1 3 J IRAN CHEM SOC DOI 10.1007/s13738-014-0551-2 ORIGINAL PAPER A simple and sensitive assay for ampicillin in pharmaceuticals using gold nanoparticles as spectroscopic probe reagent Ghodratollah Absalan · Abdolkarim Abbaspour · Marzieh Jafari · Mohsen Nekoeinia · Hamid Ershadifar Received: 12 June 2014 / Accepted: 18 October 2014 © Iranian Chemical Society 2014 is important [1]. The first antibiotic was penicillin that dis- covered in 1928 from a mold culture. All penicillins are β-lactam antibiotics. A β-lactam is a ring with a hetero- atomic structure, consisting of three carbon atoms and one nitrogen atom [2]. Ampicillin (6-[(aminophenyl acetyl) amino]-3,3-dime- thyl-7-oxo[2 s-2α,5α,6β (S*)]), Scheme 1a, is one of the important β-lactam antibiotic used to treat or prevent gram- negative bacteria and bacterial infections. The nature of ampicillin is acidic, and it inhibits the protein synthesis. The antibacterial and pharmacological properties of ampicillin are determined by side chain of this compound [3]. Ampi- cillin is used to treat some diseases such as Enterococcal endocarditis, Meningitis, etc. Ampicillin also inhibits the synthesis of bacterial cell wall and leads to cell lysis [4]. Because of its high activity, low toxicity and acid stability, ampicillin is commonly used in medical treatments [5]. In view of its pharmacological importance, considerable work has been done for its chemical analysis. Analytical methods for determination of ampicillin, in biological and pharma- ceutical samples, employ techniques such as chromatogra- phy [6–9], spectrophotometry [10–13], spectrofluorimetry [14], near-infrared spectroscopy [15, 16], mass spectrom- etry [17, 18] and NMR spectroscopy [19, 20]. Chromatogh- raphy, mass spectrometry and NMR methods are expensive and time-consuming and require expertise. Spectrophotometric techniques provide practical and significant economic advantages over other methods; there- fore, they are the best choice for pharmaceutical analysis [21, 22]. However, most pharmaceutical drugs have strong absorption bands in the range of ultraviolet and, therefore, could interfere with determination of ampicillin. Using of chromogenic or fluorogenic agent in spectroscopy is a common approach used to solve the above-mentioned prob- lem. Recently, chromogenic agents based on aggregation Abstract A novel kinetic spectrophotometric method is developed for determination of ampicillin. The method is based on aggregation of gold nanoparticles in a chemi- cal process that involved decomposition of ampicillin cata- lyzed by cadmium ion in methanol as solvent. The optimum experimental conditions for determination of ampicillin were established. The method permitted determination of ampi- cillin in a concentration range of 16.0–96.0 μg ml -1 with a detection limit of 13.0 μg ml -1 . The interferences of the spe- cies which are mostly available in biological samples were not significant in determination of ampicillin. The method is simple and sensitive for analyzing of ampicillin and is appli- cable for its assay in pharmaceutical formulations. Keywords Gold nanoparticle · Ampicillin · Spectrophotometry · Cadmium ion · ICH guidline Introduction In nature, the antibiotics are synthesized by living organ- isms that kill or stop the growth of other microorganisms. In biological science, the interest in analysis of antibiotics arises from the fact that they are responsible for the appear- ance of bacterial strains that are resistant to antibiotics which are important drugs for the treatment of many seri- ous infectious diseases and thus antibiotic’s determination G. Absalan (*) · A. Abbaspour · M. Jafari · H. Ershadifar Professor Massoumi Laboratory Department of Chemistry College of Sciences, Shiraz University, 71454 Shiraz, Iran e-mail: gubsulun@yahoo.com; absalan@susc.ac.ir M. Nekoeinia Department of Chemistry, Payame Noor University, 19395-4697 Tehran, Iran