Nuclear Instruments and Methods 181 (198t) 279-280 © North-Holland Publishing Company
ELEMENT ANALYSIS OF A CELL WALL USING PIXE Andreas JAHNKE *, Teruo SHIMMEN, Hiroko KOYAMA-ITO and Toshimitsu YAMAZAKI Faculty of Science and Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108, Japan
The elemental analysis of cell walls of internodal cells of Chara corallina, a fresh water alga, was carried out using PIXE and 28 MeV a-particles from a cyclotron. The cell wall was a suitable monitoring system for heavy metal ions in water. Special attention was paid to the ion specific differences during adsorption to the cell wall.
1. Introduction
3. Results and discussion
In using 28 MeV a-particles for induced X-ray emission of trace elements in water, the following restriction has to be considered: The bremsstrahlung background o f secondary electrons would be too high if the external a-beam hits a drop of the water being analysed. To be as sensitive as possible, three conditions have to be fulfilled. 1) to increase the sensitivity a preconcentration method is necessary; 2) to decrease the background, samples should be thin; and 3) to permit an analysis in vacuum, samples must be dry.
Comparison of the heavy metal content of entire internodal cell with that o f the cell wall showed that, apart from copper, no heavy metal could penetrate into the cell. Metals accumulated differently in the cell wall, so that their relative concentrations were increased by up to 1000 times the initial metal concentrations in the water sample. The accumulation t o o k place when either intact internodal cells or separated cell walls were exposed to the water sample. The differences of adsorption of different ions were the same in both cases. Fig. 1 shows nine representative metals being accumulated by separated cell walls. The cell wall acted as an ion exchanger, because ionized carboxyl groups o f polyuronic acids [3] can bind heavier metals instead o f calcium. The metals in the figure are ordered with decreasing affinity for the caboxyl ligand being expressed by the equilibrium constant [4]. The silver and cadmium values are less accurate than the other metal values due to interference of the L-lines with the K-line of potassium. Simultaneous accumulation o f several metals did not show any significant difference from single metal accumulation. A change of temperature from 8°C to 22°C scarcely affected the accumulation. More detailed results will be published elsewhere.
2. Experimental details The experimental set-up in our PIXE analysis has already been described [1] as has a method to estimate absolute concentrations in biological samples from the peak-to-background ratio [2]. To meet all requirements we used a freshwater alga, Chara corallina Willdenow, which was kept in a medium free o f metal ions heavier than calcium. If an internodal cell of this plant was exposed to a water sample for one day, the cell wall acted as an ion exchanger. The pH value was kept between 6 and 7. Each test resolution was supplemented with 0.01 mM metal ions of one kind. After the incubation the internodal cells were squeezed to separate the cell walls which were then dried and analyzed by PIXE.
We wish to thank Mr. Y. Kashiwa for operating the cyclotron. Funds for this work were provided by the Japanese Ministry of Education, Culture and Science. The author from Germany appreciates the receipt of a Monbusho Scholarship.
* Present address: Technische Universit//t Mfinchen, Fakult//t fiJr Physik, E 12, 8046 Garching, West-Germany. 279
X. ANALYSIS OF BIOLOGICAL SAMPLES
A. Jahnke et al. /Analysis of‘ a cell wall
280
f Ilo-
6 moles/g
dried
material] 8 equlll brlum constant
Q
0
rl CU
Hg
Zn
Fe
Fig. 1. Metal concentration in separated cell walls of internodal ple containing 0.01 mM heavy metal ions at pH 6-7.
References [l] H. Koyama-Ito, A., Jahnke, E. Wada, T. Tsumita and T. Yamazaki, Nucl. Instr. and Meth. 166 (1979) 269. 121 . . Y.J. Uemura. Y. Kuno, H. Kovama. T. Yamazaki and P. Kienle, Null. Instr. and Meth. ;53 (1978) 573.
Sr
@
n 8 n
Ba
Pb
cells of Chara corallina
m 0
Ag
Cd
after one day of exposure
to a water sam-
[3] J. Dainty, A.B. Hope and C. Denby, Aust. J. Biol. Sci. 13 (1960) 267. [4] L.G. SiIldn and A.E. MarteU, Stability constants of metalion complexes, Suppl. No. 1, Special Publication No. 25 (The Chemical Society, London, 1971).