Stability Indicating RP-HPLC and Spectrophotometric Methods for Simultaneous Estimation of Sodium Benzoate and Cefdinir in the Presence of its Degradation Products-Application to Blank Subtraction Method.

Objectives: Empower 3 software is important in modeling, optimization, and reducing the time of manual calculation of related substance by subtracting the baseline of a blank chromatogram from the unknown sample automatically; so, the major objective of the developed method is to introduce a new, selective, and economical high performance liquid chromatography (HPLC) and spectrophotometric method for simultaneous estimation of sodium benzoate (SDB) and cefdinir (CFR) in the presence of its degradation products.

Materials and methods: Chromatographic separation is optimized and adjusted using two methods; method (I) is characterized for separation of active pharmaceutical ingredient (CFR) in pure and dosage forms using Atlantis dC18 column [4.6 mm x 250 mm (5 μm particle size or equivalent)] with a mobile phase consisting of methanol: 0.02 M phosphate buffer solution pH 3.0 (40:60 v/v) at a flow rate of 1.0 mL/minute, injection volume 10 μL and wavelength 254 nm. Method (II) is identified for related substances in a Hichrom C18 column (15 x 0.46 cm), 5 μm particle size or equivalent, using a binary gradient consisting of solution A [0.1% tetramethylammonium hydroxide solution (pH: 5.5) with 0.1 M EDTA (1000:0.4 v/v)] and solution B (0.1% tetramethylammonium hydroxide solution (pH 5.5): acetonitrile: methanol : 0.1 M EDTA (500:300:200:0.4 v/v) using injection volume 10 μL for reversed-phase HPLC with a wavelength equals to 254 nm and flow rate 1.0 mL/min. Two ecofriendly spectrophotometric methods were successfully used to resolve the spectral overlap of drugs.

Results: Method A, the first derivative of ratio spectra spectrophotometric method (1stDD) where CFR was determined at two wavelengths 283.5 nm, 313.4 nm and SDB was determined at 216.7 nm, 235.5 nm. Method B, ratio subtraction method is performed to overcome the interference between CFR and the preservative SDB. The ultraviolet spectrum of the laboratory mixture is divided by that of CFR (20 μg/mL) as a divisor then subtracting the amplitudes in the plateau region at 250-315 nm (the constant) from that of the ratio spectrum. The zero-order spectra of SDB were obtained at 225 nm by multiplying the resulting ratio spectra by the divisor (CFR), zero order of CFR was been estimated at a wavelength value of 283 nm after multiplication of the divisor by the obtained constant.

Conclusion: The optimized method was adjusted and validated as per International Conference on Harmonization guidelines and could be easily utilized by quality control laboratories and for laboratory-prepared mixtures.