摘要:

JOURNAL OF ANALYTICAL ATOiMIC SPECTROMETRY OCTOBER 1991 VOL. 6 Direct Determination of Copper and Iron in Edible Oils Using Flame Atomic Absorption Spectrometry Vincente Carbonell A. R. Mauri Amparo Salvador and Miguel de la Guardia* Department of Analytical Chemistry University of Valencia 50 Doctor Moliner Street Valencia Spain 58 1 Flow Injection 46100 Burjassot A procedure based on the standard additions method has been developed for the direct determination of copper and iron in edible oils by flow injection flame atomic absorption spectrometry. An organic standard is added to the sample using a reverse single line manifold. The flow injection standard additions method allows the accurate determination of copper and iron in unrefined oil samples without any pre-treatment or dilution of the samples.Keywords Edible oils analysis; flow injection; standard additions method; flame atomic absorption spectro- metry; copper and iron determination Copper and iron are essential trace elements that are present in a wide variety of foods.' However the presence of heavy metals in edible oils has a negative effect on their oxidative stability2v3 and hence for commercial reasons it is important to monitor and control the presence of elements in the oil sample^.^?^ A series of spectrophotometric,6-12 emission spectrogra- phic,13 p~larographic'~ and chromatographiclS methods have been reported in the literature for the determination of heavy metals in samples of edible oils. However atomic absorption spectrometry (AAS) is the most selective and sensitive technique available for these determinations.Two basic approaches have been employed in the AAS analysis of oil samples one is based on the direct aspiration of the samples diluted in an appropriate organic ~ o l v e n t ~ J ~ - ~ ~ and the other on pre-treatment of the samples which can involve wet or dry ashing or an extraction step with chelating agent^.^^-^^ Methods involving electrothermal atomization can also be used for the determination of trace amounts of metals with simple chemical modification of the oil samples.30 However serious problems are encountered in the deter- mination of heavy metals in oil samples. Methods that involve dilution of the samples reduce the sensitivity and they have unacceptably high limits of detection. Prior treatment of the samples either by ashing or by solvent extraction is tedious and time consuming and so further investigations are required in order to establish direct methods for determining heavy metals in edible oils without sample dilution or pre-treatment of the samples.The use of flow injection (FI) techniques in atomic spectrometry can provide an enhancement in the sensitivity of traditional methods of analysis and several problems related to the sample introduction are a ~ o i d e d . ~ l - ~ ~ In the work described in this paper a simple procedure has been developed for the direct determination of copper and iron in edible oils by flame atomic absorption spectro- metry (FAAS) based on the standard additions method which reduces matrix interferences without excessive dilu- tion of the samples.The procedure is based on the FI standard additions method proposed by Tyson and co- w o r k e r ~ ~ ~ ~ ~ ~ for the direct determination of metals in waters. The method has been applied to the analysis of oil samples. Experimental Apparatus A flame atomic absorption spectrometer Perkin-Elmer Model 5000 equipped with a 561 recorder a deuterium ~~ ~ * To whom correspondence should be addressed. Table 1 of the elements determined Instrumental parameters used to measure the absorbance Element Parameter c u Fe Wavelengthhm 324.8 248.3 Slit-widthhm 0.7 0.2 Technique A* A-Bt Lamp currentImA 13 13 FI parameter- Flow rate/ml min-* 1 1 Loop/pl 100 100 * Atomic absorption. 1- Atomic absorptions with background correction. background corrector and multi-elemental hollow cathode lamp for chromium cobalt copper iron manganese and nickel was employed to measure the absorbances of copper and iron.The instrumental parameters chosen for the determination of both elements are summarized in Table 1. A Gilson Minipuls 2 HP-4 peristaltic pump was used to transport samples and standards through polytetrafluoro- ethylene (PTFE) tubes which had an i.d. of 0.8 mm. The single-line manifold was a reverse FI manifold in which there is a continuous flow of sample and the standards were injected using a Rheodyne injection valve Type 50 with a fixed loop of 100 pl. Reagents Copper stock solution 1000 mg I-'. Prepared from Iron stock solution 1000 mg 1 - I . Prepared by dissolution of 1 .OOOO g of metallic iron in 20 ml of 5 mol dm-3 HC1 and 5 ml of HN03 and diluting to 1 1 using distilled water.Organornetallic standard solution. CONOSTAN C-2 1 (Chemicontrol Spain) was employed as the stock solution which contained 100 mg 1-l of the following elements Ag Al B Ba Ca Cd Cr Cu Fe Mg Mn Mo Na Ni P Pb Si Sn Ti V and Zn. Organic standards of copper and iron 100 mg 1-l. Prepared by precipitating the elements in a 1% m/v solution of ammonium pyrrolidinedithiocarbamate (APDC) (i. e. ammnonium pyrrolidin- 1 -yl-dithioformate Fluka Chemie AG CH-9470 Buchs) dissolved in the minimum amount of isobutyl methylketone (IBMK) and diluting to 100 ml with refined olive oil free from copper and iron. Cu(N03)2*3HzO.5 82 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY OCTOBER 199 1 VOL. 6 Real samples of unrejned vegetal oil.Supplied by Aceites All solvents and acids were of analytical-reagent grade. Costa Blanca (Gandia Spain). Procedure Calibration graphs were prepared using the stock solutions in the range 0-10 mg 1-l of copper and iron. Synthetic samples were prepared in a metal-free oil matrix by the addition of the organometallic standards. Real samples were analysed by FAAS using a reference method,37 based on prior dry ashing of the samples and by FI standard additions using the direct injection of organic standards into the sample flow. The instrumental conditions were optimized in order to obtain the best sensitivity and repeatability for both copper and iron using direct introduction of the oil samples. Dry ashing of the oil samples Weigh 4-20 g of the oil sample depending on the copper and iron content into a porcelain crucible and heat with a Bunsen burner. Add a few drops of HN03 and dry.Place the sample in a muffle furnace at 600 "C for 1 h and then allow to cool. Add a few more drops of HN03 dry and heat at 700 "C for 1 h. Dissolve the ash in HCl and dilute with distilled water to a final volume of 10 ml. 0.06 0.04 0.02 0 -0.02 Fig. 1 Flow injection direct standard additions method for the determination of copper in edible oil (a) absorbance profile of standards with the sample as the baseline; and (b) absorbance change versus concentration of standard giving the sample concen- tration at A A = O Samples prepared in this way are fed directly to the flame. Aqueous solutions of copper and iron are used as the standards.Direct standard additions method Oil samples are continuously fed to the flame using a single manifold. Organic standard solutions of copper and iron in oil are then injected into the flow and the variation in the absorbance values above the baseline obtained for the samples is measured. Results and Discussion The samples were used as the carrier and injection of the organic standards produces FI recordings that are anala- gous to those obtained with the standard additions method. All the measurements were carried out under the optimum instrumental conditions found for the direct feeding of the oil samples to the flame i.e. a burner height of 15 mm for copper and 10 mm for iron and flow rates of 1.2 1 min-l for C2H2 and 18.25 1 min-l for air.Figs. 1 and 2 show that using the signal for the sample as the baseline injection of standards with a lower analyte concentration than the sample will give a negative peak and standards with greater concentration will give positive peaks. A plot of the change in absorbance (AA) versus the concentration of the standard injected provides the sample concentration by interpolation to a A A = O value. To carry out these measurements the single-line mani- fold described under Experimental was employed. The organic standard CONOSTAN and the APDC complexes were used for analysis of the oil samples. The direct standard additions method using FI is very fast and does not require dilution of the sample. 0.08 0.04 0 -0.04 I -0.08 t- -0.08 0 4 8 12 16 20 c (ppm) Fig.2 Flow injection direct standard additions method for the determination of iron in edible oil (a) absorbance profile of standards with the sample as the baseline; and (b) absorbance change versus concentration of standard giving the sample concen- tration at AA = 0JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY OCTOBER 1991 VOL. 6 583 Table 2 Analytical figures of merit of the determination of copper and iron in edible oils by the FI standard additions method Parameter c u Fe Analytical curve (r)* A = -0.030+0.025~ (0.9997)y A = -0.035+0.007~ (0.9995)t A= -0.028+0.019~ (0.9995)$ A = -0.05 1 +0.006~ (0.996)$ Characteristic concentration (s)§/mg I-' 0.22 i 0.005 0.6 k 0.1 Repeatability (%) 3 8 Relative standard deviation (To) 3 2 * r=Regression coefficient. 7 Standard additions curve obtained with APDC complexes.$ Standard additions curve obtained with CONOSTAN. $ s=Standard deviation. Analytical Figures of Merit of the Procedure Developed The FI standard additions determination of copper and iron in oil samples provides a sensitive and precise procedure. The analytical figures of merit such as sensi- tivity (indicated by the slope of the standard additions graph) repeatability of the absorbance peak heights of three series of injections of the same standard and the relative standard deviation of three independent determinations for each one of the samples analysed are summarized in Table 2. As can be seen for the determination of copper the use of standards of APDC complexes provides a higher sensitivity than the CONOSTAN standards.This indicates the pres- ence of inter-elemental effects in the CONOSTAN solu- tions. However one of the most interesting characteristics of the FI standard additions method is that the sample concentration is obtained by interpolation and not by extrapolation of the experimental data which results in good precision. Analysis of Synthetic Samples A series of synthetic samples were prepared by dilution of the CONOSTAN standard with a refined edible oil and then analysed by the FI direct standard additions method. Results found for the determination of copper and iron are summarized in Table 3 and as can be seen accurate results were obtained in all instances. However when synthetic samples containing copper were prepared from CONOSTAN APDC complexes could not be used as the standard.This is because the presence of a range of other ~~~~~ ~~ Table 3 Analysis of synthetic samples by the FI direct standard additions method Copper concentration/mg 1-* Sample 1 2 3 4 5 Added Found 2.0 2.0 1 .o 1 .o 1.85 1.5* 14.99 15.2 10.98 11.5 Iron concentration/mg 1-I Added Found 6 10.0 9.7 7 7.99 8.09* 8 5.55 5.37 * In this instance synthetic samples were prepared with CO- NOSTAN and solutions of copper- or iron-APDC complexes were used as standards. Table 4 Analysis of real samples of edible oils FI additions method Sample Dry ashing APDC standards CONOSTAN standards Copper determination- 1 1.1 k0.5 1.10+0.05 1.45 * 0.02 2 0.7 .+ 0.1 1.17 & 0.08 1.51 kO.01 Iron determination- 3 34.1 k0.7 - 36.0 k 0.9 4 21.2-to.2 - 20.7 k 0.4 elements in the CONOSTAN stock solution enhances the absorbance readings for copper and so inaccurate results are obtained.In the determination of iron the inter-elemental effects in the CONOSTAN standard are less important hence accurate results were obtained using both types of standard. Analysis of Real Samples Real samples of unrefined edible oils were analysed by the proposed procedure using CONOSTAN standards and standard solutions of complexes with APDC for the on-line FI standard additions method. The results obtained were compared with those found by AAS after prior dry ashing of the samples. As can be seen in Table 4 the use of APDC complexes as standards for the determination of copper provides more accurate results than the use of CONOSTAN standards.However for the determination of iron the latter standards can be used. Conclusion The direct determination of copper and iron by FAAS can be performed without sample dilution using an on-line standard additions method. References Reilly C. Metal Contamination of Food Applied Science London 1980. Banks A. Eddie E. and Smith J. G. Nature 1961 190 908. Lundberg W. O. Autoxidation and Antioxidant Wiley New York 1966. Evans C. D. Schwob A. W. Moser H. A. Hawley J. E. and Melvin E. H. J. Am. Oil Chem. Soc. 1951 28 68. List G. R. Evans C. D. and Kwolek W. F. J. Am. Oil Chern. Soc. 1971 48 438. Vioque A. and Villagram M. P. Mikrochim. Acta 1956,804. Vioque A. and Villagram M. P. Grasas Aceites (Seville) 1956 7 195.- 584 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY OCTOBER 199 1 VOL.6 8 Loury M. and Lechartier G. Rev. Fr. Corps. Gras. 1960 7 80. 9 Hogelahl 0. T. and Melson S. Anal. Chem. 1966 38 1414. 10 Labriza T. P.. and Karel M. J. Food. Sci. 1967 32 572. 1 1 Lau 0. M. and Mok Ch. S. J. Sci. Food Agric. 1982 33 1030. 12 Newlove T. H. in Laboratory Handbook for Oil and Fat Analysts. eds. Cock L. V. and Von Rede C. Academic Press London. 1966. 13 Vioque A. and Villagram M. P. Grasas Aceites (Seville) 1960 11 71. 14 Vilicic D. Gams M. and Filajdig M. Kem. Znd. 1963 12 136. 15 Sparapanoi. N. D. and Strusi A. Olivicultura 1958 13 3. 16 Guillaumin R. and Dronhin W. Rev. Fr. Corps Gras. 1965 17 Prevot A. At. ilbsorpt. Newsl. 1966 5 13. 18 Guillaumin R. At. Absorpt. Newsl. 1966 5 19. 19 Piccolo B. and O’Connor R. T. J. Am.Oil Chem. Soc. 1968 45 789. 20 Evans C. D. List G. R. and Black L. T. J. Am. Oil Chem. Soc. 197 1 48 480. 21 Zalts A. Troccoli 0. E. and Possidoni de Albirati J. F. An. Asoc. Quim. Argent. 1986 74 55. 22 Willis. J. B.. Aust. J. Dairy Technol. 1964 70. 23 Deck R. E. and Kaiser K. K. J. Am. Oil Chem. Soc. 1964 47 126. 12 735. 24 Kerber J. D. Russo A. J. Peterson G. E. and Ediger R. D. At. Absorpt. Newsl. 1973 12 106. 25 Van Raapharst J. G. Van Weers A. W. and Haremaker H. M. Analyst 1974 99 523. 26 Kundu M. K. and Prevot A. Anal. Chem. 1974,46 1591. 27 Jacob R. A. and Klevaj L. M. Anal. Chem. 1975 47 741. 28 Black L. T. J. Am. Oil Chem. Soc. 1975 52 88. 29 Farhan F. M. Rahmati H. and Ghazi-Moghaddam G. J. Am. Oil Chem. SOC. 1988,65 1961. 30 Calapaj R. Chiricosta S. Saija G. and Bruno E. A?. Spectrosc. 1988 9 107. 3 1 Flow Injection-Atomic Spectroscopy ed. Burguera J. L. Marcel Dekker New York 1989. 32 Tyson J. F. Analyst 1985 110 419. 33 RbiiEka J. Fresenius 2. Anal. Chem. 1986 324 745. 34 Tyson J. F. Anal. Chim. Acta 1988 214 57. 35 Tyson J. F. and Idris A. B. Analyst 1984 109 23. 36 Tyson J. F. Trends. Anal. Chem. 1985 4 124. 37 ASTM Reference Method D8 1 1 American Society for Testing and Materials Philadelphia 1948. Paper 0 /O 3 5 88B Received August 6th 1990 Accepted June 20th 1991

ISSN:0267-9477    

DOI:10.1039/JA9910600581

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY OCTOBER 1991 VOL. 6 CUMULATIVE AUTHOR INDEX Abell Ian. 145 Abollino O. 119 Ali Abdalla H.. 21 1 Andersen Knut-Jan 277 Apte S. C. 169 Arpadjan Sonja 487 Barnes Ramon M. 57 Barry Eugene F. 545 Baxter Douglas C. 109 Beinrohr Ernest 33 307 Belitz Ronald K. 393 Bendicho Carlos 353 Berglund Ingemar 109 Berman Shier S. 19 283 Blades Michael W. 215 Blais Jean-Simon 225 Blue James L. 26 1 Branch Simon 15 I I55 Bridenne Martine 49 Brindle Ian D. 129 Brindle Mary E. 129 Brown James A. 393 Butcher David J. 9 Butler L. R. P. 329 Bye Ragnar 389 Canals Antonio 139,573 Carbonell Vincente 233 58 1 Carre Martine 49 Cervera Maria Luisa 379,477 Chen Hengwu 129 Chou Lei 273 Collins C. S. 329 Colon Luis A. 545 Comber S. D. W. 169 Corns Warren T. 155 CsCmi Pavol 307 Dawson John B.93 de la Guardia Miguel 233 379 de Loos-Vollebregt 477,581 Margaretha T. C. 165 323 353 Diaz de Rodriguez Olga 49 Dittrich Klaus 3 13,465 Doleial Jiii 52 1 D’Ulivo Alessandro 565 Ebdon Les 15 I 155.42 1 Evans E. Hywel 421 Fairman Ben 397 Fang Zhaolun 179 301 Fell Gordon S. 559 Fernandez Sanchez Maria Luisa Forbes Kimberely A. 57 Ford Mick 15 1 397 FEBRUARY-OCTOBER 1991 Foulkes Mike 15 1 Franks Jeff 145 Frech Wolfgang 109 Fuchs Holger 3 13 Fuge Ronald 445 Furata N. 199 Garden Louise M. 159 Gardener M. J. 169 Gervais Lyne S. 4 1,493 Gilmutdinov Albert Kh. 505 Gunn A. M. 169 Hang Heng-bin 385 Hassell D. Christian 105 Haswell S. J. 339 He Bin 385 Hernandis Vincente 139 573 Hieftje G. M. 191 Hill Steve 155 Hinds Michael H. 473 HlavaC Robert 52 1 HlavZek Ivan 535 HlavhCkova Irena 535 Hoenig Michel 273 Holcombe James A.105 Huang Degui 2 15 Huang Min 22 1 Huyghues-Despointes Alexis 225 Igarashi Yasuhito 205 335 Iida Yasuo 541 Irwin Richard L. 9 Ishii Izumi 3 17 Ishizuka Toshio 54 1 Ivanov V. P. 505 Jackson Kenneth W. 473 Jiang Zucheng 22 1 Julshamm Kaare 277 Karanassios Vassili 457,527 Ketterer Michael E. 439 Kibble Helen A. B. 133 Kim Chang-Kyu 205 Kluckner Paul D. 37 Kolihova Dana 52 1 Koons Robert D. 45 1 Kunz Frank W. 393 Lampugnani Leonardo 565 Larsen Erik H. 375 Latimer Kathryn E. 473 Le Xia-chun 129 Ledingham Kenneth W. D. 73 Lee Kwang W. 431 Li Ang 385 Li F. H. 457 Littlejohn David 159 Liu B. 457 Lund Walter 389 Luong Van T. 19 L’vov Boris 19 1 Lyon Thomas D. B. 559 Maage Amund 277 Majidi Vahid 105 Marot Yves 49 Marshall John 145 159 Marshall William D.225 Masuda Kimihiko 335 Matusiewicz Henryk 283 Mauri A. R. 58 1 McInroy James F. 335 McKay Keith 559 Mentasti E. 119 Mermet Jean-Michel 49 313 Michel Robert G. 9 Millward Christopher G. 37 Miyazaki Akira 173 Momplaisir Georges Marie 225 Montaser Akbar 3 17 Montoro Rosa 379,477 Mora Juan 139,573 Morikawa Hisashi 541 Morita Shigemitsu 205 Mukhtar S. 339 Navarro Ascensio 477 Ng Kin C. 21 1 Ni Zhe-ming 385,483 Offley Stephen G. 133 O’Neill Peter 15 1 155 Park Chang J. 43 1 Parsley David H. 289 Pearce Nicholas J. G. 445 Peng Runzhong 165 Perkins William T. 445 Peters Charles A. 45 1 Peters Michael J. 439 PEtros’ Libor 52 1 Poluzzi Vanes 33 Porta V. 119 Prell Laurie J. 25 Puschel Petr 52 1 Rademeyer Cor J.329 Radziuk Bernard 465 Rapta Miroslav 33 Rebbert Pamela S. 45 1 Redfield David A. 25 Regnier Pierre 273 Ren J. M. 527 Reszke Edward E. 57 Rivikre Brigitte 313 Rowbottom William H. 123 Salin Eric D. 41,457,493 527 Salvador Amparo 233,477,581 Sampson Barry I15 585 Sanz Angel 233 Sanz-Medel Alfredo 397 Sarzanini C. 1 19 Scheeline Alexander 553 Scott Roger D. 559 Seare Nichola J. 133 Seki Riki 205 Shiraishi Kunio 335 Singhal Ravi P. 73 Slavin Walter 191 Sperling Michael 179,295 301 Stratis; John A 239 Sturgeon Ralph E. 19 283 Styris David L. 25 Sychra Vaclav 52 1 Taddia Marco 33 Takahashi Junichi 9 Takaku Yuichi 205 335 Tan Hsiaoming 3 17 Tanaka Gi-ichiro 335 Tao Hiroaki -1 73 Tiggelman Johan J. 165,323 Tisdale Preston J. 439 Travis John C. 261 Tserovsky Emil 487 Tsuge Akira 541 Tsumura Akito 205 Turk Gregory C. 26 1 Tye Chris 145 Tyson Julian F. 133 307 Uden Peter C. 57 Uwamino Yoshinori 541 Vanhoutte C. N. 323 Voloshin A. V. 505 Vysk&ilovri Olga 52 1 Wang Zuwei 553 Watters Robert L. Jr. 261 Welz Bemhard 179 295 301 Wickstrom Torild 389 Willie Scott N. 19 Winefordner James D. 2 1 1 Xu Fu-zheng 385 Yamamoto Masayoshi 205 Yamasaki Shin-ichi 205 Yan Xiu-ping 483 Ybaiiez N. 379 Yin Xuefeng 295 Yoshimizu Katsumi 335 Yu Li-Jian 261 Zachariadis George A. 239 Zakharov Yu. A. 505 Zamboni Roberto 565 Zeng Yun’e 22 I 465

ISSN:0267-9477    

DOI:10.1039/JA9910600585

出版商:RSC    

年代:1991

数据来源: RSC