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. 2018 May 22;12(6):773–780. doi: 10.1049/iet-nbt.2018.0018

CL sensitisation of tris‐(bipyridyl) ruthenium (II) – cerium (IV) reaction system by AgNPs for determination of GFX

Saikh Mohammad Wabaidur 1,✉, Seikh M Alam 2
PMCID: PMC8676307  PMID: 30104451

Abstract

The flow injection combined with tris‐(bipyridyl) ruthenium (II)‐cerium (IV) chemiluminescence (CL) method based on the sensitisation of silver nanoparticles (AgNPs) has been established for the quantitative analysis of gatifloxacin (GFX). AgNPs were synthesised using the reaction between ammonia gas and silver nitrate solution and was used to increase the CL intensity of the proposed system. The enhancement of CL intensity was linear with the concentration of GFX added. Effects of different experimental parameters were studied. Under the optimal conditions, the linear relationship was established between the concentration range of 1.4 × 10−10 –4.5 × 10−8 M, with the correlation coefficient (r2) 02E9999. The limit of detection was found to be 4.6 × 10−11 M. The relative standard deviation obtained was 3.2% for six replicate measurements of GFX (1.2 × 10−9 M). The proposed CL method was applied to the commercial drug and the result was in agreement with the labelled amount. The technique was further adopted to the analysis of GFX in spiked urine samples. Negligible interference was found (variation in CL intensity <5%) from a few common foreign excipients applied in preparation of pharmaceutical drug. The comparative results with a few reported methods indicates that the proposed method is more sensitive than other methods..

Inspec keywords: chemiluminescence, chemical sensors, optical sensors, silver, nanoparticles, nanosensors, transmission electron microscopy, measurement standards

Other keywords: CL sensitisation, tris‐(bipyridyl) ruthenium (II)–cerium (IV) reaction system, NP, GFX determination, flow injection, chemiluminescence sensitisation, nanoparticle, gatifloxacin determination, morphological characterisation, ultraviolet spectrometry, transmission electron microscopy imaging, spiked urine sample, interference, pharmaceutical drug, Ag

1 Introduction

Gatifloxacin (GFX) is a fluoroquinolone drug and chemically recognised as 1‐cyclopropyl‐6‐fluoro‐8‐methoxy‐7‐(3‐methylpiperazin‐1‐yl)‐4‐oxo‐quinoline‐3‐carboxylic acid. It is normally used as an antibacterial agent to recover various clinical infections such as pneumonia, chronic bronchitis, urinary tract infections and acute sinusitis [1, 2]. It has proven positive activity for curing common pathogens of respiratory, namely Haemophilus influenzae, Streptococcus pneumoniae, Chlamydia pneumoniae, Mycoplasma pneumoniae, Legionella and Moraxella catarrhalis [3]. Similar to other fluoroquinolones, GFX has shown dual action mechanism to inhibit both topoisomerase IV and bacterial DNA gyrase. This drug is metabolically very stable and once swallowed more than 80% of the drug is excreted in the urine without any changes. However, their applications in the curing of adults for an extensive number of infectious diseases are conducted in many countries. Thus, its extensive pharmacological and clinical uses demand rapid and sensitive analytical methods for its determination in pharmaceutical and as well as in biological samples.

Different analytical techniques have been described by the researchers for determination of GFX including spectrophotometric [4, 5, 6], first‐ and second‐derivative fluorimetric [7], high‐performance liquid chromatography (HPLC) with photodiode array and fluorescence detection [8, 9, 10, 11], thin‐layer chromatography [12], and chemiluminescence (CL) [13]. Nonetheless, no such methods reported for the quantitation of GFX using the enhancement effect of nanoparticles (NPs). The current paper reports the application of silver NPs (AgNPs) for enhancing the CL intensity of tris‐(2,2′‐bipyridyl) ruthenium (II)‐cerium (IV) [Ru(bipy)3 2+ –Ce(IV)] system due to their useful catalytic properties [14, 15, 16, 17, 18, 19]. It was found that the application of AgNP in the presence of GFX to the Ru(bipy)3 2+ –Ce(IV) reaction system, the weak CL signal of has increased by several folds. The proposed AgNP‐enhanced CL method was successfully applied to quantitate GFX in commercial tablet formulation and biological sample.

2 Experimental results

2.1 Instrumentations

The schematic diagram of the CL flow system used for the proposed research is revealed in Fig. 1. Peristaltic pumps P1 and P2 (Model 404, Ismatec, Zurich, Switzerland) were employed to carry all solutions to the flow cell. Among the pumps, pump P1 was responsible for delivering the solution of AgNP, which was incorporated with sample solution in a six‐way injection valve of Model 7125 (Rheodyne, CA, USA). On the other hand, pump P2 was employed to carry all other concerning CL reagents with a uniform flow rate in each line. Polytetrafluoroethylene tubing of internal diameter 0.8 mm was utilised throughout the flow injection manifold to convey all reagents. The fluorimetric experiments were carried out in a spectrofluorimeter of Model F111, (SPEX industries, Edison, NJ, USA) equipped with a 1.0 mm i.d. and 20 mm total diameter coiled glass flow cell. The software, Spex DM 3000 was used for all chemiluminogenic data procurement and analysis of GFX. Since the light is produced by the proposed CL reaction system, the spectrofluorimeter light source was kept turned off and the emission monochromator slit width was set to 0.25 mm. The photomultiplier tube of Model R 928 (Hamamatsu, Japan) was used as the high‐voltage source and was set to 950 V.

Fig. 1.

Fig. 1

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Schematic diagram of the FIA‐CL manifold. P1, P2 : peristaltic pumps and T1, T2 : Y‐pieces

2.2 Chemicals

All chemicals used during the experiments were of analytical chemical grade and applied without additional cleansing. Distilled deionised (DI) water was produced from MilliQ Water System (Millipore, USA) and used throughout for sample preparation and dilution purposes. The stock standard of GFX was purchased from Sigma‐Aldrich (St. Louis, USA). Stock solutions of GFX of concentration 1.0 × 10−3 M were prepared and further diluted in working concentrations range with DI water. Ru(bipy)3 2+ stock solution of 1.0 × 10−3 M was prepared by dissolving proper amount of tris(2,2′‐bipyridyl) dichloro‐ruthenium(II) (Sigma‐Aldrich, St. Louis, USA) powder in DI water. Ce(IV) solutions (1.0 × 10−3 M) was prepared using proper amount of cerium (IV) sulphate (Sigma‐Aldrich, St. Louis, USA) in proper volumes of sulphuric acid (H2 SO4) (Duksan, Ansan, Korea) and dilutes up to the mark with distilled water in 100 ml volumetric flask. All the working solutions were freshly prepared before analysis. Ammonia solution was supplied by Sigma chemicals (St. Louis, USA), while Ag nitrate and sodium citrate were supplied by Sigma Corporation.

2.3 Drug and urine sample preparations

For the drug solutions preparation, the average tablet weights were measured from a set of ten tablets randomly. Then, a certain portion of a homogeneously crushed tablet containing 200 mg of GFX (Gatizone) was transferred into a measuring flask containing DI water followed by ultrasonication for 19–20 min and filled with DI water up to 500 ml mark. The solution was protected from light to avoid any degradation. Then, the sample solution was filtered with the Millipore membrane filter and further diluted according to the requirements. On the other hand, drug‐free urine samples were obtained from healthy volunteers of definite age groups and 25 ml aliquots of collected urine samples were spiked immediately with GFX at different concentration levels for the recovery studies. From these prepared pools, half millilitre aliquots of each spiked urine samples were poured to Eppendorf and kept at minus 18°C till the analysis was performed.

2.4 Preparation of AgNPs

AgNPs were prepared adopting the previously reported technique with a few modifications [20]. The NPs were synthesised using the well‐reputed aqueous–gaseous phase chemical reaction between ammonia gas and Ag nitrate solution. Two 100–150 ml of two neck round bottom flask was taken, and in one flask 50 ml stock solution of Ag nitrate (1.0 × 10−3 M) was added and the solution was put into a hot oil bath. Then, the oil bath was kept on a magnetic stirrer. The another flask was filled with 50 ml of 1.0 M ammonia solution and kept in a water bath without applying any external temperature. Both flasks were then connected through a glass tube, which is responsible to pass the volatilised and diffused ammonia gas slowly into another flask that contains Ag nitrate solution and the mixing allows the reaction to occur between ammonia gas and Ag nitrate solution. The whole system was kept under the exposure of light of a 500 W daylight lamp. Then, another five steps were performed for the synthesis of AgNPs. In the very first step, the Ag nitrate solution holding flask was put into a ∼70°C oil bath and continuously kept under stirring for at least 6 h. Then in the next step, the flask was allowed to settle down for 6 h without any stirring and heating. After this, the first step was repeated for 5 h under continuous stirring and heating. Then again the flask was allowed for settling down by repeating step 2 and finally the first step was again repeated for 3 h.

2.5 Analytical procedures

The schematic representation of the flow injection analysis (FIA) system was comprised of a three‐channel manifold and two peristaltic pumps P1 and P2. For the proposed CL system, before the CL measurement, the Ru(II) stream was mixed with Ce(IV) solution stream in a three‐way ‘T1’ connector with the help of pump P2. On the other hand, pump P1 helps to deliver AgNP solution, which is further mixed with sample solution of GFX through a specially designed injection valve. Then, both streams were completely merged in the second connector (T2) and mixed with each other and flowed to the sample cell of the fluorimeter and resulting in an increase of the CL peak intensity. The increase in the CL intensity due to the addition of AgNPs was proportional to the sample concentrations. The FIA system has schematically shown in Fig. 1.

3 Results and discussion

3.1 Morphology and ultraviolet (UV) spectral characteristics of AgNPs

The morphology of the synthesised AgNPs was characterised using transmission electron microscopy (TEM) and it was found that the average size of the NPs is about 14 nm (Fig. 2 a). The formation of NPs was further confirmed from the UV–visible (vis) absorption spectrum of the obtained AgNPs. The absorption spectra showed a peak near 380 nm, which is corresponding to the characteristic wavelength of Ag absorbance (Fig. 2 b). On addition, the narrow absorption peak shape was suggested a high level of monodispersity of the NPs [21, 22].

Fig. 2.

Fig. 2

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Morphology and UV spectral characteristics of AgNPs

(a) TEM image of AgNPs, (b) UV–vis spectra of the AgNPs

3.2 Optimisation of experimental parameters

3.2.1 Effects of the oxidising agents

To get the best oxidising agents, the influence of the various oxidising agents on the CL intensity was investigated. A total of five different oxidising agents were tested including potassium permanganate (KMnO4), cerium(IV) sulphate [Ce(SO4)2], potassium bromate, potassium iodate and potassium ferricyanide [K3 Fe(CN)6]. For this, 1.0 × 10−4 M solutions of each oxidant were prepared in 1.0 × 10−2 M H2 SO4, while the solution of K3 Fe(CN)6 was prepared in 0.1 M solution of sodium hydroxide. The comparative results of oxidising effects are shown in Fig. 3. As shown in Fig. 3, it was obvious from the results that the CL intensity is strongly dependent on the types of oxidising agents. It was obvious from this figure that the highest CL intensity was obtained once we use Ce(SO4)2 as oxidising agents and it was used for the whole experiment.

Fig. 3.

Fig. 3

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Influence of oxidising agents on Ru(bipy)3 2+ –Ce(IV) CL intensity

3.2.2 Effects of inorganic acids

The influence of acid media was studied. For the same, 1.0 × 10−4 M Ce(SO4)2 in 1.0 × 10−2 M of each of the following acids: hydrochloric acid, phosphoric acid, nitric acid and H2 SO4 were prepared. It was noted that H2 SO4 was the acid to provide the highest CL intensity to the Ru(bipy)3 2+ –Ce(IV) CL system. This may be probably due to that Ce(SO4)2 in H2 SO4 gives enough oxidising power to oxidise Ru(bipy)3 2+ to Ru(bipy)3 3+ and permits the CL reaction to be favoured.

3.2.3 Ru(bipy)3 2+ concentration

It is well known that in the Ru(bipy)3 2+ ‐based CL system, the light emission is generated from the excited ruthenium species [Ru(bipy)3 2+]* and produces due to the reaction between Ru(bipy)3 3+ and the reluctant, which is normally the analytes and is considered as luminophore of the system. To find out the optimum concentration of this luminophore used for the chemiluminogenic determination of GFX, various concentrations of Ru(bipy)3 3+ on CL intensity was investigated. For this, the concentration of GFX was fixed at 1 × 10−4 M and the concentration of Ru(bipy)3 2+ was varied from 4.0 × 10−4 to 1.5 × 10−2 M by keeping the concentration of the other solutions constant. The results obtained are shown in Fig. 4. It is clear from the graph that the CL intensity started decreasing above the concentration of 4.0 × 10−3 M of Ru(bipy)3 2+. Hence this concentration was selected as optimum Ru(bipy)3 2+ concentration for the experiment. The increase of CL response with higher concentration of Ru(bipy)3 2+ might be due to the rapid CL reaction as it increases the reagent to analytes ratio [23]. On the other hand, the reason of the decreased CL response of the system after certain concentration of Ru(bipy)3 2+ might be due to the presence of higher amount of chloride counter anion.

Fig. 4.

Fig. 4

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Dependence of Ru(bipy)3 2+ concentration on the CL intensity for the quantitative analysis of 1.0 × 10−4 M GFX

3.2.4 Ce(IV) concentration

Ce(SO4)2 was utilised as the oxidant in this CL system and its concentration on the system played an important role as well. To obtain the optimal Ce(IV) concentration for the proposed chemiluminogenic reaction, the concentration of Ce(IV) was varied in the range of 5.0 × 10−5 –1 × 10−3 M. The effects of the Ce(IV) concentration on the CL intensity are shown in Fig. 5. The graph indicates that, after the Ce(IV) concentration exceeds 4.8 × 10−4 M, the CL response decreases. At the higher concentration of Ce(IV), the absorption of light emission by the coloured Ce(IV) solution and the scattered emitted light produced from the hydrolysis product of Ce(IV) are increased and might be responsible for decreasing the CL intensity [24]. Hence, 4.8 × 10−4 M Ce(IV) was considered as optimum for the determination of GFX.

Fig. 5.

Fig. 5

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Influence of Ce(IV) concentration on the CL intensity for the quantitative analysis of 1.0 × 10−4 M GFX

3.2.5 H2 SO4 concentration

Like other experimental parameters, the concentration of H2 SO4 has also played a significant role in the CL reaction involving Ce(IV). Thus, to find the optimal H2 SO4 concentration for the determination of GFX, the influence of H2 SO4 concentration on the proposed CL system was investigated in the concentration range of 1.0 × 10−4 –2.0 × 10−2 M. The effects of the concentrations of H2 SO4 on CL system are shown in Fig. 6. The maximum intensity of the proposed CL system has reached at 7.0 × 10−2 M H2 SO4 concentration. After this level of the H2 SO4 concentration, the light intensity was decreased which indicates that at 7.0 × 10−2 M concentration, the quantities of the reactive components of the oxidants in the solution has reached to a maximum and started to decrease the CL signal. Hence, 7.0 × 10−2 M H2 SO4 was used for subsequent studies.

Fig. 6.

Fig. 6

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Dependence of H2 SO4 concentration on the CL peak intensity for the quantitative determination of 1.0 × 10−4 M GFX

3.2.6 Flow rate

The effect of flow rate is another important parameter in CL detection. Since in this method, the time consumed to transfer the reactive species into the sample cell has played a critical role to collect the maximum emitted light [25]. Hence, the flow rates between 1.0 and 4.5 ml/min were studied, while equal flow rates were maintained in each channel of both pumps. The maximum CL response was recorded once the flow rate was 2.0 ml min−1 and no notable changes of the CL response were found further increasing the flow rate. On addition, the higher flow increases the reagent consumption and distorts the peak shape as well as affects the measurement rate. Therefore, 2.0 ml min−1 in each channel of the FIA manifold was recommended fixed considering to achieve better accuracy and low cost in the use of chemicals for the proposed method.

3.2.7 Optimisation of AgNP concentration

The influence of the AgNP concentration on the CL signal was also optimised for the studied system. The CL response was detected maximum when the concentration of applied NPs was 6.0 × 10−4 M and this concentration was chosen throughout the studies. The experimental results are shown in Fig. 7. Above this concentration, the response had started to decrease. Since when the concentration of AgNP is higher than optimum concentration, the interactions among particles become strong and the CL energy can be transferred among particles which are situated in small distances [26].

Fig. 7.

Fig. 7

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Investigation of AgNP concentration on the CL intensity for the quantitative analysis of 1.0 × 10−4 M GFX

3.3 CL spectra of the system

The CL response of Ru(bipy)3 2+ ‐Ce(IV) reaction catalysed by AgNP in the presence of GFX is shown in Fig. 8. The spectra clearly indicates that GFX has strengthening effect on Ru(bipy)3 2+ ‐Ce(IV) system, but the increment was not enough for its efficient and sensitive quantitative analysis. However, the introduction of AgNPs to this system further enhanced the CL intensity and the value of enhancement was directly proportional to the concentration of the target substance. The enhancement had provided the method better sensitivity for the sensitive determination of GFX. It is reported that, Ag ions have the ability to catalyse the oxidation of various carboxylic acids with cerium (IV) by forming 1:1 complexes with the substrate [27]. Therefore, it was considered that the enhancement of the CL from reactions between, Ru (II) and Ce (IV) could be due to the catalytic effect of Ag ions on the oxidation of Ru (II) with Ce (IV).

Fig. 8.

Fig. 8

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CL spectra for the quantitative analysis of GFX

(a) Ru(bipy)3 2+ – Ce(IV) system, (b) Ru(bipy)3 2+ – Ce(IV)–GFX system, (c) Ru(bipy)3 2+ – Ce(IV)–GFX–AgNP system; conditions: [GFX] = 1.0 × 10−5 M, [Ru(bipy)3 2+] = 4.0 × 10−3 M, [Ce(IV)] = 2.1 × 10−4 M, [H2 SO4] = 7.0 × 10−2 M, [AgNP] = 6.0 × 10−4 M

3.3.1 Proposed CL mechanism

The probable mechanism of CL sensitisation of tris‐(bipyridyl) ruthenium (II)‐cerium (IV) reaction system by AgNPs could be explained by the following reaction sequence:

  1. Oxidation of Ru(bipy)3 2+ –Ru(bipy)3 3+ by the removal of an electron.

  2. Reduction of Ru(bipy)3 3+ –Ru(bipy)3 2+* with the reaction of GFX.

  3. The highly excited Ru(bipy)3 2+* species radiate energy in terms of light (hν) and return to ground state Ru(bipy)3 2+, and CL emission occurs.

Step 1 has happened either by chemical, photochemical or electrochemical oxidation of Ru(bipy)3 2+ and the very weak oxidation potential of Ru(bipy)3 3+ enhanced by few folds once Ce (IV) is added to the reaction system [28]. The addition of Ce IV further helps to form free radicle intermediate of GFX. The intermediate specie then reacts with Ru(bipy)3 3+ and reduced to Ru(bipy)3 2+*. The excited Ru(bipy)3 2+* radiate energy (hν) and come down to the ground state and the CL emission occurs (Fig. 8). Additionally, the addition of AgNPs further enhanced the CL intensity by reducing the activation energy of the CL reaction and established better environment for the CL process [26].

3.4 Analytical parameters

The calibration curve was plotted recording CL signal of Ru(bipy)3 2+ −Ce(IV)‐AgNP system with a series of standard solutions of GFX of several concentrations under the optimised experimental conditions (Fig. 9).

Fig. 9.

Fig. 9

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Calibration curves for GFX obtained by the AgNP enhanced Ru(bipy)3 2+ –Ce(IV) CL system

It was obvious from the graph that the CL intensity was found to be linear over the GFX concentration range of 1.4 × 10−10 –4.5 × 10−8 M. The correlation coefficient (r 2) for the obtained calibration curves was found to be >0.999. The limit of detection (LOD) was calculated from the equation CLOD  = 3×Sb/m [where m is the slope of the linear regression and Sb is the standard deviation (SD) of the blank signals]. The calculated LOD value was found to be 4.6 × 10−11 M. The limit of quantitation (LOQ) was also calculated using the formula 10×SD of the blank and was found to be 1.4 × 10−10 M. The relative SD (RSD) obtained from six replicate analyses was established to be 3.2% for 1.2 × 10−9 M GFX.

3.5 Interference studies

Usually, in a real sample, the target analyte is present with other interferents, which can suppress or enhance the sensitivity of the method. Thus, the influence of some foreign species on the CL analysis assay of GFX was studied by analysing synthetically prepared sample solutions of 1.0 × 10−9 M GFX together with extra quantities of foreign species. The results of interferences from different species are shown in Table 1. The results indicate that most interferents were found to show no influence up to certain concentration levels as the variation in CL intensity was found to be <5%.

Table 1.

Maximum acceptable concentration proportions with respect to 1.0 × 10−9 M GFX

Interference species Ratio of foreign species and GFX
K+, Na+, NH4+ 499.8
Fe3+, Al3+, Co2+ 999.5
glucose, fructose 50.02
galactose, sucrose, ephedrine, dextrin 45.05
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3.6 Real sample analysis

To investigate the applicability of the method, commercial pharmaceutical formulations of label claimed 200 mg GFX was analysed with the proposed CL method. To determine the active ingredients in the tablet, ten tablets were taken and the total weight was noted. Then, all the tablets were grinded and an average weight of one tablet was thawed in DI water with vigorous shaking and placed in an ultra‐sonic bath for 20 min to achieve a completely soluble solution. The solution was then filtered using the membrane filter and diluted to the 1000 ml mark. Proper dilution was arranged from this solution to meet the linearity range of the proposed CL method. The recovery study was performed by spiking certain concentration of GFX stock and all the results for the quantitative analysis of GFX in pharmaceutical tablets including percentages of recovery are provided in Table 2.

Table 2.

Assays of GFX in pharmaceutical tablets by AgNPs enriched Ru(bipy)3 2+ −Ce(IV) CL system

Sample Claimed Found ± SD Added ( × 10−9 M) Found ± SD ( × 10−9 M) Recovery mean ± RSDa, %
Gatizone 200 mg of GFX 192.7 ± 0.22 1.0 0.95 ± 0.05 95.0 ± 0.6
5.0 4.95 ± 0.04 99.0 ± 0.5
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a Mean of three measurements.

It is well‐understood from Table 2 that the overall recovery of GFX was about 95.0–99.0%. The results are satisfactory and were in blameless agreement with label claims. The developed method is easy to perform and affords decent precision and as well as accuracy of the analysis of the real sample. In addition, to test the recovery of the proposed CL method, calibration procedure was carried out with urine samples. Thus, 2.5 × 10−9 and 5.0 × 10−9 M of GFX was added to blank urine samples. After the measurement of the CL intensity, the recoveries of each spiked samples were calculated from the calibration curve and the results are listed in Table 3. The percentage recovery was found to be between 97 and 98%. All the obtained results suggested that the method is simple, adequately sensitive and selective, and thus can be applied for the routine determination of GFX in a urine sample.

Table 3.

Analysis assays of GFX in spiked samples (urine) by the proposed CL system

Sample Added ( × 10−9 M) Found ± SD ( × 10−9 M) Recovery, % mean ± RSDa
GFX 2.50 2.41 ± 0.07 97.0 ± 1.5
5.00 4.82 ± 0.09 96.4 ± 0.6
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a Mean of three measurements.

A comparative study with a few other reported results is tabulated in Table 4. It can be clearly understood from this table that the current method has shown several advantages over the reported results in terms of wide linear range and sensitivity.

Table 4.

Comparison of reported results with the proposed CL method

Methods Linearity (r 2) LOD/LOQ Reference
spectrophotometric method 5.53 × 10−7 –3.12 × 10−5 M not reported [4]
first and second‐derivative spectrometric technique 5.53 × 10−6 –3.32 × 10−5 M not reported [5]
terbium‐sensitised spectrofluorometric assay 5.0 × 10−10 –5.0 × 10−8 M with a correlation coefficient of 0.9996 6.0 × 10−11 M [6]
fluorimetric 13 × 10−8 –2.28 × 10−6 M (0.9997), 7.67 × 10−9 M [7]
HPLC method 9.13 × 10−6 –3.19 × 10−5 M not reported [8]
thin‐layer chromatographic method 400–1200 ng/spot (0.9953) 2.73/8.27 ng/spot [9]
specific agar diffusion bioassay 4.0–16.0 μg/ml not reported [11]
NP sensitised calcein‐KMnO4 ‐GFX‐AgNP system 8.9 × 10−9 –4.0 × 10−6 M, 2.6 × 10−9 M [26]
Ru(bipy)3 2+ –Ce(IV) CL system 1.4 × 10−10 –4.5 × 10−8 M. (0.9999) 4.6 × 10−11 M–1.4 × 10−10 M proposed method
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4 Conclusions

In this work, the AgNPs were synthesised and exploited for the chemiluminometric determination of GFX. AgNPs were found to have enhancement effect to the weak CL intensity of the Ru(bipy)3 2+ ‒Ce(IV) system when applied in combination with GFX. The enhancement was directly dependent on the concentration of GFX added and was used for the CL determination of GFX. To check the interference effect, the influences of various chemical variables were investigated. Under the optimum experimental conditions, a linear calibration plot was obtained over the range of 1.4 × 10−10 –4.5 × 10−8 M. The detection limits were obtained to be 4.6 × 10−11 M, while the correlation coefficient for the linear calibration graph was 0.9999. The percentage RSD accounted from six replicate analyses was 3.2% for 1.2 × 10−4 M GFX. The method is simple, sensitive and applicable in the wide linear range. Comparative studies with some reported methods are also discussed to compare the advantages of the proposed CL assay.

5 Acknowledgments

The authors extend their appreciation to the Deanship of Scientific Research, College of Science Research Centre, King Saud University, Riyadh, Saudi Arabia for supporting this project.

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