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A BETTER CHOICE: You Can Have It All with ISO-CHEK
®
In the past, industrial hygienists, analytical chemists and other concerned parties were faced with making less than optimum choices when it came to the task of assessing the hazard presented by isocyanate containing atmospheres.
The methods available for this determination were difficult and cumbersome to use while yielding ambiguous results at best. These problems were compounded when testing was placed in the hands of inexperienced users.
The traditional method, NlOSH 5521, calls for an impinger to be used while the air sample was collected, yielding samples that were very susceptible to degradation under ambient conditions. As the result, this method required meticulous care and handling of samples, with storage and shipment to occur immediately upon collection at temperatures no higher than 4ºC, with a lower temperature strongly recommended.
Subsequent preparation of these samples required time consuming acetylation and evaporation steps under nitrogen, with the HPLC analysis producing ambiguous results while employing the difficult technique of electrochemical detection to achieve a measurable response at low levels. To this day, the accuracy and precision of this methodology is either unknown or has not been determined.
OSHA Method 42 uses impregnated glass fiber filters with 1-(2-pyridylpiperazine)or (1-2PP), enabling the formation of a derivative on the filter when the sample was collected and eliminating the need for an impinger. While a marked improvement, the coated filters were not stable, and significant loss of the derivatizing reagent could be expected over a relatively short period of time under ambient conditions 3.
Like its predecessor, this later method also suffered from the limitation of producing ambiguous results as the more toxic monomer containing vapor phase was not adequately resolved from the oligomeric aerosol phase.
As the result of stability and resolution problems, both of these methods failed to produce an accurate assessment of isocyanate exposure risk.
Fortunately, these problems have been solved with the advent of ISO-CHEK®. Suitable for use with any isocyanate, ISO-CHEK® employs a two stage filter arrangement that in the case of TDI and HDI results in the complete separation of vapor from aerosol, as shown in Figure 1 above, at the point of collection rather than relying upon the difficult integration of closely eluting chromatographic peaks. This separation allows for the use of derivatizing reagents that maximize chromatographic resolution.
Air samples collected into the ISO-CHEK® cassette first encounter a 5µm PTFE membrane which traps the aerosol phase while allowing the vapor phase to pass unaffected through to a glass fiber filter impregnated with 9-(N-methylaminomethyl) anthracene (MAMA). There, a reaction occurs resulting in the formation of a stable and highly detectable derivative. Detection limits as low as 0.2µg/m3 have been observed while utilizing an ordinary reverse phase HPLC method with UV and Fluoresence detection. In extensive testing, the coated filters have proven their stability by showing no loss of derivatizing reagent for ten months under ambient conditions. Stability.
The aerosol fraction captured on the 5µm PTFE element is easily derivatized with (Methoxy-2-phenyl-l) piperazine (MOPIP), and treated to obtain a discrete analysis of the aerosol phase.
1,2 = ASTM Standard Method D-5932-96 Patented by lRSST
3 =Poster. paper #398. 1996 AIHCE: Meyer, P.& Czarnecki,B.
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