...using bromocresol green as an indicator

https://www.ncbi.nlm.nih.gov/pubmed/21298727
Another problem is the depression of the weak peak of the compound with low concentration or weak detection response...

https://www.science.gov/topicpages/s/selectively isolate pho...

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Note added at 1 hr (2017-02-18 20:23:27 GMT)
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Also used: 'weak detection signal,' 'weak signal'

https://www.aafs.org/wp-content/uploads/ProceedingsSanAntoni...

Stains on “medium” and “bright” color types of fabric could be detected in 34%-38% of the cases with a very low rate of weak signals (“medium” fabric colors: 32% intensive detection signal, 2% weak detection signal; “bright” fabric colors: 31% intensive, 3% weak). The detection rate on “dark” fabric (black, brown, dark blue) was nearly the same (38%) but a higher rate (15%) produced only a weak signal.

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Note added at 1 day12 hrs (2017-02-20 07:10:24 GMT) Post-grading
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You're welcome.