Carbon Dots from <i>Pilosocereus gounellei</i> for Fluorimetric Determination of Tannin in Tea Using a Flow-Batch System

Silva, Kelly D.; Andrade, Stéfani I. E.; Lima, Marcelo B.; Monte-Filho, Severino S.; Araújo, Mário C. U.; Lima, Ricardo A. C.

doi:10.21577/0103-5053.20220092

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Article • J. Braz. Chem. Soc. 34 (1) • Jan 2023 • https://doi.org/10.21577/0103-5053.20220092 copy

Carbon Dots from Pilosocereus gounellei for Fluorimetric Determination of Tannin in Tea Using a Flow-Batch System

Authorship SCIMAGO INSTITUTIONS RANKINGS

In this study, xiquexique (Pilosocereus gounellei) native endemic cactus from the Brazilian semiarid was used for the first time as a natural carbon source (“green precursor”) for the synthesis of highly fluorescent carbon dots (CDs). These CDs were successfully used to develop a fast, low-cost, eco-friendly fluorescence method for the determination of tannins in teas. This method was automatized employing a flow-batch system coupled to an inexpensive ultraviolet light-emitting diode (UV-LED) used as an excitation source and a cheap handheld spectrometer used as a detector. CDs were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV-Vis, and fluorescence spectroscopy. The proposed method presented a linear range from 2.0-30.0 mg L^-1, relative standard deviation (RSD) < 3.0%, limit of detection (LOD) = 0.102 mg L^-1, and recovery rates from 90.5-109.1%. A paired t-test at a 95% confidence level indicated no statistically significant difference between the proposed and reference methods, revealing that it is a useful alternative for the determination of tannins.

Keywords:
carbon dots; Pilosocereus gounellei; flow-batch analyzer; UV-LED; tannins

Step	Description	V1	V2	V3	V4	V5	Volume / µL	time / s
1	additions of: CDs B S and W or WSS and W	on	on	on	on	off	250 300 48 and 1202 or 72-1080 and 1178-170	2.8 3.4 0.6 and 14.3 or 0.9-13.7 and 14.0-2.0
2	mixing	off	off	off	off	off	-	5.0
3	measurement	off	off	off	off	off	-	5.0
4	emptying MC	off	off	off	off	on	1800	22.8
5^a a Steps 5 and 6 are carried out in triplicate. CDs: carbon dots; MC: mixing chamber; W: quartz windows; S or WSS: sample or working standard solution.	addition of water	off	off	off	on	off	1800	21.4
6^a a Steps 5 and 6 are carried out in triplicate. CDs: carbon dots; MC: mixing chamber; W: quartz windows; S or WSS: sample or working standard solution.	emptying MC	off	off	off	off	on	1800	22.8

Tea sample	Proposed method		Reference method		Recovery ± SD / %
Tea sample	TA ± SD / (mg L^-1)	RSD / %	TA ± SD / (mg L^-1)	RSD / %	5.0 mg L ^-1	10.0 mg L^-1	15.0 mg L^-1
Green 1	25.3 ± 0.3	1.1	25.3 ± 0.3	1.0	109.1 ± 1.0	90.5 ± 2.3	103.4 ± 0.8
Black 2	5.8 ± 0.1	0.9	5.8 ± 0.1	1.6	-	-	-
Green 3	22.1 ± 0.1	0.2	22.1 ± 0.0	0.1	107.3 ± 0.5	97.6 ± 1.0	105.7 ± 2.7
Black 4	8.9 ± 0.3	2.9	8.8 ± 0.1	0.3	98.1 ± 2.2	90.9 ± 2.4	102.3 ± 0.7
Green 5	4.0 ± 0.1	1.8	3.9 ± 0.1	2.2	-	-	-
Black 6	13.4 ± 0.3	2.3	13.8 ± 0.2	1.7	99.3 ± 1.4	105.5 ± 0.7	102.4 ± 1.1

Parameter	Reference
Parameter	1	2	3	6	23	24	32	This work
Precursor	sodium citrate and aminopyrazine	6-bromohexyl-boronic acid and polyethyleneglycol bis(3-amino-propyl)	ascorbic acid and ammonia	lemon	xylan and branched polyethyleneimine	diethylenetriamine- pentaacetic acid	citric acid, melamine, and formaldehyde	Pilosocereus gounellei, and ethanolamine
Synthesis method	hydrothermal	hydrothermal	ultrasonic	hydrothermal	microwave-assisted	solid-state	hydrothermal	hydrothermal
Synthesis conditions	200 °C for 4 h	180 °C until obtaining a reddish-brown solution	50 °C for 12 h	160 °C for 3 h	180 °C for 15 min	180 ºC for 5 min	180 °C for 12 h	200 °C for 8 h
Quantum yield / %	11.8	0.3	10.2	1.4	8.0	-	63.7	13.6
Measurement	fluorescence	fluorescence	chemiluminescence	fluorescence	fluorescence	fluorescence	chemiluminescence	fluorescence
Excitation source	xenon lamp	xenon lamp	-	xenon lamp	xenon lamp	xenon lamp	-	UV-LED λ_max 370 nm
Spectrophotometer	benchtop	benchtop	benchtop	benchtop	benchtop	benchtop	benchtop	handheld
Automatic procedure	no	no	FIA	no	no	no	FIA	FBA
Sampling rate / h-¹1 Yang, H.; He, L.; Pan, S.; Liu, H.; Hu, X.; Spectrochim. Acta, Part A 2019, 210, 111. [Crossref] Crossref...	-	-	120	-	-	-	140	22
CDs consumption per determination / µL	200	100	60	-	20	600	-	250
Sample consumption per determination / µL	-	100	60	-	5000	2000	-	48
Waste generation per determination / mL	10.0	5.0	18.9	-	10.0	4.0	-	3.6
Working range / (μmol L-¹1 Yang, H.; He, L.; Pan, S.; Liu, H.; Hu, X.; Spectrochim. Acta, Part A 2019, 210, 111. [Crossref] Crossref... )	0.40-9.0	0.06-6.0	0.07-7.0	1-47.5	0.10-5.0	0.2-10.0	0.2-10.0	1.87-28.0
LOD / (nmol L-¹1 Yang, H.; He, L.; Pan, S.; Liu, H.; Hu, X.; Spectrochim. Acta, Part A 2019, 210, 111. [Crossref] Crossref... )	120	10.6	26.0	310	36.8	9.0	39.3	95.2
RSD (n = 3) / %	< 5.0	< 0.4	< 4.2	< 2.95	< 5.4	< 5.9	< 2.4	< 2.9
Sample	beer	white and red wine	Chinese gall	river water	lake water and white wine	tap and river water	red wine	green and black tea

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