Application of Green Sample Preparation Technique for Preconcentration and Spectrometric Determination of Hazardous Brilliant Green in Fish farming by Using Ionic
liquid
Malihe Dehghani Mohammad Abadi
Young Researchers and Elite Club, Quchan Branch, Islamic Azad University, Quchan, Iran
E-mail: [email protected]
Abstract
In situ solvent formation microextraction (ISFME) as a green, simple and sensitive method has been proposed for preconcentration of trace quantities of hazardous brilliant green in aqueous samples containing very high salt concentrations by UV-Vis spectrophotometry. In this technique, the extraction phase is simultaneously formed in situ. A water-miscible ionic liquid (IL) ([Hmim][BF4]), is first added to the sample, followed by addition of sodium hexafluorophosphate (NaPF6, as an ion-pairing agent) to obtain the hydrophobic IL ([Hmim][PF6]). As a result, a cloudy solution is formed due to the formation of hydrophobic IL ([Hmim][PF6]). All the critical parameters affecting the analytical performance of the method were investigated. Under the optimized conditions, the enhancement factor was 70. The detection limit and precision (RSD) were 0.1 µg L−1 and 3.3% (n=6) respectively. The applicability of the proposed method was evaluated by determination of trace amounts of brilliant green in various water samples for fish farming.
Keywords: In situ solvent formation microextraction, Brilliant green, Ionic liquid, UV-Vis spectrophotometry, Fish farming.
1. Introduction
Brilliant green (BG) is an odorless cationic dye in triphenylmethane family having shiny, golden crystals soluble in water or alcohol. The complex aromatic structure of the brilliant green dye (Fig. 1) makes it stable and difficult to biodegrade. It has anti-microbial, anti-parasitic and anti-fungal properties and it has been used in many industries such as fish farming for many years [1]. Brilliant green is also, inexpensive and readily available, being used as cationic dye for various purposes, e.g. biological stain, dermatological agent, veterinary medicine, and as additive to poultry feed to inhibit propagation of mold, intestinal parasites and fungus. It is extensively being used in textile dying and paper printing [2,3]. Brilliant green is readily absorbed on fish tissues from water exposure and is reduced metabolically by fish to the persistent leuco moiety, leucocrystal violet [4]. In spite of many uses, this dye is toxic and carcinogenic in nature and environmental contamination by BG is emerging as a serious global problem. Colored solution containing dye from industrial effluents may cause skin cancer this due to photosensitization and photodynamic damage [5]. BG exposure and inhalation leads to generation of hazards such as gastrointestinal tract, nausea, vomiting and diarrhea, while its ingestion and inhalation causes damage to target-organ [6,7]. BG may form hazardous product due to heating decomposition such as carbon dioxide, sulfur nitrogen oxides [8-10]. In consideration to toxicity of brilliant green and low level of this dye in real samples, the development of rapid, safe, sensitive and selective analytical methods for trace determination of BG in various matrix especially saline water is mandatory because BG is widely used as mentioned in saline water for fish farming. One of the important source of BG input to human body is fish. BG is applied to fish water as anti- microbial agent and for treating fungal and gram-positive bacteria infections in fish but as mentioned, this cationic dye makes adverse effects to health human. There is a vital need for reaserch in the field of green, clean and sensitive analytical techniques for separation, precocentration and determination of BG in various matrixes specially in water for fish farming.
Baghdadi and shemirani proposed an extraction procedure termed in situ solvent formation microextraction (ISFME) in 2009 [11]. In ISFME method, there is no interface between water and extractant phase, and as a result, mass transfer from aqueous phase into separating phase has no significant effect on the extraction phase. In this method ionic liquid (IL) is used as extraction solvent. IL has attracted increasing interest in analytical chemistry as extraction solvent in replacement for hazardous solvents for its unique chemical and physical properties such as negligible vapor pressure, tunable viscosity, good thermal stability and miscibility with water [12-15]. ILs are solvents having good solubility for inorganic and organic compounds
and are being used as extraction solvents for separation and preconcentration of various organic and inorganic compounds [16-20]. The important advantage of ISFME is its application in saline matrix (40%w/v). During the formation of fine droplets of the extractant phase in this method, the formed IL molecules collect the BG species, and the extraction process is complete after formation of the droplets. It seems that cationic dye is adhered to anionic part of IL, and collected as extraction phase in the tube bottom.
In comparison with other methods such as dispersive liquid liquid microextrction (DLLME) no pure disperser is used which can reduce the extraction recovery. Also, for forming a cloudy solution no syringe is required and separation of two phases after extraction is simple because of high viscosity of IL. In comparison with cold-induced aggregation microextraction (CLAME) and ultrasound-assisted emulsification microextraction (USAEME) it is faster and simpler and is applicable for salin solution [21-24]. In the present study, experiments were carried out to determine BG by ISFME method. At first, a hydrophilic ionic liquid ([Hmim][ BF4 ]) is added to the sample solution and then, a sparingly soluble ionic liquid (extractant phase, HmimPF6) is formed in situ by addition of a suitable salt as an ion-pairing agent (NaPF6). The extraction process is completed after the formation and centrifugation of fine droplets of the extractant phase and the absorbance of BG is measured at 628 nm by UV-Vis spectrophotometry. Spectrophotometric methods have been in general use for about 40 years and over this period are the most commonly used techniques and continue to enjoy their wide popularity [21]. In many applications, other techniques could be employed but none rival UV–Vis spectrophotometry for its availability, simplicity, versatility, speed, accuracy, precision, and cost-effectiveness. This technique is routinely used in analytical chemistry for quantitative determination of different analytes such as transition metal ions, highly conjugated organic compounds, and biological macromolecules. Major advantages of the presented work are high speed, easy to handle, safe, high enrichment factor and sensitivity and most important advantageous for sample solutions containing very high concentrations of salt.
Fig. 1. Structure of BG
2. Experimental
2.1. Instruments. A UV-Vis spectrophotometer (Agilent 8453) with a 250 mL quartz microcell was used for measuring the absorbance of the complex at 628 nm. A Metrohm pH meter model 632 (Herisau,
Switzerland) with a combined glass electrode was applied for pH measurements. A centrifuge (Hettich,
into centrifuge tube. After shaking, 1 ml of NaPF6 (127 mg) was rapidly injected by along needle syringe causing a cloudy state to appear in the whole solution and as a result, the droplets of [Hmim][PF6] was immediately produced in the solution. The BG molecules were extracted into the formed IL and the mixture was centrifuged at 4000 rpm for 5 min and fine droplets of IL were settled down at the bottom of the centrifuge tube.The upper aqueous phase was then manually discard with a syringe and the remaining IL- phase was diluted with 100 µL of absolute ethanol due to the high viscosity of extraction phase. Absorbance of the BG was measured at 628 nm using a 250 µL UV microcell.
3. RESULTS AND DISCUSSION 3.1. Effect of pH
The effect of pH on the analytical response was the first parameter evaluated for separation and determination of BG. A series of experiments were investigated in the range of 2-8 with hydrochloric acid and sodium hydroxide. The obtained results show that, the absorbance of BG is increased up to pH 6 and then started to decrease. Hereby, pH 6 was selected for further experiments (Fig. 2).
Fig. 2. Effect of pH on the absorbance of BG, Conditions: sample volume: 10 ml, [Hmim][BF4]:60 mg, NaPF6: 100mg, BG concentration: 10µgl−1, centrifuge time: 5min
3.2. Effect of amounts of [Hmim][BF4] and NaPF6
Effect of [Hmim][BF4] amount was studied in the range of 12 to 96 mg in the presence of 100 mg of NaPF6. The results show that the absorbance increases with the increase of [Hmim][BF4] up to 60 mgand then started to diminish slowly (Fig. 3) due to the increase of the extracted phase volume. 70 mg of [Hmim][BF4] was chosen as the optimal amounts for further experiments.
Fig. 3. Effect of [Hmim][BF4] amount on the absorbance of BG,Conditions: sample volume: 10 ml, acetate/acetic acid buffer (pH= 6, 0.5mol L-1), NaPF6: 100mg, BG concentration: 10µgl−1, centrifuge time: 5min
NaPF6 amounts was examined in the range of 10 to 204 mg in the presence of 70 mg [Hmim][BF4]. As the results show, the absorbance increased rapidly up to 108 mg, and was then nearly leveled off afterwards. By adding NaPF6 is excess, according to common ion effect, the solubility of [Hmim][PF6] decreased and as the result, the extraction recovery increased. To obtain better precision and higher enrichment factor, 127 mg of NaPF6 was chosen as the optimal amounts for further experiments.
3.3. Effect of centrifuge time
The effect of centrifugation time upon the analytical signal was studied in the range of 3–12 min. A centrifugation time of 5 min at 4000 rpm was selected for complete separation.
3.4. Effect of salt concentration
For investigating this parameter, various experiments were performed by adding different amounts of NaNO3
(0–50% w/v) into a standard solution (10 μg L–1 of BG) while other experimental conditions were kept constant. The results show (Fig. 4) that the absorbance is constant up to 35%w/v of NaNO3 which may be due to the excess of NaPF6 acting as common ion effect.
3.5. Interference studies
The effect of other ions on the determination of BG was investigated under the optimized condition. This study was performed by analyzing 10 mL of 10 μg L−1 of BG solution containing different concentrations of concomitant ions, by the proposed procedure. An ion is considered to interfere if it causes more than ±5%
relative error in the determination of BG.No adverse effects were observed at 1,0000 µg L−1 for Na+, Cu2+, Mg2+, Co2+, Cr3+, Cd2+, Pb2+,CN-, Cl-,CH3COO- and 5000 µg L−1 for Mn2+, SO42-, Br-.
3.6. Figures of merit
Under the optimized conditions, the calibration graph was linear in the concentration range of 0.5– 30 µgL−1 of BG. The detection limit, based on 3Sb was 0.1 µg L−1. The relative standard deviation (RSD) for six replicate analyses of 10 µg L−1 BG was 3.3%. The enhancement factor, calculated as the ratio of the slopes of the calibration graphs after and before the preconcentration step was 70.
3.7. Determination of BG in tap and fish water samples
In order to establish the validity and applicability of the proposed method, experiments were conducted for determination of BG in fish farming and tap water. The results from the analysis of real samples are given in Table 1. The accuracy of the method was verified by the analysis of spiked samples with different concentrations of BG. The results obtained (Table. 1) indicate that the relative recoveries are in the range of 92–106%. According to the results, no serious matrix effects were observed in the fish farming and tap water samples.
Table 1
Analysis of BG in fish farming water samples using proposed methods
Samples Added
(µg L-1)
Found (µg L-1)a
Recovery ( %)
Tap waterb 0.0 0.0 _
5.0 10.0
6.5±0.4 11.4±0.4
97.0 97.0 Fish Farming
Waterc
0.0 1.5±.0.3 _
5.0 10.0
6.4±0.3 12.0±0.4
99.0 104.0 Fish Farming
Waterd
0.0 3.0 6.0
0.60±0.02 3.5±0.2 6.4±0.3
_ 98.0 97. 0 Fish Farming
Watere
0.0 3.0 6.0
1.7±0. 2 4.7±0.3 7.5±0.3
_ 103.0
97.0
aMean± standard deviation (n=3)
bFerdowsi university of Mashhsd, Iran
cMashhadkalat
dHashtgerd, Iran
eFiroozkuh, Iran
4. Conclusion
In situ solvent formation microextraction method was developed for preconcentration of trace quantities of hazardous brilliant green in saline samples. This method is rapid, easy to handle, safe, high enrichment factor and sensitivity and robust against a rather high content of salt as most important advantageous for saline solutions. Also nontoxic ionic liquid was used as extraction solvent, so the application the toxic organic
solvents could be eliminated. By applying ISFME method, sensitivity is enhanced and valuable in comparison with the other methods which are applied for determination of BG.
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