Determination of unchanged hydralazine in plasma by gas-liquid chromatography using nitrogen-specific detection

Determination of hydralazine with flow injection chemiluminescence sensor using molecularly imprinted polymer as recognition element

A novel flow injection chemiluminescence (CL) sensor for hydralazine determination using molecularly imprinted polymer (MIP) as recognition element is reported. Hydralazine-MIP was prepared through non-covalent copolymerization using methacrylic acid (MAA) monomer, hydralazine template and ethylene glycol dimethacrylate (EGDMA) cross-linker. Particles of the MIP were packed into a v-shape glass tube for on-line adsorption of the analyte of hydralazine. The adsorbed hydralazine could be sensed by its great enhancing effect on the CL reaction between luminol and periodate. The CL intensity is linear to hydralazine concentration in the range from 2x10(-9) to 8x10(-7) g/mL. The detection limit is 6x10(-10) g/mL (3sigma) and the relative standard deviation is 2.8% (n=7) for 8x10(-9) g/mL hydralazine. The selective experiment showed that the selectivity and sensitivity of the CL method could be greatly improved when MIP was used as recognition element in the flow-injection CL sensor. The sensor was reversible and reusable. It could be used for more than 100 times. It has been used directly to determine the hydralazine in human urine.

Liquid chromatographic determination of hydralazine in human plasma with 2-hydroxy-1-naphthaldehyde pre-column derivatization

A selective and sensitive high-performance liquid chromatographic method is described for determination of hydralazine and its metabolites in human plasma. The method involves pre-column derivatization with 2-hydroxy-1-naphthaldehyde at pH 1.2. The reaction product and Methyl Red used as internal standard are extracted into dichloromethane and chromatographed in the reversed-phase mode on an ODS-2 column using acetonitrile-aqueous triethylamine phosphate buffer (80:20, v/v) at pH 3 as eluent. The plasma calibration curve of hydralazine is linear in the concentration range 10-500 ng ml-1. The detection limit is 1 ng ml-1 and the relative standard deviation is less than 2.4. In vivo pharmacokinetics of hydralazine in two volunteers after oral administration of 50 mg of the drug is studied using the proposed LC method.

Determination of hydralazine in human plasma by high-performance liquid chromatography with electrochemical detection

Hydralazine is used as an antihypertensive vasodilator drug. A specific and sensitive method for extraction and analysis of hydralazine by high-performance liquid chromatography (HPLC) with electrochemical detection was developed. Hydralazine and 4-methylhydralazine (internal standard) in plasma were derivatized at room temperature with salicylaldehyde. The derivatives were extracted in basic medium with a mixture of heptane, methylene chloride and isopentyl alcohol. A very good separation of hydralazine and 4-methylhydralazine from matrix material was achieved on a Supelcosil LC-18-DB (5 microns) reversed-phase column kept at 28 degrees C with a mobile phase of 66% methanol in 0.055 M citric acid/0.02 M dibasic sodium phosphate (pH 2.5). The hydralazine level was measured electrochemically by a screen oxidation mode. This method offers significant advantages in sensitivity, specificity and accuracy. Sample analysis by HPLC required less than 8 min. Application of the method to monitor plasma levels of hydralazine from a patient receiving the drug for the treatment of severe pregnancy-induced hypertension is discussed.

Direct derivatization of drugs in untreated biological samples for gas chromatographic analysis

The possibilities to derivatize an analyte directly in the biological sample are reviewed with examples from our own experiences and from the literature. Techniques, such as extractive acylation, alkylation and benzoylation, are frequently used. Improvement of the extractability of the drug from the matrix is a common feature, especially with hydrophilic compounds, where sometimes cyclizing reactions can be employed. Several analytes are reactive or labile in the sample and can be trapped in derivatization reactions in situ. In many cases, two-phase reactions lead to milder derivatization conditions (e.g. dealkylation of tertiary amines), which is favourable from a clean-up point of view.

Drug level monitoring: cardiovascular drugs

Methods for the determination of cardiovascular drugs in blood and plasma are critically reviewed with emphasis on gas and liquid chromatographic techniques. The importance of the various procedures is discussed, in particular sample work-up where the conditions for isolation and derivatization of the compounds are decisive for the accuracy and precision of the methods. Compared with other assay techniques chromatographic methods are generally to be preferred owing to their better selectivity. In the review the following groups are discussed: digitalis glycosides, antiarrhythmic agents, beta-adrenoceptor antagonists, vasodilating agents, antihypertensive compounds, and diuretics.

Gas chromatographic method for the simultaneous determination of hydralazine and its acetylated metabolite in serum using a nitrogen-selective detector

A relatively simple gas chromatographic method has been developed for the quantitative determination of hydralazine simultaneously with its acetylated metabolite, 3-methyl-s-triazolo[3,4-alpha]phthalazine (MTP). The proteins were removed by means of sulfosalicylic acid and Sure-Sep. On treatment with formic acid, hydralazine and its internal standard were converted into their formylated derivatives. These derivatives, MTP and its internal standard were extracted with toluene and determined by gas chromatography with a nitrogen-selective detector. The lower limits of detection for hydralazine and MTP were 0.13 and 0.27 mumol/l, respectively.

Selective high-performance liquid chromatographic assays for hydralazine and its metabolites in plasma of man

Selective high-performance liquid chromatographic assays for hydralazine (I), hydralazine pyruvic acid hydrazone (II) and the acetylation metabolites, namely s-triazolo[3,4-alpha]-phthalazine (V) and 3-hydroxymethyl (VI) and 3-methyl-s-triazolo[3,4-alpha]phthalazine (VII) in human plasma were developed. Utilizing the fluorescence of these compounds or their derivatives the limits of detection could be extended down to 5 nmole/l (1 ng/ml) for I, 1 nmole/l (0.2 ng/ml) for II and 0.5 nmole/l (0.1 ng/ml) for V--VII. The intra-assay coefficients of variation for the assays ranged from 2 to 7% over the concentration range 5.0 to 0.05 micromole/l and the inter-assay variability in the slope of the standard curves ranged rom 4 to 8%. An improved method for measuring the sum of I plus all its hydrazones (apparent I) was also developed. On addition of I to fresh plasma at 37 degrees, half the added I was converted to II within 15 min and there was no detectable level of I, 2 h after the addition. The plasma level--time course of I, and its metabolites in a healthy volunteer (slow acetylator) following separate oral and intravenous administrations of I indicated that I contributed only a small fraction (4.3 and 4.7% respectively) to the area under the plasma level--time curve of apparent hydralazine.