Fluorescence Quenching of Polycyclic Aromatic Hydrocarbons by

Article pubs.acs.org/JPCC

Fluorescence Quenching of Polycyclic Aromatic Hydrocarbons by Nitromethane within Ionic Liquid Added Aqueous Anionic Micellar Solution Shruti Trivedi and Siddharth Pandey* Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India ABSTRACT: Applicability of nitromethane as selective fluorescence quenching agent for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons (PAHs) is examined for eight PAHs dissolved in aqueous micellar sodium dodecyl sulfate (SDS) media in the absence and presence of varying wt % of water-miscible ionic liquid (IL) 1butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]). Alternant PAHs follow quenching sphere-of-action model, whereas nonalternant PAHs demonstrate simple linear Stern−Volmer type quenching behavior. Nitromethane quenched fluorescence emission of both the alternant and nonalternant PAHs dissolved in aqueous SDS micellar media where the selectivity of the nitromethane as the quencher is lost. However, the nitromethane begins to retain its selectivity in quenching fluorescence from alternant PAHs over that from the nonalternant PAHs as soon as small amount of IL [bmim][BF4] (ca. 0.5 wt %) is added to anionic SDS solution. The dual role of IL is demonstrated where initially at lower concentrations it works as an electrolyte helping to establish quenching selectivity of nitromethane and at higher concentrations as a cosolvent where quenching of nonalternant PAH fluorescence again starts to become significant due to the changes in the physicochemical properties of the micellar assemblies. Use of IL as an effective additive to the aqueous anionic micelle media for PAH separation and analysis is amply demonstrated.

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INTRODUCTION Polycyclic aromatic hydrocarbons (PAHs) are well-known potent atmospheric pollutants constituting the largest class of chemical carcinogens and mutagens.1−3 They have been classified as priority pollutants by US Environmental Protection Agency (EPA) and are becoming an increasing concern due to their significant human exposure.4 Because of their resistance to biodegradation, they are very persistent in the environment.1,2,5 The presence of these persisted PAHs in environments may lead to plethora of problems which includes cancer and genetic mutation. High prenatal exposure to PAHs results in lower IQ and childhood asthma. The detrimental properties of PAHs coupled to growing awareness of environmental pollution prompted researchers to develop analytical methods to isolate the individual organic compounds of this class. Among many classifications, one way to categorize the PAHs is to separate them as alternants and nonalternants. Alternant PAHs have fully conjugated aromatic systems (Figure 1). If each carbon atom in the aromatic structure is labeled, alternately skipping an atom between labels, then alternant PAHs have a structure such that no two atoms of the same type are adjacent. Whereas, nonalternant PAHs (Figure 2) do not have conjugated aromaticity and have a structure in which such labeling results in two adjacent atoms of the same type. These structural modifications can bring about great changes in the physicochemical and optical properties. In order to identify, separate, and detect alternant and nonalternant PAHs, © 2013 American Chemical Society

Figure 1. Alternant PAHs used.

Figure 2. Nonalternant PAHs used.

Received: December 4, 2012 Revised: January 7, 2013 Published: January 7, 2013 1818

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fluorescence spectroscopy offers high sensitivity and selectivity because the quantum yield of most PAHs is quite significant. Zander,6−9 Acree,10−19 and McGuffin20−23 groups have shown that nitromethane selectively quenches the fluorescence of alternant PAHs as opposed to the fluorescence of nonalternant PAHs. In a series of publications, Acree and co-workers using several alternant and nonalternant PAHs have amply established the nitromethane selective quenching rule.10−19,24 Anionic micellar solutions are used as media for PAH separation in micellar electrokinetic capillary chromatography (MEKC). Terabe and co-workers accounted that PAHs could be separated by cyclodextrin-modified MEKC.25 Later, Cole’s group separated PAHs by MEKC using Bile salt in the presence of organic modifier.26 Fu et al. utilized MEKC with aqueous organic solvent to separate PAHs and established that MEKC condition can be optimized by altering the alcohol content, the concentration of anionic surfactant sodium dodecyl sulfate (SDS), and the separation temperature.27 However, Acree and co-workers found that selectivity of nitromethane as fluorescence quencher for alternant PAHs over nonalternant PAHs was lost when anionic micellar solutions were used as solubilizing mediawithin anionic micellar solutions nitromethane started to quench the fluorescence from nonalternant PAHs as well.13,24 Because of their inherent nonvolatility and unique physicochemical properties, interest in ionic liquids (ILs) has grown dramatically in the past decade.28−34 Owing to their potential environmentally benign nature, ILs are utilized in concert with other environmentally friendly substances such as water,35−37 glycol family solvents,38−40 polymer solutions,41,42 supercritical fluids,43−45 and surfactant-based systems,46−49 among others. In this context, efforts have been endowed by researchers to study the behavior of ILs in modifying the properties of surfactant-based systems.50−58 ILs were found to demonstrate unique role in altering the properties of surfactant/micellar solutions.54,56,57 It is observed that at lower concentrations ILs behave similar to electrolytes due to their strong electrolytic dissociation, whereas at higher concentrations, ILs act as cosolvents when added to aqueous surfactant solutions.56,57 Behera et al. reported the dual behavior of IL 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) in altering important properties of aqueous SDS solution.57 At lower concentrations (i.e., ≤2 wt %), the role of IL appeared to be similar to that of an electrolyte as bmim+ cations locate close to the micellar surface, thus partly neutralizing anionic micellar charged surface. However, at higher concentration (2 wt % < [bmim][BF4] ≤ 30 wt %), the dissociation of IL decreases, and it behaves more like a polar cosolvent.57 To explore the potential of ILs as additive during separation processes, in this paper we present fluorescence quenching behavior of nitromethane toward select alternant and nonalternant PAHs when dissolved in aqueous anionic micellar SDS solution in the presence of water-miscible IL [bmim][BF4]. We report the important finding that addition of [bmim][BF4] to micellar SDS solution helps nitromethane retain its selectivity in quenching fluorescence of alternant PAHs as opposed to that of nonalternant PAHs. IL-added aqueous anionic micellar solutions as possible media for PAH analysis is established from these studies.

Article

EXPERIMENTAL SECTION

Materials. Anthracene (99%), perylene (99+%), fluoranthene (99%), and benzo[b]fluoranthene were purchased from Aldrich and were used as received. Pyrene and benzo[j]fluoranthene were obtained in highest purity from SigmaAldrich Co. and SUPELCO, respectively, and stored under dried conditions. Benzo[a]pyrene and indeno[1,2,3-cd]pyrene were purchased from Accustandard and stored under dried conditions. IL [bmim][BF4] was obtained from Merck (high purity, halide content perylene. This order is in agreement with the ionization potential of these PAHs (or the gap between the LUMOs of the PAHs and the nitromethane) and confirms what is reported in the literature earlier.64,65 Interestingly, however, KD decreases for all alternant PAHs as a small amount of [bmim][BF4] is added to micellar SDS solution, suggesting decrease in the efficiency of collisional

Figure 3. Quenching of fluorescence emission of anthracene (10 μM) by nitromethane dissolved in 0.1 M aqueous SDS in the absence (panel A) and presence (panel B) of 10 wt % IL [bmim][BF4] at ambient conditions (λex = 357 nm).

quenching alone were operative, linear behavior between F0/F and [CH3NO2] would be expected. Positive deviations from the Stern−Volmer equation usually occur when the extent of quenching is large. Perrin introduced the concept of an “active sphere” for rigid solutionsa volume of interaction around a quencher molecule such that the fluorophore excited within this molecule is instantaneously quenched.61 It implies that the fluorophore and quencher do not actually form a ground-state complex; instead, it seems that the apparent static component is due to the quencher being adjacent to the fluorophore at the moment of excitation. These weakly associated fluorophore−quencher pairs show weak or no fluorescence and as a result appear to be dark complexes. Frank and Vavilov modified this model by combining the Perrin model with a dynamic quenching one.62 This model is

Figure 4. F0/F versus [CH3NO2] plots showing nitromethane quenching of the fluorescence from alternant PAHs dissolved in aqueous SDS + [bmim][BF4] mixtures at ambient conditions. Solid curves represent fit to a quenching sphere-of-action model (eq 2) (recovered parameters are reported in Table 1). 1821

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Table 1. Modified Parameters of Alternant PAHs/Nitromethane “Sphere-of-Action” Quenching within Aqueous SDS + [bmim][BF4] wt % [bmim][BF4]

KD (M−1)

⟨τ⟩ (ns)

0 0.5 2 5 10 20 30

34 19 10 11 12 12 12

± ± ± ± ± ± ±

2 1 1 1 1 1 1

4.1 4.2 5.6 7.4 9.2 11.1 12.5

0 0.5 2 5 10 20 30

291 105 65 49 63 61 70

± ± ± ± ± ± ±

78 4 3 1 2 1 3

35.0 31.1 29.2 27.0 25.1 20.8 18.2

0 0.5 2 5 10 20 30

1246 506 395 316 337 380 438

± ± ± ± ± ± ±

169 16 55 10 23 3 27

0 0.5 2 5 10 20 30

12 3 4 2 3 3 3

± ± ± ± ± ± ±

3 1 1 1 1 1 1

152 153 135 131 131 123 108 5.8 5.8 5.9 5.8 5.8 5.8 5.8

kq (109 M−1 s−1) anthracene 8.4 4.5 1.8 1.5 1.3 1.1 1.0 benzo[a]pyrene 8.3 3.4 2.2 1.8 2.5 2.9 3.9 pyrene 8.2 3.3 2.9 2.4 2.6 3.1 4.1 perylene 2.0 0.5 0.7 0.4 0.5 0.5 0.5

KD ⟨τ0⟩

R (Å)

r2

1.06 0.79 0.76 0.79 0.58 1.02 1.24

± ± ± ± ± ± ±

0.06 0.02 0.04 0.02 0.12 0.03 0.01

7.5 6.8 6.7 6.8 6.1 7.4 7.9

± ± ± ± ± ± ±

0.4 0.2 0.4 0.2 1.3 0.2 0.1

0.9988 0.9998 0.9993 0.9998 0.9941 0.9998 0.9999

1.30 0.66 0.51 0.69 0.56 0.75 0.67

± ± ± ± ± ± ±

0.28 0.03 0.05 0.02 0.03 0.02 0.05

8.0 6.4 5.9 6.5 6.1 6.7 6.4

± ± ± ± ± ± ±

1.7 0.3 0.6 0.2 0.3 0.2 0.5

0.9793 0.9994 0.9986 0.9998 0.9997 0.9999 0.9993

0.90 1.16 0.74 0.98 1.18 1.00 0.97

± ± ± ± ± ± ±

0.15 0.03 0.15 0.04 0.07 0.01 0.08

7.1 7.7 6.6 7.3 7.8 7.4 7.3

± ± ± ± ± ± ±

1.2 0.2 1.4 0.3 0.5 0.1 0.6

0.9924 0.9996 0.9909 0.9996 0.9984 0.9998 0.9987

2.23 1.82 2.04 1.76 1.81 1.97 2.14

± ± ± ± ± ± ±

0.25 0.20 0.21 0.21 0.20 0.17 0.16

9.6 9.0 9.3 8.9 9.0 9.2 9.5

± ± ± ± ± ± ±

1.1 0.9 1.0 1.1 1.0 0.8 0.7

0.9673 0.9651 0.9720 0.9562 0.9648 0.9780 0.9845

Here, ⟨τ0⟩ is the average fluorescence lifetime of the PAH in the absence of quencher. The fluorescence lifetimes for alternant PAHs in aqueous SDS micellar solution with varying concentration of [bmim][BF4] were measured in the absence of quencher. Figure 5 depicts representative excited-state intensity decay curves of alternant PAHs in aqueous micellar SDS. Similarly, decay curves were also collected for [bmim][BF4] added aqueous SDS solution. While the intensity decays of all alternant PAHs satisfactorily fit to a single-exponential decay model for [bmim][BF4] ≤ 0.5 wt %, double-exponential decay scheme was needed to fit the data for [bmim][BF4] > 0.5 wt %. This is expected in a complex media such as [bmim][BF4] added aqueous micellar SDS solution where heterogeneity in PAH distribution sites is expected. Estimated ⟨τ0⟩ from recovered τ’s and kq thus calculated are presented in Table 1. Fluorescence lifetimes of PAHs show no clear trend as [bmim][BF4] is added to micellar SDS solutionit increases for anthracene, decreases for benzo[a]pyrene and pyrene, and remains same for perylene as [bmim][BF4] concentration is increased. kq, on the other hand, follows a trend similar to KD and, in the absence of [bmim][BF4], reaches close to diffusioncontrolled value. This is expected for favorable quenching of alternant PAHs by nitromethane within aqueous anionic micellar SDS media.10,12,13,17,18 Nonalternant PAHs. Figure 6 presents fluorescence spectra of nonalternant PAH fluoranthene in the absence and presence

(dynamic) quenching. This outcome is attributed in major part to the screening of the anionic micellar surface charge by bmim+, thus reducing the stabilization of partial positive charge that generates on excited PAH during the electron/charge transfer as PAHs are known to solubilize in the palisade layer close to the micellar surface.66−70 Minor contribution to decreased KD from increase in the viscosity of the milieu in which fluorescence quenching is taking place should not be ignored.71,72 At higher concentration of IL (i.e., 10−30 wt %), the changes in the properties of the micellar aggregates start to play a role where aggregation number (Nagg) decreases along with decrease in micellar size.56,57 This leads toward the quenching behavior observed in polar isotropic media where alternant PAHs are quenched significantly by nitromethane. It is interesting to note that for all four alternant PAHs the KD are found to be minimum when 5 wt % [bmim][BF4] is added to micellar SDS. All in all, KD decreases nearly 3-fold for anthracene and pyrene and nearly 4-fold for perylene and benzo[a]pyrene in the presence of 30 wt % [bmim][BF4]. Bimolecular quenching rate constants (kq) were calculated for the alternant PAHs dissolved in aqueous micellar SDS solution in the absence and presence of [bmim][BF4] using

kq =

V (M−1)

(3) 1822

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Figure 5. Excited-state intensity decay data of alternant PAHs dissolved in aqueous SDS at ambient conditions. The blue curves denote the instrumental response function (IRF) measured using a dilute glycogen suspension. The top panels provide single-exponential fits to experimental data, and the lower panels show weighted residuals of the corresponding fits. Excitation is achieved using 340 or 405 nm Nano LEDs.

F0 − 1 = KSV[CH3NO2 ] = kq⟨τ0⟩[CH3NO2 ] F

(4)

where KSV is the Stern−Volmer quenching constant, which becomes KD in case of dynamic (collisional) quenching. The quenching mechanism of nonalternant PAHs by nitromethane is different from that of the alternant PAHs. We suspect that since the electron/charge transfer process is energetically not favored in nonalternant cases (see quenching mechanism in Scheme 1), the quenching perhaps follows a simpler Stern− Volmer relationship with no transient effects. From decrease in the fluorescence lifetime in the presence of quencher, we found the quenching of nonalternant PAHs by nitromethane in [bmim][BF4]-added aqueous micellar SDS solutions to be dynamic in nature. Recovered KD are presented in Table 2 along with kq that were estimated from fluorescence lifetimes of nonalternant PAHs in the absence of quencher nitromethane. (Figure 8 depicts the excited-state intensity decay curves of nonalternant PAHs dissolved in aqueous micellar SDS. Similarly, other decay curves were collected for [bmim][BF4] added aqueous SDS solutions.) Similar to the case of alternant PAHs, intensity decay of nonalternant PAHs for [bmim][BF4] > 0.5 wt % best fit to a double-exponential decay model. A careful examination of the entries in Table 2 reveals several important outcomes. As expected and revealed by the KD, the fluorescence of all four nonalternant PAHs is quenched by nitromethane in micellar SDS media in the absence of [bmim][BF4] showing the loss of quenching selectivity as shown by the Acree group earlier.13,24 Most interestingly, KD and kq are decreased significantly as a small amount of [bmim][BF4] (0.5 wt %) is added, clearly showing nitromethane to retain its selectivity in quenching fluorescence of alternant PAHs over that of nonalternant PAHs in SDS micellar media. This is attributed to the fact that for lower IL concentrations screening of anionic micellar surface charge by

Figure 6. Quenching of fluorescence emission of fluoranthene (10 μM) by nitromethane dissolved in 0.1 M aqueous SDS in the absence (panel A) and presence (panel B) of 10 wt % IL [bmim][BF4] at ambient conditions (λex = 380 nm).

of 10 wt % [bmim][BF4] as the quencher nitromethane is added to 0.1 M aqueous SDS solution. Figure 7 presents [(F0/ F) −1] versus [CH3NO2] for all concentrations of [bmim][BF4] studied for all four nonalternant PAHs (fluoranthene, benzo[b]fluoranthene, benzo[j]fluoranthene, and indeno[1,2,3cd]pyrene). It is clear from Figure 7 that quenching of four nonalternant PAHs by nitromethane follows a simple linear Stern−Volmer relationship59 irrespective of the identity of the nonalternant PAH or the presence of IL [bmim][BF4]: 1823

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Figure 7. [(F0/F) − 1] versus [CH3NO2] plots showing nitromethane quenching of nonalternant PAHs dissolved in aqueous SDS + [bmim][BF4] mixtures at ambient conditions. Solid lines represent fit to a linear Stern−Volmer model (eq 4) (recovered parameters are reported in Table 2).

selectively is retained.) The developing partial positive charge on excited-nonalternant PAH is no longer stabilized due to the screening of micellar negative charge by [bmim]+. Further addition of [bmim][BF4] results in small increase in quenching of nonalternant PAHs. This is again attributed to the altered micellar properties of SDS at higher concentrations of [bmim][BF4]. kq for nonalternant class are 101−103 times lower than the alternant class due to the unfavorable electron/ charge transfer process between nonalternant PAH and the quencher. This leads to restricted quenching even in the presence of anionic SDS micelles. Lower kq for nonalternant PAHs indicates that the process is not diffusion-controlled only; the charge/electron transfer is simply energetically not that favored as reported by researchers earlier.7−9,14,20,21

Table 2. Parameters of Nonalternant PAHs/Nitromethane Quenching within Aqueous SDS + [bmim][BF4] (Eq 4) wt % [bmim][BF4] 0 0.5 2 5 10 20 30 0 0.5 2 5 10 20 30 0 0.5 2 5 10 20 30 0 0.5 2 5 10 20 30

KSV (M−1)

⟨τ⟩ (ns)

kq (108 M−1 s−1)

fluoranthene ±1 39.1 ± 0.11 34.1 ± 0.04 23.0 ± 0.03 16.0 ± 0.02 11.6 ± 0.01 8.3 ± 0.05 7.3 benzo[b]fluoranthene 26 ± 1 41.4 9.4 ± 0.16 41.9 2.9 ± 0.32 38.8 2.5 ± 0.18 34.0 2.7 ± 0.12 28.8 2.7 ± 0.21 22.1 3.5 ± 0.16 18.9 benzo[j]fluoranthene 1.0 ± 0.11 7.8 0.4 ± 0.02 8.3 0.2 ± 0.01 8.3 0.2 ± 0.02 8.6 0.3 ± 0.02 8.8 0.2 ± 0.03 9.4 0.3 ± 0.01 9.8 indeno[1,2,3-cd]pyrene 1.1 ± 0.1 8.0 0.3 ± 0.01 8.1 0.1 ± 0.01 8.3 0.05 ± 0.01 8.3 0.04 ± 0.01 8.1 0.02 ± 0.01 8.0 0.14 ± 0.04 7.3 14 3.5 1.0 0.7 0.6 0.7 1.0

r2

3.5 0.9 0.3 0.2 0.2 0.4 0.7

0.9687 0.9950 0.9894 0.9918 0.9958 0.9992 0.9852

6.4 2.2 0.7 0.6 0.7 0.8 1.2

0.9957 0.9985 0.9421 0.9736 0.9906 0.9699 0.9919

1.3 0.4 0.2 0.2 0.3 0.2 0.3

0.9428 0.9767 0.9774 0.9519 0.9617 0.9427 0.9939

1.3 0.4 0.1 0.1 0.05 0.02 0.3

0.9306 0.9942 0.9602 0.6608 0.9152 0.6052 0.7176

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CONCLUSIONS Nitromethane is known to quench the fluorescence of alternant PAHs but not the fluorescence of nonalternant PAHs when dissolved in polar protic and polar aprotic isotropic organic media. This establishes the selectivity of nitromethane as a fluorescence quencher to discriminate between alternant and nonalternant PAHs. When dissolved in aqueous anionic micellar media, the fluorescence of nonalternant PAHs is also quenched by nitromethane and the selectivity is lost due to the stabilization of the partial positive charge by negative anionic micellar surface that develops on the excited PAH during the electron/charge transfer. Addition of small amounts of IL [bmim][BF4] to aqueous anionic micellar media helps nitromethane retain its quenching selectivity as the fluorescence quenching of nonalternant PAHs is again inhibited due to the partial neutralization of the anionic micellar surface charge by the presence of bulky bmim+ cations of the IL as at lower concentrations; IL dissociates to good extent within the micellar media. However, at higher IL concentrations, due to the changes in the physicochemical properties of the micellar media as IL now acts as a cosolvent, the quenching of nonalternant PAHs again starts to become prominent. Alternant PAHs appear to follow quenching sphere-of-action model whereas nonalternant PAHs follow simple linear quenching behavior according to Stern−Volmer equation.

[bmim]+ helps nitromethane to retain its selectivity utilizing the electrolytic behavior of IL at lower concentrations. (In fact, quenching is reduced for both alternant and nonalternant; however, reduction for nonalternants is so high that the 1824

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Figure 8. Excited-state intensity decay data of nonalternant PAHs dissolved in aqueous SDS at ambient conditions. The blue curves denote the instrumental response function (IRF) measured using a dilute glycogen suspension. The top panels provide single-exponential fits to experimental data, and the lower panels show weighted residuals of the corresponding fits. Excitation is achieved using a 340 nm Nano LED. (11) Amszi, V. L.; Cordero, Y.; Smith, B.; Tucker, S. A.; Acree, W. E., Jr.; Yang, C.; Abu-Shaqara, S.; Harvey, R. G. Appl. Spectrosc. 1992, 46, 1156−1161. (12) Pandey, S.; Acree, W. E., Jr.; Fetzer, J. C. Mikrochim. Acta 1998, 129, 41−45. (13) Pandey, S.; Acree, W. E., Jr.; Fetzer, J. C. Anal. Chim. Acta 1996, 324, 175−181. (14) Acree, W. E., Jr.; Pandey, S.; Tucker, S. A.; Fetzer, J. C. Polycyclic Aromat. Compd. 1997, 12, 71−123. (15) Pandey, S.; Acree, W. E., Jr.; Cho, B. P.; Fetzer, J. C. Talanta 1997, 44, 413−421. (16) Pandey, S.; Acree, W. E., Jr.; Scott, L. T.; Necula, A.; Fetzer, J. C.; Mulder, P. P. J.; Lugtenburg, J.; Cornelisse, J. Polycyclic Aromat. Compd. 1999, 13, 79−92. (17) Pandey, S.; Fletcher, K. A.; Acree, W. E., Jr.; Fetzer, J. C. Fresenius J. Anal. Chem. 1998, 360, 669−674. (18) Pandey, S.; Powell, J. R.; Acree, W. E., Jr.; Cho, B. P.; Kum, J.; Yang, C.; Harvey, R. G. Polycyclic Aromat. Compd. 1997, 12, 1−19. (19) Tucker, S. A.; Griffin, J. M.; Acree, W. E., Jr. Analyst 1994, 119, 2129−2133. (20) Ogasawara, F. K.; Wang, Y.; McGuffin, V. L. Appl. Spectrosc. 1995, 49, 1−7. (21) Chen, S. H.; Evans, C. E.; McGuffin, V. L. Anal. Chim. Acta 1991, 246, 65−74. (22) Goodpaster, J. V.; Harrison, J. F.; McGuffin, V. L. J. Phys. Chem. A 2002, 106, 10645−10654. (23) Howerton, S. B.; Goodpaster, J. V.; McGuffin, V. L. Anal. Chim. Acta 2002, 459, 61−73. (24) Pandey, S.; Acree, W. E., Jr.; Fetzer, J. C. J. Lumin. 1997, 71, 189−197. (25) Terabe, S.; Miyashita, Y.; Shibata, O.; Barnhart, E. R.; Alexander, L. R.; Patterson, D. G.; Karger, B. L.; Hosoya, K.; Tanaka, N. J. Chromatogr. 1990, 516, 23−31. (26) Cole, R. O.; Sepaniak, M. J.; Hinze, W. L.; Gorse, J.; Oldiges, K. J. Chromatogr. 1991, 557, 113−123. (27) Fu, X.; Lu, J.; Chen, Y. Talanta 1998, 46, 751−756. (28) Rogers, R. D.; Seddon, K. R. Science 2003, 302, 792−793. (29) Wasserscheid, P.; Welton, T. Ionic Liquids in Synthesis; WileyVCH: Weinheim, 2003.

The dual role of IL is highlighted where initially it works as an electrolyte assisting in quenching selectivity and later as a cosolvent. The outcomes of this investigation establish ILs as additive to aqueous anionic micellar media for PAH separation and analysis.

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AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected]; Ph +91-11-26596503; Fax +91-11-26581102. Notes

The authors declare no competing financial interest.

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REFERENCES

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