Improving SALD ICP MS Repeatibility Using Cold Plasma Treatment of Substrate

 Marek Stiborek^1,, Masoud Shekargoftar^2, Jakub Kelar^2, Viktor Kanický^1,3 and Jan Preisler^1,3

                                                 ^

      ^1 Department of Chemistry, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic

^2 Regional R&D Center for Low-Cost Plasma and Nanotechnology Surface Modifications, Department of
        Physical Electronics, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic

    ^3 CEITEC-Central European Institute of Technology, Kamenice 5, 625 00 Brno, Czech Republic



    Keywords: SALD ICP MS, dried droplet sample, surface modification, plasma treatment, DCSBD



Introduction:

Substrate-assisted laser desorption inductively coupled plasma mass spectrometry (SALD ICP MS) is a
technique for inorganic analysis of liquid samples of sub-microliter volumes in the form of dried
droplets on suitable plastic substrates.[1] Here we study influence of aging effects on analysis of
cadmium and indium in samples prepared by diffuse coplanar surface barrier discharge (DCSBD)[2]
modification of plastic substrates.


Methods:

A DCSBD device (RPS400-Roplass plasma system 400 W, Roplass, Czech Republic) was used for treatment
of plastic substrates at 400 W. Contact angle of the deposited droplet with Cd and In was measured
using See System E, Advex Instruments, Czech Republic. Samples were desorbed in ablation cell
(UP213, New Wave Research, USA) with a 213-nm laser, and content of ^111Cd and ^115In analyzed by a
quadrupole ICP mass spectrometer (7500ce ICP-MS, Agilent, USA).


Results:

Four plastic substrates (polyethylene terephthalate glycol PETG, polyethylene terephthalate PET,
polycarbonate PC and styrene-acrylonitrile SAN) were exposed to cold plasma for 1, 5 and 10 s.
Droplets of Cd and In solutions in citrate, biological culture medium and cell lysate were
deposited in five replicates immediately, 1, 3, 6 days, 1, 3 or 6 months after the treatment on the
plastic substrates. Droplet contact angles as well as size of the generated stains were
characterized. Typically, longer treatment of surface substrate resulted in lower contact angle.
The stain diameter first increased to a maximum at deposition 1 day after the treatment and then
gradually decreased. Also, the longer the surface treatment was, the slower was return to the
original state (high contact angle). Using In as an internal standard for determination of Cd
significantly reduced RSD, e.g. from ~30 to less than 10 %.


Conclusions:

Aging of the surface treated by DCSBD has been monitored using physical methods and related to SALD
ICP MS of samples prepared on the surface. The initial experiments show significant changes in
contact angle, stain size and SALD ICP MS response. Using an internal standard, RSD values were
reduced to <10 %. A half-year monitoring is under progress; a procedure for surface treatment and
sample preparation will be recommended after completing the entire set of analysis.


Novel Aspect:

Substrate surface treatment by DCSBD for dried droplet preparation. Systematic characterization of
surface aging and its consequences for SALD ICP MS reproducibility.


References:


1.      Peš O., Jungová P., Vyhnánek R., Vaculovič T., Kanický V., Preisler J., Anal. Chem. 80,
8725 (2008).

2.      Černák M., Černáková L’., Hudec I., Kováčik D., Zahoranová A., Eur. Phys. J.-Appl. Phys.
47, 1 (2009).


We acknowledge the financial support of the Czech Science Foundation (GA18-16583S) and the Ministry
of Education, Youth and Sports of the Czech Republic under the project CEITEC 2020 (LQ1601).