Simple Spectrophotometric Determination of Reactive Dyes after Preconcentration using Activated Carbon. Ayman A. Issa and Yahya S.

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1 JJC Jordan Journal of Chemistry Vol. 4 o.1, 2009, pp Simple Spectrophotometric Determination of Reactive Dyes after Preconcentration using Activated Carbon Ayman A. Issa and Yahya S. Al-Degs* Chemistry Department, The Hashemite University, P.O. Box , Zarqa, Jordan. Received on Oct. 10, 2008 Accepted on March 18, 2009 Abstract The extraction efficiency of activated carbon for reactive dyes (Levafix Brilliant Blue E- 4BA and Levafix Brilliant Red E-4BA) was investigated under different experimental factors including: initial dye concentration, carbon mass, ph, ionic strength and agitation time. The equilibrium time was relatively fast and was achieved within 40 min. The distribution coefficients (Kd) were 50.6 and 24.3 dm 3 g -1 for blue and red dye; respectively. For comparison purposes, multiwalled nanotube activated carbon was tested and showed a high extraction power for reactive dyes; the Kd values were and 66.2 dm 3 g -1 for blue and red dye; respectively. The employed analytical method for dyes analysis was accurate and sensitive, Beer s plots showed good correlation in the range mg L -1 for reactive dyes. A simple solid-phase extraction procedure based on activated and nanotube activated carbons for detection of ng L -1 levels of reactive dyes is presented. The detection limits of the proposed method are 20 and 30 ng L -1 for red and blue dye; respectively. Keywords: Solid-phase extraction; Reactive dyes; H-type activated carbon; Multiwalled nanotube activated carbon. Introduction Commercially, there are more than 100,000 dyes with over tones of dyestaff produced yearly [1]. Dyes can be classified according to their structure to anionic and cationic dyes [1]. When dissolved in water, anionic dyes ionized and carried a net negative charge due to sulphonate (SO 2-3 ) groups [2], while basic dyes ionized and carried a net positive charge due to protonated amine or sulfur containing groups. Reactive dyes utilize a chromophore containing substituent that is capable of directly reacting with the fibre substrate. The covalent bonds that attach reactive dye to natural fibers make it among the most permanent of dyes. Cold reactive dyes, such as Procion MX, Cibacron F, Levafix Brilliant and Drimarene K, are very easy to use because the dye can be applied at room temperature [3]. Due to their strong interaction with many surfaces of synthetic and natural fabrics, reactive dyes are highly used for dyeing of wool, cotton, nylon, silk, and modified acrylics [3]. Some classes of dyes are harmful to aquatic life even at lower concentrations. It is pointed out that less than 1.0 mg L -1 of * Corresponding author: yahya@hu.edu.jo 89

2 dye content causes obvious water coloration [4]. Dye concentrations of 10 mg L -1 up to 25 mg L -1 have been cited as being present in dyehouse effluents [5]. After mixing with other water streams, the concentration of dyes is further diluted. The limit of concentration of some toxic dyes in water is 1.0 ng L -1 [6]. Due to their high molar absorptivities (> 10,000 M -1 cm -1 ), most dyes can be quantified in solution using simple photometer and spectrophotometer which are available in most laboratories. As mentioned earlier, dyes are present in the environmental samples at trace levels. Accordingly, their direct measurement is not possible unless the solute is preconcentrated to be detected by the instrument. Solidphase extraction (SPE) is a widely used sample preparation technique for the isolation and preconcentration of the target analyte(s) which usually present either in solid phase or liquid phase [7]. The solid-phase extraction has attracted considerable attention as a preconcentration technique because of its high enrichment efficiencies and it does not require large amount of organic solvent compare to familiar liquid-liquid extraction techniques [7]. SPE is based on the distribution of analyte between an aqueous solution and sorbent by mechanisms such as: adsorption, co-precipitation, complex formation and other chemical reactions [8]. SPE techniques were effectively applied to quantify heavy metals [9] and organic pollutants [10] that present in solution at trace levels. Many solid surfaces of different properties were tested as extractants which includes molecular imprinted polymers [8], modified silica [10], activated carbon [11], and nanotubes activated carbons [12]. The application of activated carbon (as the main extractant) and multiwalled nanotube activated carbon (for comparison with conventional activated carbon) is investigated in this work. The studied dyes are Levafix Brilliant Red E-4BA and Levafix Brilliant Blue E-4BA. These dyes have a wide application and usually present in treated water at trace levels. Effect of experimental conditions such as initial dye concentration, carbon mass, agitation time, ph, and ionic strength on extraction efficiency of activated carbon was investigated. Desorption of dyes from activated carbon was studied using different desorption agents including: water, 0.1 M HCl, and ethanol. Another aim of this study was to develop a simple procedure for spectrophotometric determination of trace levels (30 40 ng L -1 ) of reactive dyes in water using SPE as a preconcentration step. Theoretical Background The effect of treatment time, initial dye concentration, carbon mass, ph, and ionic strength on dyes extraction was determined by estimating the distribution coefficient (Kd) of dyes between solid phase and aqueous solution. The value of Kd was simply estimated using Eq. 1 [8, 13-14]: q e K d =...(1) Ce 90

3 Where Kd, qe, and Ce, and are distribution coefficient (dm 3 g -1 ), surface concentration of dye (mol g -1 ), and concentration of dye remaining in solution after time t or at equilibrium (mol dm -3 ) respectively. The value of qe can be calculated from Eq. 2: q e ( C0 Ce ) V =...(2) m Where C 0, V, and m are initial dye concentration (mol dm -3 ), volume of solution (dm 3 ), and mass of extractant (g) respectively. A large Kd (>> 1.0 dm 3 g -1 ) signifies a high affinity between dye and the extractant. Experimental Solid-phase extractants and adsorbates Powdered activated carbon was purchased from Calgon company (Pittsburgh, Pennsylvania, USA). The multiwalled activated carbon was obtained from TP Company, China. The specifications of this nanotube carbon are: range of diameter nm, length 5-15 µm, purity > 95%, specific surface area 300 m 2 g -1, ash < 0.2 wt%, and amorphous carbon < 3%. The adsorbents were used without any chemical or physical treatment. Two reactive dyes of wide industrial applications were studied; namely, Levafix Brilliant Red E-4BA (C 29 H 19 O 11 7 S 3 Cla 3 ), Levafix Brilliant Blue E- 4BA (C 31 H 19 O 9 5 S 2 Cl 2 a 2 ). Throughout the text, Levafix Brilliant Red E-4BA and Levafix Brilliant Blue E-4BA were referred to as red dye and blue dye; respectively. Reactive dyes of high purity (> 99%) were obtained from (Bayer, Frankfurt, Germany). The wavelengths of maximum absorption (λ max ) of dyes were obtained by scanning dyes solutions over the visible region ( nm), the observed λ max for dyes were and nm for red and blue dyes; respectively. The chemical structures of dyes are depicted in figure 1. O H 2 SO 3 a O H SO 3 a H Cl H H SO 3 a O O A) Levafix Brilliant Red E-4BA. H 2 H C H 2 SO 3 a SO 3 a O C C H 2 H B) Levafix Brilliant Blue E-4BA. Figure 1: The chemical structure of reactive dyes Cl Cl 91

4 Chemicals and solutions Doubly distilled water and high-purity reagents were used for all preparations of standard and sample solutions. Standard stock solutions ( mg dm -3 ) of reactive dyes were prepared individually by dissolving (±0.001) g in doubly distilled water in a cm 3 volumetric flask. Dilute solutions were prepared by the appropriate dilution of the stock solution in doubly distilled water. The ph adjustment was made by adding 0.5 M HO 3 or 0.5 M aoh to the dye solutions. The ionic strength of solutions was adjusted using pure acl. All the employed reagents (except the dyes and the extractants) were obtained from Merck chemicals. Procedures of extraction and stripping of dyes Extraction studies Extraction of reactive dyes at different initial concentrations was carried out according to the following procedure: (±0.001) g of powdered activated carbon was added to cm 3 of reactive dye solution of varying concentration: mg L -1. ph, ionic strength, and temperature of solutions were adjusted to 6.0, 0.1 M acl, and 25.0±1 0 C; respectively. The bottles were sealed and placed in a thermostated shaker (Germany GFL 1083, Germany) for 40 min to attain equilibrium. The equilibrium time for both dyes was determined in previous studies. After equilibrium, samples were removed and filtered through 0.45 µm Millipore cellulose nitrate filters and subsequently analyzed to determine the equilibrium concentration of dyes using a double beam Unicam spectrophotometer (Cary 50 UV-Vis spectrophotometer). The equilibrium concentrations of reactive dyes were determined by converting the obtained absorbances to concentrations using pre-determined linear calibration graphs. Effect of ph on dyes extraction was investigated over a wide ph range (1-12) by repeating the earlier procedures under the following conditions: mass of carbon 200 mg, dye concentration mg L -1, volume of solution cm 3, concentration of acl 0.1 M, temperature 25 0 C, and shaking time 40 min. Effect of ionic strength on dyes extraction was investigated at different concentrations of acl ( M) under the following conditions: carbon mass 200 mg, dye concentration mg L -1, volume of solution cm 3, ph=6.0, temperature 25 0 C, and shaking time 40 min. Effect of carbon mass on dyes extraction was investigated at different carbon masses ( mg) while maintaining the other experimental conditions at: dye concentration mg L -1, volume of solution cm 3, ph = 6.0, concentration of acl 0.1 M, temperature 25 0 C, and shaking time 40 min. Effect of agitation time on dyes removal was studied as follows: Five solutions of each dye (total ten solutions) were prepared separately under the following conditions: carbon mass 200 mg, dye concentration mg L -1, concentration of acl 0.1 M, volume of solution cm 3, ph=6.0, and temperature 25 o C. The solutions were placed in the shaker and two solutions (one for each dye) were removed every 10 min and analyzed for dye content 92

5 as outlined earlier. The zero-time for each solution was taken after addition of adsorbent. Stripping of reactive dyes from the solid surface For desorption of dyes from activated carbon, three common desorption agents applied for dyes were used namely; H 2 O, 0.1 M HCl and ethanol. Before desorption, activated carbon loaded with reactive dyes was prepared under the following conditions: initial dye concentration mg L -1, mass of carbon 200 mg, volume of solution cm 3, ph = 6.0, concentration of acl 0.1 M acl, and agitation time 40 min. After completion of extraction, the adsorbent was removed by filtration and placed in the desorption medium and agitated for different time intervals. The concentration of dyes was determined as outlined earlier. Desorption ratio was calculated from the following equation [8] : amount of released Desorption ratio =...(3) amount of dye adsorbed by activated carbon It is important to mention that the absorption characteristics and λ max of dyes in ethanol and acidic solution were very close to those observed in water. General procedure for solid-phase extraction and analysis of reactive dyes 200 mg of activated carbon or multiwalled nanotube activated carbon was added to cm 3 aqueous solution containing (30 40 µg l -1 ) of reactive dyes. The other experimental contortions were adjusted to: ph=6.0, concentration of acl 0.1 M and temperature 25 0 C. The solution was agitated for 40 min. The adsorbent was removed by filtration and placed in 8.0 cm 3 of ethanol and the mixture was agitated for 15 min to elute adsorbed dye. Dye concentration in the eluent was determined using the spectrophotometer as outlined earlier. Result and discussion Characterization of the solid-phase extractants Boehm titration method was used to determine the acidic and basic surface groups of the employed activated carbon [15] and 2 adsorption technique was used to estimate the surface area and the average pore diameter [16]. The results showed that the adsorbent has a total surface basicity of 0.43 mmol g -1, total surface acidity of 0.30 mmol g -1, and specific surface area of 820 m 2 g -1. Boehm method indicates that the adsorbent has high basic properties. Accordingly, the type of activated carbon employed in this work is H-type according to Mattson and Mark classification of activated carbons [17]. When contacted with distilled water, H-carbon gives a basic solution and a protonated surface, while L-carbon has an acidic solution and a deprotonated surface. Accordingly, H-type activated carbon is an effective extractor for reactive dyes due to the high electrostatic attraction between negatively charged molecules of reactive dyes (due to the presence of sulphonate groups, see figure 1) and positively charged H-activated carbon [4]. The characterization results indicated 93

6 that the adsorbent has a large specific surface area (820 m 2 g -1 ) which is essential for effective extraction of dyes from solution. anotube activated carbon was not characterized and it was used for comparison purposes with activated carbon. Characteristics of the analytical method Reactive dyes were analyzed using simple spectrophotometry. A straight line passing though the origin was obtained for the calibration graphs plotted at the maximum wavelength for each dye. Table 1 summarized the characteristics of the employed analytical method used for dyes quantification. As indicated in table 1, both dyes were analyzed using direct spectrophotometric techniques due to their large molar absorptivities. In fact, high molar absorptivities are desirable for quantitative analysis because they lead to high analytical sensitivity. Beer s law is obeyed in the concentration ranges of and mg L -1 for blue and red dye; respectively. The optimum concentration ranges for accurate determination, as investigated from the Ringbom plot are mg L -1 for blue dye and mg L -1 for red dye. The analytical method is more sensitive to red dye as can be inferred from the lower detection limit (0.10 mg L -1 ) compare to blue dye (0.17 mg L -1 ) and higher molar absorptivity of red dye. A much lower detection limit ( mg L -1 ) for florescent-reactive dyes was reported using fluorescence spectrophotometers [19]. The typical concentration of reactive dyes in the environmental samples is usually close to 40 ng L -1 and may be less in some cases [20]. Based on that, the adopted analytical method is ineffective for direct quantification of reactive dyes at that trace level. As well be shown later, activated carbon and nanotube activated carbon were effectively applied to preconcentrate reactive dyes from diluted solutions prior their spectrophotometric analysis. Table 1: Characteristics of the analytical method Parameter Blue Dye Red Dye ph (solution of 100 mg L -1 solution) λ max Beer`s law range (mg L -1 ) Ringbom range Molar absorptivity (M -1 cm -1 ) (at nm) (at nm) Detection limit (3σblank) (mg L -1 ) Limit of quantification (10σblank) (mg L -1 ) Linear calibration analysis 2 Slope (a) Intercept (b) r Effective concentration range can be obtained using the Ringbom`s plot (Transmittance % versus log concentration) [18] 2. For the linear equation: A = ac + b where A is the absorbance and C is the concentration of dye (in mg L -1 ). 94

7 Extraction efficiency of activated carbon for reactive dyes Effect of agitation time and carbon mass on dyes extraction Effect of agitation time on dyes extraction at 200 mg L -1 is shown in table 2. Furthermore, effect carbon mass on dyes extraction is also given in table 2. For both dyes, 40 min of agitation is sufficient to reach equilibrium. The distribution values were slightly changed after that time. The extraction of reactive dyes at agitation time of 40 min as a function of carbon mass indicate that 200 mg of the extractant was suitable for maximum removal of dyes from solution. The values of Kd did not unchanged by introducing carbon masses more than 200 mg. Accordingly, the optimum mass of extractant is 200 mg while the optimum agitation time is 40 min at the studied experimental conditions. Table 2: Effect of agitation time and carbon mass on the extraction of dyes Effect of agitation time 1 Effect of carbon mass 2 Time (min) Kd Blue Dye (±0.1) Kd Red Dye (±0.1) Carbon mass (mg) Kd for Blue Dye (±0.1) Kd Red Dye (±0.1) Conditions: dye concentration mg L -1, ph 6.0, mass of adsorbent 200 mg, volume of solution cm 3, temperature 25 0 C, and concentration of acl 0.1 M. 2. Conditions: dye concentration mg L -1, ph = 6.0, volume of solution cm 3, temperature 25 0 C, concentration of acl 0.1 M, and agitation time 40 min. Effect of dyes concentration The extent of extraction of activated carbon for reactive dyes was studied over a wide concentration range (1 400 mg L -1 ). The values of Kd at different initial concentrations for dyes are given in table 3. For comparison purposes, the extraction efficiencies of nanotube activated carbon are also included in table 3. Generally, activated carbon has high extraction efficiency for reactive dyes from solution as shown in table 3. For example, at 100 mg L -1 dye concentration the values of Kd for dyes are 50.6 and 24.3 dm 3 g -1 for blue and red dye; respectively. Both dyes have a high affinity for the solid surface over the studied concentration range where the values of Kd were always higher than unity. The extraction efficiency of activated carbon was diminished at higher concentrations as inferred from the decrease in the values of Kd. The values of Kd at the maximum dye concentration were 6.2 and 4.4 dm 3 g -1 for blue and red dye; receptively. It is worth to mention that the values of Kd at initial dye concentrations (1.0 and 50.0 mg L -1 ) were not estimated because the equilibrium dye concentrations were lower than the detection limit of the adopted analytical method. Accordingly, the values of Kd are suppose to be very high at lower initial dye concentration because the remaining dye concentration (Ce) will be very small. This 95

8 indicates that the adsorbent will function better for extraction of dyes from diluted solutions. anotube activated carbon was very effective for dyes extraction from solution. For example, at initial dye concentration of 400 mg L -1, the values of Kd were and 66.2 dm 3 g -1 for blue and red dye; respectively. The extraction efficiency of this material is expected to be much higher at lower dye concentration. Having said that, the high price of nanotube activated carbon would retard its application as a cheap-extractant for reactive dyes. Table 3: Effect of initial dye concentration on distribution coefficient of dyes a Initial dye concentration (mg L -1 ) Blue Dye K d Red Dye b a. Experimental conditions: dye concentration range: mg L -1, carbon mass: 200 mg, ph = 6.0, volume of solution cm 3, concentration of acl 0.1 M, and agitation time 40 min. b. For nanotube activated carbon. Effect of solution ph and ionic strength on extraction efficiency of activated carbon The extraction efficiency of activated carbon for reactive dyes was investigated at different conditions of ph and ionic strength. The results were depicted in figure 2 and 3. For blue dye, at 200 mg L -1 the Kd value was decreased from 38.0 to 33.2 dm 3 g -1 when the ph was increased from 1 to 3 and then the distribution value remained unchanged up to ph 8 (Figure 2). A similar behavior for red dye was also noted (Figure 2). Similar results were reported for reactive dyes extraction in the literature [2, 21]. Two possible mechanisms of interaction between reactive dyes and activated carbon [22] : (a) electrostatic interaction between the protonated surface of carbon and negatively charged dye molecules and (b) hydrophobic interactions between the basal planes of the carbon and the hydrophobic part of dye molecules. At basic solution (ph = 12), the distribution value for blue dye was decreased to 23.6 while for red dye it reduced to 6.2 dm 3 g -1. The large reduction in carbon extraction at basic medium can be attributed to the electrostatic repulsion between negatively charged activated carbon (due to adsorption of OH ions on the surface) and the deprotonated dye molecules [8]. As shown in figure 3, the extraction capacity of activated carbon has been considerably increased when the salt is introduced to the dye solution. At 0.1 M acl solution, Kd has been increased from 23.2 to 33.8 dm 3 g -1 for blue dye while for red dye it increased from 8.0 to 12.2 dm 3 g -1. The distribution values are almost constant over the salt concentration range M for both dyes. The high increase 96

9 in dyes removal after addition of acl can be attributed to the increase in the dimerization of dye molecules in solution. Fortunately, the dimerization constant of Levafix Brilliant Blue E-4BA was estimated in pure water and in solutions of different ionic strengths [23]. The dimerization equilibrium for two blue dye molecules can be presented as follows: 2B(aq) B B(aq) [ B B] K dim er 2 [ B] =... (4) Where [B], [B B], and K dimer represent the monomer dye concentration, dimmer concentration and dimerization equilibrium constant. The reported K dimer values of reactive blue in pure water and in a solution of 0.1 M ionic strength are 485 and 6211 at 25 0 C respectively. A number of intermolecular forces have been suggested to explain the aggregation between dye molecules in solutions and these forces include van der Waals forces, ion-dipole forces, and dipole-dipole forces which occur between dye molecules in the solution. These forces found to be more favorable when salt is added to the dye solution [23]. The high extraction efficiency of activated carbon for reactive blue in the presence of acl can be attributed to the high aggregation of dye molecules. The salt ions force dye molecules to aggregate and migrate toward carbon surface. The above discussion can be extended for red dye due to the structural similarities between both dyes. It is important to mention here that the absorption characteristics and λ max of both dyes do not changed by changing solution ph and ionic strength. Distribution Coeffecien Kd (dm 3 g -1 ) Blue Dye Red Dye Initial ph Figure 2: Effect of solution ph on K d carbon mass 200 mg, dye concentration mg L -1, volume of solution cm 3, concentration of acl 0.1 M, and shaking time 40 min. 97

10 Distribution Coefficients Kd (dm3 g-1) Blue Dye Red Dye Concentration of acl (mol dm-3) Figure 3: Effect of solution ionic strength on Kd. mass of carbon 200 mg, dye concentration mg L -1, volume of solution cm 3, ph 6.0, and shaking time 40 min. Desorption of reactive dyes For effective application of activated carbon in concentrating dyes from diluted solutions, the adsorbed dye should be completely desorbed using a suitable desorption agent. Furthermore, the volume of elution reagent should be small as possible to concentrate dyes and improve the detection limit of the instrument. Among the tested desorption agents, ethanol showed a high capacity for dyes elution as shown in table 4. Tanthapanichakoon and co-workers have been effectively used ethanol for stripping reactive dyes adsorbed on activated carbon [24]. The lower desorption ratios of red dye compare to blue dye reflects the strong interaction between red dye and activated carbon. Results of the effect of ethanol content on dyes elution are shown in table 4. It was observed that the desorption ratios gradually increased with eluent volume. Further increasing the eluent volume, the desorption ratio slightly increased. Thus, 8.0 cm 3 was chosen for optimum dyes elution. As shown in table 4, 15 min is sufficient agitation time for elution of dyes. Table 4: Desorption characteristics of dyes Dye Desorption ratios 1 Desorption agent 2 Agitation time (min) 3 Volume of ethanol (cm 3 ) 4 H 2 O 0.1M HCl Ethanol Blue Red Calculated from Eq Volume of desorption agent is 8.0 cm 3 and agitation time 15 min. 3. Desorption agent is ethanol. 4. Agitation time 15 min. 98

11 Preconcentration of dyes and analysis procedures As shown earlier, both activated carbon and nanotube activated carbon were very efficient in extraction of reactive dyes from diluted solutions, therefore, both extractants were employed to concentrate reactive dyes from solutions containing ng L -1 of dyes. At this low level of concentration, the determination of dyes by direct spectroscopic measurements is not possible. As shown in table 1, the detection limit of dyes were in the range mg L -1, accordingly, the quantitative determination of dyes is not possible in this case. Table 5 showed the result of using SPE to improve the detection limit of the employed analytical method. SPE enabled an efficient preconcentration of the dyes present at trace levels. A very low concentration of dyes (30 40 ng L -1 ) present in cm 3 was detected after extraction and elution in 8.0 cm 3 of ethanol. The recovery of blue dye (96.0%) was higher than red dye (93.30 %) which indicates that this analytical method is more sensitive for that dye. As can be noted from table (5), the pre-concentration factor (concentration after extraction/concentration before extraction) was 12.0 (for blue dye) and 11.7 (for red dye) using activated carbon as extractant. In this manner, very low detection limits of the method was achieved with the aid of SPE. Before preconcentration, the detection limit of dyes were 0.17 and 0.10 mg L -1 for blue and red dye (Table 1), while after applying SPE, dyes could be detected up to 30 ng L -1 with a high precision. The interesting part of this study is the comparable extraction efficiency of nanotube activated carbon and activated carbon for extraction of reactive dyes present at ng L -1 levels. Both extractants have comparable preconcentration factors for dyes which fall in the range: Moreover, the reported recoveries of dyes were higher when using nanotube activated carbon. The only disadvantage of nanotube activated carbon is its high cost, which may limit its application in solid-phase extraction techniques. Table 5: SPE of dyes from diluted solutions Activated carbon Multi-walled activated carbon Dye Original Conc. Original Conc. Conc. after (ppb) 2 SPE (mg L -1 ) 3 Conc. RSD Rec. (mg L -1 ) 4 (%) (%) 5 after SPE Conc. RSD Rec. (mg L -1 ) 3 (mg L -1 ) 4 (%) (%) 5 Blue ± ± Red ± ± Conditions: mass of adsorbent 200 mg, volume of solution 100 cm 3, ph = 6.0, concentration of acl 0.1 M, shaking time 40 min, temperature 25 0 C, volume of desorption agent 8.0 cm3, and desorption time 15 min. 2. Solutions were prepared from stock dyes solutions. 3. Obtained from calibration graphs of dyes. 4. Mean±standard deviation (5 determinations). 5. Recovery (%) = (amount of dye eluted / amount of dye in the starting solution) 100 Analytical precision and detection limits of the developed method The relative standard deviation (R.S.D) of the method was lower than 1% (n = 5) as shown in table 5, which confirms that the method had a good precision for dyes analysis in water even at trace levels. According to the definition of IUPAC (25), the detection limit of the proposed method for each dye was calculated based on three 99

12 times of the standard deviation of 10 runs of the blank solution. The obtained limits of detection of the proposed method are 20 and 30 ng L -1 for red and blue dye; respectively. In a similar study, Poiger and co-workers have successfully used C 18 reversed phase cartridge as a solid-phase extractant for reactive dyes from diluted solutions and reported a detection limit range of ng L -1 [20]. Pérez-Urquiza and co-workers have reported a lower detection limit for reactive dyes using SPE techniques, they reported a detection limit range of 7 28 ng L -1 [26]. Conclusion A simple analytical procedure for detection of ng levels of reactive dyes was outlined in this study. The dyes were preconcentrated from cm 3 of water samples containing trace amounts of dyes with activated carbon and nanotube activated carbon. After elution with ethanol, their presence in eluates was easily detected spectrophotometrically. Concentrations of ng L -1 of reactive dyes could be reproducibly detected; therefore the SPE step provides a means to improve the detection limit of the analytical method. The proposed method had a good precision (R.S.D. < 1.0 %, n = 5) for analysis of trace reactive dyes in water. The detection limits of the proposed method were 20 and 30 ng L -1 for red and blue dye; respectively. Acknowledgements The financial support from the Hashemite university/deanship of academic research is gratefully acknowledged. The authors are very thankful to Dr. Amajd for his generous donation for nanotube activated carbon sample. Dr. Yahya would like to thank Mr. Mazen Musa for his constant technical assistant. References [1] Robinson, T.; McMullan, G.; Marchant, R.; igam, P., Technol., 2001, 77, [2] etpradit, S.; Thiravetyan, P.; Towprayoon, S., J. Collo. Interf. Sci., 2004, 270, [3] Mottaleb, M.; Littlejohn, D., Anal. Sci., 2001, 17, [4] Al-Degs, Y.; Khraisheh, M.; Allen, S.; Ahmad, M., Wat. Res., 2000, 34, [5] O eill, C.; Hawkes, F.; Hawkes, D.; Lourenço,.; Pinheiro, H.; Delée, W., J. Chem. Technol. Biotechnol., 1999, 74, [6] Šafařík, I.; Šafaříková, M., Wat. Res., 2002, 36, [7] Korn, M.; Andrade, J.; de Jesus, D.; Lemos, V.; Bandeira, M.; dos Santos, W.; Bezerra, M.; Amorim, F.; Souza, A.; Ferreira, S., Talanta, 2006, 69, [8] Birlik, E.; Ersöz, A.; Denizli, A.; Say, R., Anal. Chim. Acta, 2006, 565, [9] Suvardhan, K.; Kumar, K.; Rekha, D.; Jayaraj, B.; aidu, G.; Chiranjeevi, P., Talanta, 2006, 68, [10] D Archivio, A.; Fanelli, M.; Mazzeo; P., Ruggieri, F., Talanta, 2007, 71, [11] Daorattanachai, P.; Unob, F.; Imyim, A., Talanta, 2005, 67, [12] Cai, Y.; Cai, Y.; Mou, S.; Yi-qiang Lu, Y., J. Chromatog. A, 2005, 1081, [13] Ersöz, A.; Say, R.; Denizli, A., Anal. Chim. Acta, 2004, 502, [14] Janoš, P.; Buchtová H.; Milena Rýznarová, M., Wat. Res., 2003, 37, [15] Boehm, H.P., Carbon, 1994, 32, [16] Gregg, S.J.; Sing K.S.W., Adsorption, Surface Area and Porosity. 2nd Edition, Academic Press, [17] Mattson, J.S., Mark, H.B., Activated Carbon: Surface Chemistry and Adsorption from Solution. 1 st edition, Marcel Dekker, ew York, [18] Hassan, W. S.; El-Henawee, M.M.; Gouda, A. A., Spectro. Acta A: Mol. Biomol. Spec., 2008, 69, [19] Hofstraat, J.; Steendijk, M.; Vriezekolk, G.; Schreurs, W.; Broer, G.; Wijnstok,., Wat. Res., 1991, 25, [20] Poiger, T.; Richardson, S.; Baughman, G., J. Chromato. A, 2000, 886,

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