Determination of Platinum and

Palladium in Chelated Systems by

GFAAS

Application Note

Atomic Absorption

Authors Introduction
Peter Watkins With the discovery of the anti-tumour properties of cis-dichlorodiammineplatinum(II)
(cisplatin) [1], intensive research has been completed which examines the role of
Elizabeth Yuriev platinum in biological systems. One major field of interest has been the interaction
Department of Environmental of cisplatin and related compounds with biological systems, especially with DNA
Management and its constituents. The interactions of palladium complexes and DNA have also
been examined. Principally, this is due to the labile nature of palladium. Platinum
Victoria University of Technology substitution reactions are known to be slow. Palladium proves to be an ideal model
Melbourne Victoria Australia 3000 because it has similar coordination properties and substitution reactions occur
generally in the order of 105 times faster when compared with platinum.

The technique of atomic absorption spectrometry (AAS) has been employed in this
area of research to measure levels of platinum. It has been used to measure the dis-
tribution of Pt in biological fluids and systems [2] as well as used to study platinum
coordination reactions [3,4].

It has been found that the species active toward the tumour is diaquodiammineplat-
inum(II). Generally, it is synthesized by the removal of the chloride ions from the
complex using silver nitrate [5]. This allows the aquated form to be present in solu-
tion. Though this process is almost always quantitative, there are circumstances
when accurate levels of platinum (and complex) need to be known. One such case
is the determination of the stability constants for Pt-DNA and Pd-DNA complexes.
In this case, it is necessary to use graphite furnace AAS [6]. This paper presents
two methods which are suitable for the determination of platinum and palladium in
systems such as cisplatin and related compounds.
Experimental
Method
An Agilent SpectrAA 400 Atomic Absorption Spectrometer
and GTA96 Graphite Tube Atomizer were employed for the
measurements.

Platinum
A platinum SpectrAA hollow cathode lamp was used and the
samples dispensed into pyrolytically coated graphite tubes.
The Pt resonance line at 265.0 nm was used with a slit width
of 0.2 nm. The lamp current setting was 5 mA.

A 1000 mg/L Pt solution (BDH Ltd, Spectrosol grade) was

used as the stock standard solution. An intermediate solution
of 10 mg/L Pt was prepared by serial dilution using
0.1% v/v HNO3. Working standards were also prepared by
serial dilution from the intermediate solution using
0.1% v/v HNO3.

Palladium
A palladium SpectrAA hollow cathode lamp was used with
pyrolytically coated tubes. The Pd resonance line at 244.8 nm
was used with a slit width of 0.3 nm. The lamp current setting
was 5 mA.

A 1000 mg/L Pd (Aldrich, USA) was used as the stock stan- Figure 1. Optimal furnace parameter results for Pt.
dard solution. An intermediate solution of 10 mg/L Pd as well
as the working standards were prepared as for platinum. Table 1. Furnace Parameters

Gas
Results and Discussion Step Temperature Time flow Gas Read
no (°C) (sec) (L/min) type command
Ashing and atomization studies were performed in order to 1 85 5.0 3.0 Normal No
determine the optimal furnace parameters. A Pt solution was 2 95 40.0 3.0 Normal No
made in the presence of KNO3 and ethylenediamine for this 3 120 10.0 3.0 Normal No
4 700 5.0 3.0 Normal No
purpose. The results are shown in Figure 1. It is clear from 5 700 2.0 3.0 Normal No
Figure 1 that the best region for ashing lies between 6 800 5.0 3.0 Normal No
800–1000 °C and a temperature of 2700 °C was chosen as the 7 800 2.0 3.0 Normal No
atomization temperature. The furnace parameters used for 8 800 2.0 0.0 Normal No
the analysis are shown in Table 1. 9 2700 1.3 0.0 Normal Yes
10 2700 2.0 0.0 Normal Yes
11 2700 2.0 3.0 Normal No

2
A comparison was performed on the use of premixed stan-
dards and those made using the automix facility of the
autosampler. The results are shown in Table 2. It can be seen
that the automix facility provides a calibration graph which is
comparable with that from the premixed standards. This is a
useful feature as it helps to minimize operator error as well as
reduce consumption of the stock solution. The autosampler
parameters are shown in Table 3. A 100 µg/L Pt solution was
used as the standard solution. Figure 2 shows a representative
calibration graph. Figure 2. Representative calibration for Pt.

The precision of the determination was established by analyz- Similar experiments were carried out for palladium. Figure 3
ing a series of five solutions containing approximately 20 mg shows the ashing and atomization curves and Table 5 shows
of K2PtCl4 in 100 mL. After serial dilution, the Pt concentration the furnace parameters used for the analysis.
was calculated. Table 4 shows these results and it can be
seen that the recovery is very good.
Table 2. Comparison of Standard Solutions

Conc Abs
(mg/L) Premixed Automixed
0.0 0.000 0.011
50.0 0.044 (7.7) 0.044 (3.3)
100.0 0.092 (5.2) 0.089 (1.0)
150.0 0.142 (1.0) 0.135 (1.1)
The values in parentheses are the relative standard deviations for 3 replicates

Table 3. Sampler Parameters

Volumes (fL)
Solution Blank Modifier
Blank – 20
Standard 1 5 15
Standard 2 10 10
Standard 3 15 5
Sample 10 10
Recalibration rage 0
Reslope rate 0
Multiple inject No Hot Inject No Pre Inject No

Table 4. Platinum Recovery

Expected Found
result result
Solution (mg/L) (mg/L) % Figure 3. Ashing and atomization curves for Pd.
1 94.5 89.8 95.0
2 93.5 91.5 97.9
3 98.7 97.4 98.7
4 96.8 93.7 96.8
5 99.6 99.9 99.4

3
Table 5. Furnace Parameters Our work has been involved with the determination of forma-
tion constants for Pt/Pd complexes of bidentate ligands. For
Gas
Step Temperature Time flow Gas Read
this task, it is therefore important to have a reliable means of
no (°C) (sec) (L/min) type command accurately measuring the concentrations of each of the
1 85 5.0 3.0 Normal No
reaction components.
2 95 40.0 3.0 Normal No
3 120 10.0 3.0 Normal No The systems which have been examined are complexes of
4 800 5.0 3.0 Normal No Pt and Pd with bidentate ligands. Tables 7 and 8 show some
5 800 1.0 3.0 Normal No results of the analyses. Some of this work has been presented
6 800 2.0 0.0 Normal No elsewhere [7].
7 2600 1.0 0.0 Normal Yes
8 2600 2.0 0.0 Normal Yes Table 7. Results of Analysis
9 2600 2.0 3.0 Normal No
Expected Experimental
A comparison was again made on the use of the automix result result %
Complex (g/L) (g/L) Yield Solvent
facility for preparing the calibration curve, and, as for plat-
inum, the graph compared very favourably with that obtained Pd(bmpe)2+ 17.5 9.9 57 water
Pd(en)2+ 17.8 17.5 98 water
from premixed standards. Table 6 shows the autosampler Pd(bmpe)2+ 9.9 8.3 84 DMSO
parameters and a representative curve is shown in Figure 4. Pd(en)2+ 10.0 8.1 81 DMSO
A 100 µg/L Pd solution was used as the standard solution. The
precision of the analysis was also found to be comparable with
The constituents of DNA shows a wide variation in their solu-
that obtained for platinum.
bilities in a number of solvents. It was therefore important to
establish the efficiency of the removal of chloride from the
complex and, consequently, the yield of the solvated species.
Table 7 shows the results for two complexes which were dis-
solved in water and dimethylsulfoxide. Once established,
proton NMR spectroscopy can be used to study the interac-
tions between the metal complexes and DNA. A number of
other ligands were also investigated and these results are
shown in Table 8.

Table 8. Results of Analysis

Figure 4. Representative calibration for Pd.
Expected Experimental
Table 6. Sampler Parameters result result Percentage
Complex (g/L) (g/L) yield
Volumes (fL) Pd (TMED)2+ 2.8 2.4 86
Solution Blank Modifier Pd (dmp)2+ 6.36 6.36 100
Blank – 20 2.2 1.7 77
Standard 1 2 18 Pd2(bispep)4+ 4.4 1.2 27
Standard 2 4 16 Pd (bpe)2+ 3.9 2.7 70
Standard 3 6 14 Pd (le)2+ 7.0 5.62 80
Sample 10 10 Pt (NH3)22+ 9.95 8.58 86
Pt (en)2+ 7.22 4.1 57
Recalibration rage 0
Reslope rate 0
Multiple inject No Hot inject No Pre inject No

4
References
1. B. Rosenberg, L. van Camp, J. E. Trosko and V.H.
Mansour, Nature (London), 222, 385 (1969).
2. (a) A. F. LeRoy, M. L. Wehling, H. S. Sponseller, W. S.
Friauf, R.E. Solomon, R. L. Dedrick, C. L. Litterst, T. E.
Gram, A. M. Guarino and D.A. Becker, Biochemical
Medicine, 18, 184 (1977).
(b) M. C. McGahan and K. Tyczkowska, Spectrochimica
Acta, 42B, 665 (1987).
3. J. P. Macquet and T. Theophanides, Atomic Absorption
Newsletter, 14, 23 (1975).
4. J. P. Macquet and T. Theophanides, Biochimica et
Biophysica Acta, 442, 142 (1976).
5. B. Lippert, Progress in Inorganic Chemistry, 37, 1 (1989).
6. (a) T. Ren, D. P. Bancroft, W. I. Sundquist, A.
Masschelein, M. V. Keck and S. J. Lippard, J. Am. Chem.
Soc., 115, 11341 (1993).
(b) K. Inagaki and Y. Kidani, Inorg. Chim. Acta, 80, 171
(1983).
7. A. T. Baker, J. K. Crass, G. B. Kok, J. D. Orbell and E.
Yuriev, Inorg. Chim. Acta, 214, 169 (1993).

Key to Ligand Abbreviations

en = ethylenediamine
TMED = tetramethylethylenediamine
bmpe = 1,2-bis(6-methylpyridin-2-yl)ethane
bispep = 1,2-di-(4-methyl-1-piperazinyl)ethane
dmp = 1,4-dimethylpiperazine
le = 1,2-bis(2-imidazolin-2-yl)ethane
bpe = 1,2-bis(pyridin-2-yl)ethane

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