[shanelinnz]

  Is there any reagent which will change color with the poo but not with the urine? or change slowly with the urine but quickly with the poo? Very appreciated for any comments.

[mike]

This might depend on exactly what you are testing for in each case. Is there something specific you want to identify in the feces that is not present in the urine?

[shanelinnz]

Yes, I am wondering if someone can solve my son's problem.
My son: 1 year old,
Problem: red rash with his buttock, often happened soon after he pooed. But has no problem if he just pass the water, even for a long time.

[mike]

I would strongly suggest NOT using any "reagents" on, near or around your baby.

I would suggest you seek the advice of your doctor.

 

[constant thinker]

See a dermatologist. They specify in skin issues.

It may also being something parasitic in his intestines. When he "poos" the parasitic creature may be able to live in/on his skin.

[billnotgatez]

Current diaper design absorbs and creates a shield against contact with urine. My knowledge base does not have any information that the feces issue has been addressed.

[Dude]

Excellent question.  I knew all of those years of listening to Howard Stern would pay off.  Here's how you do it.  Hook up a GC flame ionization detector near you're son's crib with an intake fan to draw ambient air to the detector.  Electronically interface the detector to a sign outside the door of your son's room to read either "Change diaper" or "OK".  The If-then logic circuit would be based upon the mV response of the detector (calibration will have to be done manually to set the mV number).  The beauty of #2 is that there is plenty of odor and it readily diffuses through the diaper wall, you don't need a reagent to inform you.  My first instinct was to focus on sulfur species.  Those types of detectors (ie chemiluminescence) are too tricky for routine use.  Additionally, the amount of organic material during a #2 incident is far greater than the sulfurous material that is evident based upon odor.  Older generations of GC's used to use a lead impregnated paper to detect H2S at ppb levels (it would turn black).  However, young kids are susceptible to lead poisoning so the potential for poisoning isn't worth the risk.