A very fast, economical and simple direct spectrophotometric method was investigated for Paracetamol (PC) determination in aqueous medium without using any reagent. The method is based on the photo activation of the analyte at 243 nm after dissolution in water. The change in structure of PC after addition of water was studied by comparing the corresponding FTIR spectra. Optimization studies were conducted by using a 5 μg ml-1 standard solution of the analyte. Various parameters studied include, time for stability and measurement of spectra, effect of HCl, NaOH, CH3COOH and NH3 for change in absorbance and shift in spectra, interference by some analgesic drugs and some polar solvents and temperature effect. After optimization, Beer’s law was obeyed in the range of 0.3–20 μg ml-1 PC solution with a correlation coefficient of 0.9999 and detection limit of 0.1 μg ml-1 for 3/1 S/N ratio. The newly developed method was successfully applied for PC determination in some locally available tablets and urinary samples. The proposed method is very useful for quick analysis of various types of solid and liquid samples containing PC. Another spectrophotometric work describes a simple, sensitive, rapid and economical analytical procedure for direct spectrophotometric evaluation of Diclofenac Sodium (DS) using aqueous medium without using a chemical reagent. Parameters like time, temperature, acidic and basic conditions and interference by analgesic drugs was studied for a 5μg ml-1 solution of DS at 276 nm. Under optimized parameters, a linear working range of 0.1–30 mg ml-1 with regression coefficient of 0.9998 and lower detection limit of 0.01 mg ml-1 was obtained. The method was applied for DS contents in tablets, serum and urine samples. v A new method was developed for the determination of paracetamol by differential pulse voltammetry (DPV) at carbon film electrode (CFE). The experimental parameters, such as pH of Britton-Robinson buffer and potentials for regeneration of electrode surface were optimized. Under optimized conditions in Britton-Robinson buffer pH 4.0 a linear calibration curve was obtained in the range 0.02–100 μmol L-1. The limit of determination was 0.034 μmol L-1 which showed high sensitivity of developed method. The method was applied for the quantitative determination of Paracetamol in pharmaceutical formulations as well as urine samples. A rapid, reliable and economical analytical procedure for the estimation of ibuprofen in pharmaceutical formulations and human urine samples was developed using transmission Fourier Transform Infrared (FT-IR) spectroscopy. For the determination of ibuprofen, a KBr window with 500 μm spacer was used to acquire the FT-IR spectra of standards, pharmaceuticals as well as urine samples. The Partial Least Squares (PLS) calibration model was developed based on carbonyl region (C=O) from 1807-1461 cm−1 in the range from 10- 1000 ppm. The developed model was checked by cross-validation steps to diminish standard error of the models, such as root mean square error of calibration (RMSEC), root mean square error of cross validation (RMSECV) and root mean square error of prediction (RMSEP). The good coefficient of determination (R2) was achieved 0.999 with minimum standard errors RMSEC, RMSECV and RMSEP 1.89, 1.956 and 1.38, respectively. The other method was based on indirect determination of acetylsalicylic acid (aspirin) utilizing differential pulse voltammetry at carbon film electrode as working electrode. The theory of indirect determination of ASA is based on the hydrolysis of aspirin in salicylic acid (SA) for detection. Moreover, we optimized conditions such as pH of Britton-Robinson buffer, potentials for regeneration and activation of electrode surface, amplitude and scan rate. Under optimized conditions in Britton-Robinson buffer pH 2.0 a linear calibration curve was obtained in the range 0.2 – 100 μmol L-1. The limit of determination was 0.15 μmol L-1 which showed high sensitivity of developed method. The method for indirect determination of ASA was thus developed for the quantification of pharmaceutical formulations as well in human urine model samples.