Liquid-solid extraction and HPLC determination of amiodarone metabolites in biological fluids

Summary An improved liquid-solid extraction procedure for the purification and determination of amiodarone and desethylamiodarone in biological fluids is proposed. The sample is passed through a silica-C₁₈ column, and after washing, the analytes are eluted with methanol. The determination is then accomplished by RP HPLC using an octadecyl silica column and a mobile phase of methanol containing 0.0015% of ammonium hydroxide. The effect of ammonia concentration on the capacity factors of the analytes has been used for estimating the acid dissociation constants of the investigated secondary and tertiary amines in methanol.     

HPLC method for the simultaneous analysis of valproic acid and other common anticonvulsant drugs in human plasma or serum

Summary The derivatizing procedure of Moody et al. [20] for valproic acid has been simplified and applied to the simultaneous HPLC determination of valproic acid (VPA), barbital (B), primidone (PRM), phenobarbital (PB) and carbamazepine (CBZ) in serum or plasma of epileptic patients. The sample is deproteinized with acetonitrile containing esterification agents and an aliquot of the supernatant is heated to 70°C for 15 min with 4-bromophenacyl bromide. The reaction mixture is analysed on a C18 column at ambient temperature, with gradient elution and with detection at 205 nm. The time required for the chromatographic analysis is 13 min; identification is based on retention time and quantification is by peak area determination with an internal standard. The calibration curves show good linearity in the range 6.25 to 100 mg/L. The detection limits at a signal: noise ratio 3, ranged from 1 mg/L for B and CBZ to 2–3 mg/L for PRM, PB and VPA. The method described for the simultaneous determination of the five drugs in the same plasma pool, correlated well with isocratic HPLC methods specific for each drug. The simultaneous procedure described allows a reproducible (CVs6.5% within run) and rapid (25 min for sample preparation: 13 min for chromatographic run) therapeutic monitoring of patients treated with VPA and two or more antiepileptic drugs.     

Quantitation of cortico-steroids as common adulterants in local drugs by HPLC

Summary A sensitive and specific method for quantitation of the steroids betamethasone, prednisolone and cortisone acetate commonly used as adulterants in locally produced herb extracts and in certain homeopathic drugs is described. Reverse-phase liquid chromatography with UV detection has been used.     

Highly sensitive measurement of mepindolol in biological fluids using HPLC and electrochemical detection

Summary Mepindolol, a β-blocker agent, has an indolic structure which can undergo oxidation. A high-performance liquid chromatographic technique has been used to measure mepindolol in biological fluids using pindolol as the internal standard. The chromatography has been combined with electrochemical detection (coulometric detector). This method allows the determination of very low amounts of mepindolol with good precision and accuracy, the limit of quantification being 0.6 ng · ml⁻¹.     

Determination of chlorproguanil and metabolites in biological fluids

Summary The retention behaviour of chlorproguanil and its putative metabolites chlorcycloguanil and 3,4-dichlorophenylbiguanide has been studied on a reversed phase chromatographic system incorporating sodium lauryl sulphate as hydrophobic pairing ion. On the basis of data obtained and comparison of standard compounds with components present in urine following the administration of chlorproguanil, the identity of the metabolites have been confirmed chromatographically. A third unidentified metabolite is also observed. The retention study allows selection of a solvent system which, when used with a small volume, 100 × 2 mm, 3μm ODS column, enables chlorproguanil and its two major metabolites to be determined in plasma, whole blood and urine. The analytical characteristics of the method are reported and the usefullness of the method in obtaining pharmacokinetic data on the drug and its metabolites is discussed.     

Rapid separation of some antiepileptic drugs in serum by HPLC

Summary A fast and easy, iscratic high-performance liquid chromatographic method for the simultaneous determination of primidone, phenobarbital, phenytoin, carbamazepine and thiobutabarbital from serum samples has been developed. The optimal eluent composition is 36% acetonitrile, 24% methanol and 40% phosphate buffer. Using a programmable wavelength detector very low (sub-therapeutic) levels of the drugs can be measured.     

Quantitative determination of trace amounts of L-alanine in triglycine sulphate crystals by HPLC

Summary A method for the quantitative determination of L-alanine in triglycine sulphate crystals, in the presence of excess amounts of glycine, is described. L-alanine is determined after derivatization with 4-N,N-dimethyl-aminoazobenzene-4-sulfonyl chloride (DABS-Cl) and in the presence of DABS-valine used as the internal standard. The results obtained indicate that the method permits the determination of alanine in triglycine sulphate crystals at concentrations of about 1%.     

Solid phase extraction conditions for the selective isolation of drugs from biological fluids predicted using liquid chromatography

Summary A new method to predict the most suitable conditions for the solid phase extraction of 1,4-benzodiazepines and related compounds using C18 Sep-Pak carridges is proposed. The composition of the washing and elution solvents for the solid phase extraction of a test compound can be obtained from its capacity factor on a C18 HPLC column and an equation which relates capacity factors and solid phase extraction data of other similar compounds. The solid phase extraction data given in this paper can be used by others, there by saving considerable time and effort in the development of sample preparation methods. The suitability of the method was checked with two test compounds, showing good results.     

Column purification and HPLC determination of teicoplanin and A40926

Summary A simple HPLC method for quali- and quantitative determination of teicoplanin and A40926 in fermentation broths and in biological fluids is described. The sample is purified on affinity chromatography and then analyzed on a reverse phase column using a gradient phosphate buffer-acetonitrile as mobile phase and UV detection at 254 nm. No interference from endogenous sources has been observed. The analytical method, with partial modifications, was also used to isolate on semipreparative scale the single components of these antibiotics, in order to investigate their structure and their biological activity.     

Direct injection analysis of hexamethylene bisacetamide in biological fluids by an HPLC column switching technique with a micellar mobile phase

Summary This paper describes the direct injection analysis of the anti-cancer drug hexamethylene bisacetamide (HMBA) in biological fluids by an HPLC column switching technique. The first chromatographic column, which provides for sample extraction and cleanup, employs a micellar mobile phase with SDS as the modifier. The second column, coupled on-line to the first, utilizes reversed-phase conditions for analysis. UV detection is employed at 210 nm. 282 samples from 12 cancer patients were analysed and good pharmacokinetics curves obtained. The drug gives recoveries of 94.0–100.9% with a relative standard deviation of 1.88%. A sample analysis is completed within 15 minutes. This method should be satisfactory not only for the analysis of HMBA but also, probably for other drugs in biological fluids.     

Automated high-performance liquid chromatographic determination of amphetamine in biological fluids using column-switching and on-column derivatization

Summary A rapid and simple liquid-chromatographic method has been developed for on-line quantification of amphetamine in biological fluids. Untreated samples (20 μL) are injected directly into the chromatographic system and purified on a 20 mm×2.1 mm i.d. pre-column packed with 30 μm Hypersil C₁₈ stationary phase. After clean-up the analyte is transferred to the analytical column (125 mm×4 mm i.d., 5 μm LiChrospher 100 RP₁₈) for derivatization and separation using a mixture of acetonitrile and the derivatization reagent (o-phthaldialdehyde andN-acetyl-L-cysteine) as the mobile phase. The experimental conditions for on-line derivatization and resolution of the amphetamine have been optimized, and the results have been compared with those obtained by derivatizing the analyte in pre-column mode. The method described has been applied to the determination of amphetamine in plasma and urine. Good linearity and reproducibility were obtained in the 0.1–10.0 μg mL⁻¹ concentration range, and limits of detection were 25 ng mL⁻¹ and 10 ng mL⁻¹ with UV and fluorescence detection, respectively. The procedure described is very simple and rapid, because no off-line manipulation of the sample is required; the total analysis time is approximately 8 min.     

Determination of phenol in raw and potable waters by HPLC multi-electrode electrochemical detection

Summary A method is proposed for the determination of phenol in raw and potable waters using multi-electrode electrochemical detection HPLC. The coulometric efficiency of the electrochemical cell together with an ability to ‘screen out’ other electrochemically active species precludes the need for trace enrichment concentration techniques. The development work leading up to the proposed method is discussed with reference to selection of solvent pH and electrode potentials. The method has a limit of detection of 0.034μgl⁻¹ phenol and a total standard deviation of 0.083μgl⁻¹ phenol at a phenol concentration of 1.048μgl⁻¹ phenol in river water.     

Determination of trichlormethiazide in human plasma and urine by high-performance liquid chromatography

Summary This paper describes a high-performance liquid chromatographic (HPLC) assay method for the determination of trichlormethiazide (TCM) in human plasma and urine. After extraction and separation on an ODS column TCM from plasma was detected by oxidation in an electrochemical detector (ECD) by a porous graphite electrode. The sensitivity was better than HPLC with UV detection, enabling the determination of 2 ng ml^–1 TCM in human plasma. This method also allows determination of TCM at higher concentrations by exchanging the UV for the electrochemical detector. To study the pharmacokinetics, TCM in plasma and urine was assayed with coefficients of variation in the range 2–3%. The method has the advantages of high sensitivity for plasma assay and high precision with a simple procedure for both plasma and urine samples. Small samples of 0.5 ml plasma per assay also reduced the total volume of plasma needed.     

Estimation of the band broadening contribution of HPLC equipment to column elution profiles

Summary Methods to determine the contribution of the chromatographic equipment to the total band broadening which involve replacing the column by a union or a capillary tube are not suitable as they involve a fundamental change in the chromatographic system. The linear extrapolation method, based on the estimation of the relative influence of the instrument variance on solutes with different capacity factors, is a more attractive alternative method since the column remains in the chromatographic system. This method is only valid when a number of conditions are satisfied. By meeting these conditions the error in the instrument variance by using the linear extrapolation method was determined. At the same time, ways to minimise these errors were studied. Use of the linear extrapolation method in combination with conventional columns of 4.6 mm i.d. appears to yield inaccurate results. In combination with microbore columns the method can be used, provided the columns have a maximum length of 5cm and contain a packing material with a particle size of 2 or 3μm. The error in the determined instrument variance is then of the order of 2μl².     

Limits of determination and calibration in HPLC

Summary In HPLC calibration the expressions lowest calibration limit and determination limit are defined in statistical terms. The lowest calibration limit is the minimum mass in the measured series of calibration points. It is calculated from the confidence interval of the inverse of the calibration function as the lowest mass limit that may be differentiated from zero mass with a preset probability of error. If the calculated lowest calibration limit is lower than the actual data, points at lower concentration may be measured. The determination limit is the smallest concentration of an analysis that is differentiated from the concentration zero or an apparent blind value in the calibration curve with a given probability of error.Using two different UV-detectors (variable wavelength and photodiode-array) the lowest calibration limit is experimentally evaluated and compared with specific data for the detectors.Dedicated to Prof. Dr. E. Bayer, Tübingen on ocassion of his 60th birthday.     

Prediction of the chromatographic behaviour for a series of diuretic compounds

Summary The proportion of organic modifier and the pH of the acetonitrile-water mixtures used as mobile phases were optimized in order to separate a group of diuretic compounds covering a wide range of physyco-chemical properties. The Linear Solvation Energy Relationship (LSER) formalism based either on the multiparameter π^*, β and α scales or the single solvent polarity parameterE _T ^N , have been used to predict their chromatographic behaviour as a function of the percentage of acetonitrile in the eluent. Moreover, correlation established between retention and pH of the aqueous-organic mobile phases have been used to predict the chromatographic behaviour of the diuretic compounds studied as a function of the eluent pH. Linear correlation between a function of the eluent pH. Linear correlation between the chromatographic retention and theE _T ^N polarity parameter of mobile phases containing different percentages of organic modifier has been obtained Based on the knowledge of the acid-base dissociation constant the relation between retention and mobile phase pH has also been linearized. These relationship allowed an important reduction of the experimental retention data needed for developing a given separation and a great improvement in chromatographic optimization schemes.     

Determination of the lipophilicity of some anti-hypoxia drugs: Comparison of TLC and HPLC methods

Summary The lipophilicity of 14 anti-hypoxia drugs has been determined by reversed phase thin-layer (RPTLC) and reversed phase high performance liquid chromatography (RPHPLC) in eluent systems containing different concentrations of acetonitrile and potassium dihydrogen phosphate. There was significant correlation between lipophilicity and the specific hydrophobic surface area of the drugs in RPTLC, indicating that the drugs behave as an homologous series of compounds. In RPTLC the concentration of buffer has a negligible effect on the retention of the drugs whereas in RPHPLC the buffer concentration influenced the retention. This discrepancy can be explained by the lower sensitivity of RPTLC. There was strong correlation between lipophilicity values determined by both methods, proving that both are suitable for the determination of molecular lipophilicity.     

Simultaneous Determination of Olanzapine and Fluoxetine by HPLC

A rapid, specific reversed phase HPLC method has been developed for simultaneous determination of olanzapine and fluoxetine in their formulations. Chromatographic separation of these two pharmaceuticals was carried out on an Inertsil C₁₈ reversed phase column (150 mm × 4.6 mm, 5 μm) with a 40:30:30 (v/v/v) mixture of 9.5 mM sodium dihydrogen phosphate (pH adjusted to 6.8 ± 0.1 with triethylamine), acetonitrile and methanol as mobile phase. The flow rate 1.2 mL min⁻¹ and the analytes are monitored at 225 nm. Paroxetine was used as internal standard. The assay results were linear from 25 to 75 μg mL⁻¹ for olanzapine (r ² ≥ 0.995) and 100–300 μg mL⁻¹ for fluoxetine (r ² ≥ 0.995), showed intra- and inter-day precision less than 1.0%, and accuracy of 97.7–99.1% and 97.9–99.0%. LOQ was 0.005 and 0.001 μg mL⁻¹ for olanzapine and fluoxetine, respectively. Separation was complete in less than 10 min. Validation of the method showed it to be robust, precise, accurate and linear over the range of analysis.     

Characterisation of pitch by HPLC

Summary A new high performance liquid chromatography method for the characterisation of toluene-soluble fractions of pitches has been developed. Although a chromatographic system typical of size exclusion chromatography was used, results indicate that, for these structurally complex samples, separation does not follow the usual discrimination by molecular size. A differentiation between several classes of polyaromatic hydrocarbons is achieved instead. Data are reported on the analysis of individual standard polyaromatic hydrocarbons, showing that four different elution ranges can be observed: three ofcata-condensed compounds (Cata1, Cata2 and Cata3) and one ofperi-condensed compounds (Peri). Results are reported proving the capacity of this high performance liquid chromatography method to distinguish between pitches of different origin and nature. It is also effective for the study of the chemical reactions occurring during heat treatment.     

Simple and rapid HPLC method for simultaneous determination of multiple antiepileptic drugs in human serum

Summary A very rapid, sensitive and reproducible HPLC method was developed for simultaneous determination of eight anti-epileptic drugs (AEDs): lamotrigine, primidone, ethosuximide, sulthiame, felbamate, phenobarbital, carbamazepine, phenytoin and oxcarbazepine-metabolite (10-hydroxy-carbazepine) in human serum. Sample purification requires only protein precipitation with an appropriate reagent. Separation was by reversed-phase HPLC, using a C18 column, 20% acetonitrile and 40 mM phosphoric acid buffer as mobile phase. Column temperature was set at 50°C, and measurement was by UV detection at 205 nm. The inter and intra-assay coefficients of variation (CV) ranged 1.13–7.10% and 1.14–8.49%, respectively. The absolute (measured) and relative (analytic) recoveries of the drugs ranged 96.7%–104.4% and 97.3%–106.1%, respectively. No interference with other common antiepileptic drugs and analgesics were observed. The method requires only 100 μl serum or less. It is very fast (sample preparation and analysis time approx. 23 min for all 9 AEDs), and suitable for routine clinical use, especially for epileptic patients on polytherapy.