Utility of cefixime as a complexing reagent for the ...

Utility of cefixime as a complexing reagent for the determination of Ni(II) in synthetic mixture and water samples Syed Najmul Hejaz Azmi, Bashir Iqbal, Reem Saif Al Khanbashi, Nadia Humaid Al Hamhami & Nafisur Rahman Environmental Monitoring and Assessment An International Journal Devoted to Progress in the Use of Monitoring Data in Assessing Environmental Risks to Man and the Environment ISSN 0167-6369 Volume 185 Number 6 Environ Monit Assess (2013) 185:4647-4657 DOI 10.1007/s10661-012-2894-4

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Author's personal copy Environ Monit Assess (2013) 185:4647–4657 DOI 10.1007/s10661-012-2894-4

Utility of cefixime as a complexing reagent for the determination of Ni(II) in synthetic mixture and water samples Syed Najmul Hejaz Azmi & Bashir Iqbal & Reem Saif Al Khanbashi & Nadia Humaid Al Hamhami & Nafisur Rahman

Received: 16 August 2012 / Accepted: 12 September 2012 / Published online: 23 September 2012 # Springer Science+Business Media Dordrecht 2012

Abstract A simple, sensitive, and accurate UV spectrophotometric method has been developed for the determination of nickel in synthetic mixture and water samples. The method is based on the complexation reaction of nickel ion with cefixime, thus leading to the formation of Ni–cefixime complex in ethanol-distilled water medium at room temperature. The complex showed the maximum absorption wavelength at 332 nm. Beer’s law is obeyed in the working concentration range of 0.447– 4.019 μgmL−1 with apparent molar absorptivity of 7.314×103 Lmol−1 cm−1 and Sandell’s sensitivity of 0.008 μg/cm2/0.001 absorbance unit. The limits of detection and quantitation for the proposed method are 0.016 and 0.054 μgmL−1, respectively. The factors such as cefixime concentration and solvent affecting the complexation reaction were carefully studied and optimized. The method is validated as per the International Conference on Harmonisation guideline. The method is successfully applied to the determination of Ni(II) in synthetic mixture and wadi water samples collected from Al Rustaq. The same water samples are also analyzed by S. N. H. Azmi (*) : B. Iqbal : R. S. Al Khanbashi : N. H. Al Hamhami Department of Applied Sciences, Chemistry Section, Higher College of Technology, Al-Khuwair-133, P. O. Box 74, Muscat, Sultanate of Oman e-mail: [email protected] N. Rahman Department of Chemistry, Aligarh Muslim University, Aligarh 202002, Uttar Pradesh, India

atomic absorption spectrophotometry. Both methods determined the amount of Ni(II) in water sample and found to be approximately the same. Keywords Spectrophotometry . Nickel ion . Cefixime . Ni(II)–cefixime complex . Validation

Introduction Nickel is used in a wide variety of metallurgical processes such as electroplating and alloy production as well as in nickel–cadmium batteries. Nickel is emitted to the atmosphere from natural sources including windblown dust, volcanoes, vegetation forest fires, and meteoric dust. Food and cigarette smoke are the main sources of nickel exposure in the general public (WHO 2000). Approximately 0.04–0.58 μg nickel is released with mainstream smoke of one cigarette. Smoking 40 cigarettes a day, therefore, may lead to inhalation of 2–23 μg nickel. An uptake of too large quantities of nickel has the following consequences: higher chances of development of lung cancer, nose cancer, larynx cancer, and prostate cancer as well as sickness and dizziness after exposure to nickel gas, lung embolism, respiratory failure, birth defects, asthma and chronic bronchitis, allergic reactions such as skin rashes (mainly from jewelry), and heart disorders. The determination of nickel is becoming increasingly important because of its toxic nature and its presence in industrial waste, potable water samples, and some other effluents. The literature citation revealed that

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there are various analytical techniques for the determination of nickel which include graphite furnace atomic absorption spectrometry (Sun et al. 2006), flame atomic absorption spectrometry (Ahmadi et al. 2008; Khani and Shemirani 2010), inductively coupled plasma-optical emission spectrometry (Garcia-Otero et al. 2009), reversed-phase high performance liquid chromatography (Hu et al. 2002), voltammetry (Gholivand et al. 2008; Buzica et al. 2006), and flow injection analysis (Magni et al. 2005; Albertus et al. 2001). In addition, spectrophotometric methods have also been developed to determine Ni(II) based on the reaction with reagents such as nicotinamidoxime (Garole and Sawant 2005), dimethylglyoxime (Gazda et al. 2004), dithiozone (Ozturk et al. 2000), sodium isoamylxanthate (Malik et al. 2000), salicylaldehyde 5-oxobutanoylhydrazone (Suresh et al. 2004), 2-nitroso-1-naphthol-4-sulfonic acid and tetradecyldimethylbenzylammonium chloride (Taher et al. 1998), 4-methyl 2,3-pentanedione dioxime (Dipak et al. 2005), 1-nitroso-2-naphthol (Shar and Soomro 2006), diethyldithiocarbamate (Kabil et al. 1996), and cyclohexylxanthate (Hashem et al. 2003). Most of the reported spectrophotometric methods are time consuming, employing many reagents to develop the color and extraction of nickel complex into organic solvent. Spectrophotometry is a widely used technique for determining metal ion concentration in leafy vegetables, pharmaceuticals, and natural water and soil samples. Spectrophotometers are now more economical, simple, versatile, adaptable, and affordable than ever (Czegan and Hoover 2012). Therefore, it is decided to exploit this technique to develop an optimized and validated UV spectrophotometric method for the determination of Ni (II) in synthetic mixture and water samples. The present UV spectrophotometric method is based on the complex formation of Ni(II) with cefixime in ethanol-distilled water medium at room temperature (25±1 °C). The formed complex showed maximum absorbance at 332 nm. The reaction conditions are optimized and validated as per International Conference on Harmonisation (ICH 1995).

Experimental Apparatus All spectral and absorbance measurements were made on a Helios Alpha UV–vis spectrophotometer

Environ Monit Assess (2013) 185:4647–4657

(Thermo Electron Corporation, England, UK) with 1cm matched quartz cells. An air–acetylene flame type atomic absorption spectrometer (Model iCE 3500 series; Thermo Scientific, UK) was used to determine Ni(II) in synthetic mixture and water samples. IR spectra were recorded on an IRAffinity-1 spectrophotometer (Shimadzu, Kyoto, Japan) in wave number region 4,000–400 cm−1 using KBr pellet technique. pH meter (Hanna, USA) was used to measure the pH of the Ni(II)–cefixime complex. Materials and methods All chemicals and solvents used were of analytical reagent grade. Deionized doubly distilled water was used throughout the experiment. All reagents used were of analytical reagent grade. &

&

&

1.522×10−3 M nickel sulfate hexahydrate (89.315 ppm Ni, MW 262.86; Iqba Chemie Pvt. Ltd, Mumbai, India) solution was prepared by dissolving 0.04 g nickel sulfate hexahydrate in distilled water and then diluted up to the mark with distilled water in a 100-mL volumetric flask. 3.153 × 10 −3 M cefixime trihydrate (Chemical Abstracts Service 79350-37-1, MW 507.5; Merck, USA) solution was freshly prepared in methanol. The pure cefixime trihydrate (batch no. XMEO 110023) was provided by National Pharmaceutical Industries Company, Oman. The solution was stable up to 12 h. Water samples were collected from Al Hoqain wadi in Al Rustaq (Al Batinah region, Oman).

Proposed method: procedure for the determination of Ni(II) by spectrophotometry Into a series of 10-mL standard volumetric flasks, aliquots of 0.05, 0.1, 0.2, 0.3, 0.4, and 0.45 mL of 1.522× 10−3 M nickel sulfate hexahydrate corresponding to 0.45, 0.89, 1.79, 2.68, 3.57, and 4.02 μgmL−1 Ni(II) were added followed by 1.6 mL of 3.153×10−3 M cefixime solution. The contents of the reaction mixture were mixed well and diluted up to the mark with ethanol. The absorbance was measured at wavelength 332 nm against the reagent blank prepared similarly except Ni(II) within stability period (6 h). The amount of Ni(II) was obtained either from the calibration graph or the regression equation.

Author's personal copy Environ Monit Assess (2013) 185:4647–4657

Reference method: procedure for the determination of Ni(II) by flame atomic absorption spectrophotometry Aliquots of 0.05, 0.1, 0.2, 0.3, 0.4, and 0.45 mL of 1.522 × 10 − 3 M nickel sulfate hexahydrate corresponding to 0.45, 0.89, 1.79, 2.68, 3.57, and 4.02 μgmL−1 Ni(II) were taken in 10-mL standard volumetric flask and diluted up to the mark with distilled water. The absorbance of Ni was recorded. The calibration graph was constructed by plotting the absorbance against the concentration of Ni(II). The linear regression equation was obtained by statistical treatment of calibration data. The amount of Ni(II) was estimated from the calibration graph or the regression equation. Determination of Ni(II) in synthetic mixture sample by proposed method

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1.522×10−3 M nickel sulfate solution were mixed with different volumes (2.0, 1.8, 1.6, 1.4, 1.2, 1.0, 0.8, 0.6, 0.4, 0.2, and 0 mL) of 1.522×10−3 M cefixime and diluted with ethanol in a 10-mL standard volumetric flask. The absorbance was recorded at 332 nm and plotted against the mole fraction of nickel(II). Validation The proposed method has been validated for linearity, precision, accuracy, specificity, robustness, and evaluation of bias. The linearity of the proposed method was assessed at six concentrations [0.447, 0.893, 1.786, 2.68, 3.573, and 4.019 μgmL−1 Ni(II)]. Each concentration was independently analyzed repeatedly for five times. The absorbance obtained at each concentration was plotted against the initial concentration of Ni(II) in micrograms per milliliter. The linear regression equation was evaluated by least square treatment of the calibration data. The linear regression characteristics and statistical parameters of the proposed method were calculated using OriginPro 6.1 Software. Limits of detection (LOD) and quantitation (LOQ) were calculated by the following expressions (Miller and Miller 1993):

The synthetic mixture of Ni(II) sulfate sample solution was prepared by taking 40 mg of Ni(II) sulfate with 1.90 mg CuSO4, 7.50 mg MgSO4·H2O, 5.04 mg Pb (NO 3 ) 2 , 2.18 mg ZnSO 4 ·7H 2 O, 5.70 mg Al (NO3)3·9H2O, 8.45 mg FeSO4·7H2O, and 8.10 mg CrCl3·6H2O in distilled water in a 100-mL standard volumetric flask and diluted up to the mark with distilled water. The amount of Ni(II) was determined by the proposed procedure.

LOD ¼ 3:0

S0 b

Determination of Ni(II) in wadi water sample by spectrophotometry and flame atomic absorption spectrophotometry

LOQ ¼ 10

S0 b

One hundred milliliters of wadi water sample was collected and transferred into a clean polyethylene bottle. The water samples were filtered through a Millipore 0.45-μm-pore-size membrane and analyzed within 6 h of collection. An aliquot (1.0 mL) of wadi water sample was pipetted into a 10-mL standard volumetric flask and diluted up to the mark with ethanol (or distilled water in case of Atomic Absorption Spectrophotometry). The amount of Ni(II) was determined by the proposed and reference procedures. Determination of stoichiometry The stoichiometry of the reaction was studied by Job’s method of continuous variations (Likussar and Boltz 1971). For this purpose, different volumes (0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, and 2.0 mL) of

where S0 is standard deviation of calibration line and b is the slope. The precision of the proposed method was evaluated by intra-day and inter-day precisions. The standard solution of Ni(II) sulfate at three concentrations (0.89, 2.23, and 3.57 μgmL−1) was prepared each time and assessed with five replicates for each of three working sample concentrations in a single day (intra-day precision) and over five consecutive days (inter-day precision). The accuracy of the proposed method was determined by standard addition method. For this purpose, 0.4 mL of the synthetic mixture sample solution of Ni (II) was spiked with 0, 0.05, 0.1, 0.15, and 0.2 mL standard Ni(II) solution corresponding to 0, 0.45, 0.89, 1.34, and 1.79 μgmL−1 Ni(II). The specificity of the proposed method was evaluated by determining 3.57 μg mL −1 Ni(II) in the



θ2 x21 Sp2 ttab 2 =n1 þ θð2x1 x2 Þ þ x22 Sp2 ttab 2 =n2 ¼ 0

where x1 and x2 are mean values at n1 and n2 measurements, respectively. Sp is the pooled standard deviation and ttab is the tabulated one-sided t value at 95 % confidence level. The values of θL and θU of the confidence interval were obtained as: θU &θL ¼

b

pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi b2 4ac 2a

1.0 0.9

b

0.8 0.7

Absorbance

presence of metal ions such as Cu(II), Mg(II), Pb(II), Zn(II), Al(III), Fe(II), and Cr(III), added in the form of CuSO4, MgSO4·H2O, Pb(NO3)2, ZnSO4·7H2O, Al (NO3)3·9H2O, FeSO4·7H2O, and Cr2Cl3·6H2O. The robustness of proposed method was evaluated by analyzing 3.573 μgmL−1 Ni(II) in synthetic mixture sample by varying the volume of cefixime (1.5± 0.2 mL) at room temperature (25±1 °C). The bias of the proposed and reference methods has been evaluated by point and interval hypothesis tests. Five replicate determinations were made using the proposed method and the reference method. The proposed method is compared with the reference method and considered to be acceptable if mean recovery of the proposed method is within ±2.0 % of that of the reference method. The lower (θL) and the upper (θU) acceptance limits can be calculated by the following quadratic equation (Hartmann et al. 1995):

0.6 0.5

c

0.4 0.3 0.2 0.1

a

0.0 200

225

250

275

300

325

350

37 5

40 0

Wavelength (nm)

Fig. 1 Absorption spectra of a 0.7 mL of 1.522×10−3 M nickel sulfate solution, b 0.2 mL of 9.852×10−3 M cefixime, and c 0.4 mL of 1.522×10−3 M Ni(II) sulfate+1.6 mL of 3.153×10−3 M cefixime. Cefixime and complex solution are diluted up to the mark with methanol and ethanol, respectively, in a 10-mL volumetric flask while Ni(II) solution is diluted with distilled water

310 nm. When the two solutions were mixed together, a shift in the wavelength was observed due to the complexation reaction of Ni(II) with cefixime. Thus, the complex absorbed maximally at 332 nm. The absorption spectra of nickel sulfate, cefixime, and Ni (II)–cefixime complex are shown in Fig. 1. The absorbance measurement at 332 nm as a function of the

Where 0.6

a¼

x21

Sp2 ttab 2 =n1 0.5

b ¼ 2x1 x2 Absorbance

c ¼ x22 Sp2 ttab 2 =n2

0.4

0.3

0.2

Results and discussion 0.1

The absorption spectrum of methanolic solution of cefixime exhibited two bands peaking at 201 and 290 nm, respectively, whereas the aqueous solution of nickel sulfate absorbed radiation to a very small extent (~0.036 A) in the wavelength range 225–

0.0 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Mole fraction of Ni(II)

Fig. 2 Job’s plot for Ni(II)–cefixime complex

0.8

0.9

1.0


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initial concentration of Ni(II) is exploited to develop a new and accurate spectrophotometric method for the determination of Ni(II) in synthetic mixture and in samples collected from Al Hoqain wadi in Al Rustaq (Al Batinah region, Oman). The reaction was carried out at room temperature (25 °C). Stoichiometry The stoichiometric ratio between Ni(II) and cefixime was evaluated by Job’s method of continuous variations. The Job’s plot (Fig. 2) indicated that 1 mol of Ni (II) reacted with 1 mol of cefixime. Thus, the stoichiometry of the complex is established and found to be Fig. 3 Infrared spectra of a pure cefixime and b Ni– cefixime complex

a

b

1:1 (Ni/cefixime). The resulting Ni(II)–cefixime complex remained stable for about 1 day. The apparent formation constant (Kf) for the complex between Ni(II) and cefixime is calculated using the following expression: Aobs =Aextp C i Kf ¼ h obs C CL Aobs =Aextp C CM AAextp Where Aobs. and Aextp are observed and extrapolated absorbance values of the complex at [Ni– cefixime] and C in moles per liter, respectively,



metrical and symmetrical stretching bands of carboxylate groups change from 1,543 cm −1 to 1,539 cm−1 and 1,381 to 1,423 cm−1, respectively, due to the coordination. The Ni–N stretching vibration occurred in the far IR region at 334 cm−1 (Nakamoto 2009). A tentative mechanism for the complexation of Ni(II)–cefixime complex is given in Scheme 1.

where C is the limiting concentration. Thus, Kf for the complex was found to be 3.73×104. The apparent Gibbs free energy (ΔGº) is calculated using ΔGº0−2.303 RT log Kf and found to be −26.09 kJ mol−1, confirming the feasibility of the reaction. The IR spectra of pure cefixime and Ni(II)–cefixime complex are shown in Fig. 3a and b. Cefixime has – NH2, –COOH, –CONH, and C0O lactam groups which are the potential sites for coordination with metal ions. Comparison of IR spectrum of the complex with those of pure cefixime indicates that the lactam (C0O) band appears at 1,770 cm−1 in the pure cefixime while the complex shows this band at 1,766 cm−1, suggesting that no coordination occurs with nickel ion. The amide carbonyl band (C0O)–NH in the pure cefixime appears at 1,670 cm−1 with a weak shoulder at 1,589 cm−1 while the Ni(II)–cefixime complex shows this band at 1 ,67 4 c m − 1 with a p romin ent p eak at 1,635 cm−1, suggesting that cefixime coordinated with Ni(II) through the nitrogen atom. The asymScheme 1 Reaction sequence of the proposed method

Optimization of spectrophotometric method The optimization of variables for the proposed spectrophotometric method was assessed by testing several parameters such as reaction time, concentration of cefixime, and buffer solutions of different pH. Effect of time The reaction was carried out at room temperature (25± 1 °C). Different time intervals were tested to ascertain

Step 1 O

O NOCH2COH N

C C O

S

H2N

S

H2N

H+

H N

-

NOCH2CO N

C

+

C H

COOH

Cefixime

S

O

N

O

H N

C

S

N

O

CH2

COOH

Step 2

C H

O S

H2N

Ni2+

-

NOCH2CO N

+

C C

H N

O

H2O-ethanol medium

S O

N COOH

+

O S

H2N

NOCH2CO N

C C

H Ni N

O

O

S N COOH

Ni(II)-cefixime complex

C H

CH2

C H

CH2

CH2


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the time required to complete the reaction. It was found that the highest absorbance of the complex was attained immediately.

0.4

The pH of the complex was measured and found to be 4.0. The effect of pH on the absorbance of the complex was investigated using Na2HPO4–citric acid (pH range 2.2–5) and sodium acetate–HCl (range 3.72–5.57) buffer solutions. The absorbance value in the mentioned pH range was found to be less than that obtained without buffer solution when dilution is made with ethanol. Therefore, all absorbance measurements of the complex were made in ethanol solvent without the involvement of buffer solution.

Absorbance

Effect of pH 0.3

0.2

0.1

0.0 Acetone

DMSO Acetonitrile Ethanol 1,4-dioxan DMF Distilled water

Solvent

Fig. 5 Effect of solvent on the absorbance of Ni(II)–cefixime complex

Effect of the concentration of cefixime The effect of concentration of cefixime on the absorbance of the complex (i.e., maximum formation of the complex) was studied at 3.573 μgmL−1 Ni(II) using different volumes of 3.153 × 10−3 M solution of the reagent. It was observed that the reaction of Ni(II) with cefixime was started on addition of 0.2 mL of the reagent. Increasing the volume of the reagent produces a proportional

increase in the absorbance of the product up to 1.2 mL and remains constant up to 2.0 mL (Fig. 4). Therefore, 1.6 mL of 3.153 × 10 −3 M cefixime was chosen as the optimal volume of the reagent.

Table 1 Optical and regression characteristics of the proposed method Parameters

1max (nm)

332 nm

Beer’s law limit (μg mL−1)

0.447–4.019

Molar absorptivity (L mol−1 cm−1)

7.31×103

0.40

Sandell’s sensitivity

0.008 μg/cm2/0.001 absorbance unit

0.35

Linear regression equationa

A01.27×10−4 +0.124C

Sa

5.41×10−4

±tSa

1.50×10−3

Sb

2.09×10−4

±tSb

5.79×10−4

0.45

Absorbance

Analytical data

0.30

0.25

0.20

Correlation coefficient (r)

0.9999

Variance (So2)

4.51×10−7

LOD (μg mL−1)

0.016

LOQ (μg mL−1)

0.054

0.15 0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

-3

Volume of 3.153 × 10 M cefixime (mL) −3

Fig. 4 Effect of the volume of 3.153×10 M cefixime

2.0

2.2

±tSa and ±tSb are the confidence limits for intercept and slope, respectively a

With respect to A0a+bC, where C is the concentration in micrograms per milliliter and A is absorbance



Table 2 Precision of the proposed method Parameters

Intra-day assay

Inter-day assay

Concentration taken (μg mL−1)

0.890

2.230

3.570

0.890

2.230

3.570

Concentration found (μg mL−1)

0.889

2.232

3.571

0.892

2.234

3.566

Standard deviationa (μg mL−1)

0.010

0.009

0.007

0.011

0.01

0.009

Relative standard deviation (%)

1.179

0.392

0.190

1.270

0.447

Recovery (%) a

99.99

100.10

100.01

100.17

0.256

100.18

99.88

Mean for five independent analysis

Effect of solvent

Validation

The effect of solvents such as methanol, acetone, dimethylsulfoxide, acetonitrile, ethanol, 1,4-dioxan, dimethylformamide, and distilled water was investigated at 3.573 μg mL−1 Ni(II) on the absorbance of Ni(II)–cefixime complex. The absorbance for Ni(II)–cefixime complex in the mentioned solvents is shown in Fig. 5. It is clear from the figure that the highest absorbance was obtained in ethanol. Therefore, ethanol was the best solvent for dilution of the reaction mixture of Ni(II)–cefixime complex in determination process of Ni(II) in synthetic mixture and water samples.

Linearity, limits of detection, and quantitation The calibration curve was constructed by plotting absorbance against initial concentration of nickel ion for the proposed spectrophotometric method. Beer’s law was obeyed in the concentration range of 0.447–4.019 μgmL−1 with molar absorptivity of 7.31×103 Lmol−1 cm−1. Optical, analytical, and statistical parameters of the experimental data such as regression equation computed from calibration graph, correlation coefficient, detection limit, and quantitation limit are summarized in Table 1. The high value of correlation coefficient (0.9999) for

Fig. 6 Amount of Ni(II) through standard addition technique in synthetic mixture sample (2.227 μgmL−1)

0.5

Absorbance

0.4

0.3

0.2

0.1

0.0 -3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Spiked Nominal Concentration of Ni(II), µg mL-1

2.0

2.5


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Table 3 Test of accuracy in synthetic mixture sample by standard addition technique Concentration (μg mL−1)

Recoveryb (%)

Linear regression parameters

Sample

Standard

Nominal

Error (Xe)

Intercept

Slope

ra

2.23

0, 0.45, 0.89, 1.34, 1.79

2.227

0.028

0.2776

0.1246

0.9987

a

Coefficient of correlation

b

Mean for five independent analyses

the proposed method indicated excellent linearity. In order to verify that the proposed method is free from procedural error, the experimental intercept of the calibration line was tested for significance of the deviation from the theoretical intercept, i.e., zero. For this justification, the values of t calculated from the relation, t 0 a/Sa (Nallimov 1963) was found to be 0.234, which did not exceed the theoretical t value (2.776) at 95 % confidence level. This indicated that the intercept for the proposed method is not significantly different from zero. Precision

99.87

was good. It is evident from the figure that the concentration of Ni(II) in synthetic mixture is given by intercept/slope. The ratio of the intercept and the slope of the regression line is subjected to error (SxE). SxE is calculated from the following expression 2 SxE

31=2

Sy=x 6 1 y2 7 ¼ 4 þ 2P 5 b n b ð xi xÞ 2 i

and found to be 0.028 μgmL−1 for synthetic mixture. The confidence limit for the concentration of Ni(II) in synthetic mixture is calculated by xE ± tSxE at n– 2 degrees of freedom and found to be 2.227±0.028 μg mL−1. The most attractive feature of the proposed method using standard addition method is its relative freedom from various non-targeted cations.

The intra-day and inter day precisions were evaluated by determining the concentration of Ni(II) at lower, middle, and upper concentrations for five repeated times within the same day and on five consecutive days, respectively (Table 2). It is clear from the table that percentage recovery and RSD (intra-day and inter-day precisions) were in the ranges of 99.88–100.18 % and 1.27–0.187 %, respectively. It can been seen from the table that percentage recovery and RSD values were precise and can be used to determine Ni(II) in synthetic mixture and water samples.

Table 4 Effect of metal ions on the determination of 3.57 μg mL−1 Ni(II)

Accuracy

Metal ions

Added as

The accuracy of the proposed method was investigated by performing recovery experiments through standard addition technique. The absorbance is recorded for all standard addition solutions and plotted as shown in Fig. 6. The results of analyses are summarized in Table 3. It is clear from the table and the graph that the linearity of the regression line for synthetic mixture sample

Cu2+

CuSO4

0.48

Mg2+

MgSO4·7H2O

0.74

Pb2+

Pb(NO3)2

3.15

Zn2+

ZnSO4·7H2O

0.49

Al3+

Al(NO3)3·9H2O

0.41

FeSO4·7H2O

1.69

CrCl3·6H2O

1.58

Robustness The robustness of the proposed method was established by deliberately changing the volume of 3.153×10−3 M

Fe

2+

Cr3+

Tolerance limit (μg mL−1)



cefixime, 1.2 mL (±0.4 mL) for the determination of Ni (II). The synthetic mixture sample solution containing 3.573 μgmL−1 Ni(II) was analyzed five times repeatedly by the proposed method. Percentage recovery and RSD were found to be 99.98 % and 0.464 %, respectively, indicating the robustness of the proposed method.

Table 6 Determination of Ni(II) in wadi water sample by the proposed spectrophotometric method and the reference method Sample

Wadi water

Concentration of Ni(II) (μg mL−1) Proposed method

Reference method

0.699

0.697

Specificity The effect of other ions on the determination of 3.573 μgmL−1 Ni(II) was studied. For this purpose, the varying concentrations of metal ions such as Cu(II), Mg(II), Pb(II), Zn(II), Al(III), Fe (II), and Cr(III) with 3.573 μgmL−1 Ni(II) were taken and the absorbance was recorded to know the concentration of Ni(II). Table 4 shows the maximum tolerance limit of various ions studied. The maximum permissible concentration was taken, when the absorbance value did not exceed ±2 % on addition of cations. Applicability and evaluation of bias The applicability of the proposed method for the determination of Ni(II) in synthetic mixture sample has been tested. Results of the proposed method were statistically compared with those of reference method using point and interval hypothesis tests. The paired t and the F values at 95 % confidence level were calculated and found to be less than the tabulated t (2.036 at υ08) and the F values (6.39 at υ04,4) at 95 % confidence level (Mendham et

Table 5 Significance of testing: point and interval hypothesis tests for the determination of Ni(II) in synthetic mixture sample at 95 % confidence level Proposed method

Reference method

Paired t valueb

F θLd c value

θUd

Recovery RSDa Recovery RSDa (%) (%) (%) (%)

99.98 a

0.46 100.10

0.69 0.33

2.20

0.991 1.012

Mean for five independent analyses

b

Theoretical t (ν08) and F values (ν04, 4) at 95 % confidence level are 2.306 and 6.39, respectively

c

A bias, based on recovery experiments, of ±2 % is acceptable

al. 2002). The results are summarized in Table 5. It is evident from the table that there is no significant difference between the performance of the proposed method and the reference method. The recoveries obtained revealed that the proposed procedure produces accurate results. The performance of proposed method is also tested in wadi water sample collected from Al Rustaq, Oman. Results of analysis were found in good agreement with reference method (Table 6). Thus, the proposed method can be used as alternate method for the routine analysis of Ni(II) in real water samples. The RSD value (0.464 %) in case of proposed method is less as compared to the reference method (0.688 %) indicating more accurateness and sensitivity of the proposed method.

Conclusion The proposed method is a simple and accurate for the determination of Ni(II) in synthetic mixture and water samples. The method has advantage of using a commonly available solvent, i.e., ethanol with the use of one reagent, i.e., cefixime. The proposed method has avoided the use of acid, buffer solution, and heating of reaction mixture and, hence, can be used as an alternate method for routine quality control analysis of Ni (II) in soil, vegetable, and pharmaceutical samples. The results obtained by proposed spectrophotometric method and flame atomic absorption spectrometry are quantitative and are in close agreement with each other. Acknowledgments The authors are grateful to Aligarh Muslim University, Aligarh, India and Ministry of ManPower (Higher College of Technology) Muscat, Sultanate of Oman for facilities. The authors wish to express their gratitude to M/s National Pharmaceutical Industries Company, Oman for providing the gift sample of pure cefixime.


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