Communication

Spectrophotometric Determination of U(VI) with Rifampicin in Soil

Samples

Lutfullah,a* Saurabh Sharma,a Nafisur Rahmana and Syed Najmul Hejaz Azmib

aDepartment of Chemistry, Aligarh Muslim University, Aligarh-202002, Uttar Pradesh, IndiabDepartment of Applied Sciences, Chemistry Section, Higher College of Technology, P. O. Box 74,

Al-Khuwair-133, Muscat, Sultanate of Oman

Received August 28, 2010; Accepted January 14, 2011; Published Online February 17, 2011

A validated spectrophotometric method has been developed for the determination of uranyl ion in soil

samples. The method is based on the complexation reaction between uranyl ion and rifampicin in metha-

nol-water medium at room temperature. The method is followed spectrophotometrically by measuring the

absorbance at 375 nm. Under the optimized experimental conditions, Beer’s law is obeyed in the concen-

tration range of 1.35–20.25 �g mL-1 with apparent molar absorptivity and Sandell’s sensitivity of 8.0 × 103

L mol-1cm-1 and 0.042 �g/cm2/0.001 absorbance unit, respectively. The interference of a large number of

anions and cations has been investigated and the optimized conditions developed have been utilized for

the determination of uranium(VI) in soil samples. The three sigma detection limit (n = 9) for uranyl ion

was found to be 0.20 �g mL-1. The proposed method was successfully applied to the determination of ura-

nyl ion in soil samples.

Keywords: Spectrophotometry; Validation; U(VI); Rifampicin; U(VI)-Rifampicin complex; Soil

samples.

INTRODUCTION

Uranium dioxide powder is a starting material for the

manufacture of fuel pellets which are used in nuclear

power reactors. The uranyl ion, UO22+ can be found in soils

and in low pH-water run off in and around nuclear waste

sites and processing facilities. It is reported that U(VI) is

leached out of rocks into water streams. In view of this ex-

traction and determination of U(VI) from surface and

ground water has become a matter of great interest.1,2

The literature citation revealed that there are various

analytical techniques for the estimation of uranium which

include thin layer chromatography,3 gravimetry,4 titrime-

try,5 fluorimetry,6,7 potentiometry,8 polarography,9 X-ray

fluorescence,10 inductively coupled plasma mass spec-

trometry.11 In addition, spectrophotometric methods have

also been employed to determine U(VI) in presence of tho-

rium(IV),12 ore leachates,13 natural waters,14-16 process

streams of a uranium extraction plant17 and soil.18 More-

over, the gravimetric method generally requires the prior

separation of interfering elements whereas multiple steps

are involved in the titrimetric method. Generally, the elec-

troanalytical methods are employed to determine U(VI) on

a routine basis. Spectrophotometry is the technique of

choice in process control due to its simplicity, adaptability

and reasonable sensitivity with significant economical ad-

vantages. Therefore, the methods based on spectropho-

tometry19-21 were published in reputed journals. In addi-

tion, spectrophotometric method has been widely used for

determination of pharmaceuticals in dosage forms22-24 and

metal ion.25 Therefore, there is a need for a simple spectro-

photometric method for the determination of uranium(VI)

in soil samples in the presence of some other metal ions.

The proposed method is based on the complexation of ura-

nyl ion with rifampicin in methanol-water medium at room

temperature (25 ± 1 ºC) to form a yellow colored complex

which absorbs maximally at 375 nm. The reaction condi-

tions of the proposed method are optimized and validated

as per International Conference on Harmonisation (USA).26

EXPERIMENTAL

Apparatus

All absorbance measurements were made on Spec-

tronic 20 D+ spectrophotometer (Milton Roy Company,

USA). An Elico model Li-10 pH meter was used to mea-

Journal of the Chinese Chemical Society, 2011, 58, 127-135 127

sure pH of the solutions.

IR spectra were recorded on a Perkin-Elmer FTIR

1650 spectrophotometer in wave number region 4000-400

cm-1 using KBr pellet technique.

Soil samples were collected from Chemistry Depart-

ment, Aligarh Muslim University, Aligarh, India.

Reagents and standards

All chemicals and solvents used were of analytical re-

agent grade.

� 5 × 10-4 M uranyl nitrate hexahydrate (CAS:

13520-83-7, Fluka Chemie AG, Darmstadt, Germany) was

prepared in distilled water. The apparent purity of uranyl

nitrate solution was checked by spectrophotometric titra-

tion using potassium ferrocyanide.27

� 6.1 × 10-4 M rifampicin (CAS: 13292-46-1, M.W.:

822.94, Merck, USA) was prepared in methanol.

� Buffer solutions ranging from 3.72-5.57 were pre-

pared by mixing varying volumes of 0.2 M acetic acid (9-1

mL) and 0.2 M sodium acetate (1-9 mL) in 10 mL standard

volumetric flask.28

Procedure for the Determination of uranyl ion

Aliquots of 0.1–1.5 mL of 5 × 10-4 M uranyl nitrate

solution (0.1%) were pipetted into a series of 10 mL stan-

dard volumetric flasks. To each flask, 2.0 mL of 6.1 × 10-4

M rifampicin solution was added and diluted to volume

with methanol. The contents of each flask were mixed well

at room temperature (25 ± 1 ºC) and the absorbance was

measured at 375 nm against the reagent blank prepared

similarly within the stability time period of 1d. The concen-

tration of uranyl ion was calculated from the corresponding

regression equation.

Determination of uranyl ion in soil sample

The accuracy of the proposed method for the analysis

of uranyl ion in soil was tested with synthetic mixture of

known composition of uranyl ion plus soil from our local-

ity. Therefore, air-dried soil sample (500 mg) of our local-

ity was treated with 25 mg of uranyl nitrate and decompose

it by heating with 2.0 mL concentrated H2SO4 in a closed

platinum crucible.29 After cooling the content of the cruci-

ble (reaction mixture) was transferred to 50 mL of ice-cold

water and stirred until all the soluble matters had dissolved.

Silica and other insoluble materials were filtered off

through Whatmann No. 42 filter paper (Whatmann Interna-

tional Limited, Kent, UK) in 100 mL standard volumetric

flask. The filter paper was washed with distilled water and

the filtrate was diluted up to the mark with distilled water.

20 mL of this solution was percolated through the column

packed with Amberlite IR 400 because uranium was found

to be completely adsorbed on the resin at acidities below

10-2 M sulphuric acid (pH > 1.5).30 The column was washed

with 0.1 M H2SO4 to remove unadsorbed species. The ura-

nyl ion was eluted with 2 M H2SO4 at a flow rate of 2 mL

per min. The effluent was evaporated and the residue was

dissolved in 10 mL of distilled water. The pH of the solu-

tion was adjusted to 3.9 by the addition of ammonia solu-

tion and the final volume of the solution was maintained to

20 mL. The amount of U(VI) was also estimated by the

reference method.12

Procedure for Reference Method12

Aliquots (0.125-1.5 mL) of 1.992 × 10-3 M uranyl ni-

trate were pipetted into a series of 25 mL standard volumet-

ric flasks. To each flask, 10 mL of 0.2 M HCl, 2.0 mL of

10% SnCl2.2H2O in 1.16 M HCl and 7 mL of 6.57 M

NH4SCN were added and diluted up to the mark with dis-

tilled water. The absorbance was measured at 365 nm

against the reagent blank prepared similarly and the amount

of the uranyl ion in a given sample was obtained either

from the calibration graph or the regression equation.

Determination of stoichiometry

The reaction stoichiometry of the proposed method

was studied by Job’s method of continuous variations.31

For this purpose, different volumes (0, 0.2, 0.4, 0.6, 0.8,

1.0, 1.2, 1.4, 1.6, 1.8, 2.0 mL) of 1.1 × 10-3 M uranyl nitrate

was added with different volumes (2.0, 1.8, 1.6, 1.4, 1.2,

1.0, 0.8, 0.6, 0.4, 0.2, 0 mL) of 1.1 × 10-3 M rifampicin and

diluted with methanol in 10 mL standard volumetric flask.

The absorbance was recorded at 375 nm and plotted against

the mole fraction of uranyl ion.

Validation

The proposed method has been validated for specific-

ity, precision, accuracy, linearity, robustness and evalua-

tion of bias.

The selectivity was ascertained by determining 18.9

�g mL-1 uranyl ion in the presence of metal ions such as

Pb2+, Ni2+, Cr3+, Zr4+, Ca2+ and Ba2+ which are commonly

found in soils.

The linearity was assessed by analyzing the uranyl

ion content at nine concentration levels: 1.35, 2.70, 5.40,

6.75, 10.8, 13.5, 17.55, 18.9 and 20.25 µg mL-1. Each con-

centration level was independently analyzed for five times.

The absorbance was plotted against initial concentration of

uranyl ion. The regression characteristics were calculated

using OriginPro 6.1 Software. Limits of detection and

quantitation were calculated.32

128 J. Chin. Chem. Soc., Vol. 58, No. 2, 2011 Lutfullah et al.

The intra-day and inter-day (n = 5) precisions were

evaluated at three concentrations levels (5.4, 10.8 and 18.9

µg mL-1). Five sample solutions of each concentration were

analyzed within one day (intra-day precision) and in five

consecutive days (inter day precession).

The recovery of uranyl ion from soil samples was es-

timated by the standard addition method. For this purpose,

5 mL (or 10 mL) of uranyl sample solution obtained by sep-

aration on a column loaded with Amberlite IR 400 was

spiked with 0, 1, 2, 3 and 4 mL of reference standard solu-

tion of uranyl nitrate (5 × 10-4 M) in a 100 mL standard vol-

umetric flask and the solution was diluted up to the mark

with methanol. The absorbance for all these solutions was

recorded at 375 nm and the corresponding regression line

was evaluated in order to get slope and intercept using

OriginPro 6.1 Software. Each level was repeated 5 times.

The concentration of uranyl ion in the sample solution was

calculated by the ratio of the intercept and the slope of the

regression line. The error in the concentration was evalu-

ated using the following expression:33

SxE =S

b

y / x 12

2 2

1 2

n

y

b x xi

i

��

�

�

���

�

� ( )

/

where SxE is the standard deviation of the extrapolated

x-value (xE).

The robustness was evaluated by analyzing the con-

tent of uranyl ion in soil sample. A soil sample solution

containing 16.20 µg mL-1 of uranyl ion was analyzed five

times using the proposed method. Mean percentage recov-

ery ± relative standard deviation (RSD) was calculated.

The bias34 has been evaluated to compare recovery

results of the proposed method with those of the reference

method at 95% confidence level using the following qua-

dratic equation.

�2 �x S t np tab1

2 2 2

1� / � 2�x x

1 2

+ �x S t np tab2

2 2 2

20� �/

where Sp is the pooled standard deviation and ttab is the tab-

ulated one sided t-value with n1 + n2 - 2 degrees of freedom

at the specified level of significance.

RESULTS AND DISCUSSION

The uranyl ion is known for its ability to form com-

plexes with a variety of ligands such as H2O, Cl�, NO3�,

acetic acid, lactic acid and oxalic acid.35-37 Rifampicin con-

tains more than one electron centers and assumed to be an

excellent ligand for complexation reaction. In the present

study, uranyl ion reacts with rifampicin in methanol-water

medium immediately at 25 ± 1 oC resulting in the formation

of yellow colored complex which absorbed maximally at

375 nm. The measurement of absorbance at 375 nm against

reagent blank lead to the development of a spectrophoto-

metric method for determination of U(VI). Appropriate

volumes of aqueous solution of 5.0 × 10-4 M uranyl nitrate

hexadydrate corresponding to 13.5 �g to 202.5 �g on dilu-

tion with methanol in 10 mL volumetric flask did not

show any absorption at 375 nm. The methanolic solution of

rifampicin absorbed maximally at 490 nm. Therefore, the

measurement of absorbance of the complex at 375 nm

against the reagent blank can be used successfully for de-

termination of uranyl ion without any interference from the

reagent. The complex was stable up to 1d.

Stoichiometry

The composition of the yellow complex between ura-

nyl ion and rifampicin was determined by Job’s method of

continuous variations using identical molar concentrations

of uranyl ion and rifampicin (1.10 × 10-3 M each). The

absorbance was recorded at 375 nm and plotted against the

mole fraction of uranyl nitrate (Fig. 1). It is apparent from

the figure that the combining molar ratio between uranyl

Determination of U(VI) J. Chin. Chem. Soc., Vol. 58, No. 2, 2011 129

Fig. 1. Job’s method of continuous variations of uranyl

nitrate-rifampicin complex.

ion and rifampicin is 1:1.

The I.R. spectra of free rifampicin and U(VI)-rifam-

picin complex are shown in Fig. 2a and b, respectively.

Rifampicin has –OH and –C=O potential sites for coordi-

nation with metal ions. Comparison of IR spectrum of the

complex with those of free rifampicin indicates that pheno-

lic �(C-OH) band appears at 2364 cm-1 in the free rifam-

picin while the complex does not show this band suggest-

ing that there is coordination of uranyl ion at this potential

site. The carbonyl band, �(C=O) in the free rifampicin ap-

pears at 1746 cm-1 while this band in the U(VI)-rifampicin

complex is shifted to 1719 cm-1 indicating that the uranyl

ion is chelated through coordination of oxygen atoms of the

keto group (dihydrofuranone) and the neighboring pheno-

lic group of rifampicin molecule. The phenolic O-H at car-

bon 9 in rifampicin is most deshielded,38 thus deprotonated

and followed by chelate formation through oxygen atoms

of keto and phenolic C-O groups. The characteristic fre-

quency of UO2

2� ion is seen in the complex at 901 cm-1

whereas this frequency is not present in free rifampicin.

The U(VI)-O stretching vibration occurs at 404 cm-1.39

Therefore, on the basis of these experimental findings, a re-

action sequence of the proposed method is shown in

Scheme I.

The apparent formation constant (Kf) for the complex

between uranyl ion and rifampicin was calculated using the

following equation:40

K f =( / )A A C

CA

AC C

A

A

obs extp

M

obs

extp

L

obs��

���

�

���

�

���

�

�extp

C�

���

�

���

�

���

�

where Aobs and Aextp are observed and extrapolated absorb-

ance values for the complex, respectively. CM and CL are

the initial concentration of U(VI) and rifampicin; 1.1 × 10-4

M. Kf of the complex is found to be 7.587 × 105. The appar-

ent Gibbs free energy (�G�) was calculated using �G� =

-2.303 RT log Kf and found to be –33.55 kJ mol-1 confirm-

130 J. Chin. Chem. Soc., Vol. 58, No. 2, 2011 Lutfullah et al.

Fig. 2. IR spectra of (a) free rifampicin and (b) U(VI)-rifampicin complex.

ing the feasibility of the reaction.

Optimization of Variables

The optimization of variables was investigated by

testing reaction time, concentration of rifampicin and sol-

vents.

The effect of reaction time on the absorbance of

U(VI)-rifampicin complex and its stability was investi-

gated. The U(VI)-rifampicin complex got stabilized imme-

diately at 25 ± 1 °C after mixing rifampicin and methanol as

solvent. Complex remained stable for 1 d.

The concentration of rifampicin was optimized via a

series of experiments for the maximum absorbance of the

uranyl-rifampicin complex. The effect of the volume of 6.1

× 10-4 M rifampicin was studied in the range of 0.2-2.0 mL.

The results are shown in Fig. 3. It is clear from the figure

that the maximum absorbance was obtained with 1.6 mL of

6.1 × 10-4 M rifampicin; above this volume up to 2.0 mL,

the absorbance remained constant. Therefore, 1.8 mL of

6.1 × 10-4 M rifampicin was used in all measurements.

The effect of solvents such as methanol, acetone,

acetonitrile, dimethyl sulphoxide (DMSO) and 1,4-dioxan

was tested at 20.25 �g mL-1 U(VI) on the absorbance of

uranyl-rifampicin complex. It was observed that the maxi-

mum absorbance was obtained in methanol (Fig. 4). There-

fore, methanol is preferred to be the best solvent for dilu-

tion of the reaction mixture of the complex.

The pH of the complex was measured and found to be

3.9. The effect of pH on the absorbance of the complex was

investigated using sodium acetate-acetic acid buffer solu-

tion in the pH range of 3.72-5.57. A constant absorbance

was obtained in the pH range of 3.72-5.57, but the absorb-

ance of the complex in this pH range was found to be less

Determination of U(VI) J. Chin. Chem. Soc., Vol. 58, No. 2, 2011 131

Scheme I Reaction sequence of the proposed method

Fig. 3. Effect of the volume of 6.1 × 10-4 M rifampicin

with 20.25 �g mL-1 uranyl ion on the absorb-

ance of the complex.

Fig. 4. Effect of solvent on the absorbance of the col-

oured complex.

than that obtained without buffer solution using methanol

as the diluting solvent in the reaction mixture. Therefore,

all absorbance measurements were made in methanol sol-

vent without the use of buffer solution.

Validation

The effect of potential interfering ions on the determi-

nation of U(VI) was investigated by adding known concen-

trations of each ion in a solution containing analyte and

then determining the latter. The results are summarized in

Table 1. The tolerated amounts of each ion were the con-

centration values tested that caused less than ± 2% the

absorbance alteration. These results showed that the pro-

posed method is selective for the determination of uranyl

ion in the presence of Pb2+, Ni2+, Cr3+, Zr4+, Ca2+ and Ba2+.

However, the method was not selective in the presence of

Cu2+, Mn2+, Fe3+, Zn2+, Cd2+, Mg2+ and Sr2+. The interfer-

ence of these ions can be eliminated by passing the sample

solution through a column packed with Amberlite IR 400

resin.

Under the optimized experimental conditions, the

absorbance against the initial concentration of uranyl ion

was plotted (Fig. 5) and found to be linear over the concen-

tration range 1.350-20.25 µg mL-1 with apparent molar ab-

sorptivity and Sandell’s sensitivity of 8.0 × 103 L mol-1cm-1

and 0.042 �g/cm2/0.001 absorbance unit, respectively. The

calibration data (n = 9) were treated statistically to evaluate

intercept (a), slope (b), coefficient of correlation (r), confi-

dence limits of intercept (± tSa) and slope (± tSb) at 95%

confidence level and n-2 degrees of freedom, variance and

limits of detection and quantitation. The results are summa-

rized in Table 2. The high value of correlation coefficient

(0.9999) for the proposed method indicated excellent lin-

earity. The low value of variance (2.1 × 10-4 �g mL-1) of

calibration line pointed towards the higher reproducibility

of the proposed method.

The intra-day and inter day precisions of the pro-

posed method were evaluated at three concentration levels:

5.4, 10.8 and 16.2 �g mL-1 within the same day and on five

consecutive days, respectively. The results of the analysis

are summarized in Table 3. It is evident from the table that

the percent relative error and relative standard deviation

were in the range of 0.06–0.74% and 0.44–2.57%, respec-

tively.

The accuracy of the proposed method was investi-

gated by performing recovery experiments through stan-

dard addition method. The results of the recovery experi-

ments are summarized in Table 4 and Fig. 6. It is evident

from the table that the recovery is satisfactory (100.31-

10.43%) and the most attractive feature of the method is its

relative freedom from various non targeted cations. The re-

covery experiments have confirmed that the proposed

method is accurate.

The robustness of the proposed method was critically

examined by determining uranyl ion contents (20.25 �g

mL-1) in synthetic environmental soil sample under delib-

erate small changes in experimental conditions. The results

showed that the mean % recovery ± RSD was found to be

100.18 ± 0.44 that suggested the robustness of the proposed

method.

The proposed method has been successfully applied

to the determination of uranyl ion in synthetic soil samples

containing U(VI). The results obtained by the proposed

132 J. Chin. Chem. Soc., Vol. 58, No. 2, 2011 Lutfullah et al.

Table 1. Effect of various metal ions on the determination of

18.9 �g mL–1 uranyl ion

Metal ions Added as Tolerance limit (mg mL–1)

Pb2+ Pb(NO3)2 0.662

Zr4+ ZrOCl2.8H2O 0.580

Cr2+ CrCl3.6H2O 0.534

Ca2+ Ca(NO3)2.4H2O 0.155

Ni2+ NiCl2.6H2O 0.095

Ba2+ Ba(NO3)2 0.052

Fig. 5. Calibration graph for the determination of

U(VI) in soil samples.

Determination of U(VI) J. Chin. Chem. Soc., Vol. 58, No. 2, 2011 133

Table 2. Optical and regression characteristics of the proposed and reference methods

Parameters Proposed method Reference method

Wavelength (nm) 375 365

Beer’s law limit (�g mL-1) 1.35 – 20.25 5.0-60

Molar absorptivity (L mol-1cm-1 ) 8.0 × 103 6.25 × 103

Sandell’s sensitivity 0.042 �g/cm2/0.001 absorbance unit -

Linear regression equation A = 1.39 × 10-4 + 2.37 �10-2 C A = 7.153 × 10-4 + 7.48 × 10-3 C

±t Sa 2.16 × 10-3 4.60 × 10-3

±t Sb 1.70 × 10-4 1.28 × 10-4

Correlation coefficient (r ) 0.9999 0.9998

Variance (S02) of calibration line 2.10 × 10-6 6.20 × 10-6

Detection limit (�g mL-1 ) 0.20 1.10

Quantitation limit (�g mL-1) 0.61 3.33

±t Sa and ±t Sb are confidence limits for intercept and slope, respectively.

Table 3. Test of precision of the proposed method

Parameters Intra day assay Inter day assay

Concentration taken (�g mL-1) 5.40 10.80 16.20 5.40 10.80 16.20

Concentration found (�g mL-1) 5.41 10.79 16.23 5.36 10.87 16.19

Standard deviationa (�g mL-1) 0.14 0.12 0.07 0.14 0.17 0.14

Relative error (%) 0.19 0.09 0.19 0.74 0.65 0.06

Relative standard deviation (%) 2.57 1.12 0.44 2.67 1.58 0.87

Standard analytical error (%) 0.06 0.05 0.03 0.06 0.08 0.06

Confidence limitb 0.17 0.15 0.09 0.17 0.21 0.18

a Mean for five independent determinations.b Confidence limit at 95% confidence level and four degrees of freedom (t = 2.776).

Table 4. Test of accuracy of the proposed method by standard addition method

Concentration (�g mL-1) Coefficients of regression lineSoil 1

Standard NominalError

Intercept slope ra

Recoveryb

(%)

6.75 0, 1.35, 2.7, 4.05, 5.40 6.77 0.05 0.16 2.36 � 10-2 0.99997 100.31

13.5 0, 1.35, 2.7, 4.05, 5.40 13.55 0.91 0.32 2.36 � 10-2 0.99987 100.43

a Coefficient of correlation.b Mean for five independent analyses.

Table 5. Applicability of the proposed method for the determination of uranyl ion in soil samples and the

comparison of the results with the reference method at 95% confidence level

Proposed method Reference method

Recovery RSDa Recovery RSDaSample of

uranyl ion(%) (%) (%) (%)

Paired

t- & F valuesb �Lc �U

c

Soil 1 100.18 0.44 100.09 0.83 t = 1.339

F = 3.503

0.981 1.016

Soil 2 99.94 0.43 100.09 0.83 t = 2.248

F = 3.664

0.989 1.014

a Mean for 5 independent analyses.b Theoretical t (� = 8) and F-values (� = 4, 4) at 95% confidence level are 2.306 and 6.39, respectively.c A bias, based on recovery experiments, of � 2% is acceptable.

method were compared with those obtained by the refer-

ence method12 using point and interval hypothesis tests in

terms of Student’s paired t-test, the variance ratio F-test,

lower (�L) and upper bias (�U) limits at 95% confidence

level. The results are summarized in Table 5. The calcu-

lated paired t- and F-values are less than the tabulated t- and

F-values at 95% confidence level41 suggesting that there is

no significant difference between the performance of the

proposed method and the reference method. This con-

firmed that the proposed method is accurate, precise and re-

producible. The interval hypothesis test has confirmed that

the true bias (�L and �U) for the analysis of U(VI) in soil

samples is smaller than ±2.0%; indicating that there is no

significant difference between the performances of the

methods compared.

The performance of the proposed spectrophotometric

method was compared with other methods (Table 6). It can

be seen from the table that TLC method is time consuming

and tedious. The precision is somewhat poor. ICP-MS

method is sensitive but expensive enough and requires

solid phase extraction of U(VI) before analysis. The preci-

sion of the proposed spectrophotometric method (RSD

0.44-2.67%) as compared to other spectrophotometric

methods (RSD 0.91-8.21%) is quite satisfactory. The pro-

posed method is simple, precise and accurate, thus can be

used as alternate method for the determination of U(VI) in

soil samples.

CONCLUSIONS

The proposed method has the advantage of being sim-

ple and accurate for routine analysis of uranyl ion in soil

samples. In addition, the proposed method is utilizing one

reagent with less expensive solvent (methanol) for the de-

termination process. The proposed method has avoided the

use of acid, buffer solution and heating of reaction mixture.

In addition the method is useful due to high tolerance limits

from cations and anions. Hence, the proposed method is an

effective method for the quantitative analysis of uranyl ion

in soil samples.

134 J. Chin. Chem. Soc., Vol. 58, No. 2, 2011 Lutfullah et al.

Fig. 6. Recovery graph for uranyl ion through standard

addition method: (a) 6.75 and (b) 13.5 �g mL-1

uranyl ion.

Table 6. Comparison of the proposed spectrophotometric method with other methods for the determination of uranyl ion

Reagents�max

(nm)

Beer’s law limit

(�g mL-1)RSD (%) Analysis time (min) References

Spectrophotometry

p-Carboxychlorophosphonazo 714 4-12 0.91-8.21 immediately [14]

SnCl2.H2O and NH4SCN 365 5-60 - immediately [12]a

Chromazurol S and Cetylpyridnium

bromide

625 0-100 � 3 15 [16]

Rifampicin 375 1.35-20.25 0.44-2.67 immediately at 25 ± 1 ºC This work

TLC

O-xylene: methyl ethyl ketone:

N,N�-dimethylformamide: Iso-

propyldithiophosphotic acid

254 2.5-30 - 60 [3]

ICP-MS

Duolite XAD761, 9-phenyl-3-fluorone - - � 2.3 30 [11]

a Reference method.

ACKNOWLEDGEMENT

The authors are grateful to Aligarh Muslim Univer-

sity, Aligarh, India and Ministry of ManPower (Higher

College of Technology, Muscat) Sultanate of Oman for

facilities.

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