864±0.056bcd 0.812±0.023bcde 0.109±0.003e 0.121±0.022abcde S7 0.043±0.004hı 0.049±0.004ghı 15.4±0.7bcd 13.7±3.1cde 1.11±0.18b 0.812±0.079bcde 0.111±0.003de 0.117±0.006abcde S8 0.042±0.011hı 0.050±0.002ghı 7.4±4.1ef 9.9±1.2def 0.772±0.083defg 0.621±0.073efg 0.108±0.003e 0.109±0.012e S9 0.032±0.005ı 0.043±0.006hı 10.0±0.4def 11.2±1.2def 1.11±0.12a 0.904±0.092bcd 0.108±0.001e 0.114±0.007bcde S10 0.031±0.003ı 0.039±0.005ı 10.0±0.3def 10.7±2.1def 0.962±0.038bc 0.863±0.054bcd 0.113±0.003cde 0.122±0.011abcde S11 0.076±0.002efg 0.068±0.025fgh 11.7±0.4def 12.2±2.1cdef 0.784±0.006cdef 0.732±0.048defg 0.121±0.010abcde 0.126±0.014abcd Method significance NSb NS p<0.001 p<0.05 Interaction p<0.001 NS p<0.001 NS . Cu (µg/g) . Fe (µg/g) . Mn (µg/g) . Ni (µg/g) . Sample . EIEB procedure . Microwave digestion procedure . EIEB procedure . Microwave digestion procedure . EIEB procedure . Microwave digestion procedure . EIEB procedure . Microwave digestion procedure . S1 0.095±0.004cde 0.093±0.004def 24.9±3.9a 21.8±4.8ab 0.611±0.056efg 0.711±0.050defg 0.130±0.002ab 0.133±0.012a S2 0.112±0.009abcd 0.103±0.001bcd 9.1±2.8def 12.1±3.2cdef 0.542±0.039g 0.612±0.061efg 0.132±0.002a 0.130±0.005abc S3 0.118±0.007abc 0.092±0.030def 18.6±8.5abc 15.2±4.3bcd 0.573±0.029fg 0.564±0.049fg 0.132±0.003ab 0.130±0.002ab S4 0.131±0.004a 0.118±0.019abc 5.6±1.5ef 6.7±2.4ef 0.631±0.013efg 0.614±0.035efg 0.134±0.003a 0.131±0.001ab S5 0.107±0.006abcd 0.125±0.026ab 6.0±1.5ef 7.6±2.1ef 0.582±0.048fg 0.593±0.022fg 0.131±0.004ab 0.126±0.009abcd S6 0.055±0.015ghı 0.042±0.003hı 8.4±3.0ef 9.6±2.4def 0.864±0.056bcd 0.812±0.023bcde 0.109±0.003e 0.121±0.022abcde S7 0.043±0.004hı 0.049±0.004ghı 15.4±0.7bcd 13.7±3.1cde 1.11±0.18b 0.812±0.079bcde 0.111±0.003de 0.117±0.006abcde S8 0.042±0.011hı 0.050±0.002ghı 7.4±4.1ef 9.9±1.2def 0.772±0.083defg 0.621±0.073efg 0.108±0.003e 0.109±0.012e S9 0.032±0.005ı 0.043±0.006hı 10.0±0.4def 11.2±1.2def 1.11±0.12a 0.904±0.092bcd 0.108±0.001e 0.114±0.007bcde S10 0.031±0.003ı 0.039±0.005ı 10.0±0.3def 10.7±2.1def 0.962±0.038bc 0.863±0.054bcd 0.113±0.003cde 0.122±0.011abcde S11 0.076±0.002efg 0.068±0.025fgh 11.7±0.4def 12.2±2.1cdef 0.784±0.006cdef 0.732±0.048defg 0.121±0.010abcde 0.126±0.014abcd Method significance NSb NS p<0.001 p<0.05 Interaction p<0.001 NS p<0.001 NS aMeans that don’t share the same superscript letter (for each element) are significantly different at the 0.05 level. (Tukey’s test). bNS = Not significant at the p > 0.05 level (Tukey’s test). Open in new tab Table 3. Analytical performance of the EIEB procedure for the analysis of Cu, Fe, Mn, and Ni in margarine samples Parameter . Cu . Fe . Mn . Ni . Analytical range 0.02–0.2 µg/g 1.5–24 µg/g 0.1–1.0 µg/g 0.1–0.3 µg/g Methodological LOD 4.8x10-3 µg/g 13x10-3 µg/g 1.5x10-3 µg/g 23x10-3 µg/g Methodological LOQ 16x10-3 µg/g 43x10-3 µg/g 5.0x10-3 µg/g 76x10-3 µg/g Repeatability (RSDr) ≥0.1 µg/g ≤8% ≤10 µg/g <55% >1.1 µg/g ≤16% ≥0.12 µg/g ≤8.3% ≤0.05 µg/g <27% >15 µg/g <46% <1.0 µg/g ≤10.8% ≤0.11 µg/g ≤2.8% Parameter . Cu . Fe . Mn . Ni . Analytical range 0.02–0.2 µg/g 1.5–24 µg/g 0.1–1.0 µg/g 0.1–0.3 µg/g Methodological LOD 4.8x10-3 µg/g 13x10-3 µg/g 1.5x10-3 µg/g 23x10-3 µg/g Methodological LOQ 16x10-3 µg/g 43x10-3 µg/g 5.0x10-3 µg/g 76x10-3 µg/g Repeatability (RSDr) ≥0.1 µg/g ≤8% ≤10 µg/g <55% >1.1 µg/g ≤16% ≥0.12 µg/g ≤8.3% ≤0.05 µg/g <27% >15 µg/g <46% <1.0 µg/g ≤10.8% ≤0.11 µg/g ≤2.8% Open in new tab Table 3. Analytical performance of the EIEB procedure for the analysis of Cu, Fe, Mn, and Ni in margarine samples Parameter . Cu . Fe . Mn . Ni . Analytical range 0.02–0.2 µg/g 1.5–24 µg/g 0.1–1.0 µg/g 0.1–0.3 µg/g Methodological LOD 4.8x10-3 µg/g 13x10-3 µg/g 1.5x10-3 µg/g 23x10-3 µg/g Methodological LOQ 16x10-3 µg/g 43x10-3 µg/g 5.0x10-3 µg/g 76x10-3 µg/g Repeatability (RSDr) ≥0.1 µg/g ≤8% ≤10 µg/g <55% >1.1 µg/g ≤16% ≥0.12 µg/g ≤8.3% ≤0.05 µg/g <27% >15 µg/g <46% <1.0 µg/g ≤10.8% ≤0.11 µg/g ≤2.8% Parameter . Cu . Fe . Mn . Ni . Analytical range 0.02–0.2 µg/g 1.5–24 µg/g 0.1–1.0 µg/g 0.1–0.3 µg/g Methodological LOD 4.8x10-3 µg/g 13x10-3 µg/g 1.5x10-3 µg/g 23x10-3 µg/g Methodological LOQ 16x10-3 µg/g 43x10-3 µg/g 5.0x10-3 µg/g 76x10-3 µg/g Repeatability (RSDr) ≥0.1 µg/g ≤8% ≤10 µg/g <55% >1.1 µg/g ≤16% ≥0.12 µg/g ≤8.3% ≤0.05 µg/g <27% >15 µg/g <46% <1.0 µg/g ≤10.8% ≤0.11 µg/g ≤2.8% Open in new tab The statistical test results regarding the mean values of the manganese did not show similar appearance as those found in the other three elements. Because the two procedures, EIEB and microwave gave statistically significant different results. The eight of the eleven margarine brands (S3, S4, S6, S7, S8, S9, S10, S11) had higher means in EIEB procedure that those were found in microwave procedure (S1, S2, S5). These results reveal that EIEB procedure may be superior for manganese determination in margarine samples. Also, there was statistically significant interaction between the two variables considered. As can be seen from the Table 2 that the means of the manganese were significantly different among the 11 margarine brands examined during the course of the present study. This may be due to three margarine brands which have fairly higher mean values compared to remaining eight sample means (S7, S9, and S10). Regarding the nickel, there was a similar tendency on the statistical test results those were found for the iron. As with iron, no significant interaction value was observed. However, as can be seen in Table 2, there was a significant difference between the 11 margarine brands. All procedures showed variability in mineral concentrations among the margarine samples, although it can be seen that copper and iron varied the most. This may be affected by the environment and food processing apparatus used for margarine production (34, 35). Surprisingly, nickel varied the least. Because margarine production processes result in nickel in the final product. These may sometimes result in unfavorable conditions regarding nickel in margarine production (9, 10, 12). Analytical Features of the Proposed Procedure Since the EIEB procedure results in an aqueous phase containing the analytes of interest, external calibration standards were prepared in 10% (v/v) nitric acid solution. The linearities of the analytical curves are quite satisfactory as the coefficient of determination, R2 ≥ 0.9965. Cu, Fe, Mn, and Ni from 4 g (4.6 mL) of margarine are concentrated into 2 mL of acidic extraction solution, resulting in a concentration factor of 2.3, which must be accounted for in the calculations. The Limit of Detection (LOD) and the Limit of Quantification (LOQ) were calculated for each element using 3 s/m and 10 s/m criteria, respectively, where s is the standard deviation of 10 blank readings and m is the slope of the calibration curve (36). The EIEB procedure precision was estimated by measuring six replicates of the 11 margarine samples (Table 2). The relative standard deviation (RSD) was found to be less than 8% at ≥0.1 µg/g Cu and Ni, and approximately 25% at ≤ 0.05 µg/g Cu only two samples (S6 and S8). However, for iron, the RSD values in some samples (S3, S6, S7, and S8) were found to be higher than other studied elements. The RSD of the developed procedure and the total digestion microwave procedure are similar to each other and both have satisfactory precision. Provisional Tolerable Daily Intakes (PTDI) of Cu, Fe, Mn, and Ni Analyses of the Cu, Fe, Mn, and Ni content in margarine using the EIEB procedure are presented in Tables 2 and 3. The mean concentration of Cu in the eleven samples analyzed ranged from 0.031–0.131 µg/g. The copper concentrations in this study were low compared to those reported by Szlykand and Szydlowska-Czerniak (37), Mendil (38), and Anwar et al. (22), but similar to the values reported by Mendil et al. (16) and Ieggli et al. (1). In addition, the estimated daily intake of copper found in this study was compared to the provisional tolerable daily intake (PTDI) value recommended by the FAO/WHO. The joint FAO/WHO Expert Committee on Food Additives (JECFA) PTDI value for copper is 0.5 mg/kg body weight (39). The average consumption of margarine for a person in Europe (40) was assumed to be 25 g/day, so in this study the daily intake would be 0.013–0.054 µg/kg body weight for a 60 kg person, well below the PTDI. Mean concentrations of Fe in this in this study ranged from 5.6–24.9 µg/g. The levels of Fe determined in this study were similar to those reported for Brazil and Pakistan margarines (1, 22), but were higher than those reported by Millour et al. (41), and Benzo et al. (42). However, the amount of iron was much lower than that found by Mendil et al. (16) in studies conducted on margarine produced in Turkey. The estimated daily intake of Fe from the samples in this study was found to range from 2.4–10.4 µg/kg bw/day for a 60 kg person, 0.3–1.3% of the JECFA PTDI value (43). Mn quantities in food may be affected by the food processing environment since the apparatus used in food production is often made of Mn alloy and steel (34, 35). In this study, the mean manganese concentration was found to be 0.77 µg/g margarine. This value is high compared to that found in the works of Mendil et al. (16) and Ieggli et al. (1) and very low compared to that of Anwar et al. (22). According to the Dietary Reference Intakes (DRIs), an adult person can consume up to 2.3 mg of manganese per day (44). The Mn in the margarine samples analyzed in this study ranged from 0.6–1.2% DRI. The JECFA PTDI for nickel is 5 µg/kg bw/day (45). Nickel concentrations ranged from 0.108–0.134 µg/g (Table 2). The nickel values found in this study are close to those of Lodyga-Chruscinska et al. (11) and Hartwig et al. (10) but are quite low compared to Benzo et al. (42) and Ieggli et al. (1). The estimated daily intake of Ni from the margarine samples in this work ranged from 0.045–0.055 µg/kg bw/day for a 60 kg person, with the highest value at 1.1% of PTDI. The Turkish food codex (TFC) has reported some critical levels of elements in edible oil-based products (46) including maximum acceptable limits of Cu, Fe, and Ni in margarine products of 0.1 mg/kg, 1.5 mg/kg, and 0.2 mg/kg, respectively. Copper and nickel results from margarine samples in this study using the EIEB procedure are in line with the Turkish food codex limits, but iron results are slightly above the TFC limit. However, in 2009 the mean Fe concentration as determined in margarine samples produced in Turkey was found to be 291.0 ± 28.2 µg/g, which is > 10-fold higher than the values found in this study (16). Conclusion In this study, the EIEB extraction procedure for the quantification of 4 elements (Cu, Fe, Mn, and Ni) in margarine prior to GFAAS determination was developed for the first time. The EIEB procedure is based on emulsion formation and then emulsion breaking by heating. This proposed procedure has advantages, including simplicity, speed, and low cost, over classical sample preparation procedures described in the literature. In addition, it eliminates the use of highly concentrated acids and toxic chemicals and is environmentally friendly. In the EIEB procedure, the use of oil-based standards is not required to obtain calibration curves since the aqueous phase obtained after extraction can be analyzed directly by GFAAS using external calibration. The performance characteristics showed that the EIEB procedure is a useful alternative extraction procedure for Cu, Fe, Mn, and Ni from margarine samples prior to analysis by GFAAS. 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TI - Extraction of Cu, Fe, Mn, and Ni from Margarine Samples Using Extraction Induced by Emulsion Breaking Procedure Prior to Graphite Furnace Atomic Absorption Spectrometry and Comparison of Results to Provisional Tolerable Daily Intake Values
JF - Journal of AOAC INTERNATIONAL
DO - 10.1093/jaoacint/qsaa028
DA - 2020-09-01
UR - https://www.deepdyve.com/lp/oxford-university-press/extraction-of-cu-fe-mn-and-ni-from-margarine-samples-using-extraction-Wtq1PHrPq4
SP - 1256
EP - 1263
VL - 103
IS - 5
DP - DeepDyve
ER -