Electricity + Control October 2019

ANALYTICAL INSTRUMENTATION

Plasma radial view.

However, the periscope’s three additional reflections cut light throughput significantly, with decreased light transmission in the 200 nanometre (nm) range, and even less below 185 nm. So this system cannot provide the high sensitivity of a late-model analyser with an uncompromised direct- light-path axial view. Some background emissions and interferences may further degrade analyses. Furthermore, placing the axial optical interface just above the plasma creates several problems. In samples containing high levels of total dissolved solids or organic materials, contaminants on the interface may fall back down into the plasma, causing instabilities that can skew accurate analysis. The interface also suffers high thermal stress, contributing to increased component wear and greater requirements for maintenance and replacement. Some environmental labs may therefore find this type of instrument problematic, with fairly constant demands for user intervention. The DSOI solution Perhaps the simplest, most successful single ICP-OES solution is dual side-on interface (DSOI) technology. In response to specific user requirements for an optimised ICP-OES system, SPECTRO Analytical Instruments developed

operators who must train for, use, and maintain multiple instrument technologies in a single laboratory. The goal: to purchase one instrument that can cover all ICP-OES-based testing. Conventional dual-view devices have traditionally been the answer. However, these multiplex instruments inherently favour one view – radial or axial – over the other, leading to compromised performance in at least some testing areas. Horizontal-torch axial views prioritise sensitivity; vertical-torch radial views prioritise matrix compatibility and precision of measurement. Dual- view systems have struggled to do both. In recent years, some labs have tried out newer vertical-torch dual-view systems to fill the gap. These use a vertical plasma torch and a direct radial view, plus an axial view supplied via several mirrors in a periscope optic mounted just above the plasma. So users get dual observation of the plasma in a single analysis. This helps eliminate the easily ionisable element (EIE) effect, and often achieves enough sensitivity to measure fairly low levels of challenging elements such as toxic metals (lead, cadmium, mercury, chromium, and similar).

The benefits of DSOI technology - Vertical-torch radial interface - Reduced matrix interferences - Better precision and stability - Only a single plasma view/minimal reflection - No contaminated interfaces - Significantly less maintenance.

Figure 2. Radial plasma observation.

Figure 3. Dual view plasma observation.

Electricity + Control

OCTOBER 2019

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