This study is focused on developing a sensitive analytical method for Streptozotocin (STZ) molecules which is a naturally occurring alkylating antineoplastic agent. It is also known particularly toxic to the insulin-producing beta cells of the pancreas in mammals. With this study, a separation-enrichment method based on solid phase extraction was developed for low levels of STZ. The synthetized material consist of a multi-walled carbon nanotube/CuO/Cu2O was used as an adsorbent in column type SPE. Experimental variables such as pH, ionic strength, desorption solvent, and other parameters were studied and optimized step by step. Analytical merits were obtained under the optimized conditions: linear range (100.00-1500.00 ng mL-1), limit of detection (28.57 ng mL-1), relative standard deviation (RSD) % for 250 ng mL-1 of STZ (< 4.2 %, N:3), and pre-concentration factor (125). In order to test accuracy of the method, recovery tests were applied successively by using model solutions.

This study is focused on developing a sensitive analytical method for Venlafaxine molecule which is antidepressant drug belonging to the serotonin-noradrenaline reuptake inhibitors (SNRI) group. With this study, a separation and preconcentration method based on fabric phase sorptive extraction(FPSE) method was developed for low levels of Venlafaxine in urine samples. Experimental variables such as pH, ionic strength, desorption solvent, and other parameters were studied and optimized step by step. The linearity of method under optimized conditions is in the range of 15.00-750.00 ng mL-1 while limit of detection is 4.28 ng mL-1. The relative standard deviation (RSD %) obtained from model solutions containing 300 ng mL-1 of Venlafaxine was lower than 3.1 % and pre-concentration factor was calculated as 62.50 for target molecule. In order to test accuracy of the method, recovery tests were carried out by means of spiked urine samples. As a result of recovery tests, quantative values were obtained in the range of 97.5-104.2 % successively.

An analytical approach has been developed for the sensitive determination of Phenobarbital, which is used as an antiepileptic drug molecule. The analysis of this active molecule, which has a very limited study even for its direct determination in the literature review, is mostly done with highly complex device systems such as LC-MS. In analysis with conventional HPLC systems, the limit of detection cannot be in most cases lower than 1 µg mL-1 With this study, a separation and preconcentration method based on solid phase extraction (SPE) was developed for trace phenobarbital molecules, so that even very low concentrations could be monitored. In the proposed method, the target molecules were enriched with column type SPE method, and then their analysis were carried out by with the HPLC-DAD system. As an SPE sorbent, a polymeric material, poly(ethylene glycol dimethacrylate-N-methacryloyl-L-tryptophan methyl ester) [poly(EGDMA-MATrp)], was used in extraction experiments. Experimental variables such as pH of medium, type and amount of desorption solvent, electrolyte effect have been studied and optimized step by step. The linear working range under the optimized conditions were determined in the range of 10.00-400.00 ng mL-1 with the limit of detection as 3.57 ng mL-1. Quantitative results were obtained in recovery experiments with the help of model solutions including phenobarbital molecule

An enrichment and determination method based on liquid chromatographically analysis and cloud point extraction (CPE) has been developed for trace levels of B vitamins (B1, B9 and B12) in the proposed study. Vitamin molecules were drawn into the non-ionic surfactant phase of Polyethylene Glycol (PEG-6000) in the presence of pH 9.0 medium. The surfactant-rich phase separated by centrifugation and then dissolved with 700 µL of ethanol. The obtained ethanol phase was filtered by 0.45-micron filter prior to the HPLC analysis. All parameters affecting the CPE method such as pH, buffer volume, incubation time, surfactant and electrolyte concentration, solvent for the surfactant-rich phase and its amount have been individually studied and optimized step by step. After the optimization of all parameters of the CPE process, the detection limits of the developed method for B1, B9 and B12 vitamins were calculated as 1.42 ng mL-1, 7.14 ng mL-1 and 14.28 ng mL-1 , respectively. The linear working ranges for three vitamin molecules was obtained in the range of 5.0-500.0 ng mL-1. After CPE procedure, determination of vitamin molecules was carried out by using HPLC system with diode array detector(DAD) at 244 nm for vitamin B1, 285 nm for vitamin B9, and 361 nm for vitamin B12, respectively