Development and validation of a liquid chromatographic method for the determination of amlodipine residues on manufacturing equipment surfaces

Sensitive determination of naftazone using carbon quantum dots nanoprobe by fluorimetry and smartphone-based techniques

A simple, fast, and direct mix-and-read spectrofluorimetric method has been developed for the sensitive determination of naftazone (NFZ) utilizing graphene quantum dots (GQDs) as a greener and highly luminescent nanosensor. NFZ effectively quenches the strong fluorescence of GQDs at λex/λem of 350/440 nm via the inner filter effect mechanism. The nanosensor exhibits excellent linearity for NFZ over the concentration range of 0.46 to 186 μM with a limit of detection of 0.04 μM. The proposed method was validated for the successful determination of NFZ in tablets and on manufacturing equipment surfaces with good % recoveries of 98.4-101.6 and 96.3 - 102.2%, respectively. Furthermore, an integrated smartphone-based reader has been implemented and successfully applied for the determination of NFZ. The smartphone-based reader consists of a 365 nm UV torch as an excitation source, a smartphone for recording images, and smartphone-powered image analysis software for signal interpretation, together with a paper-based analytical device (PAD) utilizing filter paper as a substrate and correction fluid as a barrier for creation of detection zones. This smart platform showed excellent sensitivity with a limit of detection down to 0.12 nmol/zone, and it could be used for in-site determination of NFZ, especially for the limited resources laboratories.

Analytical and Bioanalytical Techniques for the Quantification of the Calcium Channel Blocker - Amlodipine: A Critical Review

Hypertension is a condition in which blood pressure is elevated to an extent where benefit is obtained from blood pressure lowering. The risk of complications is proportional to the level that blood pressure raises. Calcium channel blockers are a class of compounds used in the treatment of hypertension. The dihydropyridine (DHP) group, a subclass of the calcium channel blocker works almost exclusively on L-type calcium channels in the peripheral arterioles and reduce blood pressure by reducing total peripheral resistant. Long acting DHP is preferred because they are more convenient for patients and avoid the large fluctuations in plasma drug concentration which are associated with side effects. Amlodipine is the most distinct DHP and the most popular. The drug was patented in the year 1986 and its commercial sale began by 1990. The current article provides a state of art about the analytical and bioanalytical techniques available for the quantification of drug as a single entity and in combined pharmaceutical formulations between 1989 and 2019.

Cleaning Method Validation for Estimation of Dipyridamole Residue on the Surface of Drug Product Manufacturing Equipment Using Swab Sampling and by High Performance Liquid Chromatographic Technique

Objectives

Cleaning validation is the procedure used to ensure that the cleaning process has eliminated the residues of drug substance from on the equipment surface after manufacture. A simple, sensitive, robust, and accurate high performance liquid chromatographic method was developed for the quantitative estimation of dipyridamole in swab samples obtained from the equipment surface after the manufacture of dipyridamole modified release capsules.

Materials and Methods

The method was developed by using a Hypersil BDS C18 (150×4.6 mm, 5 μm) column with mobile phase containing a mixture of buffer (potassium dihydrogen phosphate buffer, pH 7.0±0.05) and methanol in the ratio of 30:70 v/v. Flow rate was 1.5 mL/min, column temperature was 45°C, and injection volume was 5 μL.

Results

The method was validated and a specificity study was conducted to prove that there was no interference from blank and swab blank at the retention time of dipyridamole. The limit of detection and limit of quantification (LOQ) were established by using a series of linearity solutions and were found to be 0.041 μg/mL and 0.124 μg/mL, respectively. The method precision at the LOQ level was 8.6% relative standard deviation (RSD), method precision was 0.2% RSD, and ruggedness was 0.3% RSD. The method was accurate from the concentration of 0.13 μg/mL to 21.80 μg/mL and the recovery results met the acceptance criteria. The linearity of the method was found from 0.12 μg/mL to 20.14 μg/mL and the r² value was 0.997. The robustness for the flow rate, wavelength, column temperature, buffer pH, and mobile phase ratio variations was tested, and all the system suitability parameters were met.

Conclusion

The method validation was performed as per the regulatory requirements and guidelines. The validation parameters met the acceptance criteria and the proposed method can be applied for the intended routine swab analysis.

Development of UV spectrophotometry methods for concurrent quantification of amlodipine and celecoxib by manipulation of ratio spectra in pure and pharmaceutical formulation

Recently, the United States Food and Drug Administration approved a new oral dosage preparation of amlodipine besylate (AML) and celecoxib (CEL) for the management of hypertension and osteoarthritis. However, no simultaneous estimation procedures for these two analytes have been described. Hence, two simple, accurate, and precise ultraviolet spectroscopic procedures that manipulated the ratio spectra were established for concurrent quantification of AML and CEL using ethanol as a solvent. The first method involves determining the peak-to-trough amplitude difference of the ratio spectra of AML and CEL. The second method involves determining the peak amplitude of the ratio first derivative (Δλ 4 nm) spectra of AML and CEL at 334.2 nm and 254.2 nm, correspondingly. Both methods showed linearity in the range of 1–6 μg mL-1 for AML and 5–40 μg mL-1 for CEL with an excellent correlation coefficient (<0.999). The proposed procedures were validated by following the International Conference on Harmonization guidelines for accuracy, precision, selectivity, recovery, and stability studies. It is evident from the low %RSD and %RE that both analytical procedures were found to be accurate and precise, respectively. The percent recovery of AML and CEL from the formulation was found to be 99.79% and 99.34% using the ratio-difference method and 100.13% and 99.70% using the ratio first-derivative method, with a low percent relative standard deviation. Further, the proposed techniques permit concurrent quantification of AML and CEL in different concentration ratios without interference from each other; hence, these techniques can be adopted for regular quality-control studies.

Cleaning level acceptance criteria and HPLC-DAD method validation for the determination of Nabumetone residues on manufacturing equipment using swab sampling

Prevention of cross contamination with active pharmaceutical ingredients is crucial and requires special attention in pharmaceutical industries. Current method validation describes the determination of Nabumetone (NAB) residue on a stainless steel surface using swab sampling with a sensitive HPLC-DAD analysis. The acceptance limit was decided as 2 μg swab per 100 cm². Cotton swabs impregnated with extraction solution were used to determine residual drug content. Recoveries were 90.88%, 91.42%, and 92. 21% with RSD ranging from 2.2% to 3.88% at three concentration levels. Residual concentration was found to be linear in the range of 0.1–4.56 μg/mL, when estimated using a Phenomenex Luna C₁₈ (25 cm×5 μm×4.6 mm i.d.) column at 1.0 mL/min flow rate and 230 nm. The mobile phase consisted of a mixture of methanol:acetonitrile:water (55:30:15, v/v/v). The LOD and LOQ for NAB were found to be 0.05 and 0.16 μg/mL, respectively. The validated method was found to be simple, selective and sensitive for demonstration of cleaning validation of NAB residues on a stainless steel surface.

Simultaneous Analysis of Losartan Potassium, Amlodipine Besylate, and Hydrochlorothiazide in Bulk and in Tablets by High-Performance Thin Layer Chromatography with UV-Absorption Densitometry

A Simple high-performance thin layer chromatography (HPTLC) method for separation and quantitative analysis of losartan potassium, amlodipine, and hydrochlorothiazide in bulk and in pharmaceutical formulations has been established and validated. After extraction with methanol, sample and standard solutions were applied to silica gel plates and developed with chloroform : methanol : acetone : formic acid 7.5 : 1.3 : 0.5 : 0.03 (v/v/v/v) as mobile phase. Zones were scanned densitometrically at 254 nm. The R(f) values of amlodipine besylate, hydrochlorothiazide, and losartan potassium were 0.35, 0.57, and 0.74, respectively. Calibration plots were linear in the ranges 500-3000 ng per spot for losartan potassium, amlodipine and hydrochlorothiazide, the correlation coefficients, r, were 0.998, 0.998, and 0.999, respectively. The suitability of this method for quantitative determination of these compounds was by validation in accordance with the requirements of pharmaceutical regulatory standards. The method can be used for routine analysis of these drugs in bulk and in formulation.

Stability Indicating RP-HPLC Estimation of Atorvastatin Calcium and Amlodipine Besylate in Pharmaceutical Formulations

A simple, specific, accurate and stability indicating reversed phase high performance liquid chromatographic method was developed for the simultaneous determination of atorvastatin calcium and amlodipine besylate in tablet dosage forms. A phenomenex Gemini C-18, 5 μm column having 250×4.6 mm i.d. in isocratic mode, with mobile phase containing 0.02 M potassium dihydrogen phosphate:acetonitrile:methanol (30:10:60, v/v/v) adjusted to pH 4 using ortho phosphoric acid was used. The flow rate was 1.0 ml/min and effluents were monitored at 240 nm. The retention times of atorvastatin calcium and amlodipine besylate were 11.6 min and 4.5 min, respectively. The calibration curves were linear in the concentration range of 0.08-20 μg/ml for atorvastatin calcium and 0.1-20 μg/ml for amlodipine besylate. Atorvastatin calcium and amlodipine besylate stock solutions were subjected to acid and alkali hydrolysis, chemical oxidation and dry heat degradation. The degraded product peaks were well resolved from the pure drug peak with significant difference in their retention time values. The proposed method was validated and successfully applied to the estimation of atorvastatin calcium and amlodipine besylate in combined tablet dosage forms.

Validation of an HPLC-UV method for the determination of ceftriaxone sodium residues on stainless steel surface of pharmaceutical manufacturing equipments

In pharmaceutical industry, an important step consists in the removal of possible drug residues from the involved equipments and areas. The cleaning procedures must be validated and methods to determine trace amounts of drugs have, therefore, to be considered with special attention. An HPLC-UV method for the determination of ceftriaxone sodium residues on stainless steel surface was developed and validated in order to control a cleaning procedure. Cotton swabs, moistened with extraction solution (50% water and 50% mobile phase), were used to remove any residues of drugs from stainless steel surfaces, and give recoveries of 91.12, 93.8 and 98.7% for three concentration levels. The precision of the results, reported as the relative standard deviation (RSD), were below 1.5%. The method was validated over a concentration range of 1.15-6.92 μg ml(-1). Low quantities of drug residues were determined by HPLC-UV using a Hypersil ODS 5 μm (250×4.6 mm) at 50 °C with an acetonitrile:water:pH 7:pH 5 (39-55-5.5-0.5) mobile phase at flow rate of 1.5 ml min(-1), an injection volume of 20 μl and were detected at 254 nm. A simple, selective and sensitive HPLC-UV assay for the determination of ceftriaxone sodium residues on stainless steel surfaces was developed, validated and applied.

Quantitative determination of residual active pharmaceutical ingredients and intermediates on equipment surfaces by ion mobility spectrometry

Ion mobility spectrometry (IMS) is an analytical technique that separates ions based on their gas phase mobility at atmospheric pressure. Since gas phase ion mobility is a function of the shape and structure of the ion, this technique has the potential to provide unique specificity and selectivity. Furthermore, IMS is very sensitive (subnanogram detection limits for many small molecules), and a single analysis is typically completed within 1 min. In principle, these features of IMS should make it an ideal choice for use in cleaning verification analysis of pharmaceutical manufacturing equipment. This report describes the successful development and validation of three different equipment cleaning verification methods using IMS. The methods were developed for a specific intermediate (Compound A) in the synthetic route for a drug substance as well as for final drug substances (active pharmaceutical ingredients Compounds B and C). The cleaning verification methods were validated with respect to specificity, linearity, precision, accuracy, stability, and limit-of-quantitation. In all cases, the limits-of-quantitation were determined to be at the nanogram or sub-nanogram level. Both swab and rinse samples collected from the equipment surfaces were successfully analyzed and manufacturing equipment down-time was significantly minimized due to the reduction in cleaning verification analysis time (for example, the total analysis time for more than 30 samples using IMS was reduced to less than 2h).

Validation of an HPLC-UV method for the determination of digoxin residues on the surface of manufacturing equipment

In the pharmaceutical industry, an important step consists in the removal of possible drug residues from the involved equipments and areas. The cleaning procedures must be validated and methods to determine trace amounts of drugs have, therefore, to be considered with special attention. An HPLC-UV method for the determination of digoxin residues on stainless steel surfaces was developed and validated in order to control a cleaning procedure. Cotton swabs, moistened with methanol were used to remove any residues of drugs from stainless steel surfaces, and give recoveries of 85.9, 85.2 and 78.7 % for three concentration levels. The precision of the results, reported as the relative standard deviation (RSD), were below 6.3 %. The method was validated over a concentration range of 0.05-12.5 ?g mL-1. Low quantities of drug residues were determined by HPLC-UV using a Symmetry C18 column (150?4.6) mm, 5 ?m) at 20?C with an acetonitrile-water (28:72, v/v) mobile phase at a flow rate of 1.1 mL min-1, an injection volume of 100 ?L and were detected at 220 nm. A simple, selective and sensitive HPLC-UV assay for the determination of digoxin residues on stainless steel was developed, validated and applied.

Stability of amlodipine besylate and atenolol in multi-component tablets of mono-layer and bi-layer types

Multi-drug tablets of amlodipine besylate and atenolol were prepared as either mono-layer (mixed matrix) or bilayer tablets containing each drug in a separate layer by using similar excipients and processing. Each tablet batch was packed in strip and blister packs and kept under accelerated temperature and humidity conditions. The stability of two tablet and packaging types was compared by HPLC analysis after 0, 1, 3 and 4.5 months and expressed as the content of intact amlodipine and atenolol. The content of atenolol did not decline regardless of tablet and packaging type. Amlodipine content in bi-layer tablets decreased to about 95 and 88% when packed in strips and blisters, respectively. When prepared as mono-layer tablets, the content decreased to 72 and 32%, respectively.The study revealed that the bi-layer tablet formulation was more stable than the mono-layer type. Further, the stability was increased when the tablets were packed in aluminium strips as compared to PVC blisters.

Fiber-optic infrared reflection absorption spectroscopy for trace analysis on surfaces of varying roughness. Part II: Acetaminophen on stainless steel

Investigations of the effects of surface roughness on the utility of grazing-angle Fourier transform infrared reflection absorption spectroscopy (IRRAS) as a method for quantifying trace contamination of metal surfaces have been extended to acetaminophen, a model active pharmaceutical agent, on 316 stainless steel. The effects are more complicated than for the surfactant sodium dodecyl sulfate (SDS) on stainless steel; they include a strong surface-finish dependence of sensitivity and nonlinear behavior at surface loadings above approximately 1-2 microg cm(-2). Using data from samples in the loading range 0-0.5 microg cm(-2), unbiased partial least squared calibrations can be readily achieved for individual surface finishes with detection limits of L(D) approximately 0.15 microg cm(-2). However, as found for SDS on stainless steel, models built using data from samples of mixed surface roughness are more problematic.

Cleaning validation 2: Development and validation of an ion chromatographic method for the detection of traces of CIP-100 detergent

A cleaning validation method, ion chromatographic method with conductivity detection was developed and validated for the determination of traces of a clean-in-place (CIP) detergent. It was shown to be linear with a squared correlation coefficient (r(2)) of 0.9999 and average recoveries of 71.4% (area response factor) from stainless steel surfaces and 101% from cotton. The repeatability was found to be 2.17% and an intermediate precision of 1.88% across the range. The method was also shown to be sensitive with a detection limit (DL) of 0.13 ppm and a quantitation limit (QL) of 0.39 ppm for EDTA, which translates to less than 1 microL of CIP diluted in 100mL of diluent in both cases. The EDTA signal was well resolved from typical ions encountered in water samples or any other interference presented from swabs and surfaces. The method could be applied to cleaning validation samples. The validated method could be included as a suitable one for rapid and reliable cleaning validation program.

Determination and pharmacokinetic study of amlodipine in human plasma by ultra performance liquid chromatography–electrospray ionization mass spectrometry

A novel, specific and sensitive ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was developed for the determination and pharmacokinetic study of amlodipine in human plasma. The analysis was carried out on an ACQUITY UPLC BEH C(18) column (50 mm x 2.1 mm, i.d., 1.7 microm) with gradient elution at a flow-rate of 0.35 ml/min. The mobile phase was water and acetonitrile under gradient conditions (both containing 0.3% formic acid) and nimodipine was used as the internal standard. Detection was performed on a triple-quadrupole tandem mass spectrometer by multiple reaction monitoring (MRM) mode via Turbo ion spray ionization (ESI). Linear calibration curves were obtained over the concentration range 0.15-16.0 ng/ml, with a lower limit of quantification of 0.15 ng/ml. The intra- and inter-day precision (R.S.D.) values were below 15% and the accuracy (R.E.) was -2.3% to 6.9% at all three QC levels. The method was used to support clinical pharmacokinetic studies of amlodipine in healthy volunteers following oral administration.

Cleaning verification assays for highly potent compounds by high performance liquid chromatography mass spectrometry: Strategy, validation, and long-term performance

A cleaning-verification assay was validated for a highly potent family of compounds utilizing a swab-sampling procedure and high performance liquid chromatography mass spectrometry (LC-MS) for separation and detection of the analytes. Due to the high potency of the compound, the LC-MS method was validated at a level of 50 ng/25 cm(2) and 50 ng/100 cm(2) (which equates to 10 ng/ml after extraction in 5 ml of sample solvent, and 3 ng/ml after correction for sampling losses). This validation exercise included recovery estimates from all drug product contact surfaces within the clinical trial manufacturing equipment, namely, stainless steel, anodized aluminum, Rilsan coated aluminum, bronze, polyvinylchloride, and Oilon. The limit of detection for the LC-MS method was determined to be less than 0.5 ng/ml, or less than 0.1 ng/cm(2), of the analyte. This method does not employ an internal standard. Long-term performance of the validated method is also reported. The precision on replicate injections of the standard prepared in the range of 3-6 ng/ml was typically better than 8.0% relative standard deviation (R.S.D.) over the course of 1 year, which resulted from 10 cleaning-verification submissions. Those results were consistent with the data obtained during method validation.

A stability-indicating high performance liquid chromatographic (HPLC) assay for the simultaneous determination of atorvastatin and amlodipine in commercial tablets

A simple, rapid, precise and accurate isocratic reversed-phase stability-indicating HPLC method was developed and validated for the simultaneous determination of atorvastatin (AT) and amlodipine (AM) in commercial tablets. The method has shown adequate separation for AM, AT from their associated main impurities and their degradation products. Separation was achieved on a Perfectsil Target ODS-3, 5 microm, 250 mm x 4.6 mm i.d. column using a mobile phase consisting of acetonitrile-0.025 M NaH(2)PO(4) buffer (pH 4.5) (55:45, v/v) at a flow rate of 1 ml/min and UV detection at 237 nm. The drugs were subjected to oxidation, hydrolysis, photolysis and heat to apply stress conditions. The linearity of the proposed method was investigated in the range of 2-30 microg/ml (r=0.9994) for AT and 1-20 microg/ml (r=0.9993) for AM. The limits of detection were 0.65 microg/ml and 0.35 microg/ml for AT and AM, respectively. The limits of quantitation were 2 microg/ml and 1 microg/ml for AT and AM, respectively. Degradation products produced as a result of stress studies did not interfere with the detection of AT and AM and the assay can thus be considered stability-indicating.

Grazing-Angle Fiber-Optic Fourier Transform Infrared Reflection−Absorption Spectroscopy for the in Situ Detection and Quantification of Two Active Pharmaceutical Ingredients on Glass

Fourier transform infrared reflection-absorption spectroscopy has been used with a fiber-optic grazing-angle reflectance probe as a rapid, in situ method for trace surface analysis of acetaminophen and aspirin at loadings of approximately 0-2 microg cm(-2) on glass. Partial least-squares multivariate regression permits the loadings to be quantified, simultaneously, with root-mean-squared errors of prediction of RMSEP approximately 0.1 microg cm(-2) for both compounds. The detection limits are estimated to be LD approximately 0.2 microg cm(-2).

Verification of cefmetazole and cefpodoxime proxetil contamination to other pharmaceuticals by liquid chromatography-tandem mass spectrometry

Cross-contamination is a critical issue for pharmaceutical manufacturing, especially for beta-lactam antibiotics. Thus, an analytical method for the simultaneous determination of beta-lactam antibiotics cefmetazole (CMZ) and cefpodoxime proxetil (CPDXPR) contaminants in non-beta-lactam pharmaceuticals was developed using high-performance liquid chromatography-tandem mass spectrometry. The developed method was found to be sensitive at the detection limit of 0.002 ppm for both compounds. Mean recoveries of CMZ and CPDXPR from olmesartan medoxomil (OLM) tablets were 96.7 to 102.2% and 88.9 to 94.2%, respectively. The developed method was successfully applied for the verification of CMZ and CPDXPR contamination to actually manufactured OLM tablets.

LC/MS/MS method for the determination of trace amounts of cefmetazole and cefpodoxime proxetil contaminants in pharmaceutical manufacturing environments

In this study, a selective and sensitive LC/MS/MS method for the determination of trace amounts of cefmetazole (CMZ) and cefpodoxime proxetil (CPDXPR) contaminants in manufacturing environments was developed. The necessary sensitivity of this method was estimated based on the detection limit for Penicillin G required by the FDA and the total surface area and volume of the manufacturing facility. The detection limits of this method were estimated to be 10 pg/ml for CMZ and 5 pg/ml for CPDXPR from the signal to noise ratio and as a result satisfactory sensitivity was achieved. The method was linear in a concentration range from 0.20 to 3.20 ng/ml. The accuracy and precision were verified by the determination of the amount of CMZ and CPDXPR added to the sampling materials, a glass plate and a silica fiber filter. The mean recoveries of nine replicated determinations from the glass plate were 99.1% with 5.58%R.S.D. for CMZ and 97.1% with 3.80%R.S.D. for CPDXPR, and those from the silica fiber filter were 100.7% with 4.50%R.S.D. for CMZ and 95.4% with 2.85%R.S.D. for CPDXPR. This method has been successfully applied to the determination of CMZ and CPDXPR contaminants in samples collected from an actual manufacturing environment.

Determination of cefmetazole residue at pharmaceutical manufacturing facilities by chemiluminescence flow injection analysis

Application of a sensitive and rapid flow injection analysis (FIA) method with luminol chemiluminescence detection for determination of trace amounts of cefmetazole (CMZ) in cephamycin antibiotic residue in pharmaceutical manufacturing facilities and on pharmaceutical manufacturing equipment has been investigated. The method was shown to be sensitive at a level of limit of detection of 0.06 ng/ml and for linear concentrations in the range of 0.3-1.5 ng/ml. Average recoveries of CMZ from stainless steel plates and glass plates were 62.1% and 60.1%, respectively, by adding 15 ng/100 cm2, and that of air sampling filters was 91.9% by adding 3 ng/filter. The proposed method has been successfully applied to the determination of CMZ residue in samples collected from an actual manufacturing facility and equipment. According to the results, no detectable CMZ residue was observed, therefore it was verified that no contamination had occurred to other pharmaceutical products manufactured in the facility.

Cleaning validation 1: Development and validation of a chromatographic method for the detection of traces of LpHse detergent

A high performance liquid chromatography (HPLC) method for the detection of traces of LpHse (4-tert-amylphenol and 2-phenylphenol) has been developed and validated. The method was shown to be linear in the range from 0.5 to 10.00 ppm in solution. The method was also shown to be accurate with a recovery of up to 95% by area response for amylphenol and up to 94% by area response for phenylphenol from metal surfaces (4''x4'' un-polished 304 stainless steel plates) by means of swab material. The reproducibility of the method was determined to be 1.61% by area response and 1.52% by height response for amylphenol and 5.40% by area response and 13.77% by height response for phenylphenol from solutions reported as the pooled relative standard deviation. The developed method was also shown to be rugged by comparisons of different preparations by different analysts. The limit of detection was established to be 0.076 ppm by peak area, 0.079 ppm by peak height for amylphenol and 0.34 ppm by peak area, 0.82 ppm by peak height for phenylphenol from solution, and 1.77 ppb by peak area, 1.23 ppm by peak height for amylphenol and 1.23 ppm by peak area, 1.44 ppm by peak height for phenylphenol from recovery from metal studies. The limit of quantitation was established to be 0.25 ppm by peak area, 0.26 ppm by peak height for amylphenol and 1.14 ppm by peak area, 2.73 ppm by peak height for phenylphenol from solution, and 3.89 ppm by peak area, 4.11 ppm by peak height for amylphenol and 4.11 ppm by peak area, 4.79 ppm by peak height for phenylphenol from recovery from metal plates studies. This method can be employed to determine the presence of LpHse residues in cleaned equipments where the detergent was used.

Evaluation of a rinsing-based cleaning process for pipes

Pipes of various designs were constructed. Pipes were filled with a model solution resembling a dermal solution product. After the removal of the model solution, pipes were rinsed several times with ethanol and rinsing solutions of each step analyzed by gas chromatography. The results gave the information about the dependency between the configuration of the pipe and the efficiency of the cleaning operation. From concentrations measured in the reactor, expected concentrations in rinsing solutions from pipes were predicted. The obtained results confirm that the amount of residues per surface area increases when a pipe includes bends and valves. In terms of extra contamination, each bend was equal to 25 cm, while each valve was equal to 100 cm of pipe length when pipes of 1.8 cm in diameter were used. It was proven that the contributions of individual valves and bends in the pipe are additive in the calculation. The validity of the proposed model was confirmed by experimental data.

Simple and rapid HPLC method for determination of amlodipine in human serum with fluorescence detection and its use in pharmacokinetic studies

A fast, sensitive and specific high performance liquid chromatographic method using fluorescence detection is described for analysis of amlodipine in human serum. Amlodipine is extracted from serum by ethyl acetate and involves precolumn derivatization with 4-chloro-7-nitrobenzofurazan (NBD-Cl) and reverse-phase chromatography on C18 column. The mobile phase was sodium phosphate buffer (pH 2.5) containing 1 ml/l triethylamine and methanol at flow rate of 2.8 ml/min. Propranolol was used as internal standard. The standard curve was linear over the range 0.25-16 ng/ml of amlodipine in human serum. The within-day and between-day precision studies showed good reproducibility with coefficients of variation less than 12% for all the analytes. The limit of quantification was 0.25 ng/ml of serum. The method has been applied to a bioequivalence study after administration of 10 mg amlodipine in 12 normal subjects.