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Abstract  

Molar heat capacities of acetaminophen were precisely measured with a small sample precision automated adiabatic calorimeter over the temperature range from 80 to 330 K. A solid-solid transition at 149.96 K was found from the C p,m-T curve. The polynomial functions of C p,.m(J K-1 mol-1) vs. T were established on the heat capacity measurements by means of the least square fitting method. Thermal decomposition processes of acetaminophen have been studied by thermogravimetry. And the thermal decomposition kinetics parameters, such as activation energy E, pre-exponential factor A and reaction order n, were calculated by TG-DTG techniques with the Freeman-Carroll method, Kissinger method and Ozawa method. Accordingly the thermal decomposition kinetics equation of acetaminophen is expressed as: dα/dt=2.67107e-89630/RT(1-α)0.23. The process of fusion has been investigated through DSC. The melting point, molar enthalpy and entropy of fusion are to be (441.890.04) K, 26.490.44 kJ mol-1 and 59.801.01 J K-1 mol-1, respectively.

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Abstract  

This article provides a thermodynamic analysis of DSC data for acetaminophen polymorphic forms I and II by measurement of heat capacity. Form I is found to have lower heat capacity and free energy and hence better stability than Form II down to at least –30C. The transition temperature below which Form II becomes more stable was determined to be less than –120C. Form I is more stable than Form II as a consequence of its higher entropy, since its crystallographic packing arrangement is of larger energy.

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Abstract  

The degradation of acetaminophen (APAP) in aqueous solutions with heterogeneous Fenton reactions was investigated with montmorillonite KSF as catalyst. The influencing factors of the initial APAP concentration, initial pH value, initial KSF dosage and H2O2 dosage were studied. The results showed that APAP could be effectively degraded under the conditions of pH 4.0, KSF 0.2 g/L and H2O2 0.5 mM, and the degradation efficiency of 0.5 mg/L APAP reached 93.5% after reaction for 30 min. The degradation kinetics of APAP followed the pseudo first-order rate law.

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We have investigated the use of pressurized planar electrochromatography (PPEC) and planar chromatography (TLC) for reversed-phase separation of a mixture of acetylsalicylic acid, caffeine, and acetaminophen. The mixture was separated on C18 plates; the mobile phase was prepared from acetonitrile (ACN), buffer, and bidistilled water. The effects of operating conditions such as mobile phase composition, type of the stationary phase, and mobile phase buffer pH on migration distance, separation selectivity, and separation time in TLC and PPEC were compared. The results showed that pressurized planar electrochromatography of these drugs is characterized by faster separation, better performance, and different separation selectivity. In conclusion, PPEC is a very promising mode for future application in pharmaceutical analysis.

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Two fundamentally different analytical methods have been validated and used to monitor release of diclofenac and acetaminophen (paracetamol), from commercially available combination tablet formulations, in dissolution media. A sensitive HPTLC method was developed and validated for analysis of diclofenac. The filtered dissolution samples were directly spotted on to precoated silica gel 60 F 254 TLC plates and diclofenac was separated by use of chloroform-methanol-ammonia solution, 10 + 25 + 0.25 ( v/v ), as mobile phase. The spots were scanned at λ = 277 nm. Peak areas for diclofenac were found to be linearly dependent on the amount applied to the plate in the range 30–390 ng spot −1 ( r = 0.999).For estimation of acetaminophen a simple colorimetric method, involving reaction with sodium nitrite in acid then treatment with alkali to produce the 3-nitroacetaminophane anion (yellow color), was validated and used. The intensity of the yellow color, monitored at λ = 430 nm, was found to be linearly dependent on acetaminophen concentration in the range 5–30 μg mL −1 ( r = 0.999). These two methods were successfully used to study the dissolution profiles of diclofenac and acetaminophen from samples of ten different commercial diclofenac-acetaminophen combination tablets.

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Orvosi Hetilap
Authors: Gábor Lendvai, András Kiss, Ilona Kovalszky, and Zsuzsa Schaff

mtsa: Changes of micro-RNA expression in rat liver treated by acetaminophen or carbon tetrachloride – regulating role of micro-RNA for RNA expression. J. Toxicol. Sci., 2007, 32 , 401–409. Yamada H

Open access

The combination of xanthine oxidase inhibitor febuxostat (FBX) with acetaminophen (ACE) is widely used in the treatment of gout. A rapid, simple, selective, and precise densitometric method was developed and validated for the simultaneous estimation of FBX–ACE mixture in a synthetic binary mixture and in their pharmaceutical dosage forms. The method employed thin-layer chromatography (TLC) aluminum plates precoated with silica gel G 60 F254 as the stationary phase using chloroform‒methanol‒cyclohexane‒acetic acid 96% (7:1:1:0.1, v/v) as the mobile phase. The optimized mobile phase selected for development gave compact bands (R F values were 0.65 and 0.46 for FBX and ACE, respectively). Spectrodensitometric scanning integration was performed using dual-wavelength detection at 320 and 250 nm for FBX and ACE, respectively. The linear regression data for the calibration plots showed excellent linear relationship (r = 0.9997 and 0.9992 for FBX and ACE, respectively). The method was validated for precision, accuracy, robustness, and recovery. The limits of detection and quantification were calculated. The statistical analysis proved that the method is reproducible and selective for the estimation of this binary mixture.

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Journal of Thermal Analysis and Calorimetry
Authors: Y. A. Ribeiro, J. D. S. de Oliveira, M. I. G. Leles, S. A. Juiz, and M. Ionashiro

Thermogravimetry, derivative thermogravimetry (TG, DTG) and differential scanning calorimetry (DSC), were used to study the thermal behaviour of mefenamic acid, ibuprofen, acetaminophen, sodium diclofenac, phenylbutazone, dipyrone and salicylamide. The results led to thermal stability data and also to the interpretation concerning the thermal decomposition.

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Boutaud, O., Aronoff, D. M., Richardson, J. H., Marnett, L. J., Oates, J. A. (2002) Determinants of the cellular specificity of acetaminophen as an inhibitor of prostaglandin H(2) synthases. Proc. Nat. Acad. Sci. USA 99 , 7130

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with acetylsalicylic acid, acetaminophen, diflunisal, dimenhydrinate, ketoconazole, and mefenamic acid. Experimental Chemicals Acetyl salicylic acid, acetaminophen, diflunisal, dimenhydrinate, ketoconazole

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