Esmolol is a selective beta-1 receptor blocker medication used to treat hypertension, tachycardia, and atrial fibrillation. Impurities in esmolol can include residual solvents, degradation products, and other impurities that can affect the efficacy and safety of the medication. Strict quality control measures are necessary to ensure that esmolol is free from harmful impurities and meets the required standards for pharmaceutical use.