This article was downloaded by: [University of Winnipeg] On: 18 August 2014, At: 08:14 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Instrumentation Science & Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/list20 HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY DETERMINATION OF ANILINES WITH FLUORESCENT DETECTION AND PRE-COLUMN DERIVATIZATION Salma M. Z. Al-Kindy a , Azza Al-Kalbani a , Ahmed F. Al-Harasi a , FakhrEldin O. Suliman a , Haider J. Al-Lawati a & Abdalla Al-Hamadi a a Department of Chemistry, College of Science , Sultan Qaboos University , Al-Khod , Sultanate of Oman Accepted author version posted online: 05 Oct 2012.Published online: 08 Feb 2013. To cite this article: Salma M. Z. Al-Kindy , Azza Al-Kalbani , Ahmed F. Al-Harasi , FakhrEldin O. Suliman , Haider J. Al-Lawati & Abdalla Al-Hamadi (2013) HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY DETERMINATION OF ANILINES WITH FLUORESCENT DETECTION AND PRE-COLUMN DERIVATIZATION, Instrumentation Science & Technology, 41:1, 48-59, DOI: 10.1080/10739149.2012.721108 To link to this article: http://dx.doi.org/10.1080/10739149.2012.721108 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
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This article was downloaded by: [University of Winnipeg]On: 18 August 2014, At: 08:14Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Instrumentation Science & TechnologyPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/list20
HIGH-PERFORMANCE LIQUIDCHROMATOGRAPHY DETERMINATIONOF ANILINES WITH FLUORESCENTDETECTION AND PRE-COLUMNDERIVATIZATIONSalma M. Z. Al-Kindy a , Azza Al-Kalbani a , Ahmed F. Al-Harasi a ,FakhrEldin O. Suliman a , Haider J. Al-Lawati a & Abdalla Al-Hamadia
a Department of Chemistry, College of Science , Sultan QaboosUniversity , Al-Khod , Sultanate of OmanAccepted author version posted online: 05 Oct 2012.Publishedonline: 08 Feb 2013.
To cite this article: Salma M. Z. Al-Kindy , Azza Al-Kalbani , Ahmed F. Al-Harasi , FakhrEldinO. Suliman , Haider J. Al-Lawati & Abdalla Al-Hamadi (2013) HIGH-PERFORMANCE LIQUIDCHROMATOGRAPHY DETERMINATION OF ANILINES WITH FLUORESCENT DETECTION ANDPRE-COLUMN DERIVATIZATION, Instrumentation Science & Technology, 41:1, 48-59, DOI:10.1080/10739149.2012.721108
To link to this article: http://dx.doi.org/10.1080/10739149.2012.721108
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the“Content”) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.
This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
DETERMINATION OF ANILINES WITH FLUORESCENT DETECTION
AND PRE-COLUMN DERIVATIZATION
Salma M. Z. Al-Kindy, Azza Al-Kalbani, Ahmed F. Al-Harasi,
FakhrEldin O. Suliman, Haider J. Al-Lawati, and Abdalla Al-Hamadi
Department of Chemistry, College of Science, Sultan Qaboos University, Al-Khod, Sultanate of Oman
A simple, sensitive, and rapid reverse-phase high-performance liquid chromatography (RP-HPLC) method for the determination of anilines in water is proposed. The use of 2,7-diethyl-amino-2-oxo-2H-chromen-3-yl-benzothiazole-6-sulfonylchloride (coumarin 6-SO2Cl) as a fl uori-genic-labeling reagent was investigated. The label reacted with aniline within 30 min under mild conditions (ambient temperature, pH 9.0) to give sulfonamides that were separated by RP-HPLC employing fl uorescence detection with an excitation wavelength of 470 nm and an emission wave-length of 520 nm. The optimum conditions for fl uorescence, derivatization, and chromatographic separation were established. The calibration curves were linear for the range 0–800 ppb. The proposed method was applied for the determination of anilines in spiked drinking water samples and irrigation water samples with recoveries of 90.0–103.9% and relative standard deviations of 1.2–4.7%, respectively. This method showed good accuracy and repeatability that can be used for the quantifi cation of aniline in real samples.
Aromatic amines such as aniline and its substituted derivatives are an important class of environmental water pollutants. They may react with nitrosylating agents in the environment and are converted into toxic N-nitroso compounds,[1] which are precursors of cancer. They penetrate though soil and contaminate ground water, and are thus present in trace amounts in natural water. Chlorinated anilines such as p-chloroaniline and
Address correspondence to Salma M. Z. Al-Kindy, Department of Chemistry, College of Science, Sultan Qaboos University, P.O. Box 36, Al-Khod 123, Sultanate of Oman. E-mail: [email protected]
Fluorescent Detection and Pre-Column Derivatization 49
3,4-dichloroaniline are found as degradation products and intermediates of various phenylurea and phenylcarbamate pesticides.[1] Industrially, ani-lines are used in the manufacture of various products such as polymers, rubber, plastics, pharmaceuticals, and agricultural products.[2] In view of the importance of these compounds, rapid and sensitive analytical meth-ods are needed for the determination of anilines in the environment and in biological fl uids.
Several methods have been developed for the determination of trace amounts of aniline in the environmental water samples and biological fl uids in an effort to estimate human exposure to these chemicals.[3] These include high-performance liquid chromatography (HPLC) for nonvolatile aniline compounds,[2,4,5] gas chromatography (GC),[6] gas chromatography–mass spectroscopy (GC-MS),[1,7] UV-visible spectrophotometry,[8,9] capillary elec-trophoresis (CE),[10,11] and by fl uorescence quenching sensor using a new metallo-tetraazaporphyrin complex.[12]
HPLC has been widely used for the determination of trace com-pounds. This is because it has high separation effi ciency and can be adapted to various detection modes suitable for the target compounds. However, not all compounds of interest are suitable for sensitive detec-tion by HPLC. Hence chemical derivatization procedures are employed to enhance the sensitivity, selectivity, and separation effi ciency of a chro-matographic method. Among the derivatization techniques, fl uorimetric methods have attracted a great deal of interest, as they afford a simple way to offer high sensitivity. Furthermore, fl uorescence labeling methods are simple and selective for the target molecule. Hence they may avoid the tedious and time-consuming sample clean-up steps by eliminating interferences. Anilines possesses a suitable functional group that can react with many fl uorigenic labels to form derivatives, which are fl uorescent in nature. Many fl uorigenic labels have been used to derive aniline. These include dansyl chloride,[13] TAAlPC,[14] fl uorescamine,[10,15] DTAN,[9] and NBD-Cl and NBD-F.[16]
The coumarin nucleus has been modifi ed to introduce several interest-ing laser dyes and other analytical useful fl uorescent labels. Such reagents have been synthesized with reactivity to carboxylic acids, amines, amino acids, alcohols, and phenols.[17–22]
As part of our ongoing study for the development of novel labels based on the coumarin nucleus, we synthesized a label based on 2-(7-diethylamino-2-oxo-2H-chromen-3-yl)-benzothiazole (coumarin 6). The label was synthesized by direct chlorosulfonation of coumarin 6. The label was found to be reasonably stable when stored under subdued light conditions in a desiccator. The spectroscopic properties of the label were studied in solvents of various polarities and buffers of different pH. The results refl ect the importance of medium effect on the analytical
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application of 2,7-diethylamino-2-oxo-2H-chromen-3-yl-benzothiazole-6-sulfonyl chlorides (coumarin 6-SO2Cl) as a potential luminescent label for derivatization of amino groups (unpublished work). In this article, we report a simple and rapid analytical method for the determination of aniline in water samples. The method is based on the formation of highly fl uorescent derivatives when anilines are reacted with coumarin 6-SO2Cl. The derivatives will be separated using HPLC with fl uorescence detection.
EXPERIMENTAL
Reagents
All reagents used are of analytical grade and were used without fur-ther purifi cation: 2,7-diethylamino-2-oxo-2H-chromen-3-yl-benzothiazole-6-sulfonyl chlorides (coumarin 6-SO2Cl) was synthesized as previously described.[23] p-Toludine, hydrochloric acid, aniline, sodium hydroxide pel-lets, sodium dihydrogen phosphate, and disodium hydrogen phosphate were purchased from BDH Chemicals Ltd. (East Yorkshire, UK). Acetoni-trile was purchased from Panreac Quimica SA (Barcelona, Spain). Metha-nol, 3-chloroaniline, and 2,4-dichloroaniline were from Aldrich (Poole, UK). All the solvents used are of HPLC grade. Ultrapure water was used for all preparations, and it was obtained from a Millipore (Bedford, MA, USA) Milli-Q system.
Apparatus
A Perkin Elmer LS55 Luminescence Spectrometer (UK) was used to record both the emission and the excitation spectra. A quartz cell of 1 cm path length was used for measurement. The spectra were recorded with-out correction for instrumental characteristics.
The pH values of the solutions were measured on a Jenway 3015 pH meter (UK). The pH meter was calibrated before use with buffer solutions prepared from pH buffer powder of pH 4.0, 7.0, and 9.0.
The HPLC system consisted of a Water 616 separation model pump, Waters 600 controller (pump detector), Water 486 turntable absorbance detector (UV-detector), and Water 474 scanning fl uorescence detector connected to a personal computer (from Waters USA). The integration software Millennium was used was used to control the operation, data col-lection, and manipulation of all the chromatographic systems. The mobile phase was passed through a 0.45 μm fi lter and degassed by sonication for few minutes before use. Manual injections were carried out using a Rheo-dyne model 7125 injector with 20 μL sample loop. The fl uorescence detec-tion was monitored by exciting at 470 nm. and collecting the resultant
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Fluorescent Detection and Pre-Column Derivatization 51
emission at 520 nm. The analytical column used was X Terra ODS column with (250 × 4.6 mm i.d 5 μm, Supelco, Germany). The column was treated with an appreciable amount of eluent to equilibrate before measurements.
Preparation of Standards
A standard stock solution of anilines (10 ppm. was prepared in phos-phate buffer solution (pH 9). A series of standards ranging from 0.1–1.0 ppm were appropriately diluted with the buffer. The label (5.0 mM. was prepared in acetonitrile.
Derivatization Procedure
The reaction of coumarin 6-SO2Cl with the amine groups on the ani-line molecules is represented in Figure 1. The derivatization was carried out in acetonitrile–water (1:1, v/v) media. The molar ratio of aniline to coumarin 6-SO2Cl was maintained at 1:5. Aniline stock solution (50 μL) was mixed with 50 μL label and allowed to stand for 30 min under sub-dued lightning conditions at room temperature. The aliquot of the reac-tion mixture (20 μL) was diluted 75 times and fi ltered through 0.45 μm membrane fi lters prior to injection into the chromatographic system. Each sample was assayed in triplicate, and all of the assays were carried out at ambient temperature. The mean peak area of the analyte was plotted against the corresponding aniline derivative concentration.
Sample Preparation
Tap water samples from the university campus and ground water from Falaj were collected, fi ltered with a 0.45 μm membrane to remove suspended particulates, and analyzed immediately. A known volume of water sample was then spiked with aniline and p-toludine standard mix-tures. The pH was adjusted to 9.0 using 0.2 M sodium phosphate buffer. A 0.5 mL volume of the treated sample was then subjected to derivatiza-tion using optimized procedure. Aliquots (20 μL. from this solution were directly injected into the HPLC system. Triplicate injections of each sample
FIGURE 1 Derivatization reaction of aniline with coumarin 6-S02Cl.
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solution were made, and the recoveries were calculated by relating the con-centration determined in the water sample to the calibration standards.
Optimum Chromatography Condition
Initially, the chromatographic system was optimized by injecting pure standards of aniline and p-toludine derivatives. The effect of mobile phase composition on the resolution of the aniline derivative was investigated. Acetonitrile was used as the organic modifi er in the mobile phase in com-bination with water. The effect of various percentages of acetonitrile:water ranging from 75:25 to 90:10, respectively, was investigated. Each mobile phase was sonicated for 30 min to remove bubbles and vacuum fi ltered to remove any particles prior to application into the system. A mobile phase consisting of CH3CN:H2O of 75:25 was taken to be the optimum in terms of peak shape and the resolution of the components. The fl ow rate was maintained at 1 mL min–1. Using the optimum mobile phase, the optimum fl ow rate in the HPLC system was investigated by injecting standard solu-tions of aniline derivatives and coumarin 6-SO2Cl and varying the fl ow rate of the mobile phase from 0.3 to 1.0 mL min–1. The optimum fl ow rate was found to be 1.0 mL min–1 in terms of peak shape.
RESULTS AND DISCUSSION
Fluorescence Spectra
Fluorescence emission and excitation of coumarin 6-SO2Cl and its deriv-atives were measured in acetonitrile. The label exhibited emission wave-length of 520 nm when excited at 470 nm (Figure 2). The excitation and emission maximum of the derivatives are similar to the label. The results suggest that the fl uorescent properties of the derivatives are dominated by the coumarin 6 moiety and are independent of the structures of the aniline used. The fl uorescence excitation and emission spectra of the label and ani-line derivative was studied in different percentages of acetonitrile and water ranging from 100–0% acetonitrile. A slight blue shift in wavelength accom-panied by a decrease in fl uorescence intensity was observed with an increase in percentage of water in the media. Therefore the HPLC separation of aniline derivatives will be optimal in higher concentrations of acetonitrile. Similar fi ndings were previously reported for DNS-APy.[24]
Optimization of the Derivatization Procedure
The applicability of the coumarin 6-SO2Cl as a fl uorescent probe for the analysis of anilines was thoroughly investigated. The derivatization effi ciency
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Fluorescent Detection and Pre-Column Derivatization 53
is of great importance in pre-column derivatization strategy. The labeling reaction is affected by various parameters, which are determined by many factors such as the amount of labeling reagent, derivatization media, reaction time, and temperature. The derivatization conditions of coumarin 6-SO2Cl with aniline have been optimized. To achieve optimum conditions, the effects of the reaction time, pH, and concentration of coumarin 6-SO2Cl that will lead to a maximum yield of the derivatized anilines were investigated.
The optimum reaction time was studied as follows: Into a 1.5 mL vial containing 50 μL of aniline solution (0.10 mM. in phosphate buffer (pH 9.0), 50 μL of coumarin 6-SO2Cl (0.5 mM in acetonitrile) was added. The contents were mixed thoroughly. An aliquot of the reaction mixture (20 μL) was injected at 15-min intervals up to 60 min. Figure 3 represents the time profi le of the derivatization reaction obtained at different inter-vals. The formation of the derivatives gradually increased with reaction time at room temperature. The yields of the derivatives reached a pla-teau after 30 min, after which it declined slightly and remained constant. Therefore, the optimum derivatization time for the study was maintained at 30 min. Derivatization at higher temperatures may lead to a decrease in the reaction time; however the effect of temperature on the derivatization reaction was not investigated in this study.
As the derivatization reaction of anilines with coumarin 6-SO2Cl is pH-dependent, the effect of pH on the derivatization reaction was studied by using phosphate buffer of various pH values ranging from 8.0–10.0. The
FIGURE 2 The fl uorescence spectra of 1.0 × 10–8 M of coumarin 6-S02Cl and its derivatives in acetonitrile: (1) p-toludine, (2) aniline, (3) coumarin-6S02Cl; λem = 520nm, λex = 470 nm, slit widths 5 nm. (color fi gure available online.)
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54 S. M. Z. Al-Kindy et al.
content was allowed to react for 30 min at room temperature. An aliquot of 20 μL was injected onto the column. The reaction yield increased with an increase in the pH and reached a maximum value at pH 9.0. This was probably due to deprotonation of amines at the base condition, which can promote the nucleophilic addition. Upon increasing the pH further, the yield decreased. This decrease may be explained due to the hydrolysis of the sulfonyl chloride group of the label to give sulfonic acid. On the other hand, a possibility of ring opening of the coumarin nucleus may occur at high pH. Similar results were previously reported for C-6SCl.[19] The effect of concentration of the label on derivatization reaction was studied by varying the concentration of the aniline and fi xing the concentration of the label. The concentration of the aniline:label was varied in the ratio of 1:1 to 1:7.5 (Figure 4). The fl uorescence intensity of the derivative and hence yield was observed to increase with an increase in the ratio of the label, with the maximum yield observed when the ratio of the label was 5:1, after which the yield remained constant. These results suggest that an excess of the label is required for maximum derivatization yield to occur. Similar results were previously reported for the derivatization reaction between C-6SCl, and amino acids and phenols where an optimum ratio of fi ve and three was required.[18,19] Hence a 5 M-fold excess of the label to aniline was maintained in this study.
Method Validation
Having optimized the separation and derivatization condition as described above, resolution of the four-component mixture was performed.
FIGURE 3 Time course for the derivatization reaction of aniline with coumarin 6-S02Cl. (color fi gure available online.)
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Fluorescent Detection and Pre-Column Derivatization 55
The reagent did not interfere with the analysis because it elutes in less than 4 min. A baseline separation was obtained for all the derivatives using acetonitrile:water (75:25) in 15 min (Figure 5). Table 1 shows the separation
FIGURE 4 Effect of concentration ratio of coumarin 6-S02Cl:aniline on the derivatization reaction. (color fi gure available online.)
FIGURE 5 Chromatogram of coumarin 6-S02Cl and its derivatives. Chromatography conditions as in the text: (1) coumarin 6-S02Cl, (2) aniline, (3) p-toludine, (4) 3-chloroaniline, (5) 2,4-dichloroaniline. (color fi gure available online.)
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56 S. M. Z. Al-Kindy et al.
factor (α) and capacity factor (k’) for the label and its derivatives. As can be seen, the maximum theoretical plate was obtained for p-toluidine.
The performance of the proposed HPLC method was evaluated using the optimum conditions described above. Calibration curves were obtained by plotting peak area against the corresponding concentrations of aniline and p-toludine standards. Linear relationships were obtained in the concentration range 0.2–0.8 ppm. The regression equations and cor-relation coeffi cients for the two compounds were as follows:
For aniline derivative, A = (2.8 ± 0.5) × 105 C + (–1.2 ± 0.3) × 105 (R = 0.998); and for p-toluidine derivative, A = (2.8 ± 0.2) × 105 C (–1.4 ± 0.3) × 105 (R = 0.999), where A is the peak area in arbitrary units and C is the concen-tration of anilines derivative in ppm. The slope for aniline was similar to that of p-toluidine. Using the slope of the calibration curve as a measure of the sensitivity, the method exhibits comparable sensitivity for the determination of both p-toluidine and aniline. The detection limit defi ned as the total amount of derivative at a signal:noise ratio of three (S:N = 3) was 4 ppb for toluidine and 5 ppb for aniline. These detection limits are comparable to those obtained in previous studies using HPLC with fl uorescence derivatization with DTAN[9]
and with fl uram.[15]
Precision and Accuracy
The repeatability of the method was obtained from measuring the peak areas with fi ve replicated injections of 20 μL (concentration 200 ppb of ani-line). The relative standard deviations (RSDs) were all within 5%. They are acceptable in an environmental analysis. The reproducibility of the present method was investigated over fi ve days using ultrapure water spiked with 400 ppb of aniline. Recoveries of aniline were 93.6%, n = 4, RSD = 2.5%.
Application to Natural Water Samples
The developed HPLC method was applied to the analysis of tap water and Afl aj water spiked with aniline and p-toludine samples in concentrations
TABLE 1 Chromatographic Properties of Coumarin 6-SO2Cl and Its Derivatives
Fluorescent Detection and Pre-Column Derivatization 57
of 300 and 600 ppb. which were derivatized as previously described. Each sample was injected in triplicate. Analytical results are shown in Table 2. It can be seen that satisfactory results for the anilines were obtained with recovery values ranging from 90–105%. Higher recoveries in all deriva-tives were observed in 300 ppb when compared to 600 ppb. These results suggest that the method may be more suitable for low-level concentra-tions. In the future, further work needs to be done to extend the applica-bility of the method to real samples of anilines in different matrices and to explore the potential of derivatizing compounds containing hydroxyl groups and other amino groups, and to improve derivatization conditions by studying the reaction at high temperatures.
CONCLUSION
An HPLC method was established for the separation of fi ve anilines in water samples using a fl uorescence detection method, based on the pre-column derivatisation using coumarin 6-SO2Cl. The derivatization reac-tion proceeded under mild conditions at room temperature. The method is versatile and can achieve low detection limits. It also gave good repro-ducibility and reasonable recoveries for the spiked water samples we ana-lyzed. Furthermore, when combined with preconcentration techniques, very low limits of detection can be achieved. The label is modeled on dan-syl chloride, a well-known fl uorigenic derivatization reagent. Compared with dansyl chloride, coumarin 6-SO2Cl has similar reactivity as a label with the derivatization time of 30 min at room temperature similar to the time reported by Geerdink[13] at 45°C and by Zhang et al.[25] at 60°C for derivatization of amino acids. However, the reaction is much slower than anthraquinone-2-sulfonyl chloride, which achieved derivatization of
TABLE 2 Recovery Studies of Aniline and p-toluidine Derivatives
amines at room temperature in 3 min.[26] The use of coumarin 6-SO2Cl as a fl uorigenic labeling reagent is expected to provide an attractive alterna-tive method for the assay of amino-containing compounds without any sample pretreatment.
ACKNOWLEDGMENT
Financial support from SQU, grant #IG/SCI/CHEM/09/01, is grate-fully acknowledged.
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