Three simple, selective, accurate and precise spectrophotometric methods were developed for the determination of Metoclopramide Hydrochloride (MCP) in dosage forms. The first method (Method A) is based on coupling reaction of diazotized MCP with 2,5-diphenyl-2,4-dihydro-pyrazol-3-one (DPP) in alkaline medium to form azo dye. The second method (Method B) is based on Schiff’s base formation reaction between MCP and 4-hydroxybenzaldehyde (HBD). The last method (Method C) is based on the formation of colored ion–pair complex from the reaction of MCP with Eosin Y (ESN). Beer’s law was obeyed in the concentration range of 1.35-40.37, 1.01-5.05 and 1.01-10.09 μg/mL MCP at 426, 386 and 543 nm with molar absorptivity of 1.51×104 L mol-1 cm-1, 2.10×104 L mol-1 cm-1 and 3.34×104 L mol-1 cm-1 for Method A, Method B and Method C, respectively. The proposed methods were successfully applied to the determination of MCP in pharmaceutical preparations without any interference from common excipients.
Keywords: Metoclopramide; Coupling reaction; Schiff’s base; Ionpair complex; Spectrophotometry; Pharmaceutical
Metoclopramide hydrochloride (MCP), monohydrate of 4-amino-5- chloro-N-[(2-diethyl amino)ethyl]-2-methoxy benzamide mono hydrochloride (Figure 1), is a substituted benzamide and commonly used as an anti-emetic in the management of some forms of nausea and vomiting and for stimulating the motility of the upper gastrointestinal tract . MCP decreases stomach acid reflux by strengthening the lower esophagus sphincter. MCP also hastens the stomach emptying of solid and liquid meals into the intestines. Rapid emptying of meals also helps decrease the reflux of stomach acid and other contents into the esophagus . It is also used in the prevention of cancer chemotherapy induced emesis .
Different analytical methods were used for the determination of MCP. These methods include voltammetric [4-10], potentiometric [11-13], chromatographic methods [14-19]. There is no doubt that some of these methods are sensitive and selective, but they require expensive instruments, accessories, and solvents, not to mention their demand for cleaning procedures.
Although the rise of such modern sensitive analytical methods, spectral analysis remains the best choice in many laboratories, especially analytical ones aimed to drugs determination. This can be attributed to its simplicity, cost effectiveness, sensitivity and selectivity, and fair accuracy and precision. Through literature survey, it was revealed different analytical procedures were used for the spectrophotometric determination of MCP. These spectrophotometric procedures include derivative spectrophotometric [19,20], UV spectrophotometric [21-23] and sequential injection spectrophotometric [24,25]. Several spectrophotometric methods based on diazo-coupling reaction [26-36], Schiff`s base reaction [36-39], ion-pair complex reaction [40,41], charge–transfer reaction [42,43] and redox reaction [44,45] were described. Also, spectrofluorimetric methods for MCP determination were suggested [46-48].
To the best of our knowledge, little attentions had been made to spectrophotometric determination of MCP either using chargetransfer reaction or ion–pair complex and the literature are still poor in such analytical procedure. In this article, we present three simple, sensitive and selective spectrophotometric procedures for MCP determination. The first method (Method A) is based on coupling reaction of diazotized MCP with 2,5-diphenyl-2,4-dihydro-pyrazol-3- one (DPP) in alkaline medium. The second method (Method B) is based on reaction of MCP with 4-hydroxybenzaldehyde (HBD) to produce Schiff’s base colored complex. The last method (Method C) is based on the formation of colored ion-pair complex from the reaction of MCP with Eosin Y (ESN). In the studied wavelength range, individual MCP solution doesn’t have absorption maxima. So, the recorded absorption maxima are related to the formed MCP colored compound. The presented color reactions provide an inexpensive way for the spectrophotometric determination of MCP at a considerable low concentration. The developed procedures were successfully used in the determination of MCP in its pharmaceuticals preparation.
All absorption measurements were carried out using a Perkin-Elmer model Lambda 3B double-beam UV-visible programmable spectrophotometer, equipped with 1 cm quartz cell and controlled by a PC running the spectrophotometric software PECSS. PECSS Perkin- Elmer software program was used for data analysis with slit-width, 1 nm; scan speed, 120 nm/min and wavelength interval, 1 nm. All the pH measurements were made using VWR Scientific Products Model 2000, USA.
Materials and reagents
All chemicals used were analytical reagent grade and used without further purification. Metoclopramide hydrochloride (MCP) was purchased from Merck. The pharmaceutical preparations used in the present investigation were Primperan tablets and Plasil ampoules (Sanofi Aventis Egypt Company), labelled to contain 10 mg/tablet and 10 mg/ampoule, respectively. Reagents like 4-hydroxybezaldehyde (HBD) and Eosin Y (ESN) were purchased from Merck.
Preparation of MCP stock standard and reagents solutions
Standard solution of MCP: A stock standard solution of MCP (1 × 10-2 M) was prepared by dissolution 0.3363 g of the authentic drug in 100 mL volumetric flask containing distilled water, the volume was completed with the same solvent and kept in a brown volumetric flask. MCP working solutions were prepared daily by sequential dilution of the stock standard solution using distilled water.
Pharmaceuticals preparations: Ten tablets of Primperan tablets were weighed into a small dish, powdered and mixed well. A portion of the ground tablets equivalent to 0.05 g of MCP was accurately weighed and dissolved in 50 mL distilled water, shaken well and filtrated using a filter paper. An aliquot of filtrate was transferred into 50 mL volumetric flask and it was completed to the mark with distilled water. Working solutions were prepared by serial dilution of the resulting solution using the same solvent.
The content of six Plasil ampoules were quantitatively transferred into 50 mL volumetric flask and completed to the mark with distilled water. Working solutions were prepared by serial dilution of the resulting solution using the same solvent.
Reagents and buffers solutions
For the preparation of 2,5-diphenyl-2,4-dihydro-pyrazol-3-one (DPP), 19.244 g of ethyl benzoyl acetate was placed in a round flask in oil bath at about 120°C with slow drop wise addition of 10.791 g distilled phenyl hydrazine solution. The reaction mixture was maintained under the condenser for 1 hr. A crystalline deposited precipitate was separated and washed with diethyl ether several times . A Stock solution of DPP (1.7 × 10-2 M) was prepared by dissolving 2.0 g of pure material in 0.3 M NaOH, then complete to 500 mL in a volumetric flask with the same solvent.
A stock solution of HBD (8.2 × 10-2 M) was prepared by dissolving 5.0 g of HBD in glacial acetic acid, while ESN (3.6 × 10-4 M) was prepared by dissolving 0.125 g of ESN in distilled water. Either in case of HBD or ESN, complete to 500 mL in a volumetric flask with the same solvent.
Method A: Coupling reaction of diazotized MCP with DPP: In 25 mL volumetric flask (in ice bath), place aliquot of sample solution containing 1.35-40.4 μg/mL of MCP, 3.5 mL HCl (0.2 M), 2.5 mL NaNO2 (0.04 M), 5.0 mL of 0.014 M DPP, 7.0 mL KCl-NaOH buffer solution (pH ≈ 11.2) , and complete to the mark with distilled H2O. Mix the components well. After 10 min., the absorbance was measured at 426 nm against the reagent blank.
Method B: Schiff’s base colored complex formed by reaction of MCP with HBD: In 10 mL volumetric flask, place an aliquot of sample solution containing 1.01-5.04 μg/mL of MCP, 3.5 mL of 8.2 × 10-2 M HBD, 3.10 mL of Conc. H2SO4 (98%), complete to the mark with glacial acetic acid and shake well. The absorbance was measured at 386 nm against the reagent blank.
Method C: Ion-pair colored complex formed by reaction of MCP with ESN: In 10 mL volumetric flask, place an aliquot of sample solution containing 1.01-10.09 μg/mL of MCP, 2.5 mL distilled H2O and 4.0 mL 3.6 × 10-4 M ESN and 3.0 mL Mcilvaine’s buffer (pH ≈ 3.2) . Complete to the mark with distilled water and shake well. The absorbance was measured at 543 nm against the reagent blank.
Procedure for the determination of MCP in tablets and ampoules
MCP in dosage forms (tablets and ampoules) was determined according to the standard addition method. In previously described procedures, a definite volume of the sample solution was added in specified volumetric flask followed by successive additions of standard MCP solution. The absorbance was measured at 426, 386 and 543 nm for DPP, HBD and ESN, respectively.
Method A: Coupling reaction of diazotized MCP with DPP: Whereas DPP has an active methylene group; it has a great ability to form an azo colored compound with diazotized MCP in an aqueous alkaline medium. The most important feature of this product, that it’s completely soluble in reaction medium, there is no need to additional step to solubilize this product for spectrophotometric analysis. The reaction could be explained in Figure 2. The absorption spectra of blank solution (contains DPP) and coupling reaction product (diazotized MCP-DPP) are shown in Figure 3 (curves a and b, respectively). The absorption maximum of the produced azocompound was at 426 nm; hence, all measurements were made at this wavelength against reagent blank.
Method B: Schiff’s base colored complex formed by reaction of MCP with HBD: For Schiff’s base formation, HBD was selected as aromatic aldehyde to react with MCP. The condensation reaction requires the presence of an acid for the protonation of the carbonyl oxygen and thereby leaving the carbonyl carbon fully positive charge. In current procedure, Conc. H2SO4 is used for this purpose. Amino group in MCP have a great ability to donate a lone pair of electrons to the carbon present in the carbonyl group of HBD. Internal rearrangement thereafter results in the formation of imine (Schiff’s base) and then giving water and proton as by-products . The reaction mechanism can be illustrated Figure 4. The absorption spectra of blank solution (contains HBD) and MCP–HBD reaction product are shown in Figure 5 (curve a and b, respectively). The maximum absorbance of the produced Schiff’s base was observed at 386 nm. Hence, all measurements were made at this wavelength against reagent blank.
Method C: Ion-pair colored complex formed by reaction of MCP with ESN: As can be seen in Figure 6, ESN structure shows the presence of both a carboxylic and a phenolic group; the latter is highly affected by the presence of the 4-electron withdrawing bromine atoms. As a result, the pKa (OH) becomes less than pKa (COOH) (2.02 and 3.8, respectively) . Therefore, at pH 3.2 the OH group becomes most likely fully ionized and thus electrostatically interacts with the primary amino group of MCP forming the orange-red ion-pair complex. Figure 6 shows the suggested reaction pathway. The absorption spectra of the blank solution (contains ESN) and MCP-ESN ion-pair complex are shown in Figure 7 (curve a and b, respectively). MCP reacts instantly with ESN in acidic medium and a bathochromic shift of the dye about 30 nm was produced indicating the forming the orange-red ion-pair complex. All measurements were carried out at 543 nm.
Optimization of experimental variables
Different experimental parameters which affect the color intensity and stability were carefully studied and optimized. Such parameters were changed individually while keeping the others constant. The optimized experimental variables for all proposed methods were recorded in Table 1.
|Parameter||Method A||Method B||Method C|
|Procedure||MCP+HCl+NaNO2+DPP+NaOH-KCl soln.||MCP+HBD+Conc. H2SO4||MCP+ESN+Buffer solution|
|Reagent Conc. (M)||2.8 ´ 10-3||2.87 ´ 10-2||1.44 × 10-4|
|Temperature (°C)||Ice bath||Room temperature||Room temperature|
|Buffer/Medium type||NaOH-KCl||-||Mcllvaine buffer|
|Buffer/Medium volume (mL)||7||-||3|
|HCl Conc. (M)||2.8 × 10-2||-||-|
|NaNO2 Conc. (M)||4.0 ´ 10-3||-||-|
|H2SO4 Conc. (%)||-||30.6||-|
Table 1: The selected optimum conditions of suggested procedures for MCP spectrophotometric determination.
Method A: Coupling reaction of diazotized MCP with DPP: Different factors affect azo dye formation includes pH and concentration of each of HCl, NaNO2, DPP and KCl-NaOH buffer were studied and optimized. Such factors were changed individually while others were kept constant.
The effect of pH on the absorbance intensity of MCP at 426 nm was studied using Britton-Robinson buffer over the pH range of 9.2-11.8. In addition to Britton-Robinson, the absorbance was recorded in different types of buffers like KCl-NaOH, Na2HPO4-NaOH, NaHCO3- NaOH and Borax-NaOH to select the best choice to be used in further studies. The obtained results indicate that highest absorbance was recorded in KCl-NaOH (pH ≈ 11.20).
The effect of other additives concentration on the determination of MCP was studied in terms of additive volume. This study was established for HCl (4-64 mM), NaNO2 (0.8-8 mM), DPP (0.28-5.6 mM) and KCl-NaOH (2-10 mL), where absorbance was recorded at 426 nm. The results showed that reproducible color intensity and stability of formed dye was obtained at 28 mM HCl, 4 mM NaNO2, 2.8 mM DPP and 7 mL KCl-NaOH (pH ≈ 11.20). The optimum reaction time was determined by monitoring the color development. It was found that the colored product is formed immediately and becomes stable after 10 min and remains constant for more than 180 min
Method B: Schiff’s base colored complex formed by reaction of MCP with HBD: Different experimental parameters affecting the formation of Schiff’s base colored complex as a product of reaction between MCP and HBD were carefully studied and optimized. It was observed that the analytical signal increased with an increase H2SO4 and HBD concentration in range of 4.9-44.1% and 4.1 × 10-3-3.28 × 10-2 M, respectively. The selected values which corresponding maximum absorbance was 30.6% and 2.87 × 10-2 M for H2SO4 and HBD, respectively. In current procedure, MCP failed to give condensation product with HBD even in the presence of H2SO4. Yellow colored product was developed only in glacial acetic acid medium; so, glacial acetic acid was used as the solvating solvent. After optimizing all other experimental variables, further experiments were performed to ascertain the influence of order of addition of reactants on the color development. Maximum sensitivity was achieved when HBD was mixed with MCP followed by H2SO4 addition. Finally, the reaction was found to be instantaneous and the colored product approximately stable for 3 h. So, the absorbance readings were recorded instantly.
Method C: Ion-pair colored complex formed by reaction of MCP with ESN: In order to optimize the investigated reaction, different parameters were extensively studied in order to yield the highest and most reproducible absorbance readings. The acidic pH is a fundamental factor affecting the ionization of ESN thus allowing its interaction with MCP. For this reason, at constant pH value, different buffers (acetate, citrate and Mcllvaine) were studied among which the Mcllvaine buffer gave the best results. Accordingly, this buffer was further tried in different ranges of volumes (1.0-5.0 mL) and pH values (2.2-4.2). 3.0 mL of Mcllvaine buffer pH 3.2 gave the highest absorbance readings. Investigation of the effect of the ESN concentration revealed that 4.0 mL of 3.6 × 10-4 M ESN (1.44 × 10-4 M final concentration in total volume of 10 mL) gave the maximum absorbance and was chosen to be the suitable concentration for the analytical procedure. Generally, the limited aqueous solubility of the produced drug–dye complexes was solved by either extracting the complex with an organic solvent  or adding a non–ionic surfactant as methyl cellulose . Alternatively, El-Brashy et al.  reported a simpler solution for such a problem, which is based on keeping the sample concentration at maximum dilution before adding the dye solution and mixing the solution well before the addition of buffer solution. Accordingly, by adopting the above procedure, the stability and solubility of the produced MCP-ESN complex were achieved without the need of lengthy extraction steps or the use of non-ionic surfactants.
The intensity of the final color was maxima at room temperature. It was observed that with increasing temperature, a precipitate was produced which may be due to coagulation of the formed complex. Finally reaction was found to be instantaneous and the colored product approximately stable for about 3 h. So, the absorbance readings were taken immediately.
Validation of the proposed methods
Linearity and concentration ranges: Under the specified optimum conditions, the calibration curves for the determination of MCP either with Method A, Method B and Method C were constructed. A good linear relationship was observed within the ranges of 1.35-40.37, 1.01-5.05 and 1.01-10.09 μg/mL at 426, 386 and 543 nm for Method A, Method B and Method C, respectively. The molar absorptivity (ε) values were calculated from the slope of the calibration graphs and it was found as 1.51 × 104, 2.10 × 104 and 3.34 × 104 L mol-1 cm-1 for DPP, HBD and ESN. The Limits of Detection (LOD) and Quantification (LOQ) were calculated as 3.3σ/b and 10σ/b, respectively, where σ is the standard deviation of five reagent blank determinations and b is the slope of the calibration curve. The calculated LOD values were 0.669, 0.135 and 0.124 μg/mL, while LOQ were found to be 2.23, 0.453 and 0.414 μg/mL, for Method A, Method B and Method C, respectively. The precision of the methods used for MCP determination was calculated  using 5 identical samples containing 1.35, 4.04 and 3.03 μg/mL MCP, respectively. Relative Standard Deviations (RSD) did not exceed 2% indicating the good reproducibility of the proposed methods. However, Table 2 illustrates the statistical analysis data for the proposed methods. Based on above data, we can conclude that Method C is more sensitive than Method A and Method B.
|Parameter||Method A||Method B||Method C|
|Linearity range (μg/mL)||1.35-40.37||1.01-5.05||1.01-10.09|
|ε (Lmol-1cm-1)||1.51 × 104||2.10 × 104||3.34 × 104|
|Sandell’s sensitivity (μg/cm2)||0.022||0.016||0.012|
|Correlation coefficient (r)||0.999||0.9993||0.9997|
|Regression equation (Y)a||A=0.044 C+1.5 × 10-2||A=0.062 C+2.5 × 10-3||A=0.087 C+7.2 × 10-4|
Table 2: Statistical analysis for the spectrophotometric determination of MCP using either of the proposed procedures. aA=b C+a where A is absorbance and C is the MCP concentration (μg/mL), bLOD=3.3σ/b and LOQ=10σ/b where σ=standard deviation of the blank and b=slope of the regression
Interferences study: For all proposed methods, the influence of diverse ions on the determination of 2.018 μg/mL MCP was conducted by added various concentration of different salts in which anions may be chloride, nitrate or sulfate, and the cations as Al+3, Ca+2, Sr+2, Cd+2, Ni+2, Co+2, Mg+2, Cu+2 and NH4+. Also, in presence of 2.018 μg/mL MCP, another interference study was conducted by addition of several concentrations of some common excipients and additives which used in pharmaceutical preparations (e.g. glucose, sucrose, lactose and fructose). Either studies was conducted in presence of equimolar concentration or even at higher molar excess (10000:1) (foreign ion/ excipient: MCP) under the optimum experimental conditions. The obtained results revealed that no interference was observed from any of these excipients with the proposed methods. The calculated recovery value was 98.3-099.5 ± 0.10%. The obtained results indicate that there is no interference may be occurred from these excipients.
It was mentioned that drugs usually eliminated from body principally by urinary excretion . In case of MCP, as reported in official methods [58,59], about 60% of an oral dose is excreted in human urine in the first 24 h. So, the proposed methods for spectrophotometric determination of MCP in this work can be easily applied without any interfere can be occurred as a result of MCP distribution in human body. The same result we had got before in earlier work .
Comparison with other spectrophotometric methods: In comparison with the other spectrophotometric methods used for MCP determination, the proposed methods utilizing DPP, HBD and ESN have the advantage of being simple, reproducible, time saving, highly selective and sensitive. Table 3 summarizes the analytical characteristics of the proposed methods along with frequently used spectrophotometric methods for MCP determination.
|Reaction||Reagent||λmax||ε × 104*||Linearity range**||LOD**||LOQ**||Remarks||Ref.|
|Benzoylacetone||411||2.97||0.8-13.2||0.0332||0.1006||Use an organic solvent|||
|Doxycycline hyclate||452||3.81||0.1-10||0.012||0.043||Narrow concentration range and use an expensive reagent|||
|Acetyl acetone||430||2.2||2-16||0.044||0.1334||Use an organic solvent|||
|2,5-Dimethoxyaniline||486||4.55||0.1-12||0.016||0.054||Use an organic solvent|||
|Diphenylamine||530||4.73||0.3-7.5||0.22||0.67||Narrow concentration range and use an organic solvent|||
|Α-Naphthol||550||3.49||0.4-18||0.5448||–||Use an organic solvent|||
|Aniline||410||3.53||0.5-12||0.047||0.156||Use an organic solvent and require heating|||
|Dibenzoyl methane||440||2.85||1-12||0.0333||0.1009||Use an organic solvent|||
|Imipramine hydrochloride||570||4.5||0.5-5||0.0144||0.0437||Narrow concentration range and use an expensive reagent|||
|Chromtropic acid||540||0.416||2-24||–||–||Less sensitive anduse an expensive reagent|||
|Β-Napthol||553||2.74||1-10||–||–||Narrow concentration range|||
|2,5-diphenyl-2,4-dihydro-pyrazol-3-one (DPP)||426||1.51||1.35-40.37||0.669||2.23||This work|
|Schiff’s Base||4-Dimethylaminobenzaldehyde||438||0.211||10-100||–||–||Less sensitive|||
|1,2-Naphthoquinone-4-sulphonate||471||4.124||0.1-26||0.0416||0.1386||Use cetylpyridinium chloride as surfactant and required heating|||
|p-Dimethylaminocinnamaldehyde||548||–||5-30||–||–||Less sensitive and use an organic solvent|||
|4-Hydroxybenzaldehyde (HBD)||386||2.10||1.01-5.05||0.135||0.453||This work|
|Mo(V) thiocyanates Co(II) thiocyanates||472
|–||–||Require extraction step using an organic solvent|||
|Bromothymol Blue||–||–||1-10||–||–||Use an organic solvent|||
|Eosin Y (ESN)||543||3.34||1.01-10.09||0.124||0.414||-||This work|
3: Comparison between the proposed procedures and other correspondence procedures used for spectrophotometric determination of MCP. *Molar Absorptivity (ε) in Lmol-1cm-1, **Linearity range, Lower limit of detection (LOD) and Lower limit of quantifcation (LOQ) in μg/mL.
Application of the proposed methods: The applicability of either of the developed methods was investigated when used for the determination of MCP in different pharmaceutical preparations; Primperan ts and Plasil ampoules. The validity of the proposed methods was assessed by applying the standard addition method. The obtained results summarized in Table 4 shows satisfactory recoveries and confirmed the validity and the accuracy of the proposed methods. The results given by the proposed methods and the reference method  were statistically compared.
|Method A||Method B||Method C||Reference
Table 4: Spectrophotometric determination of MCP in dosage forms by standard addition method. aAverage of five separate measurements, bLabeled to contain 10 mg MCP per tablet, cLabeled to contain 10 mg MCP per ampoule
2,5-diphenyl-2,4-dihydro-pyrazol-3-one (DPP), 4-hydroxy benzaldehyde (HBD) and Eosin Y (ESN) were presented in this work as a new reagents for the spectrophotometric determination of MCP. The suggested procedures have the advantages of being simple, reproducible and inexpensive. The optimum experimental conditions for each method were studied in details. The proposed methods were selective, accurate and precise as indicated by the good recoveries of two different series of MCP and low RSD values. Either of the proposed methods was successfully applied for the determination of MCP in pharmaceutical formulations.