Chemical Engineering and Science, 2013, Vol. 1, No. 1, 1-6 Available online at http://pubs.sciepub.com/ces1/1/1 © Science and Education Publishing DOI:10.12691/ces-1-1-1 Quantitative Determination of Milnacipran by Simple Colorimetric Methods Md. Mubarakunnisa 1 , Avula Prameela Rani 1 , Seelam Harika 1 , Chandra Bala Sekaran 2,* 1 University College of Pharmaceutical Sciences, Acharya Nagarjuna University, Nagarjuna Nagar, India 2 Department of Biotechnology, Jagarlamudi Kuppuswamy Choudary College, Guntur, India *Corresponding author: balumphil@gmail.com Received December 23, 2012; Revised January 22, 2013; Accepted February 28, 2013 Abstract In the present study, two sensitive, precise and accurate spectrophotometric methods have been developed for the determination of milnacipran in bulk and capsule formulation. The first method is based on the reaction of milnacipran with ninhydrin in N,N'-dimethylformamide medium at 80°C temperature to form a colored Ruhemann's purple, which exhibits absorption maximum at 575nm. The second method is based on extraction of milnacipran into chloroform as ion-pair with bromothymol blue. The yellow colored ion-pair complex exhibits absorption maximu m at 410n m. Beer’s law is obeyed in th e concentration ranges 2.5-37.5ȝg/mL and 2-12ȝg/ mL of milnacipran for methods I and II, respectively. The effect of experimental variables were investigated and optimized. The validation parameters like linearity, sensitivity, accuracy, precision and robustness were checked by following the ICH guidelines. The proposed methods were applied for the analysis of milnacipran in capsule formulation with good results. Keywords: milnacipran, ninhydrin, bromothymol blue, Ruhemann's purple, ion-pair complex 1. Introduction Milnacipran (MCN) or 1R 2S)-2 aminomethyl-N-N- dimethyl-1-phenyl cyclopropane carboxamine ( Figure 1) is an antidepressant, effective in the treatment of fibromyalgia. MCN acts by inhibiting the reuptake of serotonin and nor epinephrine neurotransmitters in 1:3 ratio [1,2,3] . Figure 1. Structure of Milnacipran The analytical methods reported for the determination of MCN are based on chromatographic techniques. They include RP-HPLC [4,5,6], LC-MS [7] , U-HPLC [8] and HPTLC [9] . Most of the reported chromatographic methods have tedious extraction procedures, time- consuming, complex, multiple sample preparation steps, expensive and requires a skilled person to operate the instrument. Hence these methods are not suitable for routine analysis of MCN in quality control and quality assurance laboratories. Compared with the above mentioned chromatographic methods, spectrophotometry is considered as the most convenient analytical technique in many of the quality control and quality assurance laboratories because of its advantages, such as good selectivity, less expensive, simple instrumentation and less time consuming. To the best of our knowledge, there are only few reports on the determination of MCN using spectrophotometric method [10,11,12,13]. These methods have drawbacks such as insensitivity, lack of selectivity, use of expensive reagent and rigid control of pH. In the present paper, we report two spectrophotometric methods for the estimation of MCN in bulk and capsules by using ninhydrin and bromothymol blue as analytical reagents. 2. Materials and Methods 2.1. Apparatus The absorption spectra and measurements were recorded using a systronics (Schimadzu Corporation, Tokyo, Japan), model visiscan-167, digital spectrophotometer with 1-c m matched quartz cells. Samples were weighed using a schimadzu electronic weighing balance (Schimadzu Corporation, Tokyo, Japan) BL 220H model. 2.2. Chemicals and Reagents All reagents and chemicals were of analytical reagent grade 1. Milnacipran was kindly provided by Matrix laboratories (Hyderabad, India). 2. Milza capsules (Intas pharmaceuticals, Dehradun, India), labeled to contain 50 mg milnacipran/capsule, were purchased from hetero pharmacy (Guntur, India).