Tracers

1.      Tracer Selection:

The primary assumption of this method is that tracer color of any type equals a deposit, no matter how small, so being able to differentiate the tracer from the collector and other contaminants is critical. There are a myriad of tracer options; here, a few will be discussed. Some should not be used: the author has attempted to use the fluorescent tracers pyranine and pyrene tetrasulfonic acid (PSTA) (Hoffman et al. 2014), however tracer concentrations in the spray needed to be so high to be detected by visible light optical scanners as to not be practical. Choose a color that is unlikely to be encountered in the environment for the highest quality data. The following concentrations are suggestions based on experience. Experiment with your situation before going to the field and adjust as necessary to gain the proper intensity.

 

Rhodamine WT 20%. Used at .2% volume/volume in a spray solution, rhodamine WT makes a strong magenta stain that is easy to threshold.  There are many concentrations of rhodamine available, take care to source the 20% grade or adjust your concentration accordingly. Using rhodamine WT also gives the option to do quantitative fluorescent tracer analysis along with the qualitative work.

 

FD&C Blue #1: Is a clear, bright, food grade blue available as powder or liquid. It is reasonably priced, and the blue tends to blend in with green foliage in application making the residue less obtrusive than red dyes. If food grade is not necessary, blue marker or pond dye can be good, easily available alternatives. One that the author has good experience with is Cygnet Select™ (Cygnet Industries). Depending on the form purchased, you may need to experiment with the final rate, but target .2% of whatever concentrate you get, or mix powder to a 20% mass/mass solution and try .2% of this liquid to start. FD&C Blue #1 and Cygnet Select can be mixed with PTSA fluorescent tracer to allow both qualitative and quantitative evaluation.

 

Black Food Grade Dye: Was used primarily in the mid 80’s to early nineties to do spray studies, but choosing black dye will eliminate your ability to threshold out contaminants and background texture in your analysis, so avoid black shades unless it is otherwise not feasible to use a more vibrant color.


DAY-GLO® Fluorescent Dyes: Are really ultra-fine grind wettable powder dispersions, often heavily surfacted to overcome the natural hydrophobicity of the vinyl powder that the pigment is compounded in. Most of the available colors make good, clear, readable marks that are easy to detect with a visible light scanner due to the naturally hydrophobic powder pigment that migrates to the edge of the stain as the liquid evaporates. As a powder, handling can be a consideration due to dust-off; If DAY-GLO pigments are to be used, processing should happen relatively soon after exposure and with as little disturbance to the surface as possible. 






 

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Mark Ledebuhr,
Feb 3, 2015, 11:41 AM
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Mark Ledebuhr,
Feb 3, 2015, 11:32 AM
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Mark Ledebuhr,
Feb 3, 2015, 11:31 AM