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Quantification of Se(IV) and Co(II) in Macrobrachium lamarrei, fresh water prawns and their feeding materials
⁎Corresponding author. Tel.: +91 9441252489, 877 2283990. suvardhank@gmail.com (S. Kanchi)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Simple, sensitive and rapid methodology was developed for the separation and identification of selenium(IV) and cobalt(II) in Macrobrachium lamarrei, fresh water prawn samples and their feeding materials after pre-capillary complexation with ammonium piperidine-1-carbodithioate (APC) by using capillary electrophoresis. Microwave assisted procedure was adapted to analyze selenium(IV) and cobalt(II) in prawn samples which was eco-friendly to environment. Various parameters such as effect of pH, effect of complexing agent concentration, buffer nature, applied voltage and interferences by other metal ions were also investigated to enhance the sensitivity and detection limits of the present method. The obtained results were in good agreement and correlated with AAS method in terms of Student's “t”-test and Variance ratio “f”-test. The method was applied for the analysis of selenium(IV) and cobalt(II) in various M. lamarrei, fresh water prawn samples and their feeding materials.
Keywords
Capillary electrophoresis(CE)
Selenium(IV)
Cobalt(II)
Microwave assisted digestion
Ammonium piperidine-1-carbodithioate (APC)
M. lamarrei (fresh water prawn) and feeding materials
1 Introduction
Selenium is an essential trace element for human health and has received considerable attention for its possible role as an effective and naturally occurring anti-carcinogenic agent (Chen et al., 2002). Several investigations revealed that selenium is necessary for the effective process of many aspects of immune system in both animals and humans (Arthur et al., 2003). Epidemiological studies showed that selenium intake correlates inversely with death from various types of cancers (Clark et al., 1996). However, the concentration and the species of selenium and cobalt in different foods may be variable and their bio-availability is fairly unusual. Typical signs of selenium toxicity in humans and animals are hair and nail loss, brittle nails or hooves, and gastrointestinal disturbances. Exposure to cobalt can have a toxic effect on the heart and may result in “Cardiomyopathy” (characterized by an increase in the size of the heart). The degree of toxicity may be influenced by the duration and level of exposure to the cobalt from various environments.
The recommended dietary levels of selenium & cobalt are in a very narrow range and consumption of food containing less than 0.1 mg kg–1 of this element[selenium(IV)] will result in its deficiency, whereas dietary levels above 1 mg kg–1 will lead to toxic manifestations (Chen et al., 2002) of selenium. According to RDI 10 mg to 20 mg dosage of cobalt activates the normal metabolic functions in the body. It is also observed that various health problems can arise from excess or deficiency of selenium, and the danger lies in the relatively narrow margin between its essential and toxic actions.
Various analytical methods such as Inductively coupled plasma atomic emission spectrometry (ICP-AES) (Emteborg et al., 1998; Harwood and Su, 1997; Yang et al., 1996) Spectrofluorometry (Ipolyi et al., 2001; Vilanó and Rubio, 2000; Mazej et al., 2006; Dietz et al., 2004), Atomic absorption spectrometry (AAS) (Saygi et al., 2007; Tuzen et al., 2007; Bidari et al., 2007), High performance liquid chromatography(HPLC) (Hawkes and Kutnink, 1996), Inductively coupled plasma mass spectrometry (ICP-MS) (Montes-Bayon et al., 2006), Inductively coupled plasma optical emission spectrometry (ICP-OES) (Akter et al., 2005; Jitmanee et al., 2005; Karthikeyan and Hirata, 2003; Suarez and Gine, 2005), UV–Visible Spectrophotometry (Ahmed and Uddin, 2007; Afridi et al., 2009; Safavi et al., 2004; Sabermahani and Taher, 2008; Tajodini and Moghimi, 2010), Voltammetric techniques (Crouch et al., 2005; Singh et al., 2009), Graphite furnace atomic absorption spectroscopy (GFAAS) (Cai et al., 2002) were reported in the literature for the separation and determination of selenium(IV) and cobalt(II) in different matrices of environmental importance.
Sample preparation techniques required prior to the instrumental analysis of metal ions in order to remove the interferences and preconcentrate the analytes present in matrices. Liquid–liquid extraction requires more solvent for extraction procedure (Psillakis and Kalogerakis, 2003), solid phase micro extraction is a solvent free technique and it is expensive (Stack et al., 2000). The problem which is faced in the LLE and SPE is excluded by using single drop micro-extraction (SDME). It is a simple, inexpensive, rapid, effective and virtually solvent-free sample pretreatment technique. However, SDME is not very robust, and the droplets may be lost from the needle tip of the micro-syringe during the extraction. Determination of selenium(IV) in biological and environmental samples is usually difficult due to its trace or ultra-trace quantities, pre-concentration stages, destruction of organic matrices by acid digestion and oxygen plasma combustion followed by separation from interfering metal ions such as ion exchange separation, solvent extraction or hydride generation. Selective separation of selenium(IV) was particularly important in the determination of small amounts of the element in complex materials. These are all time consuming procedures and losses of selenium(IV) and cobalt(II) are also possible. It was therefore very important to accomplish methods with minimal interference. In order to determine the selenium and cobalt effectively, it is necessary to develop convenient and appropriate fast analytical method for separation and detection of selenium(IV) and cobalt(II) in various biological samples.
This paper deals with the simple, sensitive and rapid method for the separation and determination of selenium(IV) and cobalt(II) coupled with a capillary electrophoresis detector. The developed method was economically advantageous (low reagent consumption), provides reproducible results of statistical importance (elimination of subjective analytical errors and foreign species) and a useful tool for the quantification of samples in a variety of real natural matrices at low detection level for series analysis of selenium(IV) and cobalt(II) in Macrobrachium lamarrei, fresh water prawns and their feeding materials. The method was based on pre-capillary complexation of selenium(IV) and cobalt(II) with ammonium piperidine-1-carbodithioate (APC) and their prior separation and determination with capillary electrophoresis. The obtained results were acceptable and compared with AAS method in terms of Student's “t”-test and Variance ratio “f”-test, which makes the analytical data statistically sound.
2 Experimental
2.1 Instrumentation
A Hewlett–Packard 3D Capillary Electrophoresis System with a diode array UV detector and HP chemstation software was used (Agilent, Palo Alto, CA, USA). Polyimide-coated fused-silica capillaries (57 cm to window, 65 cm total length, 50 μm I.D. × 360 μm O.D.) were obtained from Polymicro Technologies (Phoenix, AZ, USA). A match flame was used to burn a small section of the polyimide coating to form a window for optical detection 8 cm from the end of the capillary. Samples were introduced hydrodynamically by applying a pressure of 50 mbar for 8 s. The separation voltage was set at +20 kV. The temperature of the capillary was kept at 25 °C using the thermoregulation equipment of the instrument.
A Shimadzu 240 UV–Visible spectrophotometer with a 1.0 cm quartz cell was used for absorbance studies of selenium(IV) and cobalt(II) in various prawns and their feeding samples. The studied complexes were detected at 351 nm and 450 nm for selenium(IV) and cobalt(II) species, respectively. All pH measurements were made using pH meter, model Li-120 (Elico Pvt. Limited, India) which include a combined electrode of pH range 0–13.
2.2 Reagents
All the chemicals used were of high purity, without further purification. De-ionized doubly distilled water was used throughout the experiment. Piperidine (SD Fine Chemicals, India), Carbon disulfide (SD Fine Chemicals, India), Sodium selenite (SD Fine Chemicals, India) and Cobalt acetate (SD Fine Chemicals, India), Dihydrogen potassium phosphate (SD Fine Chemicals, India), Dipotassium hydrogen phosphate (SD Fine Chemicals, India) and Ammonium (SD Fine Chemicals, India) were used in the present investigation.
Standard solution of selenium(IV) and cobalt(II)[1 μg mL−1] was prepared by appropriate dilution in de-ionized doubly distilled water and made up to the mark in 1000 mL standard flask. 2.0 mM ammonium piperidine-1-carbodithioate (APC) was prepared by weighing appropriate amount of ammonium piperidine-1-carbodithioate (APC) in 100 mL de-ionized doubly distilled water.
2.2.1 Synthesis of ammonium piperidine dithiocarbamate (APC)
Carbon disulfide (80 g) was slowly added to a solution of piperidine (85 g) in 25 ml of de-ionized doubly distilled water at 5 °C with constant stirring, followed by ammonium hydroxide. The product (Scheme 1) was warmed to room temperature and washed repeatedly 2–3 times with purified acetone. The reaction product was purified by recrystallization in acetone. The purified compound having melting point of 196–199 °C at 740 mm pressure was previously synthesized in our laboratory and reported in the literature (Kanchi et al., 2011a,b, 2012).
Synthetic pathway for the preparation of ammonium piperidine dithiocarbamate (APC).
2.3 Significance of sample collection area
NELLORE District is well known for aquaculture and it is also known as “Aquaculture capital of India” or “Blue City” and is situated in the south eastern portion of the state with a costal length of 163 KM bounded by Bay of Bengal on the east. Nellore District, the southern most coastal district of Andhra Pradesh lies between 13-30′ and 15-6′ of the northern latitude and 70-5′ and 80-15′ of the eastern longitude and extending over an area of 13076 Sq Kms, accounting for 4.75% of the total area of the state. It is bounded on the north by Prakasam district on the east by Bay of Bengal on the south by Chittoor district and Chengalpattu district of Tamil Nadu and on the west by Veligonda hills which separate it from Kadapa district. For the present investigation, samples (M. lamarrei) were collected from different aquaculture ponds situated around Kota Mandal, Nellore District, A.P., INDIA.
2.4 Microwave assisted digestion of prawn samples
The studied M. lamarrei, fresh water prawn samples were freshly collected from aquaculture ponds. Three hundred grams of prawn samples were accurately weighed on the micro-analytical balance and processed with a mixture of 5 mL of nitric acid and 3 mL of hydrogen peroxide in the microwave digestion system. The prawn samples were digested according the flow chart shown Scheme 2.
Schematic representation of flow-chat for the microwave assisted digestion of M. lamarrei, fresh water prawn samples for determination of selenium(IV) and cobalt(II) ions.
2.5 General procedure for capillary electrophoretic separation & determination of Se(IV) and Co(II) ions
The capillary was rinsed with 0.1 M NaOH for 5 min, de-ionized doubly distilled water for 5 min and a buffer electrolyte for 30 min, respectively, at the beginning of each day. Before each separation, the capillary was rinsed with buffer electrolyte for 2 min. Pre-capillary ligand–metal complexation was achieved by mixing the metal ions and appropriate amount of ammonium piperidine-1-carbodithioate directly at room temperature before injection as shown in Scheme 3. The separation voltage was +20 kV and the injection was performed by applying 50 mbar pressure for 8 s and the well separated electropherogram of selenium(IV), cobalt(II) and mixture of selenium(IV) and cobalt(II) were shown in the Fig. 1a, Fig. 1b, Fig. 1c.
Complexation mechanism of metals (selenium and cobalt) with ammonium piperidine dithiocarbamate in resonance form.
Electropherogram of standard solutions of selenium(IV) species complexed with ammonium piperidine-1-carbodithioate in phosphate buffer(pH 8.5).
Electropherogram of cobalt(II) species complexed with ammonium piperidine-1-carbodithioate in phosphate buffer(pH 8.5).
Electropherogram for the mixture of standard solutions of selenium(IV) and cobalt(II) species complexed with ammonium piperidine-1-carbodithioate in phosphate buffer(pH 8.5).
3 Results and discussion
3.1 Effect of pH
pH effect plays a vital role in the complexation of metal ions [selenium(IV) & cobalt(II)] with ammonium piperidine-1-carbodithioate. The pH of electrophoretic buffer was controlled, as it affects the conditional formation constant of the complexes. In the present study sample pH was varied in the range of 6.5–9.0 and identified the separation efficiency of the metal complexes. It clearly shows that peak height increases with the increase in pH from 6.5 to 8.5 which indicate the maximum separation efficiency of selenium(IV) and cobalt(II). Further increase in pH, smaller peak areas and zone spreading were observed. Moreover, on further decreasing the sample pH below 6.5 very broad and even splitting was observed (Fig. 2) Therefore; moderately alkaline sample pH (8.5) was selected for further optimization studies.
Effect of electrolyte pH on the peak area for the separation of determination of selenium(IV) and cobalt(II) in prawn and their feeding materials.
3.2 Applied voltage
Resolution capacity mainly depends on applied voltage of the system. Enhancement in the resolution was observed with slight increase in the applied voltage. Higher efficiency was obtained by applying higher voltages, but the smaller differences in migration time observed tend to level the applied voltage effect. Thus, applied voltage was insufficiently effective for the increase in resolution. In this study positive current of +20 kV, was chosen to reduce the analysis time.
3.3 Acetate buffer nature and its concentration
In the present study various buffers such as acetate, phosphate and borate were used to achieve more complexation, better detectability and resolution capacity. Acetate buffer high resolution capacity and low detection limits with sharp and smooth curved electropherogram were observed. Low mobility of ions [selenium(IV) & cobalt(II)], larger peak boarding(due to less stability of the complex) were observed in case of phosphate and borate buffers. The less efficiency was due to the counter action from borate and phosphate ions (as a stronger complexing agent than the acetate ions). An acetate buffer provides good selectivity with average mobility and lesser analysis time (less than 5 min). Table 1 shows the calculations of electrophoretic mobilities (EPM) of metal complexes at different acetate buffer concentrations together with the corresponding electroosmatic mobility (EOM) values (Timerbaev et al., 1993). As the buffer concentration was increased, the EPM gradually decreased, reaching some constant level at a concentration of 2 mM. The EOM related to buffer concentration displays approximately the same dependence. Thus, varying the buffer concentration within the range 0.5–3 mM influenced the migration time to minor extent only. Improvement in the resolution of selenium(IV) and cobalt(II) was observed at higher acetate concentrations as a result, increase in efficiency with increasing current cannot be obtained, as shown in Fig. 3. Based on these data, an acetate buffer concentration of 2.0 mM was chosen to enhance the selectivity and detectability.
Concentration of buffer (mM)
Electroosmatic flow (μos)(10−4 cm2/V s)
Electrophoretic mobility (μep) (10−4 cm2/V s)
Se(IV)
Co(II)
0.5
4.63
9.00
9.42
1.0
3.59
7.30
7.79
1.5
2.31
5.73
6.50
2.0
2.69
4.52
4.93
2.5
2.00
4.64
4.26
3.0
2.32
3.90
4.16
Effect of acetate buffer concentration on resolution of selenium(IV) and cobalt(II) in prawn and their feeding materials CE.
3.4 Concentration of ammonium piperidine-1-carbodithioate (APC)
Effect of concentration of ammonium piperidine dithiocarbamate on the EPM was investigated. Metal ions with strong chelating capacity were very stable and show identical mobilities over a wide range of APC concentrations. Whereas the EPM values of metal ions with weak chelating capacity were not so stable, gradually reach constant values and their peak heights, peak areas become larger with increase in the concentration of ammonium piperidine dithiocarbamate (Shoji et al., 1994) as shown in Fig. 4. Hence, 1.5 mM of ammonium piperidine dithiocarbamate in the carrier solution was selected for optimum separation of selenium(IV) and cobalt(II) in various M. lamarrei, fresh water prawns and their feeding materials.
Effect of concentration of complexing agent for the separation efficiency of selenium(IV) and cobalt(II) in prawn and their feeding materials.
3.5 Method validation
The developed method was evaluated in terms of reproducibility, accuracy, linearity, repeatability and limits of detection under optimized conditions to enhance the sensitivity and selectivity for the determination of selenium(IV) and cobalt(II) in various M. lamarrei, fresh water prawns and their feeding samples. The CE peak area counts were plotted against the respective analyte concentrations to generate calibration curves. The calibration plots were linear over the range of 0.10–1 μg mL−1 with correlation coefficient (r) between 0.9998 and 0.9993 for selenium(IV) and cobalt(II), respectively. The limits of detection (LODs) for selenium(IV) and cobalt(II) were determined by progressively decreasing the concentrations of analytes until signals were just detected at a signal-to-noise ratio of 3 (S/N = 3). The LODs ranged for selenium(IV) was 3.0 μg mL−1 and for cobalt(II) was 5.0 μg mL−1, respectively.
3.5.1 Reproducibility
To test the reproducibility of the present method, six repetitive analysis cycles of each sample were run. A % R.S.D. of 2.00 & 3.00 for selenium(IV) & cobalt(II), respectively was obtained as shown in Table 2.
Month
Capillary electrophoresis methodb
AAS methodb
Se(IV) in μg mL−1
Co(II) in μg mL−1
t-testc
f-testd
Se(IV) in μg mL−1
Co(II) in μg mL−1
Pond-I
Pond-II
Pond-I
Pond-II
Pond-I
Pond-II
Pond-I
Pond-II
Pond-I
Pond-II
May
Sample-1
0.562
0.557
0.431
0.623
2.83
0.26
0.564
0.558
0.431
0.624
Sample-II
0.589
0.560
0.464
0.591
1.52
0.14
0.589
0.561
0.465
0.593
June
Sample-1
0.791
0.720
0.500
0.503
3.60
1.32
0.790
0.722
0.502
0.505
Sample-II
0.832
0.799
0.595
0.599
1.46
0.10
0.834
0.799
0.596
0.600
July
Sample-I
0.958
0.900
0.642
0.605
1.25
0.07
0.959
0.900
0.643
0.608
Sample-II
0.991
0.937
0.689
0.642
2.69
0.21
0.993
0.939
0.689
0.640
August
Sample-I
1.040
1.093
0.863
0.930
3.42
1.22
1.041
1.092
0.863
0.930
Sample-II
1.528
1.792
0.920
0.992
2.06
0.17
1.527
1.794
0.923
0.922
Product name
Composition
Capillary electrophoresis methoda
AAS methodb
Se(IV) in μg mL−1
Co(II) in μg mL−1
t-Testc
f-Testd
Se(IV) in μg mL−1
Co(II) in μg mL−1
HydroGela
Vitamin-E, Selenium, Cobalt, Vitamin-B12, Betaine
0.53
0.317
1.59
0.14
0.54
0.318
3.5.2 Accuracy
The accuracy of the proposed method was evaluated by comparing the results with those obtained by the AAS method. The results shown in Table 2 reveal the good correlation between the two methods indicative of present method is more sensitive than the AAS method.
3.6 Interferences of common metal ions
The interferences of common metal ions which could interfere with the determination of selenium(IV) and cobalt(II) were studied. For this purpose, solutions of 10 and 5 μg mL−1 of selenium(IV) and cobalt(II) containing the corresponding interfering ions were prepared and operated according to the recommended procedure. It was found that the studied coexisting ions such as Mg2+, Al3+, Fe3+, Ca2+ (120 μg mL−1), Mn2+, Cr3+ (70 μg mL−1), As5+, Sn2+(50 μg mL−1), Na+, K+(150 μg mL−1), Pb2+, Zn2+ (40 μg mL−1), Cu2+(50 μg mL−1) and Bi3+ (40 μg mL−1) do not significantly interfere with the separation and determination of selenium(IV) and cobalt(II) in various M. lamarrei, fresh water prawns and their feeding materials which indicate the validity and selectivity of the proposed method.
3.7 Collection of prawn samples
M. lamarrei, fresh water prawn samples were collected from different ponds around Kota Mandal, Nellore District, A.P.,INDIA in which culture started in the month of April 2009 and the samples were collected during the month of May 2009 to August 2009 in regular intervals of twice a month with total eight samples for the analysis of selenium(IV) and cobalt(II). According to farmers’ statement, the prawns were fed three times a day with the Hydrogel (Manufactured by Doctor's Vet-Pharma Pvt Ltd, Hyderabad-82, A.P.,INDIA) which acts as growth promoter as per to the prescription of prawn & fisheries’ technician.
3.8 Determination of selenium(IV) and cobalt(II) in prawn samples and their feeding materials
To test the validity of the proposed method, 300 g of M. lamarrei, fresh water pawn samples were collected in a cleaned dry tray and were subjected to microwave assisted digestion as mentioned in earlier sections. Hydrogel (Manufactured by Doctor's Vet-Pharma Pvt. Ltd., Hyderabad 82, AP, India) material was directly soluble in doubly distilled water and aforesaid procedure was adopted for the determination of concentration of selenium(IV) & cobalt(II) and obtained electropherogram is shown in Fig. 5. The results are presented in Table 2 indicates that the low concentration of selenium(IV) and cobalt(II) was accumulated in prawns at the initial stages of aqua culture. As the days progressed there was significant increase in the concentration of selenium(IV) and cobalt(II) in prawns as shown in Fig. 6. The observed levels of selenium and cobalt concentrations in prawn samples collected from different ponds were within the tolerance limits. Prawn samples were also collected from ponds without growth promoter usage, and investigated the selenium(IV) & cobalt(II) concentrations. It was surprised that no selenium(IV) & cobalt(II) concentration was found.
Electropherogram for the analysis of selenium(IV) and cobalt(II) in M. lamarrei, fresh water prawns and their feeding materials.
Graphical representation of enhancement of concentration of selenium(IV) and cobalt(II) with months.
4 Conclusions
The separation and determination of selenium(IV) and cobalt(II) in M. lamarrei, fresh water prawn and their feeding materials as pre capillary derivatization using ammonium piperidine-1-cabodithioate as the complexing agent with capillary electrophoresis-UV detector were carried out. The method has added advantages owing to its:
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It was more practical, faster than on-capillary complexation method.
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The synthesis of ammonium piperidine-1-carbodithioate was easy, cost effective and it can soluble in water. Hence, the present CE ligand was eco-friendly.
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The ammonium piperidine-1-carbodithioate was highly selective toward selenium(IV) and cobalt(II) hence present developed method was free from interferences.
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Metal–ligand complexation protocol developed in experimental column by pre-capillary methodology was facile and handy than post-capillary procedure, as it was highly commercial, consumes more time to prepare modified capillary and may be prone to contamination of samples.
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Finally, the present method was reliable, robust and economical for the separation and determination of selenium(IV) and cobalt(II) in various prawns and their feeding materials.
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