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Elemental analysis of horse hair by optical emission spectroscopy
Elemental
Analysis of Horse Hair by Optical Emission Spectroscopy
AND
INTRODUCTION In veterinary science, the knowledge of trace elements in biological materials of farm animals is important from the point of view of their production, feeding, and health requirements. The trace element analysis of hair has a further possibility of helping forensic sciences as these are capable of storing the quantities of elements in excess concentration. Few optical emission spectroscopic (OES) methods (2, 3) are reported for the analysis of human hair but there is no method reported in literature for the analysis of horse hair. The methods reported for human hair are normally developed for the determination of one or two elements at a time and there is a lack of simultaneous multielement determination approach. The method described here is developed for the simultaneous determination of 26 trace elements in horse hair. MATERIALS
AND METHODS
(I ). Prepurmtion qf the Sample The hair is cleaned with acetone to remove any grease and washed with EDTA (ethylenediaminetetraacetic acid) to remove the superficial contaminants. 500 mg of cleaned hair is ashed in a platinum crucible inside a muffle furnace (Thermolyne-2000) having a temperature controller. The temperature of the furnace is kept at 300°C for 1 hr and then raised to 450°C for 4 hr. The ash is dissolved in a minimum amount of pure nitric acid and 100 mg graphite powder (National Spectroscopic) is added to the solution. Enough distilled water is added to wet the graphite and the Xl
88
CHANDOLA
AND
LORDELLO
sample is dried on a hot plate. The graphite now contains trace elements from hair, concentrated five-fold. (2). Preparation
of Standards
The standards are prepared on graphite powder (National Spectroscopic). Since there was no previous knowledge about the elements present in horse hair, Spex Mix powder (Spex Industries, Metuchen, New Jersey) is used to provide the analyte elements. The Spex Mix contains compounds of 49 common elements such that each element is present at the concentration of 1.28% in the mixture. Ten standards in the range I- 1000 ppm of each element are prepared. These standards provide a wide scope for qualitative detection and quantitative determination of many elements simultaneously. (3). Internal
Standard Mixture
A noble metal element palladium (Pd) is chosen as an internal standard since it gives two suitable lines at 2476.42 A and 3242.7 A for use with low and high wavelength lines, respectively. An internal standard mixture containing 0.002% Pd (added as ammonium chloro palladite) on graphite is prepared. This mixture is added to samples and standards in the weight ratio 1:l to provide 0.001% Pd as an internal standard. (4). Electrode Assembly and Volatilization
Studies
A complete burn of the sample was necessary for quantitative estimation of all the volatile and refractory elements in the sample. A Scribner Mullins shallow cup electrode 4030 (Union Carbide Corporation, New York) was specially under-cut (1) by us for the purpose. A volatilization study with the modified electrode showed that all the elements from the sample volatilized from this electrode in 30 set as against in more than 75 set from the original electrode. This electrode sits on a pedestal electrode 9068 and the counter electrode used is 4036 (UCC). (5). Experimental
Conditions
A 10 mg charge consisting of sample and internal standard mixture (1: 1) is loaded in the cup of electrode assembly described in (4) and an analytical gap of 4 mm is maintained. The sample electrode is made an anode in a DC arc (Standard Varisource, Jarrel Ash Co.) run at 10 A and the resulting spectrum is dispersed by a 15,000 lines per inch grating (reciprocal linear dispersion 2.5 A/mm in second order) in a Jarrel Ash 3.4 m spectrograph having an Ebert mount. The wavelength region 2300-3500 A is recorded on two Kodak SA-1 plates of lo-in. length. A nonrecording type microphotometer is used for finding the transmittances of selected analysis lines which are converted to intensity value through Seidel func-
ANALYSIS
OF HORSE
HAIR
BY OES
80
TABLE I DATA ON ANAI.YSIS OF H~RSF HAIR
No.
Element
I 2 3 4 5 6 7 8 9 IO II 12 I3 I4 IS I6 I7 I8 I9 20 21 22 23 24 2s 26
A& Al AS” B Be” Bi” Ca Cd” Cd’ CT” CU Fe Ga” Mg Mn Md’ Nil Ni” P Pb Sb” Si Sn” Ti V Zn
4nalytical line (A, 3280.68 2561.99 2780.20 2491.73 3131.07 3067.72 31.58.87 3261.06 2424.93 2835.63 3273.Yh 2599.57 2943.64 2779.83 2605.69 3132.59 3302.99 3050.82 2534.01 2833.07 2598.06 2435.16 2839.99 3199.91 3183.41 3282.33
Estimation range I” (pm
Estimated amount 2’ (wm)
Standard deviation Cc;
l-20 100-1000 so 1000 s- IO0 I -so s -500 20- IO00 so--1000 IO- 1000 5 -- IO00 I -50 IO-500 5 -500 2s -520 l-100 10-1000 loo- 1000 10-1000 200- 1000 so- 500 20- IO00 ho- 1050 S-IO00 IO-200 35-225 IO0 ~- 1000
IO 900 ND 3 ND ND 400 ND ND ND IO 70 ND 200 s ND 200 ND I50 60 ND 200 ND 5 20 3.50
I5 I4 24 16 IO I0
IO IO II -
/Vofc. ND-not detected. ” Semiquantitative. ’ On graphite. ” On hair.
tion. The emulsion is calibrated with the help of a seven step rotating sector with a step ratio 2:l. (6). Ancllytical
Lines und Working Cur\les
The analytical lines are chosen to cover the predetermined concentration range and are not necessarily the most sensitive lines in the recorded region of the spectrum. The lines chosen and the concentration range covered by them are given in Table 1. The working curves relating log intensity ratio to log concentration are drawn only for the elements found in horse hair, viz., Ag, Al, B, Ca, Cu, Fe, Mg, Mn, Na, P, Pb, Si, Ti, V. and Zn and these are found to be
90
CHANDOLA
AND
LORDELLO
straight lines. The working curves for elements Mg, Si, and V are drawn after a residual correction of 20 ppm, 50 ppm, and 25 ppm, respectively, since the electrodes used contribute these elements. The internal standard line Pd 2476.42 A is used for elements Al, B, Fe, Mg, Mn, Pb, and Si; while Pd 3242.70 8, is used for elements Ag, Ca, Cu, Ti, V, and Zn. For the elements P and Na, the relative intensity to concentration curves give a better fit for straight lines and therefore intensity ratios are not calculated for them. RESULTS
The quantitative estimates of 15 elements found in horse hair are given in Table 1. Eleven other elements, which were looked for but were not detected, are marked ND. The precision of the determinations was calculated in terms of relative standard deviations and is given in the last column of Table 1. CONCLUSION
The capability of OES method to perform a simultaneous multielemental analysis has been utilized for the first time for the analysis of hair (human or animal). This method can first qualitatively look for the elements present and then esimate them quantitatively. The method is simple and can be adopted by any laboratory doing OES analysis. SUMMARY A spectrographic method is developed for the simultaneous determination of trace elements in horse hair. The quantitative estimates ofelements Ag. Al, B, Ca. Cu, Fe. Mg, Mn, Na, P. Pb, Si, Ti, v, and Zn are reported and the precision of determination for some elements is given.
ACKNOWLEDGMENTS This work was done at Institute the Energia Atomica (IEA), Sao Paula, Brazil. The authors express their thanks to Drs. Alcidio Abrao and Claudio Rodrigues for their keen interest in the work. One of the authors (L.C.C.) thanks Professor Romulo Ribeiro Pieroni for the invitation to work in IEA as an international collaborator and to Dr. N. A. Narasimham of BARC for arranging the leave of absence.
REFERENCES 1. Chandola, L. C., Modifications to Scribner Mullins shallow cup (SMSC) electrode for rapid volatilisation. Clrrr. SC,;. 50, 581-582 (1981). 2. Hambidge, K. M., Use of static argon atmosphere in emission spectrochemical determination of chromium in biological materials. Atrtr/yt. C‘hcm. 43, 103- 107 (1971). 3. Lichte, F. E.. and Skogerboe, R. K., The emission spectrometric determination of arsenic. Au~r/~~r. Chum. 44, l480- 1482 (1972).
Analysis of Horse Hair by Optical Emission Spectroscopy
AND
INTRODUCTION In veterinary science, the knowledge of trace elements in biological materials of farm animals is important from the point of view of their production, feeding, and health requirements. The trace element analysis of hair has a further possibility of helping forensic sciences as these are capable of storing the quantities of elements in excess concentration. Few optical emission spectroscopic (OES) methods (2, 3) are reported for the analysis of human hair but there is no method reported in literature for the analysis of horse hair. The methods reported for human hair are normally developed for the determination of one or two elements at a time and there is a lack of simultaneous multielement determination approach. The method described here is developed for the simultaneous determination of 26 trace elements in horse hair. MATERIALS
AND METHODS
(I ). Prepurmtion qf the Sample The hair is cleaned with acetone to remove any grease and washed with EDTA (ethylenediaminetetraacetic acid) to remove the superficial contaminants. 500 mg of cleaned hair is ashed in a platinum crucible inside a muffle furnace (Thermolyne-2000) having a temperature controller. The temperature of the furnace is kept at 300°C for 1 hr and then raised to 450°C for 4 hr. The ash is dissolved in a minimum amount of pure nitric acid and 100 mg graphite powder (National Spectroscopic) is added to the solution. Enough distilled water is added to wet the graphite and the Xl
88
CHANDOLA
AND
LORDELLO
sample is dried on a hot plate. The graphite now contains trace elements from hair, concentrated five-fold. (2). Preparation
of Standards
The standards are prepared on graphite powder (National Spectroscopic). Since there was no previous knowledge about the elements present in horse hair, Spex Mix powder (Spex Industries, Metuchen, New Jersey) is used to provide the analyte elements. The Spex Mix contains compounds of 49 common elements such that each element is present at the concentration of 1.28% in the mixture. Ten standards in the range I- 1000 ppm of each element are prepared. These standards provide a wide scope for qualitative detection and quantitative determination of many elements simultaneously. (3). Internal
Standard Mixture
A noble metal element palladium (Pd) is chosen as an internal standard since it gives two suitable lines at 2476.42 A and 3242.7 A for use with low and high wavelength lines, respectively. An internal standard mixture containing 0.002% Pd (added as ammonium chloro palladite) on graphite is prepared. This mixture is added to samples and standards in the weight ratio 1:l to provide 0.001% Pd as an internal standard. (4). Electrode Assembly and Volatilization
Studies
A complete burn of the sample was necessary for quantitative estimation of all the volatile and refractory elements in the sample. A Scribner Mullins shallow cup electrode 4030 (Union Carbide Corporation, New York) was specially under-cut (1) by us for the purpose. A volatilization study with the modified electrode showed that all the elements from the sample volatilized from this electrode in 30 set as against in more than 75 set from the original electrode. This electrode sits on a pedestal electrode 9068 and the counter electrode used is 4036 (UCC). (5). Experimental
Conditions
A 10 mg charge consisting of sample and internal standard mixture (1: 1) is loaded in the cup of electrode assembly described in (4) and an analytical gap of 4 mm is maintained. The sample electrode is made an anode in a DC arc (Standard Varisource, Jarrel Ash Co.) run at 10 A and the resulting spectrum is dispersed by a 15,000 lines per inch grating (reciprocal linear dispersion 2.5 A/mm in second order) in a Jarrel Ash 3.4 m spectrograph having an Ebert mount. The wavelength region 2300-3500 A is recorded on two Kodak SA-1 plates of lo-in. length. A nonrecording type microphotometer is used for finding the transmittances of selected analysis lines which are converted to intensity value through Seidel func-
ANALYSIS
OF HORSE
HAIR
BY OES
80
TABLE I DATA ON ANAI.YSIS OF H~RSF HAIR
No.
Element
I 2 3 4 5 6 7 8 9 IO II 12 I3 I4 IS I6 I7 I8 I9 20 21 22 23 24 2s 26
A& Al AS” B Be” Bi” Ca Cd” Cd’ CT” CU Fe Ga” Mg Mn Md’ Nil Ni” P Pb Sb” Si Sn” Ti V Zn
4nalytical line (A, 3280.68 2561.99 2780.20 2491.73 3131.07 3067.72 31.58.87 3261.06 2424.93 2835.63 3273.Yh 2599.57 2943.64 2779.83 2605.69 3132.59 3302.99 3050.82 2534.01 2833.07 2598.06 2435.16 2839.99 3199.91 3183.41 3282.33
Estimation range I” (pm
Estimated amount 2’ (wm)
Standard deviation Cc;
l-20 100-1000 so 1000 s- IO0 I -so s -500 20- IO00 so--1000 IO- 1000 5 -- IO00 I -50 IO-500 5 -500 2s -520 l-100 10-1000 loo- 1000 10-1000 200- 1000 so- 500 20- IO00 ho- 1050 S-IO00 IO-200 35-225 IO0 ~- 1000
IO 900 ND 3 ND ND 400 ND ND ND IO 70 ND 200 s ND 200 ND I50 60 ND 200 ND 5 20 3.50
I5 I4 24 16 IO I0
IO IO II -
/Vofc. ND-not detected. ” Semiquantitative. ’ On graphite. ” On hair.
tion. The emulsion is calibrated with the help of a seven step rotating sector with a step ratio 2:l. (6). Ancllytical
Lines und Working Cur\les
The analytical lines are chosen to cover the predetermined concentration range and are not necessarily the most sensitive lines in the recorded region of the spectrum. The lines chosen and the concentration range covered by them are given in Table 1. The working curves relating log intensity ratio to log concentration are drawn only for the elements found in horse hair, viz., Ag, Al, B, Ca, Cu, Fe, Mg, Mn, Na, P, Pb, Si, Ti, V. and Zn and these are found to be
90
CHANDOLA
AND
LORDELLO
straight lines. The working curves for elements Mg, Si, and V are drawn after a residual correction of 20 ppm, 50 ppm, and 25 ppm, respectively, since the electrodes used contribute these elements. The internal standard line Pd 2476.42 A is used for elements Al, B, Fe, Mg, Mn, Pb, and Si; while Pd 3242.70 8, is used for elements Ag, Ca, Cu, Ti, V, and Zn. For the elements P and Na, the relative intensity to concentration curves give a better fit for straight lines and therefore intensity ratios are not calculated for them. RESULTS
The quantitative estimates of 15 elements found in horse hair are given in Table 1. Eleven other elements, which were looked for but were not detected, are marked ND. The precision of the determinations was calculated in terms of relative standard deviations and is given in the last column of Table 1. CONCLUSION
The capability of OES method to perform a simultaneous multielemental analysis has been utilized for the first time for the analysis of hair (human or animal). This method can first qualitatively look for the elements present and then esimate them quantitatively. The method is simple and can be adopted by any laboratory doing OES analysis. SUMMARY A spectrographic method is developed for the simultaneous determination of trace elements in horse hair. The quantitative estimates ofelements Ag. Al, B, Ca. Cu, Fe. Mg, Mn, Na, P. Pb, Si, Ti, v, and Zn are reported and the precision of determination for some elements is given.
ACKNOWLEDGMENTS This work was done at Institute the Energia Atomica (IEA), Sao Paula, Brazil. The authors express their thanks to Drs. Alcidio Abrao and Claudio Rodrigues for their keen interest in the work. One of the authors (L.C.C.) thanks Professor Romulo Ribeiro Pieroni for the invitation to work in IEA as an international collaborator and to Dr. N. A. Narasimham of BARC for arranging the leave of absence.
REFERENCES 1. Chandola, L. C., Modifications to Scribner Mullins shallow cup (SMSC) electrode for rapid volatilisation. Clrrr. SC,;. 50, 581-582 (1981). 2. Hambidge, K. M., Use of static argon atmosphere in emission spectrochemical determination of chromium in biological materials. Atrtr/yt. C‘hcm. 43, 103- 107 (1971). 3. Lichte, F. E.. and Skogerboe, R. K., The emission spectrometric determination of arsenic. Au~r/~~r. Chum. 44, l480- 1482 (1972).