A Comparison Of Measurement of Homovanillic Acid in Brain Tissue by Gas Chromatography Mass Spectrometry and Liquid Chromatography with Electrochemical Detection

Abstract

A comparison of liquid chromatography with electrochemical detection (LCEC) and gas chromatography mass spectrometry (GCMS) has been made for analysis of homovanillic acid (HVA) in rat brain tissue. The LCEC procedure gave slightly higher average values of HVA in the samples measured; however, the HVA content determined by both methods related significantly. Rat brain meostriatum was used as representative samples for comparison of the two analytical procedures.     

Comparison of Full Factorial Design,Central Composite Design,and Box-Behnken Design in Chromatographic Method Development for the Determination of Fluconazole and Its Impurities

This paper presents the development and optimization of a liquid chromatographic method for the determination of fluconazole and its impurities by experimental design methodology. Four experimental design types were applied: two-level full factorial design, central composite design, Box-Behnken design, and three-level full factorial design. The advantages and drawbacks of each design are described and detailed statistical evaluation of mathematical models was performed. The central composite design and three-level full factorial design created significantly better models comparing to the other methods. As the central composite design requires a smaller number of experiments, its models were used for theoretical examination of experimental space. Multiobjective optimization aiming to achieve maximal separation of all investigated substances and minimal analysis duration was performed by a grid point search. The defined optimal separation was achieved on a C₁₈ (125 mm × 4 mm, 5 µm particle size) column with a mobile phase consisting of acetonitrile and water (5 mM ammonium formate) (15:85, v/v); a column temperature of 25°C; a flow rate of 1.2 mL min^?1; and a detection wavelength of 260 nm.     

Determination of Nitrofurans in Chicken Feed by High-Performance Liquid Chromatography–Tandem Mass Spectrometry

Liquid chromatography with tandem mass spectrometry was used for the determination of nitrofurantoin, nitrofurazone, furazolidone, and furaltadone in chicken feed. The nitrofurans were extracted with phosphate buffer (pH 7) and sodium chloride. Proteins and lipids were removed with acetonitrile and hexane before purification with ethyl acetate, dilution in 1:1 acetonitrile-5 millimolar ammonium acetate at pH 7.3, and filtration prior to analysis. The limits of detection were 1.69, 1.74, 2.01, and 1.45 microgram per kilogram for nitrofurantoin, nitrofurazone, furazolidone, and furaltadone, respectively. The mean recoveries were between 84.6 and 110.6 percent. The method was employed to determine nitrofurans in chicken feed.     

Simultaneous Determination of Five Nonsteroidal Anti-Inflammatory Drugs and Two Glucocorticoids in Adulterated Traditional Herbal Medicines for the Treatment of Rheumatism

The adulteration of traditional herbal medicines (THMs) with synthetic drugs is prevalent and represents a serious risk for public health. A rapid and novel reversed-phase high-performance liquid chromatography (HPLC) method was established and validated for the simultaneous determination of five nonsteroidal anti-inflammatory drugs (NSAIDs) and two glucocorticoids in THMs for rheumatoid treatment. Glipizide was used as the internal standard (IS). The separation was completed on a C₁₈ column with a mobile phase consisting of methanol and a buffer solution containing 10 mM ammonium acetate and 0.1% formic acid with a gradient elution. All calibration curves showed good linear regression (r ² > 0.9996), and the recoveries of the seven analytes were in the range of 96.94%–105.37%. A liquid chromatography-mass spectrometry (LC-MS) method was developed to confirm the identity of the adulterants. The proposed method was applied to identify and determine the five NSAIDs and two glucocorticoids in THMs for rheumatism.     

Separation and Quantitation of Urinary Phthalates by HPLC

Abstract

A method was developed for the separation and quantitation of plasticizers and their metabolites from human urine using HPLC, Urine was diluted with an equal volume of water and extracted at pH 2.0 with diethyl ether, The extract was dried, the solvent vacuum stripped, and the residue dissolved in methanol for injection into the chromatograph. A C₁₈ reverse phase column containing 10 μ particles was used for the analysis. Ionic suppression, 0.5% acetic acid in water, at pH 3.0 was used to resolve the acidic components. A step gradient of acetonitri1e:water (containing acetic acid) was used to elute the polar metabolites as well as the non-polar plasticizers. Mass spectrometry was used t o identify the compounds in the HPLC fractions. From the HPLC fractions of the urine extract collected, phthalic acid, MEHP, DEHP and normal urinary constituents (e.g., hippuric and benzoic acid derivatives) were identified     

Persistent Organic Pollutants – Are Our Methods Sensitive and Selective Enough?

Due to the exponential growth of the world population and a strong worldwide economic development, humans are increasingly exposed to chemicals. This is particularly true for persistent, toxic chemicals that accumulate in organisms including humans. The presence of these persistent organic pollutants (POPs) has been reported since the 1960s. Analytical methods developed for the determination of POPs in wildlife, food, feed, sediments, dust, air, and humans have seen a tremendous improvement in sensitivity and selectivity. Detection limits of 0.1 mg/kg for pesticides in the 1960s have decreased down to < 0.1 ng/kg for dioxins presently. On the other hand, due to new toxicological insights, authorities nowadays often demand much lower detection limits than in the early days of discovery. This paper compares the lowest effectual levels of a number of POPs with the analytical capabilities of modern laboratories in terms of sensitivity and selectivity. Methods discussed are gas chromatography (GC), including multi-dimensional GC and liquid chromatography (LC), combined with electron capture detection (for GC) or with different mass spectrometric detectors. The conclusion is that the still improving sensitivity of current methods is sufficient to allow detection of POPs at a level clearly below the lowest observable adverse effect levels. Selectivity has also improved, but given the high complexity of some of the POPs and the multitude of POPs and other chemicals to which we are exposed, further developments in selectivity are still badly needed. To limit and focus the information for regulators, an effect-directed analysis is proposed as an alternative approach.     

High Performance Liquid Chromatographic Determination of Pirenzepine Dihydrochloride in Its Pharmaceutical Formulation

Abstract

A high-performance liquid chromatographic procedure for the determination of pirenzepine dihydrochloride as a bulk material and in its tablet dosage form (Gastrozepin^R) is presented. Normal phase liquid chromatography has been performed on a Micro-pack Si-10 column using ammonium hydroxide (28–30% NH₃) in methanol (0.75: 99.25% v/v) as mobile phase at a flow rate of 2 ml/min. Clobazam has been used as internal standard with retention times of 1.9 and 2.8 minutes for clobazam and pirenzepine dihydrochloride, respectively at 254 nm. Analytical calibration yields a linear relationship between 5 and 25 μg/ml, with correlation coefficient of 0.999. Tablets each labelled to contain 25 mg pirenzepine dihydrochloride give mean percentage found of 99.98 ± 0.4. A plot of logarithm of concentration against time for a solution in 6 N hydrochloric acid gives a straight line with a slope of - 0.197 day^?1. The proposed method is, therefore, a stability indicating method.     

Electrochemical Behavior of Azo Compounds in Liquid Ammonia

Abstract

At -40°C, the behavior of lO compounds, differing widely in their standard potentials, has been investigated in liquid ammonia, using cyclic voltammetry at a smooth platinum electrode. The purpose of this study was the realization of a redox scale with reversible systems. With azobenzene, pyridazine, cin-noline, benzocinnoline and 4,4′-azobis-(pyridine-N-oxide), the first electron transfer is reversible and leads to the formation of the corresponding radical anions which are stable; the second electron transferleads to the ciianions which can be protonated yielding the corresponding hydrazo. Other compounds, such as azoxybenzene, 3-amino-1,2,4-triazine, pyridine-N-oxide, 8-azaadenine and 1H-tetrazole, have an electrochemical behavior which i s more intricate.     

Determination of Organotin Compounds in Wine by Microwave-Assisted Extraction and High Performance Liquid Chromatography–Inductively Coupled Plasma Mass Spectrometry

A new analytical procedure for the determination of five organotin compounds in several matrix wine samples is reported. The organotin compounds were extracted by microwave-assisted extraction with n-hexane. Extraction conditions, such as volume of n-hexane required, extraction temperature, and extraction time, were investigated and optimized by an orthogonal array experimental design. The determination of organotin compounds in the final extracts was carried out by liquid chromatography–inductively coupled plasma mass spectrometry. The procedure showed limits of detection between 0.029–0.049 µg · L^?1. The linearity was in the range of 0.5 to 100 µg · L^?1. The precision expressed as relative standard deviation (RSD) was below 9.43%. The developed method was successfully employed to analyze different matrix wine samples, and some analytes were detected at the level of 0.053 to 1.14 µg · L^?1.