Utility of cefixime as a complexing reagent for the determination of Ni(II) in synthetic mixture and...

Utility of cefixime as a complexing reagent for the determinationof 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 spectro-photometric method has been developed for the determi-nation of nickel in synthetic mixture and water samples.The method is based on the complexation reaction ofnickel ion with cefixime, thus leading to the formation ofNi–cefixime complex in ethanol-distilled water mediumat room temperature. The complex showed the maxi-mum absorption wavelength at 332 nm. Beer’s law isobeyed in the working concentration range of 0.447–4.019 μgmL−1 with apparent molar absorptivity of7.314×103Lmol−1cm−1 and Sandell’s sensitivity of0.008 μg/cm2/0.001 absorbance unit. The limits of de-tection and quantitation for the proposed method are0.016 and 0.054 μgmL−1, respectively. The factors suchas cefixime concentration and solvent affecting the com-plexation reaction were carefully studied and optimized.The method is validated as per the InternationalConference on Harmonisation guideline. The method issuccessfully applied to the determination of Ni(II) insynthetic mixture and wadi water samples collected fromAl Rustaq. The same water samples are also analyzed by

atomic absorption spectrophotometry. Both methods de-termined the amount of Ni(II) in water sample and foundto be approximately the same.

Keywords Spectrophotometry . Nickel ion .

Cefixime . Ni(II)–cefixime complex . Validation

Introduction

Nickel is used in a wide variety of metallurgical process-es such as electroplating and alloy production as well asin nickel–cadmium batteries. Nickel is emitted to theatmosphere from natural sources including windblowndust, volcanoes, vegetation forest fires, and meteoricdust. Food and cigarette smoke are the main sources ofnickel exposure in the general public (WHO 2000).Approximately 0.04–0.58 μg nickel is released withmainstream smoke of one cigarette. Smoking 40 ciga-rettes a day, therefore, may lead to inhalation of 2–23 μgnickel. An uptake of too large quantities of nickel has thefollowing consequences: higher chances of developmentof lung cancer, nose cancer, larynx cancer, and prostatecancer as well as sickness and dizziness after exposure tonickel gas, lung embolism, respiratory failure, birthdefects, asthma and chronic bronchitis, allergic reactionssuch as skin rashes (mainly from jewelry), and heartdisorders. The determination of nickel is becoming in-creasingly important because of its toxic nature and itspresence in industrial waste, potable water samples, andsome other effluents. The literature citation revealed that

Environ Monit Assess (2013) 185:4647–4657DOI 10.1007/s10661-012-2894-4

S. N. H. Azmi (*) :B. Iqbal :R. S. Al Khanbashi :N. H. Al HamhamiDepartment of Applied Sciences, Chemistry Section,Higher College of Technology,Al-Khuwair-133, P. O. Box 74, Muscat, Sultanate of Omane-mail: [email protected]

N. RahmanDepartment of Chemistry, Aligarh Muslim University,Aligarh 202002, Uttar Pradesh, India

there are various analytical techniques for the determi-nation of nickel which include graphite furnace atomicabsorption spectrometry (Sun et al. 2006), flame atomicabsorption spectrometry (Ahmadi et al. 2008; Khani andShemirani 2010), inductively coupled plasma-opticalemission 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 etal. 2005; Albertus et al. 2001). In addition, spectropho-tometric methods have also been developed to determineNi(II) based on the reaction with reagents such as nic-otinamidoxime (Garole and Sawant 2005), dimethyl-glyoxime (Gazda et al. 2004), dithiozone (Ozturk et al.2000), sodium isoamylxanthate (Malik et al. 2000), sal-icylaldehyde 5-oxobutanoylhydrazone (Suresh et al.2004), 2-nitroso-1-naphthol-4-sulfonic acid and tetrade-cyldimethylbenzylammonium chloride (Taher et al.1998), 4-methyl 2,3-pentanedione dioxime (Dipak etal. 2005), 1-nitroso-2-naphthol (Shar and Soomro2006), diethyldithiocarbamate (Kabil et al. 1996), andcyclohexylxanthate (Hashem et al. 2003). Most of thereported spectrophotometric methods are time consum-ing, employing many reagents to develop the color andextraction of nickel complex into organic solvent.Spectrophotometry is a widely used technique for deter-mining metal ion concentration in leafy vegetables, phar-maceuticals, and natural water and soil samples.Spectrophotometers are now more economical, simple,versatile, adaptable, and affordable than ever (Czeganand Hoover 2012). Therefore, it is decided to exploit thistechnique to develop an optimized and validated UVspectrophotometric method for the determination of Ni(II) in synthetic mixture and water samples. The presentUV spectrophotometric method is based on the complexformation of Ni(II) with cefixime in ethanol-distilledwater medium at room temperature (25±1 °C). Theformed complex showed maximum absorbance at332 nm. The reaction conditions are optimized and val-idated as per International Conference on Harmonisation(ICH 1995).

Experimental

Apparatus

All spectral and absorbance measurements were madeon a Helios Alpha UV–vis spectrophotometer

(Thermo Electron Corporation, England, UK) with 1-cm matched quartz cells.

An air–acetylene flame type atomic absorptionspectrometer (Model iCE 3500 series; ThermoScientific, UK) was used to determine Ni(II) in syn-thetic mixture and water samples.

IR spectra were recorded on an IRAffinity-1 spectro-photometer (Shimadzu, Kyoto, Japan) in wave numberregion 4,000–400 cm−1 using KBr pellet technique.

pH meter (Hanna, USA) was used to measure thepH of the Ni(II)–cefixime complex.

Materials and methods

All chemicals and solvents used were of analyticalreagent grade. Deionized doubly distilled water wasused throughout the experiment. All reagents usedwere of analytical reagent grade.

& 1.522×10−3M nickel sulfate hexahydrate (89.315ppm Ni, MW 262.86; Iqba Chemie Pvt. Ltd,Mumbai, India) solution was prepared by dissolv-ing 0.04 g nickel sulfate hexahydrate in distilledwater and then diluted up to the mark with distilledwater in a 100-mL volumetric flask.

& 3.153×10−3M cefixime trihydrate (ChemicalAbstracts Service 79350-37-1, MW 507.5; Merck,USA) solution was freshly prepared in methanol. Thepure cefixime trihydrate (batch no. XMEO 110023)was provided by National Pharmaceutical IndustriesCompany, Oman. The solution was stable up to 12 h.

& Water samples were collected from Al Hoqainwadi in Al Rustaq (Al Batinah region, Oman).

Proposed method: procedure for the determinationof Ni(II) by spectrophotometry

Into a series of 10-mL standard volumetric flasks, ali-quots of 0.05, 0.1, 0.2, 0.3, 0.4, and 0.45 mL of 1.522×10−3M nickel sulfate hexahydrate corresponding to0.45, 0.89, 1.79, 2.68, 3.57, and 4.02 μgmL−1 Ni(II)were added followed by 1.6 mL of 3.153×10−3M cefix-ime solution. The contents of the reaction mixture weremixed well and diluted up to the mark with etha-nol. The absorbance was measured at wavelength332 nm against the reagent blank prepared simi-larly except Ni(II) within stability period (6 h).The amount of Ni(II) was obtained either fromthe calibration graph or the regression equation.

4648 Environ Monit Assess (2013) 185:4647–4657

Reference method: procedure for the determinationof Ni(II) by flame atomic absorption spectrophotometry

Aliquots of 0.05, 0.1, 0.2, 0.3, 0.4, and 0.45 mLof 1.522× 10−3M nickel sulfate hexahydratecorresponding to 0.45, 0.89, 1.79, 2.68, 3.57, and4.02 μgmL−1 Ni(II) were taken in 10-mL standardvolumetric flask and diluted up to the mark with distilledwater. The absorbance of Ni was recorded. The calibra-tion graph was constructed by plotting the absorbanceagainst the concentration of Ni(II). The linear regressionequation was obtained by statistical treatment of cali-bration data. The amount of Ni(II) was estimated fromthe calibration graph or the regression equation.

Determination of Ni(II) in synthetic mixture sampleby proposed method

The synthetic mixture of Ni(II) sulfate sample solutionwas prepared by taking 40 mg of Ni(II) sulfate with1.90 mg CuSO4, 7.50 mg MgSO4·H2O, 5.04 mg Pb(NO3)2, 2.18 mg ZnSO4·7H2O, 5.70 mg Al(NO3)3·9H2O, 8.45 mg FeSO4·7H2O, and 8.10 mgCrCl3·6H2O in distilled water in a 100-mL standardvolumetric flask and diluted up to the mark withdistilled water. The amount of Ni(II) was determinedby the proposed procedure.

Determination of Ni(II) in wadi water sampleby spectrophotometry and flame atomic absorptionspectrophotometry

One hundred milliliters of wadi water sample was col-lected and transferred into a clean polyethylene bottle.The water samples were filtered through a Millipore0.45-μm-pore-size membrane and analyzed within 6 hof collection. An aliquot (1.0 mL) of wadi water samplewas pipetted into a 10-mL standard volumetric flask anddiluted up to the mark with ethanol (or distilled water incase of Atomic Absorption Spectrophotometry). Theamount of Ni(II) was determined by the proposed andreference procedures.

Determination of stoichiometry

The stoichiometry of the reaction was studied by Job’smethod of continuous variations (Likussar andBoltz 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

1.522×10−3M nickel sulfate solution were mixed withdifferent 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 1.522×10−3M cefixime anddiluted with ethanol in a 10-mL standard volumetricflask. The absorbance was recorded at 332 nm andplotted against the mole fraction of nickel(II).

Validation

The proposed method has been validated for linearity,precision, accuracy, specificity, robustness, and evalu-ation of bias.

The linearity of the proposed method was assessed atsix concentrations [0.447, 0.893, 1.786, 2.68, 3.573, and4.019 μgmL−1 Ni(II)]. Each concentration was indepen-dently analyzed repeatedly for five times. The absor-bance obtained at each concentration was plotted againstthe initial concentration of Ni(II) in micrograms permilliliter. The linear regression equation was evaluatedby least square treatment of the calibration data. Thelinear regression characteristics and statistical parame-ters of the proposed method were calculated usingOriginPro 6.1 Software. Limits of detection (LOD)and quantitation (LOQ) were calculated by the follow-ing expressions (Miller and Miller 1993):

LOD ¼ 3:0� S0b

LOQ ¼ 10� S0b

where S0 is standard deviation of calibration line and bis the slope.

The precision of the proposed method was evaluatedby intra-day and inter-day precisions. The standard so-lution of Ni(II) sulfate at three concentrations (0.89, 2.23,and 3.57 μgmL−1) was prepared each time and assessedwith five replicates for each of three working sampleconcentrations in a single day (intra-day precision) andover five consecutive days (inter-day precision).

The accuracy of the proposed method was deter-mined 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 mLstandard 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 evalu-ated by determining 3.57 μgmL−1 Ni(II) in the

Environ Monit Assess (2013) 185:4647–4657 4649

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 ofCuSO4, MgSO4·H2O, Pb(NO3)2, ZnSO4·7H2O, Al(NO3)3·9H2O, FeSO4·7H2O, and Cr2Cl3·6H2O.

The robustness of proposed method was evaluatedby analyzing 3.573 μgmL−1 Ni(II) in synthetic mix-ture 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 hasbeen evaluated by point and interval hypothesis tests.Five replicate determinations were made using theproposed method and the reference method. The pro-posed method is compared with the reference methodand considered to be acceptable if mean recovery ofthe proposed method is within ±2.0 % of that of thereference method. The lower (θL) and the upper (θU)acceptance limits can be calculated by the followingquadratic equation (Hartmann et al. 1995):

θ2 x21 � S2p ttab2=n1

� �þ θ �2x1 x2ð Þ þ x22 � S2p ttab

2=n2� �

¼ 0

where x1and x2 are mean values at n1 and n2 measure-ments, respectively. Sp is the pooled standard devia-tion and ttab is the tabulated one-sided t value at 95 %confidence level.

The values of θL and θU of the confidence intervalwere obtained as:

θU&θL ¼ �b�ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffib2 � 4ac

p

2a

Where

a ¼ x21 � S2p ttab2=n1

b ¼ �2x1 x2

c ¼ x22 � S2p ttab2=n2

Results and discussion

The absorption spectrum of methanolic solution ofcefixime exhibited two bands peaking at 201 and290 nm, respectively, whereas the aqueous solutionof nickel sulfate absorbed radiation to a very smallextent (~0.036 A) in the wavelength range 225–

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

Wavelength (nm)200 225 250 275 300 325 350 375 400

Abs

orba

nce

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

a

b

c

Fig. 1 Absorption spectra of a 0.7 mL of 1.522×10−3M nickelsulfate solution, b 0.2 mL of 9.852×10−3M cefixime, and c0.4 mL of 1.522×10−3M Ni(II) sulfate+1.6 mL of 3.153×10−3

M cefixime. Cefixime and complex solution are diluted up tothe mark with methanol and ethanol, respectively, in a 10-mLvolumetric flask while Ni(II) solution is diluted with distilledwater

Mole fraction of Ni(II)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Abs

orba

nce

0.0

0.1

0.2

0.3

0.4

0.5

0.6

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


initial concentration of Ni(II) is exploited to develop anew and accurate spectrophotometric method for thedetermination of Ni(II) in synthetic mixture and insamples collected from Al Hoqain wadi in Al Rustaq(Al Batinah region, Oman). The reaction was carriedout at room temperature (25 °C).

Stoichiometry

The stoichiometric ratio between Ni(II) and cefiximewas evaluated by Job’s method of continuous varia-tions. The Job’s plot (Fig. 2) indicated that 1 mol of Ni(II) reacted with 1 mol of cefixime. Thus, the stoichi-ometry of the complex is established and found to be

1:1 (Ni/cefixime). The resulting Ni(II)–cefixime com-plex remained stable for about 1 day.

The apparent formation constant (Kf) for the com-plex between Ni(II) and cefixime is calculated usingthe following expression:

Kf ¼Aobs=Aextp

� �C

CM � AobsAextp

� �C

h iCL � Aobs=Aextp

� �C

� �

Where Aobs. and Aextp are observed and extrap-olated absorbance values of the complex at [Ni–

cefixime] and C in moles per liter, respectively,

a

b

Fig. 3 Infrared spectra of apure cefixime and b Ni–cefixime complex


where C is the limiting concentration. Thus, Kf

for the complex was found to be 3.73×104. Theapparent Gibbs free energy (ΔGº) is calculated usingΔGº0−2.303 RT log Kf and found to be −26.09 kJmol−1, confirming the feasibility of the reaction.

The IR spectra of pure cefixime and Ni(II)–cefiximecomplex are shown in Fig. 3a and b. Cefixime has –NH2, –COOH, –CONH, and C0O lactam groupswhich are the potential sites for coordination withmetal ions. Comparison of IR spectrum of thecomplex with those of pure cefixime indicates thatthe lactam (C0O) band appears at 1,770 cm−1 inthe pure cefixime while the complex shows thisband at 1,766 cm−1, suggesting that no coordina-tion occurs with nickel ion. The amide carbonylband (C0O)–NH in the pure cefixime appears at1,670 cm−1 with a weak shoulder at 1,589 cm−1

while the Ni(II)–cefixime complex shows this bandat 1 ,674 cm−1 with a prominent peak at1,635 cm−1, suggesting that cefixime coordinatedwith Ni(II) through the nitrogen atom. The asym-

metrical and symmetrical stretching bands of car-boxylate groups change from 1,543 cm−1 to1,539 cm−1 and 1,381 to 1,423 cm−1, respectively,due to the coordination. The Ni–N stretching vi-bration occurred in the far IR region at 334 cm−1

(Nakamoto 2009). A tentative mechanism for thecomplexation of Ni(II)–cefixime complex is givenin Scheme 1.

Optimization of spectrophotometric method

The optimization of variables for the proposedspectrophotometric method was assessed by testingseveral parameters such as reaction time, concen-tration of cefixime, and buffer solutions of differ-ent pH.

Effect of time

The reaction was carried out at room temperature (25±1 °C). Different time intervals were tested to ascertain

Step 1

Step 2

N

SH2N

NO

S

COOHCH

CH2

C

NOCH2COH

C

O

HN

O

H+ +N

SH2N

NO

S

COOHCH

CH2

C

NOCH2CO-

C

O

HN

O

N

SH2N

NO

S

COOHCH

CH2

C

NOCH2CO-

C

O

HN

O

Ni2++

H2O-ethanol medium

N

SH2N

NO

S

COOHCH

CH2

C

NOCH2CO

C

O

HN

O

Ni

+

Ni(II)-cefixime complex

Cefixime

Scheme 1 Reactionsequence of the proposedmethod


the time required to complete the reaction. It wasfound that the highest absorbance of the complexwas attained immediately.

Effect of pH

The pH of the complex was measured and foundto be 4.0. The effect of pH on the absorbance ofthe complex was investigated using Na2HPO4–cit-ric acid (pH range 2.2–5) and sodium acetate–HCl(range 3.72–5.57) buffer solutions. The absorbancevalue in the mentioned pH range was found to beless than that obtained without buffer solutionwhen dilution is made with ethanol. Therefore,all absorbance measurements of the complex weremade in ethanol solvent without the involvementof buffer solution.

Effect of the concentration of cefixime

The effect of concentration of cefixime on theabsorbance of the complex (i.e., maximum forma-tion of the complex) was studied at 3.573 μgmL−1

Ni(II) using different volumes of 3.153×10−3Msolution of the reagent. It was observed that thereaction of Ni(II) with cefixime was started onaddition of 0.2 mL of the reagent. Increasing thevolume of the reagent produces a proportional

increase in the absorbance of the product up to1.2 mL and remains constant up to 2.0 mL(Fig. 4). Therefore, 1.6 mL of 3.153×10−3Mcefixime was chosen as the optimal volume ofthe reagent.

Table 1 Optical and regression characteristics of the proposedmethod

Parameters Analytical data

1max (nm) 332 nm

Beer’s law limit (μg mL−1) 0.447–4.019

Molar absorptivity (L mol−1cm−1) 7.31×103

Sandell’s sensitivity 0.008 μg/cm2/0.001absorbance unit

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

Correlation coefficient (r) 0.9999

Variance (So2) 4.51×10−7

LOD (μg mL−1) 0.016

LOQ (μg mL−1) 0.054

±tSa and ±tSb are the confidence limits for intercept and slope,respectivelyaWith respect to A0a+bC, where C is the concentration inmicrograms per milliliter and A is absorbance

Solvent

Acetone DMSO Acetonitrile Ethanol 1,4-dioxan DMF Distilled water

Abs

orba

nce

0.0

0.1

0.2

0.3

0.4

0.5

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

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

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

Abs

orba

nce

0.15

0.20

0.25

0.30

0.35

0.40

0.45

Fig. 4 Effect of the volume of 3.153×10−3M cefixime


Effect of solvent

The effect of solvents such as methanol, acetone,dimethylsulfoxide, acetonitrile, ethanol, 1,4-diox-an, dimethylformamide, and distilled water wasinvestigated at 3.573 μgmL−1 Ni(II) on the ab-sorbance of Ni(II)–cefixime complex. The absor-bance for Ni(II )–cefixime complex in thementioned solvents is shown in Fig. 5. It is clearfrom the figure that the highest absorbance wasobtained in ethanol. Therefore, ethanol was thebest solvent for dilution of the reaction mixtureof Ni(II)–cefixime complex in determination pro-cess of Ni(II) in synthetic mixture and watersamples.

Validation

Linearity, limits of detection, and quantitation

The calibration curve was constructed by plottingabsorbance against initial concentration of nickelion for the proposed spectrophotometric method.Beer’s law was obeyed in the concentration rangeof 0.447–4.019 μgmL−1 with molar absorptivity of7.31×103Lmol−1cm−1. Optical, analytical, and sta-tistical parameters of the experimental data such asregression equation computed from calibrationgraph, correlation coefficient, detection limit, andquantitation limit are summarized in Table 1. Thehigh value of correlation coefficient (0.9999) for

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 0.256

Recovery (%) 99.99 100.10 100.01 100.17 100.18 99.88

aMean for five independent analysis

Concentration of Ni(II), µg mL-1

-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

Abs

orba

nce

0.0

0.1

0.2

0.3

0.4

0.5

Spiked Nominal

Fig. 6 Amount of Ni(II)through standard additiontechnique in synthetic mix-ture sample (2.227 μgmL−1)


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

Precision

The intra-day and inter day precisions were eval-uated by determining the concentration of Ni(II)at lower, middle, and upper concentrations forfive repeated times within the same day and onfive consecutive days, respectively (Table 2). It isclear from the table that percentage recovery andRSD (intra-day and inter-day precisions) were inthe ranges of 99.88–100.18 % and 1.27–0.187 %,respectively. It can been seen from the table thatpercentage recovery and RSD values were preciseand can be used to determine Ni(II) in syntheticmixture and water samples.

Accuracy

The accuracy of the proposed method was inves-tigated by performing recovery experimentsthrough standard addition technique. The absor-bance is recorded for all standard addition solu-tions and plotted as shown in Fig. 6. The resultsof analyses are summarized in Table 3. It is clearfrom the table and the graph that the linearity ofthe regression line for synthetic mixture sample

was good. It is evident from the figure that theconcentration of Ni(II) in synthetic mixture is giv-en by intercept/slope. The ratio of the interceptand the slope of the regression line is subjectedto error (SxE). SxE is calculated from the followingexpression

SxE ¼ Sy=xb

1

nþ y2

b2Pi

xi � xð Þ2

264

3751 2=

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

Robustness

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

Table 3 Test of accuracy in synthetic mixture sample by standard addition technique

Concentration (μg mL−1) Linear regression parameters Recoveryb (%)

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 99.87

a Coefficient of correlationbMean for five independent analyses

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

Metal ions Added as Tolerance limit(μg mL−1)

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

Fe2+ FeSO4·7H2O 1.69

Cr3+ CrCl3·6H2O 1.58


cefixime, 1.2 mL (±0.4 mL) for the determination of Ni(II). The synthetic mixture sample solution containing3.573 μgmL−1 Ni(II) was analyzed five times repeated-ly by the proposed method. Percentage recovery andRSD were found to be 99.98 % and 0.464 %, respec-tively, indicating the robustness of the proposedmethod.

Specificity

The effect of other ions on the determination of3.573 μgmL−1 Ni(II) was studied. For this pur-pose, the varying concentrations of metal ionssuch as Cu(II), Mg(II), Pb(II), Zn(II), Al(III), Fe(II), and Cr(III) with 3.573 μgmL−1 Ni(II) weretaken and the absorbance was recorded to knowthe concentration of Ni(II). Table 4 shows themaximum tolerance limit of various ions studied.The maximum permissible concentration was tak-en, when the absorbance value did not exceed±2 % on addition of cations.

Applicability and evaluation of bias

The applicability of the proposed method for thedetermination of Ni(II) in synthetic mixture samplehas been tested. Results of the proposed methodwere statistically compared with those of referencemethod using point and interval hypothesis tests.The paired t and the F values at 95 % confidencelevel were calculated and found to be less than thetabulated t (2.036 at υ08) and the F values (6.39at υ04,4) at 95 % confidence level (Mendham et

al. 2002). The results are summarized in Table 5.It is evident from the table that there is no signif-icant difference between the performance of theproposed method and the reference method. Therecoveries obtained revealed that the proposed pro-cedure produces accurate results.

The performance of proposed method is also testedin wadi water sample collected from Al Rustaq,Oman. Results of analysis were found in good agree-ment with reference method (Table 6). Thus, the pro-posed method can be used as alternate method for theroutine analysis of Ni(II) in real water samples. TheRSD value (0.464 %) in case of proposed method isless as compared to the reference method (0.688 %)indicating more accurateness and sensitivity of theproposed method.

Conclusion

The proposed method is a simple and accurate for thedetermination of Ni(II) in synthetic mixture and watersamples. The method has advantage of using a com-monly available solvent, i.e., ethanol with the use ofone reagent, i.e., cefixime. The proposed method hasavoided the use of acid, buffer solution, and heating ofreaction mixture and, hence, can be used as an alter-nate method for routine quality control analysis of Ni(II) in soil, vegetable, and pharmaceutical samples.The results obtained by proposed spectrophotometricmethod and flame atomic absorption spectrometry arequantitative and are in close agreement with eachother.

Acknowledgments The authors are grateful to Aligarh MuslimUniversity, Aligarh, India and Ministry of ManPower (HigherCollege of Technology) Muscat, Sultanate of Oman for facilities.The authors wish to express their gratitude to M/s National Phar-maceutical Industries Company, Oman for providing the gift sam-ple of pure cefixime.

Table 5 Significance of testing: point and interval hypothesistests for the determination of Ni(II) in synthetic mixture sampleat 95 % confidence level

Proposedmethod

Referencemethod

Paired tvalueb

Fvaluec

θLd θU

d

Recovery RSDa Recovery RSDa

(%) (%) (%) (%)

99.98 0.46 100.10 0.69 0.33 2.20 0.991 1.012

aMean for five independent analysesb Theoretical t (ν08) and F values (ν04, 4) at 95 % confidencelevel are 2.306 and 6.39, respectivelyc A bias, based on recovery experiments, of ±2 % is acceptable

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

Sample Concentration of Ni(II) (μg mL−1)

Proposed method Reference method

Wadi water 0.699 0.697


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