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Microwaves spark emission spectroscopy for the analysis of cations: A simple form of atomic emission spectroscopy
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Chinese Chemical Letters 22 (2011) 1084–1086 www.elsevier.com/locate/cclet
Microwaves spark emission spectroscopy for the analysis of cations: A simple form of atomic emission spectroscopy Zahid Hussain a,*, Khalid Mohammed Khan b, Khadim Hussain c, Sadam Hussain d, Shahnaz Perveen e b
a Department of Chemistry, Abdul Wali Khan University, Mardan, Pakistan H. E. J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi 75270, Pakistan c Department of Chemistry, Hazara University, Mansehra, Pakistan d Department of Electronics, Quaid-I-Azam University, Islamabad, Pakistan e PCSIR Laboratories Complex, Shahrah-e-Dr. Salimuzzaman Siddiqui, Karachi 75280, Pakistan
Received 27 December 2010 Available online 25 June 2011
Abstract A novel method for the cation analysis was investigated. The analysis is based on the sparking of the salts of metals in a microwave oven after placing in a graphite cell. The graphite cell absorbs microwaves and produces high temperature which converts the salt into light emitting species. The colour of light was found to dependent on the nature of cation, however, the intensity of the emitted light was found to be depending upon the form and shape of the graphite assembly in addition to the concentration of the salt. This communication presents explanation for all these observations and for the systematic and quantitative analysis using microwave spark emission technique. # 2011 Zahid Hussain. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Microwave spark; Cation analysis; Spark colour; Graphite cell; Atomic emission
Microwaves are electromagnetic radiations of widespread use. Its applications range from heating and cooking to the synthesis and plasma generation. Microwave heating is a volumetric and rapid method of heating [1,2]. Microwave heats up the dielectric materials by changing the rotational energies [3,4]. Now it is also used for heating the materials which are not microwave interactive by adding microwave absorbing materials [5,6]. The microwave absorbing materials include oxides of metals and graphite [7,8]. Graphite absorbs microwaves and generates heat and raises the temperature in the range of 1000 8C. Therefore, it is used for high temperature reactions like pyrolysis of coal, sludge, waste plastics [9–12], The use of microwave energy for the generation of plasma is also reported [13]. Microwave induced plasma is used for the atomization in fluorescence spectroscopy. Emission spectroscopy is one of the important analytical tools and among the emission techniques flame photometry is important for the analysis of alkali and alkaline earth metals where the source of excitation and vaporization is a flame. However, it is associated with some of the serious problems like the variation in response due to fluctuation in fuel to oxidant ratio. Further more it is * Corresponding author. E-mail address: [email protected] (Z. Hussain). 1001-8417/$ – see front matter # 2011 Zahid Hussain. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2011.03.019
Z. Hussain et al. / Chinese Chemical Letters 22 (2011) 1084–1086
1085
restricted to the use of solutions. There is need to have an effective analytical technique having the potential to be used as excitation source as well as atomization source.In the present work use of graphite is aimed to develop an easy and sensitive method for the cation analysis based on emission. Graphite was used as heat producing material by absorbing the microwaves and also acts as a cell for the analyte and the generated heat was used for atomization as well as excitation. 1. Experimental The experiments for microwave spark emission spectroscopy were carried out in a medium sized domestic on/off microwave oven of the 2450 MHz frequency. A window was made by cutting the side of the microwave oven for observations. The graphite rod was obtained from a used dry cell. A pit of about 1 mm depth and diameter was made at the end of the rod for holding the sample. It was placed on a ceramic disc and a piece of another rod of about 10 mm length was placed on the sample pit after the charging of pit with dry salt. The whole assembly was placed in the microwave oven and the microwaves were applied which resulted the coloured spark. Three important experiments were carried out; the analysis of the multi mineral tablet, the copper wire piece and the solid copper sulphate. 2. Results and discussion 2.1. The light emission process and mechanism Graphite was used as microwave absorbing antenna and cell for the sample to be analyzed. This experiment was designed to atomize and excite the atoms of the analyte by the high temperature produced due to the absorption of microwaves. Graphite is a microwave absorbing material which generates large quantity of heat on interaction with microwaves and this heat was used for the atomization of the metal salts. It is believed that atomization and excitation of the atoms is a combine process of the high temperature and absorption of the microwaves by the sample to be analyzed. The heat produced by the graphite alters the microwave absorbing capacity of the sample and the absorption of microwaves by the graphite directs the flux of microwaves to the sample which results greater absorption of the microwaves energy by the sample which resulted in atomization. These atoms emit characteristic light on relaxation and it was observed that sodium chloride emits golden yellow light on placing in the sample pit in the graphite rod, however, the light from potassium chloride was found violet. In case of the calcium the colour was yellowish and in case of copper sulphate the colour of spark was found green. The intensity of emitted lights was found to depend upon the form and shape of graphite antenna or cell in addition to the concentration of sample. When a plate of 3 in. 4 in. was used the intensity of the emitted light was low, whereas in case of the graphite rod the intensity of light was found to be higher. The intensity was further enhanced when a piece of the rod was placed on the sample pit in the graphite rod. This is due to the increased amount of heat due to greater microwave flux which amplified the atomization efficiency. Nonetheless, when a T-shape was formed by placing another graphite rod on the sample pit, further increase in intensity was observed. This technique can be used for the quick qualitative and quantitative analysis of metal salts mixtures as well as a single salt. When a 0.1 g piece of multivitamin and mineral combination tablet Stress tablet1 of Wyeth was placed in the sample pit a combination of colours was observed after pyrolysis of the sample. During this experiment interesting observation was also made which was the appearance of different colours with the rotation of the microwave disc. It may either be correlated with the differential vaporization or the separation during the destruction of organic lattice by microwaves. The colour observed for the Stress tablet1 were, green, yellowish and intense white. While the composition provided by the manufacturer was calcium pentothenate, cupric oxide and zinc sulphate along with organic compounds. This experiment leads to the conclusion that microwave spark emission spectroscopy may be a method of choice for the analysis of metal salts and its mixtures if shaped into proper instrument. 2.2. Analysis of metals and salts of metals The spark behaviour of the copper metal and copper sulphate was studied using microwave induced sparking. It was observed that the piece of copper give whitish light in the early shots of the microwaves. But after two seconds the colour of the light turned greenish and green. This change in colour is believed due to the compounds of the copper
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Z. Hussain et al. / Chinese Chemical Letters 22 (2011) 1084–1086
which is in this case mainly oxide of copper. The interaction of copper with air in the microwave oven results the formation of copper oxide. The concentration of this compound increases with the passage of time. That is why the change in the colour of and intensity of light is observed. This colour transition leads to three conclusions, the green light emits from the copper compounds, the intensity of light depends upon the concentration of compound and the method is useful in studying the rate of reactions and can analyze micro layers. The dependence of the intensity of radiations on the concentration was investigated by placing small quantity of solid copper sulphate in the sample pit instead of copper. It was observed that copper sulphate give intense green spark in the early shots of microwaves. This technique was initially used for the solid samples but it can also be extended to the solutions. 2.3. The base of IR emission spectroscopy and thermo-gravimetry using the microwaves spark emission spectroscopy Microwave spark emission spectroscopy was initially applied for the qualitative analysis of the solid samples. The process involves heat generation. This heat and microwaves are used for the excitation and atomization. The heat generation process is faster and volumetric. This can be extended to two more analytical techniques. It can be observed from the multi mineral tablet analysis that the process is associated with the weight loss, but in case of the copper wire experiment increase in weight is expected due to the oxide formation. Based on these observations this technique can further be extended to the rapid thermal analysis. This process involves rapid heating of the cell and sample. One of the other conclusions is the emission of the characteristic IR radiations according to the nature of the compound. The use of high resolving instrument enables to determine the nature of compound based on the emitted IR radiations in addition to the UVand visible radiations of the characteristic frequency. It is because of the rapid microwave heating and the dependence of the intensity of emitted light the detection range can be extended to the nano gram level. 3. Conclusion A new atomic emission spectroscopic technique was investigated. The excitation and atomization were carried out by exploiting the microwave absorption and heat generation of the graphite. This technique can be used for the demonstration of the electronic excitation experiments in the laboratory. Based on this process a spectrometer is proposed which will be used both for qualitative and quantitative analysis. This could be a faster emission technique due to the rapid volumetric absorption of microwave and generation of heat which result faster excitation process. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
T.J. Appleton, R.I. Colder, S.W. Kingman, I.S. Lowndes, A.G. Read, Appl. Energy 81 (1) (2005) 85. V. Santagada, E. Persssuti, G. Caliendo, Curr. Med. Chem. 9 (2002) 1252. M. Hamid, Heat Transfer Eng. 13 (1992) 73. C. Ludlow-Palafox, A.C. Howard, Ind. Eng. Chem. Res. 40 (2001) 4749. J.A. Menendez, M. Inguanzo, J.J. Pis, Water Res. 36 (2002) 3261. P. Monsef-Mirzai, M. Ravindran, W.R. McWhinnie, P. Burchill, Fuel 74 (1995) 20. A. Dominguez, J.A. Menendez, M. Inguanzo, et al. J. Chromatogr. A 1012 (2003) 193. M. Juma, Z. Korenˇova´, J. Markosˇ, et al. Petrol. Coal 48 (2006) 15. B. Kriegerbrockett, Res. Chem. Intermed. 20 (1) (1994) 39. M.B. Chanaa, M. Lallemant, A. Mokhlisse, Fuel 73 (1994) 1643. K. El harfi, A. Mokhlisse, M.B. Channa, A. Outzourhit, Fuel 79 (2000) 733. Z. Hussain, K.M. Khan, K. Hussain, J. Anal. Appl. Pyrolysis 89 (1) (2010) 39. L.L. Gasner, A.O. Denloyet, T.M. Regan, Chem. Eng. Commun. 48 (1986) 349.
Chinese Chemical Letters 22 (2011) 1084–1086 www.elsevier.com/locate/cclet
Microwaves spark emission spectroscopy for the analysis of cations: A simple form of atomic emission spectroscopy Zahid Hussain a,*, Khalid Mohammed Khan b, Khadim Hussain c, Sadam Hussain d, Shahnaz Perveen e b
a Department of Chemistry, Abdul Wali Khan University, Mardan, Pakistan H. E. J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi 75270, Pakistan c Department of Chemistry, Hazara University, Mansehra, Pakistan d Department of Electronics, Quaid-I-Azam University, Islamabad, Pakistan e PCSIR Laboratories Complex, Shahrah-e-Dr. Salimuzzaman Siddiqui, Karachi 75280, Pakistan
Received 27 December 2010 Available online 25 June 2011
Abstract A novel method for the cation analysis was investigated. The analysis is based on the sparking of the salts of metals in a microwave oven after placing in a graphite cell. The graphite cell absorbs microwaves and produces high temperature which converts the salt into light emitting species. The colour of light was found to dependent on the nature of cation, however, the intensity of the emitted light was found to be depending upon the form and shape of the graphite assembly in addition to the concentration of the salt. This communication presents explanation for all these observations and for the systematic and quantitative analysis using microwave spark emission technique. # 2011 Zahid Hussain. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Microwave spark; Cation analysis; Spark colour; Graphite cell; Atomic emission
Microwaves are electromagnetic radiations of widespread use. Its applications range from heating and cooking to the synthesis and plasma generation. Microwave heating is a volumetric and rapid method of heating [1,2]. Microwave heats up the dielectric materials by changing the rotational energies [3,4]. Now it is also used for heating the materials which are not microwave interactive by adding microwave absorbing materials [5,6]. The microwave absorbing materials include oxides of metals and graphite [7,8]. Graphite absorbs microwaves and generates heat and raises the temperature in the range of 1000 8C. Therefore, it is used for high temperature reactions like pyrolysis of coal, sludge, waste plastics [9–12], The use of microwave energy for the generation of plasma is also reported [13]. Microwave induced plasma is used for the atomization in fluorescence spectroscopy. Emission spectroscopy is one of the important analytical tools and among the emission techniques flame photometry is important for the analysis of alkali and alkaline earth metals where the source of excitation and vaporization is a flame. However, it is associated with some of the serious problems like the variation in response due to fluctuation in fuel to oxidant ratio. Further more it is * Corresponding author. E-mail address: [email protected] (Z. Hussain). 1001-8417/$ – see front matter # 2011 Zahid Hussain. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2011.03.019
Z. Hussain et al. / Chinese Chemical Letters 22 (2011) 1084–1086
1085
restricted to the use of solutions. There is need to have an effective analytical technique having the potential to be used as excitation source as well as atomization source.In the present work use of graphite is aimed to develop an easy and sensitive method for the cation analysis based on emission. Graphite was used as heat producing material by absorbing the microwaves and also acts as a cell for the analyte and the generated heat was used for atomization as well as excitation. 1. Experimental The experiments for microwave spark emission spectroscopy were carried out in a medium sized domestic on/off microwave oven of the 2450 MHz frequency. A window was made by cutting the side of the microwave oven for observations. The graphite rod was obtained from a used dry cell. A pit of about 1 mm depth and diameter was made at the end of the rod for holding the sample. It was placed on a ceramic disc and a piece of another rod of about 10 mm length was placed on the sample pit after the charging of pit with dry salt. The whole assembly was placed in the microwave oven and the microwaves were applied which resulted the coloured spark. Three important experiments were carried out; the analysis of the multi mineral tablet, the copper wire piece and the solid copper sulphate. 2. Results and discussion 2.1. The light emission process and mechanism Graphite was used as microwave absorbing antenna and cell for the sample to be analyzed. This experiment was designed to atomize and excite the atoms of the analyte by the high temperature produced due to the absorption of microwaves. Graphite is a microwave absorbing material which generates large quantity of heat on interaction with microwaves and this heat was used for the atomization of the metal salts. It is believed that atomization and excitation of the atoms is a combine process of the high temperature and absorption of the microwaves by the sample to be analyzed. The heat produced by the graphite alters the microwave absorbing capacity of the sample and the absorption of microwaves by the graphite directs the flux of microwaves to the sample which results greater absorption of the microwaves energy by the sample which resulted in atomization. These atoms emit characteristic light on relaxation and it was observed that sodium chloride emits golden yellow light on placing in the sample pit in the graphite rod, however, the light from potassium chloride was found violet. In case of the calcium the colour was yellowish and in case of copper sulphate the colour of spark was found green. The intensity of emitted lights was found to depend upon the form and shape of graphite antenna or cell in addition to the concentration of sample. When a plate of 3 in. 4 in. was used the intensity of the emitted light was low, whereas in case of the graphite rod the intensity of light was found to be higher. The intensity was further enhanced when a piece of the rod was placed on the sample pit in the graphite rod. This is due to the increased amount of heat due to greater microwave flux which amplified the atomization efficiency. Nonetheless, when a T-shape was formed by placing another graphite rod on the sample pit, further increase in intensity was observed. This technique can be used for the quick qualitative and quantitative analysis of metal salts mixtures as well as a single salt. When a 0.1 g piece of multivitamin and mineral combination tablet Stress tablet1 of Wyeth was placed in the sample pit a combination of colours was observed after pyrolysis of the sample. During this experiment interesting observation was also made which was the appearance of different colours with the rotation of the microwave disc. It may either be correlated with the differential vaporization or the separation during the destruction of organic lattice by microwaves. The colour observed for the Stress tablet1 were, green, yellowish and intense white. While the composition provided by the manufacturer was calcium pentothenate, cupric oxide and zinc sulphate along with organic compounds. This experiment leads to the conclusion that microwave spark emission spectroscopy may be a method of choice for the analysis of metal salts and its mixtures if shaped into proper instrument. 2.2. Analysis of metals and salts of metals The spark behaviour of the copper metal and copper sulphate was studied using microwave induced sparking. It was observed that the piece of copper give whitish light in the early shots of the microwaves. But after two seconds the colour of the light turned greenish and green. This change in colour is believed due to the compounds of the copper
1086
Z. Hussain et al. / Chinese Chemical Letters 22 (2011) 1084–1086
which is in this case mainly oxide of copper. The interaction of copper with air in the microwave oven results the formation of copper oxide. The concentration of this compound increases with the passage of time. That is why the change in the colour of and intensity of light is observed. This colour transition leads to three conclusions, the green light emits from the copper compounds, the intensity of light depends upon the concentration of compound and the method is useful in studying the rate of reactions and can analyze micro layers. The dependence of the intensity of radiations on the concentration was investigated by placing small quantity of solid copper sulphate in the sample pit instead of copper. It was observed that copper sulphate give intense green spark in the early shots of microwaves. This technique was initially used for the solid samples but it can also be extended to the solutions. 2.3. The base of IR emission spectroscopy and thermo-gravimetry using the microwaves spark emission spectroscopy Microwave spark emission spectroscopy was initially applied for the qualitative analysis of the solid samples. The process involves heat generation. This heat and microwaves are used for the excitation and atomization. The heat generation process is faster and volumetric. This can be extended to two more analytical techniques. It can be observed from the multi mineral tablet analysis that the process is associated with the weight loss, but in case of the copper wire experiment increase in weight is expected due to the oxide formation. Based on these observations this technique can further be extended to the rapid thermal analysis. This process involves rapid heating of the cell and sample. One of the other conclusions is the emission of the characteristic IR radiations according to the nature of the compound. The use of high resolving instrument enables to determine the nature of compound based on the emitted IR radiations in addition to the UVand visible radiations of the characteristic frequency. It is because of the rapid microwave heating and the dependence of the intensity of emitted light the detection range can be extended to the nano gram level. 3. Conclusion A new atomic emission spectroscopic technique was investigated. The excitation and atomization were carried out by exploiting the microwave absorption and heat generation of the graphite. This technique can be used for the demonstration of the electronic excitation experiments in the laboratory. Based on this process a spectrometer is proposed which will be used both for qualitative and quantitative analysis. This could be a faster emission technique due to the rapid volumetric absorption of microwave and generation of heat which result faster excitation process. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
T.J. Appleton, R.I. Colder, S.W. Kingman, I.S. Lowndes, A.G. Read, Appl. Energy 81 (1) (2005) 85. V. Santagada, E. Persssuti, G. Caliendo, Curr. Med. Chem. 9 (2002) 1252. M. Hamid, Heat Transfer Eng. 13 (1992) 73. C. Ludlow-Palafox, A.C. Howard, Ind. Eng. Chem. Res. 40 (2001) 4749. J.A. Menendez, M. Inguanzo, J.J. Pis, Water Res. 36 (2002) 3261. P. Monsef-Mirzai, M. Ravindran, W.R. McWhinnie, P. Burchill, Fuel 74 (1995) 20. A. Dominguez, J.A. Menendez, M. Inguanzo, et al. J. Chromatogr. A 1012 (2003) 193. M. Juma, Z. Korenˇova´, J. Markosˇ, et al. Petrol. Coal 48 (2006) 15. B. Kriegerbrockett, Res. Chem. Intermed. 20 (1) (1994) 39. M.B. Chanaa, M. Lallemant, A. Mokhlisse, Fuel 73 (1994) 1643. K. El harfi, A. Mokhlisse, M.B. Channa, A. Outzourhit, Fuel 79 (2000) 733. Z. Hussain, K.M. Khan, K. Hussain, J. Anal. Appl. Pyrolysis 89 (1) (2010) 39. L.L. Gasner, A.O. Denloyet, T.M. Regan, Chem. Eng. Commun. 48 (1986) 349.