Influence of the storage conditions on the concentration of clenbuterol in cattle urine samples

A novel potentiometric approach for detection of beta-adrenergics and beta-adrenolytics in high-performance liquid chromatography

Potentiometric approach enabling sensitive and reliable detection for a series of 20 autonomic beta-adrenergic ligands with the use of poly(vinyl chloride) (PVC) based liquid membrane electrode coatings in the normal-bore cation exchange HPLC and narrow-bore reversed phase HPLC system is presented. It was found that in both kinds of HPLC modes with a contemporary hybrid polymer-silica packings an application of electrodes containing a tetrakis(p-chlorophenyl)borate (TCPB) gives limits of detection below to 8.0x10(-7) mol l(-1) (injected concentrations). In case of highly hydrophobic beta-adrenergic drugs the use of binary aqueous mobile phases with high concentrations of acetonitrile (up to 25% v/v) shifting an observable detection limits (DL) down to 2.0x10(-8) mol l(-1), especially for electrodes with addition of trioctylated alpha-cyclodextrin. The characteristics of developed potentiometric detectors was established by proposed a quantitative structure-potentiometric response relationships (QSPRRs) for a series of diversified beta-adrenergic compounds and for a set of the PVC based electrodes using TCPB alone as well as in combination with trioctylated alpha-cyclodextrin, dibenzo-18-crown-6, or calix[6]arene hexaethylester as the neutral macrocycle ionophore. A highly significant QSPRRs equations were obtained leading to reasonable prediction of the DL of specified electrodes in terms of the computationally derived set of molecular descriptors of beta-adrenergics and beta-blocking agents and similar amino alcohol type xenobiotics.

Potentiometric detection of exogenic beta-adrenergic substances in liquid chromatography

Potentiometric detection with poly(vinyl chloride) (PVC) based liquid membrane electrode coatings is presented for a series of 18 exogenic beta-adrenergic substances in cation-exchange-HPLC and RP-HPLC systems. In both types of HPLC modes employing hybrid polymer-silica packings we observed that use of tetrakis(p-chlorophenyl)borate (TCPB) containing electrodes yielded limits of detection (DL) down to 10(-7)-10(-8) M (injected concentrations). The use of eluents with high concentrations of acetonitrile (up to 55%) yielded detection limits down to 10(-9) M (injected concentrations). A quantitative structure-potentiometric response activity relationship (QSAR) was developed for the set of beta-adrenergic substances and for a set of PVC-based electrodes using TCPB alone or in admixture with trioctylated alpha-cyclodextrin, dibenzo-18-crown-6, or calix[6]arene hexaethylester. A multiple linear regression model based on a computationally derived set of 14 molecular descriptors allowed prediction of the detection limits of beta-adrenergic substances and other amine substances from their molecular structure.