In this work, a highly accurate and sensitive method with low cost analyzer NAG/ADF/(300-2) homemade instrument coupled under continuous flow injection (CFIA) analysis was used to determine promethazine hydrochloride in pure and pharmaceutical drug tablets. This method is dependent on the reaction between promethazine hydrochloride and phosphomolybdic acid (PMA) in the presence of ammonium chloride to form a brownish-yellowish ion-pair complex as precipitate. The turbidity of the formed complex has measured at an angle of 0-180° through the attenuation of incident light by precipitating. The chemical and physical parameters have been studied and optimized to enhance the sensitivity for the developed method of the promethazine hydrochloride-PMA-NH4Cl system. The calibration curve of the proposed method was linear over the range 0.5-30 mmole.L-1 for both cells (Cell no.1 and Cell no.2), the detection limit for cell A = 2.1659 µg/sample and for cell B = 0.4332 µg/sample from the visual evaluation of the lowest concentration at which the analyte can be reliably detected with the correlation coefficient (r) = 0.9984, 0.9997 for cell A and cell B, respectively. For promethazine-HCl concentrations (5 and 10 mmole.L-1) for both cells (n=8), the relative standard deviation percent (RSD%) was lower than 0.5%. The method has been successfully applied for the promethazine HCl determination in two pharmaceutical medicines. A comparison was made using the standard addition curve between the newly proposed method (NAG-ADF-300-2 analyzer) and the reference methods, mainly British Pharmacopoeia (B.P), turbidimetry, and UV- spectrophotometry (λmax =249 nm) using paired t-test. It was noticed that there was no significant difference between the methods at 95% confidence level. The statistical procedures have shown that a homemade NAG/ADF/(300-2) analyzer which contains two identical detections units ( cell A and cell B) is the best choice with an excellent prolonged detection, widespread application and extra sensitive.