Sample Microwave Digestion for the Determination of Manganese, Iron, Zinc, Copper and Nickel in Catfish Consumed in Syria by Flame Atomic Absorption Spectrometry

 

Saad Antakli^1*, Nazira Sarkis², Firas Nahas²

¹Department of Chemistry, Faculty of Science, University of Aleppo, Syria.

 

ABSTRACT:

The present research work describes a microwave-assisted digestion procedure using a new digestion mixture Nitric Acid and Hydrogen Peroxide (4:1) for the determination of Manganese, Iron, Zinc, Copper and Nickel in Catfish samples by flame atomic absorption spectrometry (FAAS). The optimization conditions involve the following factors: Theamount of Catfish (ACF), the microwave power (MP) and the power time (PT). The experimental results of these factors were carried out on local Catfish consumed in Syria. The relative standard deviations of the method were found to be not more than 3.97% for the five studied elements. The proposed method was used for the determination of Manganese, Iron, Zinc, Copper and Nickel in muscle tail and skin of species of common local Catfish consumed in Syria. The concentrations of the analyzed Catfish samples were varied in muscle for Manganese, Iron, Zinc, Copper and Nickel, between 0.82 – 1.55,32.00 – 43.18, 31.50 – 41.00, 1.04 – 1.54 and 0.67 – 0.80 (µg/g) respectively, in tail between 1.13 –1.81, 31.60 – 52.40, 42.40 – 49.80, 1.30 – 1.67 and 0.65 – 0.83 (µg/g) respectively, and in skin between 2.03 – 2.41, 60.79 –64.51, 65.30 – 76.94, 1.29 – 1.69 and 0.75 – 0.99 (µg/g) respectively.

 

 

 

INTRODUCTION:

Fish are one of the most important and the largest groups of vertebrates in the aquatic system. Trace metals can be accumulated via both food chain and water¹. Heavy metals coming through industrial, automobile, and human waste. Heavy metals in inland water bodies can be monitored by measuring the metals levels in water, sediments and resident biota especially fish².

 

Some of the metals found in the fish might be essential as they play important role in biological system of the fish as well as in human body.

 

For years, the American Heart Association has recommended eating an average of two to three fish meals each week to help reduce cholesterol, high blood pressure, and hardening of arteries. Research shows that consuming fish increases high quality protein with fewer calories, and it is rich in omega-3 fatty acids. Fish are also low in sodium and a good source of potassium. Several trace elements are found in fish, including Aluminum, Boron, Cadmium, Cobalt, Chromium, Copper, Iron, Manganese, Nickel, Lead, and Zinc. Several of these elements are beneficial as nutrients for humans³. On the other hand some of them may also be toxic as might cause a serious damage in human health even in trace amount at a certain limit⁴.

 

Most digestion methods have used variations of the conventional dry ashing and wet ashing techniques⁵. However, a relatively recent innovation uses microwave radiation for the digestion⁶. Microwave techniques are widely applied for decomposition of various samples such as sediments, soil, mushroom, dust, vegetables, wheat and botanical⁷.

 

A microwave digestion system was used to prepare the fish samples for analysis.⁸ Different digestion methods were used as sample preparation methods for determination of heavy metals in fish samples. Digestion of fish samples as following: 2 g of the sample was added to the mixture of HNO₃-H₂O₂ (1:1) and digested for 2 hours at 160 ◦C. Another digestion technique called microwave digestive technique for fish digestion samples, the sample was weighted in the Teflon vessel, followed by addition of one or more oxidizer and kept for 8 hours at room temperature⁹. There are different heating systems that can be used for digestion such as, sand-bath, heating plate, pressure digestion bombs and Aluminum blocks. The introduction of microwaves, with both open and closed pressurized systems, has allowed a considerable reduction in the total time of analyses as well as in the risk of sample contamination¹⁰.

A wide range of techniques have been used for determination of trace heavy metalssuch as Inductively coupled plasma-optical emission spectrometry (ICP-OES)¹¹, Inductively coupled plasma–mass spectrometry (ICP-MS)¹², X-ray fluorescence spectrometry¹³, Capillary electrophoresis (CE)¹⁴ and Graphite furnace (AAS–GF)¹⁵–Flame atomic absorption spectrometry (FAAS)¹⁶.

 

Flame atomic absorption spectrometry (FAAS) is one of the techniques most extensively used for determining various elements with a significant precision and accuracy. This analytical technique is remarkable for its selectivity, speed and low operation cost¹⁷.

 

MATERIAL AND METHODS:

Materials and reagents:

All reagents used in this research work were of analytical reagent grade. Double distilled deionized water was used to prepare all solution.HNO₃ and H₂O₂ were of high quality. HNO₃ supplied by (Poch) Poland and H₂O₂ supplied by (Merck) Germany. All the plastic and glassware were cleaned by soaking in dilute HNO₃ and were rinsed with double distilled deionized water prior to use. The standard solutions of analyses used for calibration were produced by diluting a stock solution of 1000 mg L⁻¹ of the given element supplied by (Merck) Germany.

 

The calibration curves for analyzing metals were drawn after setting various parameters of FAAS including wavelength, slit width, lamp current at an optimum level.

 

Sampling:

The Catfish samples were kindly supplied from local supermarkets of Aleppo city, in Syria during 2017.

Instruments and apparatus:

A Phoenix 986 AAWin V2.1 Atomic absorption spectrometer with self-reversal background correction mode (SR lamp-BGC mode) was used in this study. The operating parameters for working elements were set as recommended by the manufacturer. The elements were determined by using air–acetylene flame.

 

The microwave digestions were carried out in an Ethos D (Milestone, Sorisole, Italy) with maximum pressure 1450 psi and maximum temperature 300 ◦C. The experimental digestion program parameterswere fixed in our laboratory, given in Table1.

 

Table 1:The microwave program for digestion of Catfish samples.

Step	Time (min)	Power (W)	Temperature (◦C)
1	2	250	180
2	2	0	180
3	2	250	200
4	4	400	210
5	8	600	220
Ventilation	10	0	0

 

RESULTS AND DISCUSSION:

Determination of the experimental factors for microwave digestion:

Microwave digestion factors were studied as: The amount of Catfish (ACF), the microwave power (MP) and the power time (PT). These factors were studied onmuscle sample of Catfish (weight 750 g and length 41 cm).

 

The effect of Catfish amount(ACF):

Concentrations of metals were studied in function to amount of Catfish (ACF) by using a mixture of Nitric Acid and Hydrogen Peroxide HNO₃–H₂O₂ (4:1) using the digestion program Table. 1. The digestion samples weight were at the range between 0.1 – 1 g. The metals concentrations results were reported to 1g. We found that all the metals concentrations in muscle were constant until 0.7 g, so we chose 0.5gas sample to obtain completed digestion as seen in Table. 2 and Figure. 1.

 

 

Figure 1: The effect of Catfish amount (ACF) on digestion of muscle samples.

Table 2: The effect of Catfish amount (ACF) on digestion of Catfish samples (n=3).

ACF (g)	Mean concentrations of elements  µg/g (dw) *
	Mn		Fe		Zn		Cu		Ni
	(µg/g)	RSD %	(µg/g)	RSD %	(µg/g)	RSD %	(µg/g)	RSD %	(µg/g)	RSD %
0.1	1.31	3.19	32.44	2.70	34.11	3.60	1.42	2.56	ND	ND
0.2	1.33	2.47	32.25	3.12	34.54	1.44	1.41	3.87	ND	ND
0.3	1.34	3.65	32.36	3.80	34.30	2.12	1.40	3.15	ND	ND
0.4	1.36	3.22	32.49	3.70	34.25	3.64	1.43	2.14	ND	ND
0.5	1.35	1.95	32.62	2.50	34.10	1.72	1.49	3.25	0.71	3.45
0.6	1.36	3.18	32.48	3.66	34.75	3.95	1.41	3.82	0.73	2.16
0.7	1.32	1.84	32.95	3.04	34.69	3.06	1.45	3.93	0.75	3.49
0.8	1.21	3.63	29.28	3.70	34.84	3.28	1.24	3.18	0.74	3.65
0.9	0.97	3.16	26.06	2.70	30.77	3.25	1.09	3.29	0.70	3.57
1	0.96	3.27	25.13	1.39	28.79	3.64	0.93	2.58	0.71	2.65

* dw =dry weight

 

The effect of microwave power (MP):

Concentrations of metals were studied in function to microwave power (MP) between 300-700 watt by usingamount of Catfish (0.5 g). Expedience microwave power for good and completed digestion was(600 watt). As seen in Table. 3 and Figure. 2.

 

The effect ofpower time (PT):

Concentrations of metals were studied in function to power time (PT) between 2-12 minutes by usingamount of fish (0.5 g) and microwave power (600 watt) was chosen. Expedience power timefor good and completed digestion was 8 min. as seen in Table. 4 and Figure. 3.

 

 

Figure 2:The effect of microwave power (MP) on digestion of muscle samples.

 

 

Table 3:The effect of microwave power (MP) on digestion of Catfish samples (n=3).

* dw =dry weight

 

 

 

Table 4:Theeffect of power time (PT) on digestion of Catfish samples (n=3).

*dw = dry weight

 

 

Figure 3: The effect of power time (PT) on digestion of muscle samples.

 

Microwave digestion:

After the optimization of the digestion conditions, the selected factors (the optimum conditions) were applied to an oven-dried Catfish samples. 0.5 gram of Catfish sample, 8ml of concentrated HNO₃ and 2ml of concentrated H₂O₂ were put in microwave refills. Then, refills were closed tightly, put in the microwave and digested by using digestion program, given in Table 1. The sample transferred to beaker and evaporated to about 5 ml then, transferred to standard flask 10 ml and complete to the volume with double distilled deionized water. A blank digest was carried out by the same way (for all the constituents without the sample).

 

Application:

Sample:

Theproposed microwave digestion procedure was applied for the determination of Manganese, Iron, Zinc, Copper and Nickel in muscletail and skin of Catfish samples,consumed in Syria, for six different Catfish samples were purchase from Aleppo market in different weight and length as shown in the table(5):

 

Table 5: Properties of six Catfish samples.

 

As the application, five elements of heavy metals as: Manganese, Iron, Zinc, Copper and Nickel were determined in muscle, tail and skin for six different weight and length Catfish samples. The obtained results are presented in Tables 6, 7, 8.

 

Table 6: Content of Manganese, Iron, Zinc, Copper and Nickel in Catfish muscle (n=3).

*dw =dry weight

 

Table 7: Content of Manganese, Iron, Zinc, Copper and Nickel in Catfish tail (n=3).

 * dw =dry weight

Table 8: Content of Manganese, Iron, Zinc, Copper and Nickelin Catfish skin (n=3).

* dw =dry weight

The found concentrations of Manganese, Iron, Zinc, Copper and Nickel in muscle were varied 0.82 – 1.55, 32.00 – 43.18, 31.50 – 41.00, 1.04 – 1.54 and 0.67 – 0.80 (µg/g) respectively, in tail between 1.13 –1.81, 31.60 – 52.40, 42.40 – 49.80, 1.30 – 1.67 and 0.65 – 0.83 (µg/g) respectively, and in the skin between 2.03 – 2.41, 60.79 –64.51, 65.30 –76.94, 1.29 – 1.69 and 0.75 – 0.99 (µg/g) respectively.

 

Recovery:

The recovery test was applied on muscle, tail and skin for one sample of Catfish (weight 1.4 kg and length 55 cm). The results were presented in Tables 9, 10, 11.

 

Table 9: Addition-recovery test for muscle sample of Catfish (n=3).

Metal	Sample    (µg/g)	Standard added (µg/g)	Total (µg/g)	Recovery %	SD	RSD%	Average Recovery %
Mn	1.36	1	2.39	102.21	3.25	3.18	100.00
		1.5	2.90	102.94	2.05	2.00
		2	3.29	94.85	1.37	1.44
Zn	48.60	40	87.20	97.12	2.04	2.10	100.87
		50	99.40	101.65	1.93	1.88
		60	110.47	103.85	1.73	1.68
Fe	38.32	30	66.12	94.26	2.70	2.84	95.12
		40	77.45	97.73	1.06	1.09
		50	85.78	93.37	0.96	0.92
Cu	1.59	1.2	2.87	105.03	3.26	3.10	99.16
		1.6	3.10	94.34	2.35	2.49
		1.8	3.36	98.11	1.79	1.82
Ni	0.85	0.6	1.50	105.88	3.77	3.56	100.39
		0.8	1.59	92.94	3.60	3.89
		1.0	1.87	102.35	3.62	3.54

 

Table 10: Addition-recovery test for tail sample of Catfish (n=3).

Metal	Sample    (µg/g)	Standard added (µg/g)	Total (µg/g)	Recovery %	SD	RSD%	Average Recovery %
Mn	1.23	1.00	2.18	95.93	3.50	3.65	95.39
		1.50	2.59	88.62	1.32	1.49
		2.00	3.25	101.63	2.49	2.45
Fe	42.35	30	69.78	93.93	2.30	2.45	97.54
		40	80.48	95.58	1.71	1.79
		50	93.67	103.12	2.98	2.89
Zn	33.74	20	52.21	95.47	2.00	2.13	100.66
		30	65.25	104.48	3.69	3.49
		40	74.43	102.05	1.74	1.69
Cu	1.47	1.00	2.45	98.64	3.11	3.15	102.04
		1.50	3.04	104.76	4.16	3.97
		2.00	3.51	102.72	3.58	3.49
Ni	0.82	0.60	1.32	87.80	2.96	3.37	93.90
		0.80	1.51	86.59	3.09	3.57
		1.00	1.88	107.32	5.25	3.89

 

Table11: Addition-recovery test for skin sample of Catfish (n=3).

Metal	Sample    (µg/g)	Standard added (µg/g)	Total (µg/g)	Recovery %	SD	RSD%	Average Recovery %
Mn	2.10	1.50	3.58	99.05	3.62	3.65	99.68
		2.00	3.98	94.29	3.88	3.11
		2.50	4.72	105.71	2.59	2.45
Fe	62.17	45	104.12	95.09	3.92	3.12	96.34
		60	119.45	95.62	3.10	3.24
		75	136.12	98.31	3.72	3.78
Zn	74.32	60	131.12	95.69	1.97	2.06	99.96
		75	150.69	101.84	1.99	1.95
		90	166.45	102.36	0.80	0.78
Cu	1.68	1.00	2.59	94.64	2.95	3.12	99.20
		1.50	3.20	101.19	3.02	2.98
		2.00	3.71	101.78	1.26	1.24
Ni	1.09	0.80	1.79	90.83	2.76	3.04	92.05
		1.00	1.97	88.99	3.37	3.79
		1.20	2.25	96.33	4.78	3.96

CONCLUSION:

In this study, the levels of Manganese, Iron, Zinc, Copper and Nickel were determined in samples of Catfish, in three tissues muscle tail and skin. The results showed that the mean concentrations of five studied elements higher in the skin than other tissues (muscle and tail), the purposed method showed non-considerable difference in concentrations of metals for muscle and tail. Closed-refills microwave digestion by the mixture HNO₃−H₂O₂ (4:1) avoided the metals volatilization during the digestion processes.

 

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Accepted on 29.03.2018          © RJPT All right reserved

Research J. Pharm. and Tech 2018; 11(5):2094-2099.