This document describes the development and evaluation of the Diffusive Gradients in Thin-films (DGT) technique for measuring platinum group elements (PGEs; Rh, Pd, Pt) in natural waters. Key findings include: 1) Different binding resins showed higher selectivity and accumulation for specific PGEs (e.g. Purolite S985 for Rh). 2) Measurements of PGEs in river and effluent samples using DGT were successfully conducted. 3) Evaluation experiments determined the diffusion coefficients and elution factors needed for DGT measurement calculations.

1. Ehab ABDULBUR ALFAKHOURY1, Martine LEERMAKERS1
1Department of Analytical, Environmental and Geo- Chemistry (AMGC), Vrije Universiteit Brussel (VUB), Belgium
DGT principles and typical flow work
0.45µm membrane
Binding gel
Diffusive gel
DGT base
DGT cap
DGT assembly
SF-ICP-MS Measurements
from eluent solutionDGT deployment in the
test solution
DGT
disassembly
Elution step (24 h)
𝑪 𝑫𝑮𝑻
=
𝑴×∆𝒈
𝑫× 𝒕 × 𝑨
Where:
M: mass accumulated of the analyte (ng)
∆g: thickness of both the diffusive gel
and the filter (cm)
D: the effective diffusive coefficient of the
analyte (cm2S-1)
t: deployment time ( sec)
A: exposure window (cm2)
Calculation of the concentration
measured by DGT
DGT laboratory evaluation Results and dicussion Field applications
1- In situ DGT field trial (Zenne River)
Zenne River Basin and sampling stations.
Z5
Z7
Z9
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
0.0016
0.0018
Z5 Z7 Z9
µg L-1
Pd
MP102-AGA MPX317-AGA S985-AGA
0
0.0001
0.0002
0.0003
0.0004
0.0005
0.0006
0.0007
Z5 Z7 Z9
µg L-1 Pt
0
0.0001
0.0002
0.0003
0.0004
0.0005
0.0006
0.0007
0.0008
Z5 Z7 Z9
µg L-1
Rh
The measured concentration CDGT of Pt, Pd and Rh in (µg L-1) over 3 days using DGT
units (n=3) with AGA diffusive gel layers overlaid on binding resin gel of AGA and
deployed in Zenne river.
2- In situ DGT field trial (UZ effluent)
0
0.5
1
1.5
2
2.5
1
µg L-1
Pt
MP 102 MPX 317 Purolite S985
0
0.01
0.02
0.03
0.04
1
µg L-1
Pd
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
1
µg L-1
Rh
The measured concentration CDGT of Pt, Pd and Rh in (µg L-1) over 3 days using DGT units
(n=3) with AGA diffusive gel layers overlaid on binding resin gel of AGA and deployed in
UZ effluent.
Evaluating the diffusive gradients in thin-films technique (DGT) for the measurement of
platinum group elements Rh, Pd & Pt in natural waters
Prospective
1- Develop protocol for total dissolved concentration Ctot PGEs concentration in surface
water.
2- Comparison of the measured concentration by DGT (CDGT) and Ctot.
3- Study the selectivity order for the developed DGTs, which has linear accumulation for
PGEs in function of the time.
4- Apply speciation modelling to predict labile PGEs concentration.
Contacts
Prof. Dr. Martine LEERMAKERS : mleermak@vub.ac.be
PhD-Student Ehab ABDULBUR ALFAKHOURY : eabdulbu@vub.ac.be
The 32nd international conference on environmental geochemistry and health, Brussels
Cross section of DGT probe Solution
Diffusive gel
Concentrationofanalyte
Filter
Bindinggel
∆g
Flux Csolution
C = 0
The concentration gradient through
a DGT device at steady state.
**
** measured concentration is one time higher than the limit of the detection.
Acknowledgements
Higher accumulation for Pt, Pd and Rh with respective agarose resin gel impregnated
with MPX 317, MP 102 and S985. Each individual tested resin shows higher
selectivity for one element of the PGEs group.
Context
The increased application of Platinum Group Elements (PGEs) (Pt, Pd, Rh, Ru, Os and Ir) in the last decades, especially as car catalysts but also in other
applications, makes it necessary to monitor the concentration of these elements in the environment, investigate their environmental transformations and
bioavailability.
The passive sampling technique diffusive gradients in thin films (DGT), which is based on the diffusion of labile metal species through a diffusive hydrogel overlaid
on a binding gel allows the determination of time-weighted average concentrations of labile metal species in situ. Moreover, it provides an important pre-
concentration of the analytes on the binding gel which makes it possible to measure very low concentrations of trace elements in aquatic systems. The technique
is well established for many elements, but has not yet been developed for PGEs.
AR is the efficient general eluent for PGEs from the
developed resins’ gels.
* The resin gel dissolved in AR and a clear solution is formed hence the
recovery is considered Max fe=1.
2-Elution Factor fe determination:
Elution step (24 h)
Aqua Regia at 70⁰C
Or
0.2 M Thiourea in 0.01 M HNO3
SF-ICP-MS
Measurements from
eluent solution
M=
𝐶 𝑒
(V 𝑒
+V 𝑔
)
𝐟e
resin gel disk
spiked with PGEs
(24 h)
fe =
mass recovered
mass adsorbed
where Ce is the concentration of the ion in the elution solution, Vg is the volume of gel
in the binding-layer and Ve is the volume of the eluate.
3-The diffusive coefficient D (cm2s-1) determination:
y = 2.95x
R² = 0.9973
y = 3.78x
R² = 0.995
y = 2.58x
R² = 0.994
0
50
100
150
200
250
300
350
0 20 40 60 80
[ng]
Deployment time [h]
103Rh 106Pd 195Pt
Seawater spiked with PGEs.
6,12.....72 h (n=2)
𝐃 =
∆g
Csolution × A
×
∆𝐌
∆𝒕
Elution
&
Measurement The DGT unit uptake with
binding gel impregnated with
Purolite S985.
0.00E+00
1.00E-06
2.00E-06
3.00E-06
4.00E-06
5.00E-06
6.00E-06
MPX 317 MP 102 S985
The diffusion coefficients D (cm2s-1) in AGA
Rh
Pd
Pt
0.00E+00
5.00E-07
1.00E-06
1.50E-06
2.00E-06
2.50E-06
3.00E-06
3.50E-06
4.00E-06
MPX 317 MP 102 S985
The diffusion coefficients D (cm2s-1) in PAM
Rh
Pd
Pt
D is dependant on the resin gel.
The diffusion coefficients D (cm2s-1), of PGEs in the diffusive layers
using DGT units with agarose (AGA) or polyacrylamide (PAM) diffusive gel
layers overlaid on binding gel impregnated with MPX317, MP 102 or S985
and deployed in spiked seawater. Not tested.
D is higher in AGA .
0
0.2
0.4
0.6
0.8
1
1.2
Rh Pd Pt Rh Pd Pt Rh Pd Pt
MP 102 MPX 317 S985
Elution factor
Thiourea AR
MAX* * *
0
50
100
150
0 50 100
µg/L
Pt
0
50
100
150
0 50 100
µg/L
Pd
0
50
100
150
0 50 100
µg/L
Time (h)
Rh
The content of PGEs in the
diffusive gel is constant over time
hence no interaction between
PGEs in the deployment solution
and agarose diffusive gel.
1-PGEs interaction with the agarose (AGA )
diffusive layer:
Seawater spiked with PGEs.
24.....96 h (n=1)
Elution step
2%HCl (24 h)
SF-ICP-MS Measurements
from eluent solution
Not tested.