Demonstration of the compatibility of narrow-bore packed column high-performance liquid chromatography with conventional detection systems

Measurement of urinary catecholamines in small samples for mice

INTRODUCTION

Analysis of catecholamines in small samples of urine is difficult and sensitive to stress. Current techniques require pooling of samples or expensive separation by double mass spectrometry. A method for extraction of unconjugated catecholamines in 20μL urine samples has been developed using alumina extraction prior to separation by high performance liquid chromatography (HPLC) and electrochemical detection (ECD).

METHODS

Three murine experiments tested the application of the procedure. In the first, collection occurred in the morning and evening prior to handling, and in the morning after three days of handling. In the second, passively obtained urine was compared to stressfully obtained urine in the same mice. Finally, basal collections were compared to urinary catecholamine levels 15 and 30min into novel cage stress. Urine was extracted alongside 2,3-dihydroxybenzoic acid (DHBA) internal standard via alumina and brought to pH 8.5 with tris buffer. The mixture underwent two wash steps for depuration and eluted with perchloric acid for analysis on HPLC with ECD.

RESULTS

This novel extraction method using low amounts of urine yielded 48% recovery in the samples and 60% recovery in the standard extraction on average. With a signal to noise ratio of 3:1, the limit of detection (LOD) of a standard is 1.2pg/mL, which allows for the detection of 3.6pg/mL in urine or 72fg in a 20μL sample. Thus resting catecholamine levels are 216 times higher than the LOD. Unconjugated norepinephrine and epinephrine levels were significantly increased 15min after novel cage stress and epinephrine remained elevated after 30min, but did not show significant differences when comparing collection time, handling exposure, or specific collection technique.

DISCUSSION

The technique is an effective measure for sympathetic activity in micro samples, with a limit of detection in the attomole range for 20μL samples.

Kinetics of the acidic and enzymatic hydrolysis of benazepril HCl studied by LC

A reversed-phase high-performance liquid chromatographic (HPLC) method was developed and validated for the kinetic investigation of the chemical and enzymatic hydrolysis of benazepril hydrochloride. Kinetic studies on the acidic hydrolysis of benazepril hydrochloride were carried out in 0.1 M hydrochloric acid solution at 50, 53, 58 and 63 degrees C. Benazepril hydrochloride appeared stable in a pH 7.4 phosphate buffered solution at 37 degrees C and showed susceptibility to undergoing in vitro enzymatic hydrolysis with porcine liver esterase (PLE) in a pH 7.4 buffered solution at 37 degrees C. Benazeprilat appeared to be the major degradation product in both (chemical and enzymatic) studies of hydrolysis. Statistical evaluation of the proposed HPLC methods revealed their good linearity and reproducibility. Relative standard deviation (R.S.D.) was less than 4.76, while detection limits for benazepril hydrochloride and benazeprilat were 13.0 x 10(-7) and 9.0 x 10(-7) M, respectively. Treatment of the kinetic data of the acidic hydrolysis was carried out by non-linear regression analysis and k values were determined. The kinetic parameters of the enzymatic hydrolysis were determined by non-linear regression analysis of the data using the equation of Michaelis-Menten.

Simultaneous determination of benazepril hydrochloride and hydrochlorothiazide by micro-bore liquid chromatography

A micro-bore liquid chromatographic method was developed for the simultaneous determination of benazepril hydrochloride and hydrochlorothiazide in pharmaceutical dosage forms. The use of a BDS C-18 micro-bore analytical column, results in substantial reduction in solvent consumption and increased sensitivity. The mobile phase consisted of a mixture of 0.025 M sodium dihydrogen phosphate (pH 4.8) and acetonitrile (55:45, v/v), pumped at a flow rate of 0.40 ml min(-1). Detection was set at 250 nm using an ultraviolet detector. Calibration graphs are linear (r better than 0.9991, n = 5), in concentration range 5.0-20.0 microg ml(-1) for benazepril hydrochloride and 6.2-25.0 microg ml(-1) for hydrochlorothiazide. The intra- and interday R.S.D. values were <1.25% (n = 5), while the relative percentage error (Er) was <0.9% (n = 5). The detection limits attained according to IUPAC definition were 0.88 and 0.58 microg ml(-1) for benazepril hydrochloride and hydrochlorothiazide, respectively. The method was applied in the quality control of commercial tablets and content uniformity test and proved to be suitable for rapid and reliable quality control.

Analysis of paralytic shellfish poisoning toxins by automated pre-column oxidation and microcolumn liquid chromatography with fluorescence detection

Periodate oxidation of the toxins responsible for paralytic shellfish poisoning (PSP) yields fluorescent purines suitable for trace analysis by reversed-phase LC. Mobile phases containing perfluorinated acids, such as heptafluorobutyric acid, as ion-pair agents were found to provide high capacity factors for the oxidized products. Gradient elution on a microbore column with large volume injections and fluorescence detection permitted the detection of femtomole quantities of PSP toxins. A fully automated pre-column oxidation procedure was developed for an LC autosampler system in order to improve precision and allow unattended analyses. The complete method was applied successfully to various samples, including shellfish and toxic phytoplankton.