140 Research article Drug Testing and Analysis Received: 9 November 2010 Revised: 10 December 2010 Accepted: 10 December 2010 Published online in Wiley Online Library: 9 March 2011 (www.drugtestinganalysis.com) DOI 10.1002/dta.256 Quantification of sub-nanomolar levels of Penicillin G by differential pulse adsorptive stripping voltammetry S. Abbasi, a* K. Khodarahmian a and A. Farmany b A novel selective and sensitive method is developed for determination of Penicillin G by Differential Pulse Adsorptive Stripping Voltammetry (DPAdSV). Penicillin G gave well-resolved diffusion-controlled cathodic peaks at -0.42 and -0.584 V, respectively (vs Ag/AgCl) in pH 7.50 of borate buffer. Optimal conditions were obtained as pH 7.50, accumulation potential of -0.2V(vs Ag/AgCl), accumulation time of 120 s, and scan rate of 100 mV/s. Under the optimized conditions, a linear calibration curve was established for the concentration of Penicillin G in the range of 0.007 – 2.13 μg/ml with a detection limit of 0.000717 μg/ml. The procedure was successfully applied to the determination of Penicillin G in various medicine and biological samples. The relative standard deviation of the method at 0.05 and 0.5 μg/ml Penicillin G, for 10 runs, was 2.55% and 2.06%, respectively. Copyright c  2011 John Wiley & Sons, Ltd. Keywords: Penicillin G; differential pulse adsorptive stripping voltammetry; medicine and biological samples Introduction Penicillin is a group of antibiotics derived from Penicillium fungi. Penicillin antibiotics are historically significant because they are the first drugs that were effective against many serious diseases, such as syphilis and Staphylococcus infections. Penicillins are still widely used today, though many types of bacteria are now resistant. All penicillins are Beta-lactam antibiotics and contain bulky side-chains and a carboxylic grope (Figure 1) which are used in the treatment of bacterial infections caused by susceptible, usually Gram-positive, organisms. Penicillins are among the oldest and most frequently prescribed natural antimicrobial. These compounds have high selectivity and low toxicity because they are adiaphorous to human cells which do not have a cell wall. Owning to the extensive appli- cation of these drugs in clinic, [1–3] the toxic side-effects from these drugs are generally minimal. [4–6] Because antibiotics are frequently administered in large doses, it is sometimes important to be able to monitor their concentrations in serum, especially in patients with impaired renal function. Several reports for the determination of penicillin antibiotics have been developed, in- cluding chemiluminescence, [7,8] potentiometry and amperometry using biosensors, [9 – 18] potentiometric ion-selective electrodes based on anion exchangers, [19,20] capillary electrophoresis, [21] spectrophotometry, [22 – 25] liquid chromatography, [26,32] high per- formance liquid chromatography (HPLC), [28,29] direct current and differential pulse polarography (DPP), [30] tandem mass spectrometry, [27,32] etc. HPLC was very useful for the determination of trace penicillin antibiotics but it needed complex pretreatments. Although some other reported methods have their respective ad- vantages, they also have some deficiencies in the sensitivity, selectivity, simplicity, and unsuitability for automatic or continuos analysis. So, it is necessary to develop a simpler, more sensitive, and selective method for the determination of penicillin antibiotics. At this time there is no report on the differential pulse adsorptive stripping voltammetry determination of Penicillin G. In this paper we report a Differential Pulse Adsorptive Stripping Voltammetry (DPAdSV) procedure for determination of Penicillin G. The method is applied to the determination of Penicillin G in various medicine and biological samples with satisfactory results. Experimental Apparatus DPAdSV measurements were made using a 746 VA-Trace Analyzer, (Metrohm, Switzerland Herisau) connected to an electrode stand, 747 VA-Stand, (Metrohm, Switzerland Herisau) The three-electrode configuration was used comprising a Metrohm multimode electrode (MME) in hanging mercury drop electrode (HMDE) state as working electrode, a double junction Ag/AgCl (3M KCl, saturated AgCl, and 3M KCl in the bridge) reference electrode and a Pt wire auxiliary electrode. All potentials quoted are relative to the Ag/AgCl reference electrode. A rotating Teflon rod stirred solutions in the voltammetric cell. The mercury was triple-distilled quality, and the medium drop size of the HMDE was selected. All experiments were done at room temperature. pH measurements were made with a Metrohm pH meter model 780 (Switzerland Herisau). Eppendorf reference variable micropipettes (10 – 100 and 100 – 1000 μl) were used to pipette microlitre volume of solutions. All glassware and storage bottles were soaked in 10% HNO 3 overnight and thoroughly rinsed with water prior to use. ∗ Correspondence to: S. Abbasi, Department of Chemistry, Ilam University, Ilam, Iran. E-mail: s.abbasi@mail.ilam.ac.ir abosina2000@yahoo.com a Department of Chemistry, Ilam University, Ilam, Iran b Islamic Azad University, Young Researchers Club, Hamedan Branch, Hamedan, Iran Drug Test. Analysis 2012, 4, 140–144 Copyright c  2011 John Wiley & Sons, Ltd.