H-Point standard additions method for resolution of overlapping Chromatographic peaks with diode array detection by using area measurements Determination of phenol and cresols in waters

Unbiased spectrophotometric method for estimating phenol or o-cresol in unknown water samples

The generalised H-point standard addition method (GHPSAM) was applied to quantify phenol and o-cresol in waters and compared with other analytical approaches. The method is based on spectroscopic and kinetic measurement of the formation of derivatives with p-aminophenol and KIO(4) in presence of NaOH. First, pseudo-first order kinetic behaviour of the reaction products was demonstrated. The unbiased formation rate constants of phenol and o-cresol derivatives were calculated. The analytical figures of merit were determined using the GHPSAM as calibration method. Detection limits achieved were 0.2 microg L(-1) of phenol and 0.2 microg L(-1) of o-cresol using a preconcentration factor of 10. Styrene-divinyl benzene cartridges were used in the preconcentration step. Repeatability values were 3.7% for phenol and 2.0% for o-cresol; reproducibility values were 6.9% and 3.5%, respectively. Accurate and precise results were obtained when the method was applied to real samples of natural water.

H-point curve isolation method for coupled liquid chromatography and UV-visible spectrophotometry

The H-point curve isolation method (HPCIM) for the detection of unknown interferences in chromatography is proposed. The method allows one to estimate the UV-vis spectra of interfering species in a sample as well as to test the purity of the chromatographic peaks. Besides the detection of the unknown interferences in a sample, this method allows one to calculate the concentration of an analyte in the presence of unknown compounds. To illustrate the reliability of the proposed method, samples of diuretics and amphetamines have been analyzed by normal- and reversed-phase high-performance chromatography.

Generalised H-point standard addition method for the isolation of the analyte signal from the sample signal when coelution of unknown compounds occurs in liquid chromatography

The generalised H-point standard addition method (GHPSAM) is proposed for isolating the analytical signal of an analyte from the signal of an unknown sample. Samples containing two and three coeluting compounds have been analysed. The accuracy of the predictions depends on the shape of the analyte and interferent spectra but not on the degree of chromatographic overlap. This methodology involves the location of linear intervals for the unknown interference spectrum from the spectrum of the sample. Once the linear interval has been found the selection of three wavelengths within the interval will allow the cancellation of the signal of the unknown interferent. The method has been applied to the determination of diuretics, amphetamines and phenols in water.