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Trace element analysis of human hair by PIXE
Nuclear I n s t r u m e n t s and Methods 181 (1981) 2 6 9 - 2 7 3 © North-Holland Publishing C o m p a n y
TRACE ELEMENT ANALYSIS OF HUMAN HAIR BY PIXE
CHEN Jian-xin, GUO Yuan-zhuang, LI Hong-kou, REN Chi-gang, TANG Guo-hun, WANG Xi-de, YANG Fu-chia and YAO Hui-ying Van de Graaff Laboratory, Fudan University, Shanghai, China
P1XE was used to analyze trace elements in h u m a n hair. Using an external beam, hair from workers exposed to GaAs was examined. The results are in fairly good agreement with those obtained by atomic absorption spectroscopy. Using t h e PIXE technique in v a c u u m hair from mentally defective children was analyzed and compared with the hair of normal children. In a similar way, hair from a 3200 year old preserved m u m m y was studied.
destructive method and very time-consuming. It is relatively easy to detect some elements (e.g. Zn), but difficult to detect others (e.g. As). For a given sample, one can only analyze one element. Hence it is very hard to use AAS to analyze the As content of a large number of workers. Moreover, it is not easy to get a large quantity of hair from male workers. PIXE is ideal in all these respects, but it is difficult to quantify the results. Our procedure is as follows: by the external beam (non-vacuum) PIXE technique, small amounts o f hair from each worker were analyzed rapidly and non-destructively. The same samples were
1. Introduction
Analysis of human hair can supply interesting information about human diseases, and in this context the PIXE method is relatively easy to use and has a high sensitivity. However, it is difficult to obtain quantitative results [I]. In this paper we present two methods which attempt to overcome these difficulties. First of all, to analyze hair from workers who had been working in a factory using gallium arsenide, PIXE was used in combination with the atomic absorption spectroscopy method (AAS). AAS is a
Cup Fig. 1. V a c u u m target chamber for PIXE. 269
X. ANALYSIS OF BIOLOGICAL SAMPLES
Chen Jian-xin et al. /Analysis o f human hair
270
then analyzed quantitatively by AAS, but only for Zn. From the ratio of As/Zn obtained using PIXE, the As content will be known quantitatively as well. For some samples, the As content was also measured by AAS and the results agree fairly well with the PIXE results. Secondly, to analyze the hair from mentally defective children and make a comparison with samples from normal children, the hair was placed into a plasma incinerator. The ash samples are dissolved in nitric acid with an appropriate amount of yttrium dissolved in it as an internal standard. A droplet of such a solution was placed on a target backing and dried. The dried sample is then removed to the vacuum target chamber and analyzed by the PIXE method. From the ratio of the peak area relative to that of the yttrium peak, the proportions of all elements measured can be calculated. This is also a quantitative but destructive method. Using it, the hair from a 3200year old mummified human body was also analyzed.
Ep I ¢ 8 HeV Absorber Be 4 5mg/cm 2 Ip 30hA
AL 37mglcm 2
(i
PVC 3 6 mglcm 2
40jsC
I03~
• 102 L_J
/
Fe V7 Mn Ca
10
I
__
5.0
I
l
100
150
X-Ray E n e r g y (keV) Fig. 3. P I X E spectrum o f V Y N S foils.
2. Experimental method 2.1. General arrangement
The set-up for PIXE with an external beam was described in a previous paper [2]. For internal (in
vacuum) beam analysis, a chamber made of lucite, shown schematically in fig. 1 is used. Ease of fabrication is the main advantage of using lucite, in addition to lower X-ray background and transparency. After passing two 6ram diameter carbon collimators
E~ 1.L,8MeV Absorber Be a.5rnglcm 2 Ip 30nA AL 3.7mg/cm 2 O, ¢0uC PVC 3.6mg/crn 2
Ep 19NeV Absorber Be ¢ 5mg/cm 2 Ip 20hA 0, &0 pC
I(~ 7
PVC 12mg/cm 2
104
E __1
K Series
o
o
g -.iIlJ ..I-
4--
E
103
g
1(] e
o LJ
E c
102
o
20 10-9
30
I
I V MnCoCu
C~
Cr F e N J Z n
K
Afomic
¢0
50
I As
Rb Y
I No
*• Z.* • •
__
Number
Fig. 2. M i n i m u m d e t e c t i o n limit curve, using v a c u u m chainbet.
••
• "• ".".d•:
Pd
I
50
I __
10.0 X-Roy Energy (keV)
" I••
150
Fig. 4. P I X E spectrum o f hair containing arsenic.
271
Chen Jian-xin et al. /Analysis of human hair
Table 1 Arsenic contents in some workers. Samples
CI
AAS (ppm)
PIXE (ppm)
Fe Ca
I0 A
No. 1 No. 2 No. 3
Ep 1 A8 HeV Absorber Be t. 5 mg/tm 2 Ip 30hA At 3 7mglcm 2 & A0~C FV~ 3 6mg/cm 2
Zn
As
As
1 l 2.9 122.8 148.7
13.5 4 7
12.4 -+ 1.4 5.7 +- 1.5 11.0 -+ 2.6
103 -'~ g
separated by 48 cm, a 1.48 MeV proton beam was made to impinge on the target. Twelve targets can be put on the reolving target turret. The chamber window for outgoing X-rays was made of 1.2 mg/cm z thick Kapton foil. The X-rays were detected by a 80 rnm z X3 m m thick Si(Li) detector with 185 eV resolution at 5.9 keV. The detector was placed at 135 ° to the incident beam to reduce the background
[3].
Hn
~r
,
tr}
zn cu
t .. 50
100 X-Ray Energy {keY)
1. 150
Fig. 6. PIXE spectrum of hair (defective child).
Tire sensitivity calibration curve and the minimum detection limit curve for K X-rays were measured. The latter is shown in fig. 2. For most elements, the lower limit is about 10 -9 g. 2.2. Sample preparation
Hair containing As was obtained from workers working in a factory handling GaAs. The workers selected were asked to wash their hair using a neutral
[p I Z,S M e V
Ct
i0 A
Absorber
Ip 30hA
CQ
Be A S m g l c m 2 AI 3 7mg/cm 2
Ep t~OJ~C
PVC 3 6 m g / c m 2
Zn
10 3
cleaning agent, followed by several ion-free water rinses. The hair was then cut as near to the roots as possible. It was placed on a thin collodion foil, using a 3% solution of polystyrene in toluene as adhesive agent. The hairs from the children and the m u m m y were cut into pieces of 2 - 3 nun in length and carefully weighed. The weighed hair samples were then placed in a 1 ml pyrex beaker and inserted into the plasma incinerator. The temperature reached is at most 120°C, and the total time for reduction to ash is 12 1 4 h . The recovery efficiency for all elements of interest was greater than 90% as checked by the AAS method. The PIXE spectrum from the VYNS foil which was used as target backing is shown in fig. 3.
~n
o~
u
3. Experimental results
10 2
.,'I
1°I
' !:-:?::.. • O
I
O j
I
5,0
I____
10.0
15.0
X-Ray Energy (keV)
Fig. 5. PIXE spectrum of hair (normal child).
In fig. 4, the PIXE spectrum of hair containing As is shown. F r o m the net counts in the As and Zn peaks, the As contents in the hair samples were calculated. Several factors were considered in these calculations: (1) Since the diameter o f hair is about 70/am, which is larger than the range of 1.9 MeV protons ( ~ 4 0 #m), the hair is treated as a thick target; (2) a hair is assumed to contain many layers with each layer having a thickness of 0.725 ~zm. Since the cross section for PIXE in each layer is nearly constant, each X. ANALYSIS OF BIOLOGICAL SAMPLES
272
Chen Jian-xin et al. / Analysis o f human hair
Normal
children
HentatLy defective children
1.0
o
c o o
=
t.J
.o 4--
o
o
0.5
o
o
o
0
_
0
I
5
I
10
I
I
I
I
I
I
[
15
20
25
30
35
t+0
t+5
Number of cases
Fig. 7. Comparison of Cu/Zn ratio in hair from normal and defective children.
layer can be considered to be a thin target; (3) 90% o f hair consists of light elements, so the absorption of outgoing X-rays can be neglected. Some o f the results are shown in table 1, and compared with those obtained using the AAS method. Further experiments showed that the As content depends strongly upon the length of time the worker has been handling GaAs. As soon as the worker discontinues this work, the As content in his hair gradually decreases. Figs. 5 and 6 show PIXE spectra from the hair of normal children, and of mentally defective children, respectively. F r o m the results of 22 defective children o f about 10 years o f age and 23 normal children of the same age, it is clear that the Cu/Zn ratio in the hair o f defective children is about five times less than for normal children (see fig. 7). Other differences are also apparent. For example, the Fe content in the hair of defective children is much greater. Such information may be helpful to the medical profession in determining the origins o f the defects. Hairs from five bodies from different periods were analyzed. The oldest one is 3200 years old and is that o f a female it is known as the Ha-mi m u m m y , unearthed in 1978 in Ha-mi, Xin-jiang province. It is a dry body and very well preserved. The PIXE spec-
10/+ I
Ca ~
El
Ep It~8MeV Absorber Be /+ 5mglcm 2 Ip 30nA A[ 3 7mg/cm 2 CI ~O]JC PVC 3 6mg/~m 2
I03 I ~n
¢e
[
K
~ Hn
Zn
y
Cu ~ 7
r ~
u 102_
Sr
5.0
10.0 X-Ray Energy (keV)
15.0
Fig. 8. PLXE spectrum o f hair from a 3200-year old human body.
trum o f its hair is shown in fig. 8, and the main results are listed in table 2. The error is estimated at about 30%. After careful comparison with other
Table 2 Trace elements in the hair of a mummy Element
K
Ca
Ti
Cr
Mn
Fe
Cn
Zn
ppm
82.6
3974.9
3.65
57.36
16.26
77.69
43.26
237.9
Chen Jian-xin et al. /Analysis o f human hair
archaeological data, some interesting information should be forthcoming. We wish to thank the Peking Institute of Atomic Energy for their kind support. Appreciation is expressed to Dr. De-qing Zheng for furnishing AAS data and many helpful suggestions, as well as to Prof. G.M. Temmer for his kind help and careful reading of this manuscript.
273
References [ 1 ] N.E. WHitehead, Nucl. Instr. and Meth. 164 (1979) 381. [2] J.X. Chen, H.K. Li, C.G. Ren, G.H. Tang, X.D. Wang, F.C. Yang and H.Y. Yao, Nucl. Instr. and Meth. 168 (1980) 437. [31 H. Kaji, T. Shiokawa, K. Ishii, S. Morita, M. Kamiya, K. Sera and H. Yawara, Nucl. Instr. and Meth. 142 (1977) 21.
X. ANALYSIS OF BIOLOGICAL SAMPLES
TRACE ELEMENT ANALYSIS OF HUMAN HAIR BY PIXE
CHEN Jian-xin, GUO Yuan-zhuang, LI Hong-kou, REN Chi-gang, TANG Guo-hun, WANG Xi-de, YANG Fu-chia and YAO Hui-ying Van de Graaff Laboratory, Fudan University, Shanghai, China
P1XE was used to analyze trace elements in h u m a n hair. Using an external beam, hair from workers exposed to GaAs was examined. The results are in fairly good agreement with those obtained by atomic absorption spectroscopy. Using t h e PIXE technique in v a c u u m hair from mentally defective children was analyzed and compared with the hair of normal children. In a similar way, hair from a 3200 year old preserved m u m m y was studied.
destructive method and very time-consuming. It is relatively easy to detect some elements (e.g. Zn), but difficult to detect others (e.g. As). For a given sample, one can only analyze one element. Hence it is very hard to use AAS to analyze the As content of a large number of workers. Moreover, it is not easy to get a large quantity of hair from male workers. PIXE is ideal in all these respects, but it is difficult to quantify the results. Our procedure is as follows: by the external beam (non-vacuum) PIXE technique, small amounts o f hair from each worker were analyzed rapidly and non-destructively. The same samples were
1. Introduction
Analysis of human hair can supply interesting information about human diseases, and in this context the PIXE method is relatively easy to use and has a high sensitivity. However, it is difficult to obtain quantitative results [I]. In this paper we present two methods which attempt to overcome these difficulties. First of all, to analyze hair from workers who had been working in a factory using gallium arsenide, PIXE was used in combination with the atomic absorption spectroscopy method (AAS). AAS is a
Cup Fig. 1. V a c u u m target chamber for PIXE. 269
X. ANALYSIS OF BIOLOGICAL SAMPLES
Chen Jian-xin et al. /Analysis o f human hair
270
then analyzed quantitatively by AAS, but only for Zn. From the ratio of As/Zn obtained using PIXE, the As content will be known quantitatively as well. For some samples, the As content was also measured by AAS and the results agree fairly well with the PIXE results. Secondly, to analyze the hair from mentally defective children and make a comparison with samples from normal children, the hair was placed into a plasma incinerator. The ash samples are dissolved in nitric acid with an appropriate amount of yttrium dissolved in it as an internal standard. A droplet of such a solution was placed on a target backing and dried. The dried sample is then removed to the vacuum target chamber and analyzed by the PIXE method. From the ratio of the peak area relative to that of the yttrium peak, the proportions of all elements measured can be calculated. This is also a quantitative but destructive method. Using it, the hair from a 3200year old mummified human body was also analyzed.
Ep I ¢ 8 HeV Absorber Be 4 5mg/cm 2 Ip 30hA
AL 37mglcm 2
(i
PVC 3 6 mglcm 2
40jsC
I03~
• 102 L_J
/
Fe V7 Mn Ca
10
I
__
5.0
I
l
100
150
X-Ray E n e r g y (keV) Fig. 3. P I X E spectrum o f V Y N S foils.
2. Experimental method 2.1. General arrangement
The set-up for PIXE with an external beam was described in a previous paper [2]. For internal (in
vacuum) beam analysis, a chamber made of lucite, shown schematically in fig. 1 is used. Ease of fabrication is the main advantage of using lucite, in addition to lower X-ray background and transparency. After passing two 6ram diameter carbon collimators
E~ 1.L,8MeV Absorber Be a.5rnglcm 2 Ip 30nA AL 3.7mg/cm 2 O, ¢0uC PVC 3.6mg/crn 2
Ep 19NeV Absorber Be ¢ 5mg/cm 2 Ip 20hA 0, &0 pC
I(~ 7
PVC 12mg/cm 2
104
E __1
K Series
o
o
g -.iIlJ ..I-
4--
E
103
g
1(] e
o LJ
E c
102
o
20 10-9
30
I
I V MnCoCu
C~
Cr F e N J Z n
K
Afomic
¢0
50
I As
Rb Y
I No
*• Z.* • •
__
Number
Fig. 2. M i n i m u m d e t e c t i o n limit curve, using v a c u u m chainbet.
••
• "• ".".d•:
Pd
I
50
I __
10.0 X-Roy Energy (keV)
" I••
150
Fig. 4. P I X E spectrum o f hair containing arsenic.
271
Chen Jian-xin et al. /Analysis of human hair
Table 1 Arsenic contents in some workers. Samples
CI
AAS (ppm)
PIXE (ppm)
Fe Ca
I0 A
No. 1 No. 2 No. 3
Ep 1 A8 HeV Absorber Be t. 5 mg/tm 2 Ip 30hA At 3 7mglcm 2 & A0~C FV~ 3 6mg/cm 2
Zn
As
As
1 l 2.9 122.8 148.7
13.5 4 7
12.4 -+ 1.4 5.7 +- 1.5 11.0 -+ 2.6
103 -'~ g
separated by 48 cm, a 1.48 MeV proton beam was made to impinge on the target. Twelve targets can be put on the reolving target turret. The chamber window for outgoing X-rays was made of 1.2 mg/cm z thick Kapton foil. The X-rays were detected by a 80 rnm z X3 m m thick Si(Li) detector with 185 eV resolution at 5.9 keV. The detector was placed at 135 ° to the incident beam to reduce the background
[3].
Hn
~r
,
tr}
zn cu
t .. 50
100 X-Ray Energy {keY)
1. 150
Fig. 6. PIXE spectrum of hair (defective child).
Tire sensitivity calibration curve and the minimum detection limit curve for K X-rays were measured. The latter is shown in fig. 2. For most elements, the lower limit is about 10 -9 g. 2.2. Sample preparation
Hair containing As was obtained from workers working in a factory handling GaAs. The workers selected were asked to wash their hair using a neutral
[p I Z,S M e V
Ct
i0 A
Absorber
Ip 30hA
CQ
Be A S m g l c m 2 AI 3 7mg/cm 2
Ep t~OJ~C
PVC 3 6 m g / c m 2
Zn
10 3
cleaning agent, followed by several ion-free water rinses. The hair was then cut as near to the roots as possible. It was placed on a thin collodion foil, using a 3% solution of polystyrene in toluene as adhesive agent. The hairs from the children and the m u m m y were cut into pieces of 2 - 3 nun in length and carefully weighed. The weighed hair samples were then placed in a 1 ml pyrex beaker and inserted into the plasma incinerator. The temperature reached is at most 120°C, and the total time for reduction to ash is 12 1 4 h . The recovery efficiency for all elements of interest was greater than 90% as checked by the AAS method. The PIXE spectrum from the VYNS foil which was used as target backing is shown in fig. 3.
~n
o~
u
3. Experimental results
10 2
.,'I
1°I
' !:-:?::.. • O
I
O j
I
5,0
I____
10.0
15.0
X-Ray Energy (keV)
Fig. 5. PIXE spectrum of hair (normal child).
In fig. 4, the PIXE spectrum of hair containing As is shown. F r o m the net counts in the As and Zn peaks, the As contents in the hair samples were calculated. Several factors were considered in these calculations: (1) Since the diameter o f hair is about 70/am, which is larger than the range of 1.9 MeV protons ( ~ 4 0 #m), the hair is treated as a thick target; (2) a hair is assumed to contain many layers with each layer having a thickness of 0.725 ~zm. Since the cross section for PIXE in each layer is nearly constant, each X. ANALYSIS OF BIOLOGICAL SAMPLES
272
Chen Jian-xin et al. / Analysis o f human hair
Normal
children
HentatLy defective children
1.0
o
c o o
=
t.J
.o 4--
o
o
0.5
o
o
o
0
_
0
I
5
I
10
I
I
I
I
I
I
[
15
20
25
30
35
t+0
t+5
Number of cases
Fig. 7. Comparison of Cu/Zn ratio in hair from normal and defective children.
layer can be considered to be a thin target; (3) 90% o f hair consists of light elements, so the absorption of outgoing X-rays can be neglected. Some o f the results are shown in table 1, and compared with those obtained using the AAS method. Further experiments showed that the As content depends strongly upon the length of time the worker has been handling GaAs. As soon as the worker discontinues this work, the As content in his hair gradually decreases. Figs. 5 and 6 show PIXE spectra from the hair of normal children, and of mentally defective children, respectively. F r o m the results of 22 defective children o f about 10 years o f age and 23 normal children of the same age, it is clear that the Cu/Zn ratio in the hair o f defective children is about five times less than for normal children (see fig. 7). Other differences are also apparent. For example, the Fe content in the hair of defective children is much greater. Such information may be helpful to the medical profession in determining the origins o f the defects. Hairs from five bodies from different periods were analyzed. The oldest one is 3200 years old and is that o f a female it is known as the Ha-mi m u m m y , unearthed in 1978 in Ha-mi, Xin-jiang province. It is a dry body and very well preserved. The PIXE spec-
10/+ I
Ca ~
El
Ep It~8MeV Absorber Be /+ 5mglcm 2 Ip 30nA A[ 3 7mg/cm 2 CI ~O]JC PVC 3 6mg/~m 2
I03 I ~n
¢e
[
K
~ Hn
Zn
y
Cu ~ 7
r ~
u 102_
Sr
5.0
10.0 X-Ray Energy (keV)
15.0
Fig. 8. PLXE spectrum o f hair from a 3200-year old human body.
trum o f its hair is shown in fig. 8, and the main results are listed in table 2. The error is estimated at about 30%. After careful comparison with other
Table 2 Trace elements in the hair of a mummy Element
K
Ca
Ti
Cr
Mn
Fe
Cn
Zn
ppm
82.6
3974.9
3.65
57.36
16.26
77.69
43.26
237.9
Chen Jian-xin et al. /Analysis o f human hair
archaeological data, some interesting information should be forthcoming. We wish to thank the Peking Institute of Atomic Energy for their kind support. Appreciation is expressed to Dr. De-qing Zheng for furnishing AAS data and many helpful suggestions, as well as to Prof. G.M. Temmer for his kind help and careful reading of this manuscript.
273
References [ 1 ] N.E. WHitehead, Nucl. Instr. and Meth. 164 (1979) 381. [2] J.X. Chen, H.K. Li, C.G. Ren, G.H. Tang, X.D. Wang, F.C. Yang and H.Y. Yao, Nucl. Instr. and Meth. 168 (1980) 437. [31 H. Kaji, T. Shiokawa, K. Ishii, S. Morita, M. Kamiya, K. Sera and H. Yawara, Nucl. Instr. and Meth. 142 (1977) 21.
X. ANALYSIS OF BIOLOGICAL SAMPLES