The determination of 3-nitrophenol and some other aromatic impurities in 4-nitrophenol by reversed phase HPLC with peak suppression diode array detection. 
In this work the peak suppression technique is used for the determination of 3-nitrophenol and some other aromatic impurities in 4-nitrophenol by reversed phase HPLC with diode array detection.  Taking into account the differences between the absorption spectra of the two compounds, two wavelengths were selected in order to obtain the maximum difference between the spectral contribution for 3-nitrophenol and to maintain a small, similar spectral contribution for 4-nitrophenol (the main compound).  Then we used the wavelength corresponding to a small spectral contribution of 3-nitrophenol as the reference wavelength.  It was shown that taking lambda(an) = 266 nm and lambda(ref) = 364 nm, a broad elution peak of 4-nitrophenol was suppressed deconvoluting the peak of 3-nitrophenol.  Moreover, quantitation of 3-nitrophenol was achieved without chemometric tools.  Under the proposed conditions the detection limits for 3-nitrophenol and other common impurities of 4-nitrophenol used in the pharmaceutical industry (4-chlorophenol, 4-nitrophenol, 1-chloro-2-nitrobenzene, 1-chloro-4-nitrobenzene, 4,4'-bisfenilether, and 4,4'-dichloroazobenzene) were not significantly affected as compared with respective detection limits evaluated in the absence of 4-nitrophenol and using standard detection conditions (lambda(an) = 280 nm and lambda(ref) = 420 nm).