A high performance liquid chromatographic method for the screening of 17 diuretics in human urine

Multi-scale optimisation vs. genetic algorithms in the gradient separation of diuretics by reversed-phase liquid chromatography

Multi-linear gradients are a convenient solution to get separation of complex samples by modulating carefully the gradient slope, in order to accomplish the local selectivity needs for each particular solute cluster. These gradients can be designed by trial-and-error according to the chromatographer experience, but this strategy becomes quickly inappropriate for complex separations. More evolved solutions imply the sequential construction of multi-segmented gradients. However, this strategy discards part of the search space in each step of the construction and, again, cannot deal properly with very complex samples. When the complexity is too large, the only valid alternative for finding the best gradient is the use of global search methods, such as genetic algorithms (GAs). Recently, a new global approach where the level of detail is increased along the search has been proposed, namely Multi-scale optimisation (MSO). In this strategy, cubic splines are applied to build intermediate curves to define any arbitrary solvent variation function. Subdivision schemes are used to generate the cubic splines and control their level of detail. The search was subjected to a number of restrictions, such as avoiding long elution and favouring a balanced peak distribution. The aim of this work is evaluating and comparing the results of GAs and MSO. Both approaches were tested with a set of 14 diuretics and probenecid, eluted with acetonitrile-water mixtures using a C18 column. Satisfactory baseline resolution was obtained with an analysis time of 15-16 min. We found that GAs optimisation offered results equivalent to those provided by MSO, when the penalisation parameters were included in the cost function.

Validated reverse-phase high-performance liquid chromatography for quantification of furosemide in tablets and nanoparticles

A simple, sensitive, and specific method for furosemide (FUR) analysis by reverse-phase-HPLC was developed using a Spherisorb C18 ODS 2 column. A chromatographic analysis was carried out using a mobile phase consisting of acetonitrile and 10 mM potassium phosphate buffer solution: 70 : 30 (v/v) at pH 3.85, at a flow rate of 1 mL·min(-1). The UV-detection method was carried out at 233 nm at room temperature. Validation parameters including limit of detection (LOD), limit of quantitation (LOQ), linearity range, precision, accuracy, robustness, and specificity were investigated. Results indicated that the calibration curve was linear (r (2) = 0.9997) in the range of 5.2 to 25,000 ng·mL(-1), with ε value equal to 3.74 × 10(4) L·M(-1) ·cm(-1). The LOD and LOQ were found to be 5.2 and 15.8 ng·mL(-1), respectively. The developed method was found to be accurate (RSD less than 2%), precise, and specific with an intraday and interday RSD range of 1.233-1.509 and 1.615 to 1.963%. The stability of native FUR has also been performed in simulated perilymph and endolymph media (with respective potency in each medium of 99.8 ± 2.3% and 96.68 ± 0.7%, n = 3) after 6 hours. This method may be routinely used for the quantitative analysis of FUR from nanocarriers, USP tablets and release media related to hearing research.

Screening Procedure for Detection of Diuretics and Uricosurics and/or Their Metabolites in Human Urine Using Gas Chromatography-Mass Spectrometry After Extractive Methylation

A gas chromatography-mass spectrometry (GC-MS)-based screening procedure was developed for the detection of diuretics, uricosurics, and/or their metabolites in human urine after extractive methylation. Phase-transfer catalyst remaining in the organic phase was removed by solid-phase extraction on a diol phase. The compounds were separated by GC and identified by MS in the full-scan mode. The possible presence of the following drugs and/or their metabolites could be indicated using mass chromatography with the given ions: m/z 267, 352, 353, 355, 386, and 392 for thiazide diuretics bemetizide, bendroflumethiazide, butizide, chlorothiazide, cyclopenthiazide, cyclothiazide, hydrochlorothiazide, metolazone, polythiazide, and for canrenoic acid and spironolactone; m/z 77, 81, 181, 261, 270, 295, 406, and 438 for loop diuretics bumetanide, ethacrynic acid, furosemide, piretanide, torasemide, as well as the uricosurics benzbromarone, probenecid, and sulfinpyrazone; m/z 84, 85, 111, 112, 135, 161, 249, 253, 289, and 363 for the other diuretics acetazolamide, carzenide, chlorthalidone, clopamide, diclofenamide, etozoline, indapamide, mefruside, tienilic acid, and xipamide. The identity of positive signals in such mass chromatograms was confirmed by comparison of the peaks underlying full mass spectra with reference spectra. This method allowed the detection of the abovementioned drugs and/or their metabolites in human urine samples, except torasemide. The limits of detection ranged from 0.001 to 5 mg/L in the full-scan mode. Recoveries of selected diuretics and uricosurics, representing the different chemical classes, ranged from 46% to 99% with coefficients of variation of less than 21%. After ingestion of the lowest therapeutic doses, furosemide was detectable in urine samples for 67 hours, hydrochlorothiazide for 48 hours, and spironolactone for 52 hours (via its target analyte canrenone). The procedure described here is part of a systematic toxicological analysis procedure for acidic drugs and poisons.

Determination of lauroyl-indapamide in rat whole blood by high-performance liquid chromatography

A method based on a liquid-liquid extraction procedure followed by high-performance liquid chromatography (HPLC) coupled with UV-visible detection is described and validated for the determination of lauroyl-indapamide in rat whole blood. The blood sample was extracted with diethyl ether after the addition of 10% trifluoroacetic acid (aq.). The chromatographic separation was performed on a Chromasil ODS column, using methanol-acetonitrile-tetrahydrofuran-0.2% trifluoroacetic acid (170:20:15:38, v/v/v/v) as the mobile phase. The UV detection wavelength was set at 240 nm. The extraction recovery of lauroyl-indapamide was ranged from 76.5 to 82.6%, and the calibration curve had a good linearity in the range of 0.048-200 microg/ml (r = 0.9976). The method presents appropriate intra-day and inter-days repeatabilities, showing values below 7.4% in terms of the percentage of relative standard deviation (R.S.D.). The method proposed is simple, rapid and sensitive, being useful for pharmacokinetic studies in rats.

Liquid chromatography–electrospray tandem mass spectrometry method for determination of indapamide in serum for single/multiple dose bioequivalence studies of sustained release formulations

Indapamide and internal standard (5-chloro-2-methoxy-N-[2-(4-sulphamoylphenyl)ethyl]benzamide) were isolated from plasma by a single step liquid-liquid extraction in t-butyl methyl ether. The chromatographic separation was achieved on a reversed-phase C(18) monolithic column with a mobile phase consisting in a methanol/aqueous 0.1% formic acid mixture and a flow rate of 0.8 ml/min, in isocratic conditions, within 11 min. Target compounds were transferred in an ion trap analyzer via an atmospheric pressure electrospray interface (AP-ESI). The mass analyzer was used in a selected reaction monitoring (SRM) mode, in order to enhance on detection selectivity. Whole method produces quantitation limit for indapamide of 1 ng/ml. Method was successfully applied to assess bioequivalence of two sustained release marketed pharmaceutical formulations of indapamide 1.5 mg coated tablets, carried-out in a single/multiple doses, randomized design.

Electrochemical study of hydrochlorothiazide and its determination in urine and tablets

A voltammetric study of hydrochlorothiazide (HCTZ) at glassy carbon electrode was carried out. The drug in Britton-Robinson buffer (pH 3.3) is oxidized at +1040mV, giving rise to a well-defined peak. Cyclic voltammetric study indicates that the oxidation process is irreversible and diffusion-controlled. A sensitive, simple and time-saving differential pulse anodic voltammetric procedure has been developed. The procedure has been applied for the drug determination in human urine with no prior extraction and in commercial tablets. The proposed method has been validated. The limit of detection for the standard solution was 5.0ngml(-1) and for the drug in urine was 14.0ngml(-1). The results obtained from the analysis of commercial tablets were compared statistically with those obtained from the USP 26 high-performance liquid chromatographic (HPLC) method.

Direct determination of triamterene by potentiometry using a coated wire selective electrode

A coated wire triamterene-selective electrode based on the incorporation of a triamterene-tetraphenylborate ion-pair in a poly(vinylchloride) coating membrane was constructed. The influence of membrane composition, temperature, pH of the test solution, and foreign ions on the electrode performance were investigated. The electrode showed a Nernstian response over a triamterene concentration range from 1.0 x 10(-6) to 3.5 x 10(-2) M, at 25 degrees C, and was found to be very selective, precise, and usable within the pH range 4.5-7.5. The standard electrode potentials, E degrees, were determined at 15, 20, 25, 30, 35, 40 and 45 degrees C and used to calculate the isothermal temperature coefficient (dE degrees /dt) of the electrode. Temperatures higher than 45 degrees C seriously affected the electrode performance. The electrode was successfully applied to the potentiometric determination of triamterene hydrochloride both in pure solutions and in pharmaceutical preparations.

Flow injection and HPLC determination of furosemide using pulsed amperometric detection at microelectrodes

The flow-injection and HPLC determination of the diuretic drug furosemide using pulsed amperometric detection (PAD) at cylindrical carbon fibre microelectrodes (CFMEs) is reported. Experimental conditions such as pH (6.5) and buffer concentration (0.05 mol l(-1) HPO4(2-)/H2PO4(-)) were optimized using square-wave voltammetry (SWV). Repetitive flow-injection amperometric measurements at +1.25 V for furosemide showed a continuous decrease in the peak current, probably as a consequence of the microelectrode surface fouling. However, a suitable amperometric detection of furosemide was achieved using a PAD program consisting of a two-step potential waveform with alternating anodic and cathodic polarization. The anodic (detection) potential was +1.25 V (time of application 0.1 s), and the cathodic (cleaning) potential was -0.20 V (t=0.2 s). A linear calibration graph was obtained for furosemide in the 5.0 x 10(-7)-1.0 x 10(-4) mol l(-1) concentration range, with a limit of detection of 1.7 x 10(-7) mol l(-1). HPLC-PAD at carbon fibre microelectrodes was used for the determination of furosemide in the presence of several thiouracil drugs and oxytetracycline (OTC). The mobile phase selected was a 25:75 acetonitrile:5.0 x 10(-3) mol l(-1) NaH2PO4 (pH 5.0) mixture. A linear calibration graph was obtained for furosemide in the 1-100 microM range, with a limit of detection of 0.55 microM. The usefulness of this method for the determination of furosemide in real samples was evaluated by performing the analysis of commercial milk samples spiked with furosemide at a concentration level of 4.5 x 10(-7) mol l(-1) (150 ng ml(-1)), as well as with other thiouracil drugs and OTC. A mean recovery of 95+/-5% furosemide was obtained.

Determination of antiepileptic drugs in biological material

Current analytical methodologies applied to the determination of antiepileptic drugs in biological material are reviewed. The role of chromatographic techniques is emphasized. Special attention is focused on new chemical entities as well as current trends such as high-speed liquid chromatographic techniques, hyphenated techniques and electrochromatography techniques. A review with 542 references.

Use of a three-factor interpretive optimisation strategy in the development of an isocratic chromatographic procedure for the screening of diuretics in urine samples using micellar mobile phases

Screening of diuretics in urine is feasible through direct injection of the samples into the chromatographic system and isocratic reversed-phase liquid chromatography (RPLC) with micellar-organic mobile phases of sodium dodecyl sulfate (SDS) and 1-propanol. The surfactant coverage of the chromatographic column makes the addition of organic competing amines less necessary than in conventional aqueous-organic RPLC to achieve well-shaped peaks. Also, the range of elution strengths of micellar mobile phases required to elute mixtures of hydrophobic and hydrophilic diuretics is smaller. This allows the isocratic separation of the diuretics within adequate analysis times. An interpretive methodology is applied to optimise the resolution of a mixture of 15 diuretics of diverse polarity and acid-base behaviour (althiazide, amiloride, bendroflumethiazide, benzthiazide, bumetanide, canrenoic acid, chlorthalidone, ethacrynic acid, furosemide, piretanide, probenecid, torasemide, triamterene, trichloromethiazide and xipamide), using pH and concentrations of surfactant and organic modifier in the mobile phase as separation factors. Twelve diuretics were resolved in 25 min using 0.055 M SDS-6.0% 1-propanol at pH 3.0. The mixture of 15 diuretics was also resolved with two mobile phases showing complementary behaviour: 0.05 M SDS-5.6% 1-propanol at pH 5.4 and 0.11 M SDS-5.4% 1-propanol at pH 4.2. The results were applied to the analysis of urine samples with limits of detection similar to those usually reported for aqueous-organic RPLC, taking into account that the samples were injected without any previous treatment to separate or preconcentrate the analytes.