ToF-SIMS – Time of Flight-Secondary Ion Mass Spectroscopy

A surface analytical technique

• Routine analytical technique

• Detailed chemical structure information

• High sensitivity

• New primary ion sources (Au, Bi, & buckministerfullerene

General Schematic

Principles of ToF-SIMS

Pulsed primary ion beam

Emission of particles – SECONDARY IONS

Ions are mass analyzed by FLIGHT TIMES

Two modes of analysis: static & spectroscopic

TOF-SIMS

                                                                                                                                                                

                                                                                

Bombard surface with gallium and run through mass spectrometer

Gives both chemical composition of surface and “SEM-like” image of where chemicals are located

Lightly used on lignocellulosic materials

Find concentrations as low as 10 ppm

http://www.phi.com/genf.asp?ID=83

Static Mode

Delicate organics (biomaterials)

Undamaged (opposed to X-ray fluorescence microscopy)

Surface sensitive (outermost couple of nm)

Spectroscopic Mode

ONLY mass spectral (MS) data provided

Chemical imaging is POSSIBLE

Raster a micro-focused ion beam (sound familiar???) over surface

Collect MS

Map distribution of species

Organic imaging technique

Previously, limted by most significant signals – polyatomic clusters

For example, most biomaterials dominated by fragments (CxHy

+/-) at low mass (< m/z 100) – MORE than one species

NOT DIAGNOSTIC

Higher-order chemical imaging

Larger masses (m/z > 200) more structurally assignable and unique

Chemical mapping possible

Ga+ bombardment doesn’t allow for sufficient sensitivity for good imaging

Polyatomic primary ion sources overcomes deficiency (Aun

+, Bin+, C60+) 100x increases in

secondary ion yields

Chemical imaging of pharmaceuticals

Drug-loaded particles can be visualized with Bi3+, whereas with Ga+ they cannot

Due to low intensity of molecular ion peak

Tablet formulations can be studied – distribution of drug, excipient(s), lubricant(s) on surface and in bulk

Thickness & uniformity can be assessed

ToF-SIMS Images

Nylon mesh – 10 micron depth Plasma cleaned scalpel blade

Distribution of materials

10 micron diameter hair fibers

Lignocellulosic biomaterials The work of Thompson with superoxide (Potassium

superoxide) in DMSO found attack in amorphous regions first

Hemicellulose and lignin removed more rapidly than cellulose

The work of Kim with periodate oxidation suggests that the attack on crystalline cellulose proceeds highly heterogeneously

Once an area is damaged, however, the area becomes more susceptible to damage due to loss of crystalline order

Thompson, N.S., Corbett, H.M, “The effect of potassium superoxide on cellulose”, TAPPI, 68:12, pp. 68-72, 1985.

Kim, U., Kuga, S., Wada, M., Okano, T., Kondo, T. “Periodate oxidation of crystalline cellulose”, Biomacromolecules, 1:488-492, 2000.

TOF-SIMS hypotheses Lind studied the ability of hydroxyl radicals to induce viscosity

loss in cellulose fibers

In their work they found that the decrease in viscosity was proportional to the imparted irradiation dose

This can be read to mean that as the number of hydroxyl radicals increases, so does the cellulose degradation

The work of Lind studied the role of hydroxyl radicals in viscosity loss using ionizing radiation

In their work they found that almost no amount of radical scavenger could protect against depolymerization of the cellulose

This means that hydroxyl radicals produced outside the cellulose surfaces have a minimal effect on degradation and are more likely produced very near to their consumption point

Lind, J., Merényi, G., “Hydroxyl radical induced viscosity loss in cellulose fibers”, J. Wood Chem. Technol., 17,(1,2), pp. 111-117 (1997).

TOF-SIMS hypotheses, continued

Metal-induced peroxide cellulose degradation causes the creation of carboxylic acid content

Work of Lind shows that hydroxyl radicals are formed and react very near to the carbohydrate surface

Work of Kleen has been used to measure metals on fiber surface as compared to bulk during bleaching, Found majority of metals, 5 to 55 times bulk, on surface

Not likely to be precipitates due to the fact that the sheets were made at a pH of 5

M. Kleen, Sixth European Workshop on Lignocellulosics and Pulp, 41-44 (2000)

Central hypothesis of work

Hypothesis: We are seeing metals bound to carboxylic acid groups caused by radical degradation of cellulose

Metal distribution begins rather homogeneous in the unbleached case, but becomes heterogeneous in the bleached cases

Attack appears heterogeneous concentrated and surface orientated due to the fact it does not appear “deep” enough to be seen by SEM under comparable resolutions

Total Ion Image Unbleached Mg Bleached Mg Bleached + 50ppm iron Fe

ESCA

Used to identify carbon and oxygen and the oxidation level

Has been utilized for the detection of carboxyl content (mostly fiber modification work) in literature and is comparable to other methods

We appear to have a difference between the bleached and unbleached samples in COOH content

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Binding Energy (eV)c/

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C-C

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C=O

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Viscosity and physical testing

As the load bearing structure of a fiber, the cellulose chains, are being cleaved or “peeled” the mechanical strength of a fiber should decrease

This change should manifest itself in test to include the zero-span tensile and the standard tensile test

Viscosity and physical testing Chain scission count increases as

degradation conditions become more favorable

Zero-span tensile tests show strength decrease as well. Perhaps we also see chemical refining

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Summary

TOF-SIMS appears to visualize degradation through the indirect measurement of COOH groups

The analysis of this degradation can be coupled with other techniques including ESCA, viscosity, and zero-span tensile

Degradation appears to be a heterogeneous surface phenonemon

Other work

Phytic Acid Chelation

Relatively unstudied chelant that is a product of unwanted by-products of corn

Current data shows performance on par with DTPA/EDTA, but effectiveness is very pulp dependent

Agriculture literature says excellent chelant for iron

Studying it as a bleaching additive and chelant on many different pulp samples and at differing pH

What direction next?