Question: what is the purpose of the bromophenol blue dye in the samples
[{'answer': 'a pH indicator', 'provenance': [{'wikipedia_id': '883203', 'title': 'Bromophenol blue', 'start_paragraph_id': 1, 'start_character': 89, 'end_paragraph_id': 1, 'end_character': 103, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'a color marker', 'provenance': [{'wikipedia_id': '883203', 'title': 'Bromophenol blue', 'start_paragraph_id': 1, 'start_character': 105, 'end_paragraph_id': 1, 'end_character': 119, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'a dye', 'provenance': [{'wikipedia_id': '883203', 'title': 'Bromophenol blue', 'start_paragraph_id': 1, 'start_character': 125, 'end_paragraph_id': 1, 'end_character': 130, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'as a pH indicator', 'provenance': [{'wikipedia_id': '883203', 'title': 'Bromophenol blue', 'start_paragraph_id': 1, 'start_character': 86, 'end_paragraph_id': 1, 'end_character': 103, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '883203', 'title': 'Bromophenol blue', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 0, 'bleu_score': 1.0, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1349144495445228282}, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '883203', 'title': 'Bromophenol blue', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 248, 'bleu_score': 0.79520077898447, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1349144495445228282}, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '883203', 'title': 'Bromophenol blue', 'section': 'Section::::Abstract.', 'start_paragraph_id': 1, 'end_paragraph_id': 1, 'meta': {'evidence_span': ['color', 'Bromophenol blue (3,3,5,5-tetrabromophenolsulfonphthalein, BPB, albutest) is used as a pH indicator, a color marker, and a dye.', 'Bromophenol blue (3,3,5,5-tetrabromophenolsulfonphthalein, BPB, albutest) is used as a pH indicator, a color marker, and a dye. It can be prepared by slowly adding excess bromine to a hot solution of phenolsulfonphthalein in glacial acetic acid.']}}]}, {'provenance': [{'wikipedia_id': '60943', 'title': 'Pleochroism', 'section': 'Section::::Abstract.', 'start_paragraph_id': 1, 'end_paragraph_id': 1, 'meta': {'evidence_span': ['Pleochroism (from Greek πλέων, "pléōn", "more" and χρμα, "khrôma", "color") is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light.', 'Pleochroism (from Greek πλέων, "pléōn", "more" and χρμα, "khrôma", "color") is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light.']}}]}, {'provenance': [{'wikipedia_id': '3527488', 'title': 'Quinizarine Green SS', 'section': 'Section::::Abstract.', 'start_paragraph_id': 1, 'end_paragraph_id': 1, 'meta': {'evidence_span': ['Quinizarine Green SS, also called Solvent Green 3 is an anthraquinone derivative. It is a black powder that is soluble in polar organic solvents, but insoluble in water. It is used as a dye for adding greenish coloring to cosmetics and medications. It is used in some colored smoke formulations. According to X-ray crystallography, the anthroquinone portion of the molecule is planar. Both amine protons form hydrogen bonds to the carbonyls. This dye is a component in some smoke grenades, and questions have been raised about its toxicity', 'Quinizarine Green SS, also called Solvent Green 3 is an anthraquinone derivative. It is a black powder that is soluble in polar organic solvents, but insoluble in water. It is used as a dye for adding greenish coloring to cosmetics and medications. It is used in some colored smoke formulations. According to X-ray crystallography, the anthroquinone portion of the molecule is planar. Both amine protons form hydrogen bonds to the carbonyls. This dye is a component in some smoke grenades, and questions have been raised about its toxicity']}}]}]