Research article Received: 23 September 2013,
Revised: 11 February 2014,
Accepted: 15 February 2014
Published online in Wiley Online Library: 14 April 2014
(wileyonlinelibrary.com) DOI 10.1002/bio.2665
A simple and sensitive fluorescence method for the determination of trace ozone in air using acridine red as a probe Qingye Liu, Chenyin Lin, Xinghui Zhang,* Guiqing Wen and Aihui Liang* ABSTRACT: The ozone in an air sample was trapped by H3BO3-LK solution to produce iodine (I2) that interacted with excess I– to form I–3. In pH 4.0 acetate buffer solutions, the I–3 reacted with acridine red to form acridine red–I3 ion association particles that resulted in the fluorescence peak decreased at 553 nm. The decreased value ΔF553 nm is linear to the O3 concentration in the range 0.08–53.3 × 10–6 mol/L, with a detection limit of 4 × 10–8 mol/L. This fluorescence method was used to determine ozone in air samples, and the results were in agreement with that of indigo carmine spectrophotometry. Copyright © 2014 John Wiley & Sons, Ltd. Keywords: ozone; acridine red; associated particle; fluorescence method
Introduction
1102
Ozone is a light blue gas layer in the atmosphere, which is 10–50 km from the ground, has a strong function of absorbing ultraviolet (UV) rays, especially UVB from the sun, which is biologically harmful. Therefore, ozone can effectively protect all life on earth from UV rays and ensure that all life can exist, reproduce and develop. However, ozone is a strong oxidizer and it can oxidize all metals except gold and platinum, can destroy C-C bonds and corrode non-metallic materials. Under sunlight, the NOx from vehicle exhaust emissions and volatile organic compounds in factory waste gas take part in a photochemical reaction to form ozone. If the cloud is small, the wind is weak and the formed ozone accumulates continuously, ozone pollution will occur. Thus, the rapid and accurate detection of ozone is very important. At present, spectrophotometry (1–4), fluorescence method (5,6), resonance Rayleigh scattering (7), chemiluminescence (8–10), high-performance liquid chromatography–mass spectrometry (11) and electrochemistry (12,13) have been used to determine ozone. The sensitivity of the colorimetric method (3) is low. Chemiluminescence has a high sensitivity, fast speed and good specificity, but its operation and production process are complicated. High-performance liquid chromatography– mass spectrometry is expensive. The electrochemical method (13) was used with a reactor with a composite multilayer hydrophobic C-18 to absorb ozone selectively, and its detection limit is 60 μmol/L. Lin et al. (7) reported a new resonance Rayleigh scattering method for the determination of 0.25–25 μmol/L O3 using rhodamine 6G as probe. The fluorescence method is simple and sensitive, and has been applied to analyze ozone. Amos (5) used 2-diphenylacetyl-1,3-indandione-1-hydrazone as a fluorescence reagent to determine ozone as low as 20 ng/mL. Based on the known ozonolysis of indigo dye to fluorescence sulfoanthranilate (6), 7 ppb ozone can be determined. However, to the best of our knowledge, a rapid, convenient and sensitive fluorescence method for the detection of ozone has not yet been reported. Acridine dye is an important analytical reagent, which has good stability, and
Luminescence 2014; 29: 1102–1106
has been used in analysis (14–17). However, the method for the fluorescence spectrometric determination of ozone associated with acridine dye has not yet been reported. This paper studies a new fluorescence method for determining ozone in air, coupling the ozone oxidation reaction with the acridine red (ADR)associated particle reaction.
Experimental Instruments and reagents A F-7000 fluorescence spectrophotometer (Hitachi Co., Tokyo, Japan), a 2 g/h portable ozone generator (West Electronic Purification Equipment Limited, Qingdao, China), NaNo-ZS90 nanometer particle size and zeta potential analyzer (Malvern Co., Malvern, UK), and a TQC-1500-z atmospheric sampler (Tianrui Apparatus Limited, Yancheng, China) were used. H3BO3-KI (BKI) absorbent solution: 1.55 g H3BO3 and 2.5 g KI were dissolved by water and diluted to 250 mL with pH 5.5. The concentration, calculated as KI, is 0.06 mol/L. A 0.2% starch indicator: 0.2 g starch was added to 5 mL water and mixed into a paste. Then, 80 mL boiling water was added while stirring and kept boiling for 2 min before being cooled to room temperature and diluted to 100 mL. A 0.1 mol/L Na2S2O3 solution: 6.5 g Na2S2O3and 0.05 g Na2CO3 were dissolved with 20 mL water and the solution was boiled for 10 min before cooling and dilution to 250 mL. The solution was stored in a brown bottle, placed in the dark for several days and filtered before use. Calibration of * Correspondence to: Xinghui Zhang and Aihui Liang, Guangxi Key Laboratory of Environmental Pollution Control Theory and Technology, College of Environment and Resource, Guangxi Normal University, Guangxi, Guilin 541004, China. E-mail: [email protected], [email protected] Guangxi Key Laboratory of Environmental Pollution Control Theory and Technology, College of Environment and Resource, Guangxi Normal University, Guangxi, Guilin 541004, China
Copyright © 2014 John Wiley & Sons, Ltd.
ADR fluorescence method for ozone Na2S2O3 solution: 0.2 g K2Cr2O7 was added to a conical bottle and dissolved in 25 mL water, then 2 g KI, 20 mL 2 mol/L H2SO4 and 250 mL water were added in turn. After KI was dissolved, the mixture was placed in the dark for 10 min. Then it was titrated by Na2S2O3 solution to near end-point before 7.5 mL 0.2% starch indicator was added. The titration finished when the solution changed from blue to bright green. At the same time, the blank solution without K2Cr2O7 was titrated according to the above procedure. The parallel titration was operated three times and the volume difference of Na2S2O3 consumption should not be greater than 0.10 mL. The concentration of Na2S2O3 was calculated by the following formula, C1 = 6G2/(M2 × V1 × 10–3) = (6 × 0.2)/(294.18 × V1 × 10–3) = 4.079/V1. Where G2 is the weight of K2Cr2O7 (g), M2 is the molecular weight of K2Cr2O7 and V1 is the consumption volume of Na2S2O3 solution (mL). Preparation of O3 standard solution:. A 300 mL BKI absorbent was added to a jar and O3 was introduced for 10 min through an O3 generator. Then the solution was transferred into a brown bottle and stored at 4 °C in a refrigerator. A 10 mL O3 solution (V, mL), 2 mL 2 mol/L H2SO4 and 3 mL 0.2% starch indicator were added into a conical bottle in turn. Then it was titrated using 5.0 × 10–3 mol/L Na2S2O3 solution (C1, mol/L), which has been calibrated. The titration reached the end-point when the solution changed to achromatic color. The consumption volume of Na2S2O3 solution was recorded as V1 (mL). The parallel titration was operated three times and the volume difference of Na2S2O3 consumption should not be greater than 0.10 mL. The concentration of I2 (C, mol/L) was calculated from the formula C = C1V1/(2 V) = 5.0 × 10–3 V1 (2 × 10) = 2.5 × 10–4 V1, and the concentration of O3 is equal to that of I2. All reagents were of analytical grade and the water was doubly distilled.
Procedure A 100 μL 5.0 × 10–4 mol/L ozone standard solution, a 250 μL 0.02 mol/L pH 4.0 HAc-NaAc solution and 40 μL 1.0 × 10–3 mol/L ADR were added to a 5 mL calibrated tube in turn. The mixture was then diluted to 3.0 mL and mixed well and the solution poured into the quartz cell. On the fluorescence spectrophotometer,
with a detector voltage of 450 V, slit of 5 nm and λex = 500 nm, the fluorescence intensity at 553 nm (F) was recorded. A blank (F0) without O3 was recorded and the value of ΔF553nm = F0 – F was calculated.
Results and discussion Principle O3 reacted with KI-H3BO3 absorption solution to produce I2, which can combine with the excess I2 to form I–3. Then I–3 reacted with ADR to form the ADR–I3 ion association molecule that were aggregated to big particles by means of intermolecular forces, in which ADR fluorescence molecules were entrapped in the particle that caused the fluorescence quenching. Under chosen conditions, more I–3 was produced when the O3 concentration was higher, and consequently more ADR–I3 association particles were formed, the less free ADR, and the fluorescence intensity decreased at 553 nm correspondingly. Thus, a highly sensitive and selective, simple and rapid fluorescence method is proposed to detect O3 (Fig. 1). Fluorescence spectra In pH 4.0 HAc-NaAc buffer solution, when λex = 500 nm, ADR exhibited a strong fluorescence peak at 553 nm, and a Rayleigh scattering peak at 500 nm. With the addition of O3, large quantities of I–3 were produced and more ADR molecules were entrapped in the (ADR–I3)n associated particles that resulted in fluorescence intensity at 553 nm decreasing accordingly, and the resonance Raman spectroscopy intensity increasing (Fig. 2). For the acridine orange (ADO) system, it exhibited a fluorescence peak at 530 nm and a Rayleigh scattering peak at 442 nm (Fig. 3), the sensitivity is lower than the ADR system. Absorption spectra ADR exhibited a strong absorption peak at 524 nm. With the addition of ozone solution, more I–3 produced and more ADR–I3 association particles were formed to lead the absorption peak
Luminescence 2014; 29: 1102–1106
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Figure 1. Scheme of the fluorescence quenching method for ozone. ADR, acridine red.
Q. Liu et al.
Figure 2. Fluorescence spectra of the acridine red-associated particle system. –5 (a) 1.67 mmol/L pH 4.0 HAc-NaAc 1.33 × 10 mol/L ADR; (b) 0.83 μmol/L O3; (c) 3.33 μmol/L O3; (d) 6.67 μmol/L O3; (e) 16.7 μmol/L O3; (f) 26.67 μmol/L O3; (g) 33.3 μmol/L O3; (h) 40.0 μmol/L O3; (i) 46.7 μmol/L O3; (j) 53.3 μmol/L O3.
Figure 4. Absorption spectra of the acridine red-associated particle system. –5 (a) 1.67 mmol/L pH 4.0 HAc-NaAc 1.33 × 10 mol/L acridine red; (b) 6.67 μmol/L O3; (c) 10.0 μmol/L O3; (d) 13.3 μmol/L O3; (e) 26.7 μmol/L O3; (f) 33.3 μmol/L O3; (g) 40.0 μmol/L O3; (h) 46.7 μmol/L O3; (i) 53.3 μmol/L O3; (j) 60.0 μmol/L O3.
Figure 3. Fluorescence spectra of the acridine orange-associated particle system. (a) –5 1.67 mmol/L pH 4.0 HAc-NaAc 1.33 × 10 mol/L acridine orange; (b) 0.83 μmol/L O3; (c) 6.67 μmol/L O3; (d) 13.3 μmol/L O3; (e) 20.0 μmol/L O3; (f) 26.7 μmol/L O3; (g) 33.3 μmol/L O3; (h) 40.0 μmol/L O3; (i) 46.7 μmol/L O3; (j) 53.3 μmol/L O3.
at 524 nm decrease accordingly. Meanwhile, a new absorption peak appeared at about 590 nm due to the formation of associated particles (Fig. 4). ADO exhibited a strong absorption peak at 490 nm. With the addition of ozone solution, more I–3 produced and more ADO–I3 association particles were formed to lead the absorption peak at 490 nm decrease accordingly. Meanwhile, the absorption values at wavelengths of 350–440 nm and 520–600 nm were enhanced owing to the formation of associated particles (Fig. 5).
Figure 5. Absorption spectra of the acridine orange-associated particle system. –5 (a) 1.67 mmol/L, pH 4.0 HAc-NaAc 1.33 × 10 mol/L acridine orange; (b) 1.67 μmol/L O3; (c) 3.33 μmol/L O3; (d) 5.0 μmol/L O3; (e) 6.67 μmol/L O3; (f) 8.33 μmol/L O3; (g) 10.0 μmol/L O3; (h) 11.7 μmol/L O3; (i) 13.3 μmol/L O3; (j) 16.7 μmol/L O3; (k) 20.0 μmol/L O3; (l) 26.7 μmol/L O3; (m) 33.3 μmol/L O3.
Laser scatting
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In pH 4.0 HAc-NaAc buffer solution, the ADR cation is a free molecule. When O3 was added, the produced anion I–3 combined with the ADR cation to form the ADR–I3 associated complex through the ionic bond. Owing to hydrophobic interaction and intermolecular force of associated complexes, large (ADR–I3)nassociated particles were formed, with an average particle size of 520 nm (Fig. 6). This result showed that there are particles in
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Size/ (nm) Figure 6. Laser scattering graph of the acridine red-associated particle system. –5 pH 4.0 HAc-NaAc 1.33 × 10 mol/L, acridine red 13.3 μmol/L O3.
Copyright © 2014 John Wiley & Sons, Ltd.
Luminescence 2014; 29: 1102–1106
ADR fluorescence method for ozone the system that also caused the fluorescence quenching and enhanced Rayleigh scattering.
ADR was chosen. The effect of pH value on HAc-NaAc buffer solution on ΔF was tested. When the pH is 4.0, the ΔF533nm is the largest, so pH 4.0 HAc-NaAc buffer solution was used. When the concentration of Ac– (pH 4.0 HAc-NaAc buffer) is 1.67 × 10– 3 mol/L, the system has a stable of ΔF, so 250 μL pH 4.0 HAc-NaAc buffer (0.02 mol/L Ac–) was chosen.
Optimization of analytical conditions The effect of ADR concentration on ΔF533nm was tested. As shown in Fig. 7, when the concentration of ADR is 1.33 × 10–5 mol/L, the system has a maximum of ΔF533nm. Therefore, 40 μL 1.0 × 10–3 mol/L
Effect of coexisting ions According to the procedure, the effect of coexisting ions on the determination of O3 was investigated. Results showed (Table 1) that common substances such as metal ions, amino acids and glucose in the certain concentration ranges, did not interfere with the determination of 1.0 × 10–5 mol/L O3, and the relative error was less than ± 5%. Hence, the method has good selectivity.
Working curve According to the procedure, the working curve was obtained, and the O3 concentration (C) from 0.08 × 10–6 to 53.3 × 10–6 mol/L has a good linear relationship with the ADR fluorescence intensity (Table 2). The linear regression equation is ΔF553 nm = 85.1C + 3.8, linear correlation coefficient 0.9977 and detection limit 4.0 × 10–8 mol/L.
–6
Figure 7. Effect of acridine red concentration 26.7 × 10 mol/L O3 pH 4.0, HAcNaAc buffer–acridine red.
Table 1. Effect of coexisting substances Coexisting substance
Tolerance (times)
Relative error (%)
Coexisting substance
Tolerance (times)
Relative error (%)
100 150 100 10 100 50
–5 4 –2 –5 – 3.5 4.5
2+
100 100 80 60 100 40
4.8 – 3.4 4.6 –5 5 5
+
K Ca2+ Ag+ Fe3+ Glucose L-Phenylalanine
Cu Mg2+ Hg2+ Cr2O2– 7 L-valine L-lysine
Table 2. Comparison of analytical features of two acridine dyes Dye
λex (nm)
λem (nm)
Regress equation
Linear range (μmol/L)
Coefficient
Detection limit (μmol/L)
ADR ADO
500 442
553 530
ΔF533nm = 85.1C + 3.8 ΔF530nm = 30.2C – 20.5
0.08–53.3 0.42–53.3
0.9977 0.9929
0.04 0.20
Table 3. The analytical results Samples A1 A2 A3 B1 B2 B3 C1 C2 C3
Found (μg/m3 O3) 60.3, 61.4, 59.8, 42.0, 42.1, 40.8, 45.3, 47.9, 48.3,
59.7, 58.8 61.1, 62.6 59.0, 61.8 43.4, 41.7 43.5, 41.1 41.1, 42.4 45.3, 47.5 45.6, 46.5 49.5, 47.8
Mean (μg/m3 O3)
RSD (%)
Ref. results (μg/m3 O3)a
59.6 61.7 60.2 42.4 42.2 41.4 46.0 46.7 48.5
1.2 1.3 2.4 2.1 2.6 2.1 2.8 2.5 1.8
60.2 60.8 58.4 42.8 40.8 40.0 47.9 48.5 47.4
a
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Copyright © 2014 John Wiley & Sons, Ltd.
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Indigo carmine spectrophotometry.
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Q. Liu et al. Sample analysis
References
A 6.0 mL BKI absorbing solution was added to the TQC-1500-z atmospheric sampler bottle that collected an air sample for 3 h with sampling flow rate of 1.0 L/min. Then, the absorbing solution was diluted to 6.0 mL with water to obtain the sample solution. A 1.0 mL of the sample solution was used to determine the ozone content according to the procedure. The fluorescence method results are listed in Table 3 that were agreement with that of the indigo carmine spectrophotometric method (2). The A1–A3 samples were collected in Laboratory 222 of the Environmental School of Guangxi Normal University, between 11:10 and 14:10 h, when sunny and cloudy and at a temperature of 24 °C. The B1–B3 samples were collected at the gate of the School of Guangxi Normal University, between 14:28 and 17:28 h, when sunny and at a temperature of 28 °C. The C1–C3 samples were collected at the gate of the School of Guangxi Normal University, at between 18:32 and 21:32 h, when sunny and cloudy, and at a temperature of 23 °C. From Table 3, we can see that the content of sample A is highest owing to the ozone generated from the lamp and electric equipment. Next, the ozone content of sample C was generated from the traffic and photochemical reaction. The ozone content of sample B is lowest.
1. GB 3095-2012. Air Quality Standard(S). Beijing: Chinese Environmental Scientific Press, 2012. 2. HJ 504-2009. Determination of O3 in Air-Indigo Carmine Spectrophotometry. Beijing: Chinese Environmental Scientific Press, 2009. 3. HJ 590-2010. Determination of O3 in Air-UV Spectrophotometry. Beijing: Chinese Environmental Scientific Press, 2010. 4. Tomiyasu H. Colorimetric determination of ozone in water based on reaction with bis(terpyridine)iron(II). J Am Chem Soc 1984;56:752–4. 5. Amos D. Specific spectrofluorometric determination of atmospheric ozone using 2-diphenylacetyl-1,3-indandione-1-hydrazone. Anal Chem 1970;42:842–4. 6. Felix EP, Filho JP, Garcia G, Cardoso AA. A new fluorescence method for determination of ozone in ambient air. Microchem J 2011;99:530–4. 7. Lin CY, Wen GQ, Liang AH, Jiang ZL. A new resonance Rayleigh scattering method for the determination of trace O3 in air using rhodamine 6G as probe. RSC Adv 2013;3:6627–30. 8. Ermel M, Oswald R, Mayer JC, Moravek A, Song G, Beck M, et al. Preparation methods to optimize the performance of sensor discs for fast chemiluminescence ozone analyzers. Environ Sci Techol 2013;47:1930–6. 9. Qi W, Wu D, Zhao JM, Liu ZY, Zhang W, Zhang L, et al. Electrochemiluminescence resonance energy transfer based on ru (phen)32 + -doped silica nanoparticles and its application in “turn-on” detection of ozone. Anal Chem 2013;85:3207–12. 10. Eipel C, Jeroschewski P, Steinke I. Determination of ozone in ambient air with a chemiluminescence reagent film detector. Anal Chim Acta 2003;491:145–53. 11. Wentworth Jr PW, Nieva J, Takeuchi C, Galve R, Wentworth AD, Dilley RB, et al. Evidence for ozone formation in human atherosclerotic arteries. Science 2003;302:1053–6. 12. Ishii Y, Ivandini TA, Murata K, Einaga Y. Development of electrolytefree ozone sensors using boron-doped diamond electrodes. Anal Chem 2013;85:4284–8. 13. Stergiou DV, Prodromidis MI, Veltsistas PG, Evmiridis NP. Ozone monitoring based on a biosensor concept utilizing a reagentless alcohol oxidase electrode. Anal Chem 2006;78:4676–82. 14. Vitagliano V, Ortona O, Parrill M. Spectrophotometric behavior of a bifunctional acridine dye. J Phys Chem 1978;82:2819–23. 15. Martí-Centelles V, Burguete MI, Galindo F, Izquierdo MA, Kumar DK, – White AJP, et al. Fluorescent acridine-based receptors for H2PO4. J Org Chem 2012;77:490–500. 16. Xu H, Li Y, Liu CM, Wu QS, Zhao Y, Lu L, et al. Fluorescence resonance energy transfer between acridine orange and rhodamine 6G and its analytical application for vitamin B12 with flow-injection laserinduced fluorescence detection. Talanta 2008;77:176–81. 17. Rumphorst A, Duschner H, Seeger S. Optical determination of pH on surfaces using immobilized fluorescent dyes. J Fluoresc 1994;4:45–8.
Conclusion In summary, O3 is trapped by a KI-H3BO3 absorption solution to produce I3, which can combine with the ADR fluorescence probe to form (ADR–I3)n-associated particles that caused fluorescence quenching. Under the chosen conditions, more I3 was produced when the O3 concentration was higher, and more ADR–I3 association particles were formed. The fluorescence intensity at 553 nm quenched correspondingly. Thus, a highly sensitive and selective, simple and rapid fluorescence method was developed to detect O3 in air samples. Acknowledgments This work was supported by 21367005, the National Natural Science Foundation of China (No. 21307017, 21267004, 21165005), the Natural Science Foundation of Guangxi (No. 2013GXNSFFA019003) and 2013YB035 the Science Foundation of Guangxi Education Department (No. ).
1106 wileyonlinelibrary.com/journal/luminescence
Copyright © 2014 John Wiley & Sons, Ltd.
Luminescence 2014; 29: 1102–1106
Revised: 11 February 2014,
Accepted: 15 February 2014
Published online in Wiley Online Library: 14 April 2014
(wileyonlinelibrary.com) DOI 10.1002/bio.2665
A simple and sensitive fluorescence method for the determination of trace ozone in air using acridine red as a probe Qingye Liu, Chenyin Lin, Xinghui Zhang,* Guiqing Wen and Aihui Liang* ABSTRACT: The ozone in an air sample was trapped by H3BO3-LK solution to produce iodine (I2) that interacted with excess I– to form I–3. In pH 4.0 acetate buffer solutions, the I–3 reacted with acridine red to form acridine red–I3 ion association particles that resulted in the fluorescence peak decreased at 553 nm. The decreased value ΔF553 nm is linear to the O3 concentration in the range 0.08–53.3 × 10–6 mol/L, with a detection limit of 4 × 10–8 mol/L. This fluorescence method was used to determine ozone in air samples, and the results were in agreement with that of indigo carmine spectrophotometry. Copyright © 2014 John Wiley & Sons, Ltd. Keywords: ozone; acridine red; associated particle; fluorescence method
Introduction
1102
Ozone is a light blue gas layer in the atmosphere, which is 10–50 km from the ground, has a strong function of absorbing ultraviolet (UV) rays, especially UVB from the sun, which is biologically harmful. Therefore, ozone can effectively protect all life on earth from UV rays and ensure that all life can exist, reproduce and develop. However, ozone is a strong oxidizer and it can oxidize all metals except gold and platinum, can destroy C-C bonds and corrode non-metallic materials. Under sunlight, the NOx from vehicle exhaust emissions and volatile organic compounds in factory waste gas take part in a photochemical reaction to form ozone. If the cloud is small, the wind is weak and the formed ozone accumulates continuously, ozone pollution will occur. Thus, the rapid and accurate detection of ozone is very important. At present, spectrophotometry (1–4), fluorescence method (5,6), resonance Rayleigh scattering (7), chemiluminescence (8–10), high-performance liquid chromatography–mass spectrometry (11) and electrochemistry (12,13) have been used to determine ozone. The sensitivity of the colorimetric method (3) is low. Chemiluminescence has a high sensitivity, fast speed and good specificity, but its operation and production process are complicated. High-performance liquid chromatography– mass spectrometry is expensive. The electrochemical method (13) was used with a reactor with a composite multilayer hydrophobic C-18 to absorb ozone selectively, and its detection limit is 60 μmol/L. Lin et al. (7) reported a new resonance Rayleigh scattering method for the determination of 0.25–25 μmol/L O3 using rhodamine 6G as probe. The fluorescence method is simple and sensitive, and has been applied to analyze ozone. Amos (5) used 2-diphenylacetyl-1,3-indandione-1-hydrazone as a fluorescence reagent to determine ozone as low as 20 ng/mL. Based on the known ozonolysis of indigo dye to fluorescence sulfoanthranilate (6), 7 ppb ozone can be determined. However, to the best of our knowledge, a rapid, convenient and sensitive fluorescence method for the detection of ozone has not yet been reported. Acridine dye is an important analytical reagent, which has good stability, and
Luminescence 2014; 29: 1102–1106
has been used in analysis (14–17). However, the method for the fluorescence spectrometric determination of ozone associated with acridine dye has not yet been reported. This paper studies a new fluorescence method for determining ozone in air, coupling the ozone oxidation reaction with the acridine red (ADR)associated particle reaction.
Experimental Instruments and reagents A F-7000 fluorescence spectrophotometer (Hitachi Co., Tokyo, Japan), a 2 g/h portable ozone generator (West Electronic Purification Equipment Limited, Qingdao, China), NaNo-ZS90 nanometer particle size and zeta potential analyzer (Malvern Co., Malvern, UK), and a TQC-1500-z atmospheric sampler (Tianrui Apparatus Limited, Yancheng, China) were used. H3BO3-KI (BKI) absorbent solution: 1.55 g H3BO3 and 2.5 g KI were dissolved by water and diluted to 250 mL with pH 5.5. The concentration, calculated as KI, is 0.06 mol/L. A 0.2% starch indicator: 0.2 g starch was added to 5 mL water and mixed into a paste. Then, 80 mL boiling water was added while stirring and kept boiling for 2 min before being cooled to room temperature and diluted to 100 mL. A 0.1 mol/L Na2S2O3 solution: 6.5 g Na2S2O3and 0.05 g Na2CO3 were dissolved with 20 mL water and the solution was boiled for 10 min before cooling and dilution to 250 mL. The solution was stored in a brown bottle, placed in the dark for several days and filtered before use. Calibration of * Correspondence to: Xinghui Zhang and Aihui Liang, Guangxi Key Laboratory of Environmental Pollution Control Theory and Technology, College of Environment and Resource, Guangxi Normal University, Guangxi, Guilin 541004, China. E-mail: [email protected], [email protected] Guangxi Key Laboratory of Environmental Pollution Control Theory and Technology, College of Environment and Resource, Guangxi Normal University, Guangxi, Guilin 541004, China
Copyright © 2014 John Wiley & Sons, Ltd.
ADR fluorescence method for ozone Na2S2O3 solution: 0.2 g K2Cr2O7 was added to a conical bottle and dissolved in 25 mL water, then 2 g KI, 20 mL 2 mol/L H2SO4 and 250 mL water were added in turn. After KI was dissolved, the mixture was placed in the dark for 10 min. Then it was titrated by Na2S2O3 solution to near end-point before 7.5 mL 0.2% starch indicator was added. The titration finished when the solution changed from blue to bright green. At the same time, the blank solution without K2Cr2O7 was titrated according to the above procedure. The parallel titration was operated three times and the volume difference of Na2S2O3 consumption should not be greater than 0.10 mL. The concentration of Na2S2O3 was calculated by the following formula, C1 = 6G2/(M2 × V1 × 10–3) = (6 × 0.2)/(294.18 × V1 × 10–3) = 4.079/V1. Where G2 is the weight of K2Cr2O7 (g), M2 is the molecular weight of K2Cr2O7 and V1 is the consumption volume of Na2S2O3 solution (mL). Preparation of O3 standard solution:. A 300 mL BKI absorbent was added to a jar and O3 was introduced for 10 min through an O3 generator. Then the solution was transferred into a brown bottle and stored at 4 °C in a refrigerator. A 10 mL O3 solution (V, mL), 2 mL 2 mol/L H2SO4 and 3 mL 0.2% starch indicator were added into a conical bottle in turn. Then it was titrated using 5.0 × 10–3 mol/L Na2S2O3 solution (C1, mol/L), which has been calibrated. The titration reached the end-point when the solution changed to achromatic color. The consumption volume of Na2S2O3 solution was recorded as V1 (mL). The parallel titration was operated three times and the volume difference of Na2S2O3 consumption should not be greater than 0.10 mL. The concentration of I2 (C, mol/L) was calculated from the formula C = C1V1/(2 V) = 5.0 × 10–3 V1 (2 × 10) = 2.5 × 10–4 V1, and the concentration of O3 is equal to that of I2. All reagents were of analytical grade and the water was doubly distilled.
Procedure A 100 μL 5.0 × 10–4 mol/L ozone standard solution, a 250 μL 0.02 mol/L pH 4.0 HAc-NaAc solution and 40 μL 1.0 × 10–3 mol/L ADR were added to a 5 mL calibrated tube in turn. The mixture was then diluted to 3.0 mL and mixed well and the solution poured into the quartz cell. On the fluorescence spectrophotometer,
with a detector voltage of 450 V, slit of 5 nm and λex = 500 nm, the fluorescence intensity at 553 nm (F) was recorded. A blank (F0) without O3 was recorded and the value of ΔF553nm = F0 – F was calculated.
Results and discussion Principle O3 reacted with KI-H3BO3 absorption solution to produce I2, which can combine with the excess I2 to form I–3. Then I–3 reacted with ADR to form the ADR–I3 ion association molecule that were aggregated to big particles by means of intermolecular forces, in which ADR fluorescence molecules were entrapped in the particle that caused the fluorescence quenching. Under chosen conditions, more I–3 was produced when the O3 concentration was higher, and consequently more ADR–I3 association particles were formed, the less free ADR, and the fluorescence intensity decreased at 553 nm correspondingly. Thus, a highly sensitive and selective, simple and rapid fluorescence method is proposed to detect O3 (Fig. 1). Fluorescence spectra In pH 4.0 HAc-NaAc buffer solution, when λex = 500 nm, ADR exhibited a strong fluorescence peak at 553 nm, and a Rayleigh scattering peak at 500 nm. With the addition of O3, large quantities of I–3 were produced and more ADR molecules were entrapped in the (ADR–I3)n associated particles that resulted in fluorescence intensity at 553 nm decreasing accordingly, and the resonance Raman spectroscopy intensity increasing (Fig. 2). For the acridine orange (ADO) system, it exhibited a fluorescence peak at 530 nm and a Rayleigh scattering peak at 442 nm (Fig. 3), the sensitivity is lower than the ADR system. Absorption spectra ADR exhibited a strong absorption peak at 524 nm. With the addition of ozone solution, more I–3 produced and more ADR–I3 association particles were formed to lead the absorption peak
Luminescence 2014; 29: 1102–1106
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Figure 1. Scheme of the fluorescence quenching method for ozone. ADR, acridine red.
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Figure 2. Fluorescence spectra of the acridine red-associated particle system. –5 (a) 1.67 mmol/L pH 4.0 HAc-NaAc 1.33 × 10 mol/L ADR; (b) 0.83 μmol/L O3; (c) 3.33 μmol/L O3; (d) 6.67 μmol/L O3; (e) 16.7 μmol/L O3; (f) 26.67 μmol/L O3; (g) 33.3 μmol/L O3; (h) 40.0 μmol/L O3; (i) 46.7 μmol/L O3; (j) 53.3 μmol/L O3.
Figure 4. Absorption spectra of the acridine red-associated particle system. –5 (a) 1.67 mmol/L pH 4.0 HAc-NaAc 1.33 × 10 mol/L acridine red; (b) 6.67 μmol/L O3; (c) 10.0 μmol/L O3; (d) 13.3 μmol/L O3; (e) 26.7 μmol/L O3; (f) 33.3 μmol/L O3; (g) 40.0 μmol/L O3; (h) 46.7 μmol/L O3; (i) 53.3 μmol/L O3; (j) 60.0 μmol/L O3.
Figure 3. Fluorescence spectra of the acridine orange-associated particle system. (a) –5 1.67 mmol/L pH 4.0 HAc-NaAc 1.33 × 10 mol/L acridine orange; (b) 0.83 μmol/L O3; (c) 6.67 μmol/L O3; (d) 13.3 μmol/L O3; (e) 20.0 μmol/L O3; (f) 26.7 μmol/L O3; (g) 33.3 μmol/L O3; (h) 40.0 μmol/L O3; (i) 46.7 μmol/L O3; (j) 53.3 μmol/L O3.
at 524 nm decrease accordingly. Meanwhile, a new absorption peak appeared at about 590 nm due to the formation of associated particles (Fig. 4). ADO exhibited a strong absorption peak at 490 nm. With the addition of ozone solution, more I–3 produced and more ADO–I3 association particles were formed to lead the absorption peak at 490 nm decrease accordingly. Meanwhile, the absorption values at wavelengths of 350–440 nm and 520–600 nm were enhanced owing to the formation of associated particles (Fig. 5).
Figure 5. Absorption spectra of the acridine orange-associated particle system. –5 (a) 1.67 mmol/L, pH 4.0 HAc-NaAc 1.33 × 10 mol/L acridine orange; (b) 1.67 μmol/L O3; (c) 3.33 μmol/L O3; (d) 5.0 μmol/L O3; (e) 6.67 μmol/L O3; (f) 8.33 μmol/L O3; (g) 10.0 μmol/L O3; (h) 11.7 μmol/L O3; (i) 13.3 μmol/L O3; (j) 16.7 μmol/L O3; (k) 20.0 μmol/L O3; (l) 26.7 μmol/L O3; (m) 33.3 μmol/L O3.
Laser scatting
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In pH 4.0 HAc-NaAc buffer solution, the ADR cation is a free molecule. When O3 was added, the produced anion I–3 combined with the ADR cation to form the ADR–I3 associated complex through the ionic bond. Owing to hydrophobic interaction and intermolecular force of associated complexes, large (ADR–I3)nassociated particles were formed, with an average particle size of 520 nm (Fig. 6). This result showed that there are particles in
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Size/ (nm) Figure 6. Laser scattering graph of the acridine red-associated particle system. –5 pH 4.0 HAc-NaAc 1.33 × 10 mol/L, acridine red 13.3 μmol/L O3.
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Luminescence 2014; 29: 1102–1106
ADR fluorescence method for ozone the system that also caused the fluorescence quenching and enhanced Rayleigh scattering.
ADR was chosen. The effect of pH value on HAc-NaAc buffer solution on ΔF was tested. When the pH is 4.0, the ΔF533nm is the largest, so pH 4.0 HAc-NaAc buffer solution was used. When the concentration of Ac– (pH 4.0 HAc-NaAc buffer) is 1.67 × 10– 3 mol/L, the system has a stable of ΔF, so 250 μL pH 4.0 HAc-NaAc buffer (0.02 mol/L Ac–) was chosen.
Optimization of analytical conditions The effect of ADR concentration on ΔF533nm was tested. As shown in Fig. 7, when the concentration of ADR is 1.33 × 10–5 mol/L, the system has a maximum of ΔF533nm. Therefore, 40 μL 1.0 × 10–3 mol/L
Effect of coexisting ions According to the procedure, the effect of coexisting ions on the determination of O3 was investigated. Results showed (Table 1) that common substances such as metal ions, amino acids and glucose in the certain concentration ranges, did not interfere with the determination of 1.0 × 10–5 mol/L O3, and the relative error was less than ± 5%. Hence, the method has good selectivity.
Working curve According to the procedure, the working curve was obtained, and the O3 concentration (C) from 0.08 × 10–6 to 53.3 × 10–6 mol/L has a good linear relationship with the ADR fluorescence intensity (Table 2). The linear regression equation is ΔF553 nm = 85.1C + 3.8, linear correlation coefficient 0.9977 and detection limit 4.0 × 10–8 mol/L.
–6
Figure 7. Effect of acridine red concentration 26.7 × 10 mol/L O3 pH 4.0, HAcNaAc buffer–acridine red.
Table 1. Effect of coexisting substances Coexisting substance
Tolerance (times)
Relative error (%)
Coexisting substance
Tolerance (times)
Relative error (%)
100 150 100 10 100 50
–5 4 –2 –5 – 3.5 4.5
2+
100 100 80 60 100 40
4.8 – 3.4 4.6 –5 5 5
+
K Ca2+ Ag+ Fe3+ Glucose L-Phenylalanine
Cu Mg2+ Hg2+ Cr2O2– 7 L-valine L-lysine
Table 2. Comparison of analytical features of two acridine dyes Dye
λex (nm)
λem (nm)
Regress equation
Linear range (μmol/L)
Coefficient
Detection limit (μmol/L)
ADR ADO
500 442
553 530
ΔF533nm = 85.1C + 3.8 ΔF530nm = 30.2C – 20.5
0.08–53.3 0.42–53.3
0.9977 0.9929
0.04 0.20
Table 3. The analytical results Samples A1 A2 A3 B1 B2 B3 C1 C2 C3
Found (μg/m3 O3) 60.3, 61.4, 59.8, 42.0, 42.1, 40.8, 45.3, 47.9, 48.3,
59.7, 58.8 61.1, 62.6 59.0, 61.8 43.4, 41.7 43.5, 41.1 41.1, 42.4 45.3, 47.5 45.6, 46.5 49.5, 47.8
Mean (μg/m3 O3)
RSD (%)
Ref. results (μg/m3 O3)a
59.6 61.7 60.2 42.4 42.2 41.4 46.0 46.7 48.5
1.2 1.3 2.4 2.1 2.6 2.1 2.8 2.5 1.8
60.2 60.8 58.4 42.8 40.8 40.0 47.9 48.5 47.4
a
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Indigo carmine spectrophotometry.
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Q. Liu et al. Sample analysis
References
A 6.0 mL BKI absorbing solution was added to the TQC-1500-z atmospheric sampler bottle that collected an air sample for 3 h with sampling flow rate of 1.0 L/min. Then, the absorbing solution was diluted to 6.0 mL with water to obtain the sample solution. A 1.0 mL of the sample solution was used to determine the ozone content according to the procedure. The fluorescence method results are listed in Table 3 that were agreement with that of the indigo carmine spectrophotometric method (2). The A1–A3 samples were collected in Laboratory 222 of the Environmental School of Guangxi Normal University, between 11:10 and 14:10 h, when sunny and cloudy and at a temperature of 24 °C. The B1–B3 samples were collected at the gate of the School of Guangxi Normal University, between 14:28 and 17:28 h, when sunny and at a temperature of 28 °C. The C1–C3 samples were collected at the gate of the School of Guangxi Normal University, at between 18:32 and 21:32 h, when sunny and cloudy, and at a temperature of 23 °C. From Table 3, we can see that the content of sample A is highest owing to the ozone generated from the lamp and electric equipment. Next, the ozone content of sample C was generated from the traffic and photochemical reaction. The ozone content of sample B is lowest.
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Conclusion In summary, O3 is trapped by a KI-H3BO3 absorption solution to produce I3, which can combine with the ADR fluorescence probe to form (ADR–I3)n-associated particles that caused fluorescence quenching. Under the chosen conditions, more I3 was produced when the O3 concentration was higher, and more ADR–I3 association particles were formed. The fluorescence intensity at 553 nm quenched correspondingly. Thus, a highly sensitive and selective, simple and rapid fluorescence method was developed to detect O3 in air samples. Acknowledgments This work was supported by 21367005, the National Natural Science Foundation of China (No. 21307017, 21267004, 21165005), the Natural Science Foundation of Guangxi (No. 2013GXNSFFA019003) and 2013YB035 the Science Foundation of Guangxi Education Department (No. ).
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