Zero-crossing Technique Research Articles

Development of Simultaneous Derivative Spectrophotometric and HPLC Methods for Determination of 17-Beta-Estradiol and Drospirenone in Combined Dosage Form.

Simple, rapid spectrophotometric, and reverse-phase high performance liquid chromatographic methods were developed for the concurrent analysis of 17-beta-estradiol (ESR) and drospirenone (DRS). The spectrophotometric method was based on the determination of first derivative spectra and determined ESR and DRS using the zero-crossing technique at 208 and 282 nm, respectively, in methanol. The linear range was 0.5–32.0 µg·mL−1 for DRS and 0.5–8.0 µg·mL−1 for EST. The limit of detection (LOD) values were 0.14 µg·mL−1 and 0.10 µg·mL−1 and limit of quantification (LOQ) values were 0.42 µg·mL−1 and 0.29 µg·mL−1 for ESR and DRS, respectively. The chromatographic method was based on the separation of both analytes on a C18 column with a mobile phase containing acetonitrile and water (70 : 30, v/v). Detection was performed with a UV-photodiode array detector at 279 nm. The linear range was 0.08–2.5 µg·mL−1 for DRS and 0.23–7.5 µg·mL−1 for EST. LOD values were 0.05 µg·mL−1 and 0.02 µg·mL−1 and LOQ values were 0.15 µg·mL−1 and 0.05 µg·mL−1 for ESR and DRS, respectively. These recommended methods have been applied for the simultaneous determination of ESR and DRS in their tablets.

Simultaneous Determination of Sulphamethoxazole and Trimethoprim in Binary Mixtures and in Tablet Using Derivative Spectrophotometry

Derivative spectrophotometric (first, second, third and fourth derivative) were developed for the determination of Sulphamethoxazole)SMX) and trimethoprim (TMP)antibiotic binary mixture by applying zero-crossing technique for pure synthetic mixture while simultaneous determination of (SMX) and (TMP) in tabletsusing D 4 at waveleanth 257.8 nm and 251.5 nm for (SMX) and (TMP) the correlation coefficient of calibration curves were 0.9992 and 0.9995. Linearity is maintained within a wide concentration range from 2.00 to 25.00 mg/l, with relative error (-0.11 and 0.60) the LOD (0.360 and 0.382 mg/L) and LOQ and (1.200 and1.275 mg/L) respectively.No interference found between both determined and those of matrices. A good accuracy and precision of simultaneous determination of (SMX), and (TMP) were confirmed by statistical analysis.The percentage recovery of the individual drugs under the established conditions is ranged from 97.23% to 102.13 %. This method was compared with the British pharmacopoeiamethodusing F test. The procedures do not require any separation step.

Validation of Dispersion Curve Reconstruction Techniques for the A0 and S0 Modes of Lamb Waves

The properties of ultrasonic Lamb waves, such as relatively small attenuation and high sensitivity to structural changes of the object being investigated, allow performing of non-destructive testing of various elongated structures like pipes, cables, etc. Due to the dispersion effect of Lamb waves, a waveform of the received informative signal is usually distorted, elongated and overlapping in the time domain. Therefore, in order to investigate objects using the ultrasonic Lamb waves and to reconstruct the dispersion curves, it is necessary to know the relationship between frequency, phase and group velocities and thickness of the plate. The zero-crossing technique for measurement of phase velocity of Lamb waves (the A0 and S0 modes) has been investigated using modelled dispersed signals and experimental signals obtained for an aluminium plate having thickness of 2 mm. A comparison between two reconstruction methods of Lamb wave phase velocity dispersion curves, namely, the two-dimensional fast Fourier transform (2D-FFT) and zero-crossing technique, along with the theoretical (analytical) dispersion curves is presented. The results indicate that the proposed zero-crossing method is suitable for use in reconstruction of dispersion curves in the regions affected by strong dispersion, especially for the A0 mode.

Validated spectrophotometric methods for the evaluation of Oseltamivir counterfeit pharmaceutical capsules

Four rapid, reliable and economical spectrophotometric methods have been established for the quantitative determination of Oseltamivir phosphate (OST) without the interference of ascorbic acid (ASC) found in some of its counterfeit capsules. The first method involves the use of derivative spectrophotometry with the zero-crossing technique where OST was easily determined using its 1D (Δλ=3) at 219nm. The second method is based on a first-order derivative ratio spectrophotometry (1DD, Δλ=5) where 218nm was selected for its quantification, while the third method applies a more advanced spectrophotometric method based on the ratio difference spectrophotometry (RD) in which the difference in absorbance ratio was measured between 217 and 210nm. In the fourth method, difference spectrophotometric method (ΔA) is applied by subtracting absorbance at 252 from that at 263nm where the difference in absorbance was zero for ASC. The proposed methods were validated for linearity, accuracy, precision and selectivity. Synthetic mixtures of different proportions and commercial capsules were assayed by the proposed methods and the results revealed good accuracy and repeatability of the developed methods.

Sample Data Synchronization and Harmonic Analysis Algorithm Based on Radial Basis Function Interpolation

The spectral leakage has a harmful effect on the accuracy of harmonic analysis for asynchronous sampling. This paper proposed a time quasi-synchronous sampling algorithm which is based on radial basis function (RBF) interpolation. Firstly, a fundamental period is evaluated by a zero-crossing technique with fourth-order Newton’s interpolation, and then, the sampling sequence is reproduced by the RBF interpolation. Finally, the harmonic parameters can be calculated by FFT on the synchronization of sampling data. Simulation results showed that the proposed algorithm has high accuracy in measuring distorted and noisy signals. Compared to the local approximation schemes as linear, quadric, and fourth-order Newton interpolations, the RBF is a global approximation method which can acquire more accurate results while the time-consuming is about the same as Newton’s.

Four Derivative Spectrophotometric Methods for the Simultaneous Determination of Carmoisine and Ponceau 4R in Drinks and Comparison with High Performance Liquid Chromatography

Four simple, rapid, and accurate spectrophotometric methods were developed for the simultaneous determination of two food colorants, Carmoisine (E122) and Ponceau 4R (E124), in their binary mixtures and soft drinks. The first method is based on recording the first derivative curves and determining each component using the zero-crossing technique. The second method uses the first derivative of ratio spectra. The ratio spectra are obtained by dividing the absorption spectra of the binary mixture by that of one of the components. The third method, derivative differential procedure, is based on the measurement of difference absorptivities derivatized in first order of solution of drink samples in 0,1 N NaOH relative to that of an equimolar solution in 0,1 N HCl at wavelengths of 366 and 451 nm for Carmoisine and Ponceau 4R, respectively. The last method, based on the compensation method is presented for derivative spectrophotometric determination of E122 and E124 mixtures with overlapping spectra. By using ratios of the derivative maxima, the exact compensation of either component in the mixture can be achieved, followed by its determination. These proposed methods have been successfully applied to the binary mixtures and soft drinks and the results were statistically compared with the reference HPLC method (NMKL 130).

A new time-domain method for frequency measurement of sinusoidal signals in critical noise conditions

Frequency measurement of sinusoidal signals corrupted by noise is dealt with. A new time-domain, digital signal processing method, based on an enhanced version of the zero-crossing technique, is in particular proposed. To obtain the desired frequency value, the method exploits the histogram of time intervals between consecutive zero-crossing events, and works with success in the presence of zero-mean additive noise.Several tests conducted on simulated and actual sinusoidal signals highlight the good performance of the method also in critical noise conditions, which make high-end measurement instruments like digital counters poorly fail. Moreover, the obtained results concur with those granted by competitive digital signal processing proposals operating in the frequency domain. With respect to these latter, the main advantage of the method relies on the limited computational resources required, which suggests its implementation even in low-performance processing devices for the realization of cost-effective measurement instruments.

Development and validation of spectrophotometric and HPTLC methods for simultaneous determination of rosiglitazone maleate and metformin hydrochloride in the presence of interfering matrix excipients

Two simple methods have been developed and validated for the simultaneous determination of rosiglitazone maleate (ROS) and metformin hydrochloride (MET) in synthetic mixtures and coated tablets in a ratio of 1:250 (ROS:MET). The first method was a spectrophotometric one. The minor component, ROS was determined by measuring the values of absorbance at λmax 312 nm and the D1 amplitudes at 331 nm where MET shows no absorption contribution. However, absorbance interferences from tablet excipients were successfully corrected by D1 at 331 nm zero-crossing technique. Study of spectral interference from tablet excipients was included in the text. Standard curves for Amax and D1 methods were in the concentration range 20.0–80.0 μg mL−1. The major component, MET was determined both in binary mixtures and tablets by measuring its Amax at 236 nm. Extensive dilution eliminated any absorption contribution from the coexisting ROS or tablet matrix. Standard curves showed linearity in the concentration range 4.0–12.8 μg mL−1. The second method was based on high performance thin layer chromatography (HPTLC) separation of the two drugs followed by densitometric measurements of their spots at 230 nm. The separation was carried out on Merck HPTLC aluminium sheets of silica gel 60 F254 using methanol:water:NH4Cl 1% w/v (5:4:1 v/v/v) as the mobile phase. Linear calibration graphs of peak area values were obtained versus concentrations in the range of 0.4–2.0 μg band−1 and 20.0–100.0 μg band−1 for ROS and MET, respectively. According to International Conference on Harmonisation (ICH) guidelines, different validation parameters were verified for the two methods and presented.

A Low-Cost Power-Quality Meter With Series Arc-Fault Detection Capability for Smart Grid

This paper presents a low-cost digital single-phase power-quality measurement device for consumer use with a wide range of features, including series arc-fault detection, load trip on failure, and phase/neutral line wiring mix up indication. A wavelet multiresolution analysis technique was utilized for the voltage transient event detection and the current drop pattern recognition, specifically to arc fault. The last feature also involved the use of adaptive thresholding, peak detection, and repetition frequency calculation. A computationally efficient and accurate Goertzel filter was used for total harmonic distortion calculation. In addition, this meter can measure phase fundamental frequency (using the zero-crossing technique), rms values, and power. MATLAB and MathCAD packages were used to build and simulate arc-fault model and phase voltage distortion, to design and test part of the developed algorithms, which were further implemented in Embedded C and Assembler programming languages. A prototype circuit board with the required sensors and relay, analog isolation, indication, user controls, communication link, and a low-cost microchip microcontroller (MCU) dsPIC33 was designed and built to validate implemented algorithms and conduct experiments.

Measurement of Angular Vibrations in Rotating Shafts: Effects of the Measurement Setup Nonidealities

In this paper, the authors discuss a measurement method, based on the zero-crossing demodulation technique of FM signals, to estimate the angular velocity vibrations of a rotating shaft. The demodulation algorithm is applied without any filtering to the direct voltage output issued by some probes sensing the passages of arbitrarily shaped targets installed on the rotating shaft. The authors discuss a theoretical approach to analyze the measurement problem taking into account the chief nonidealities related to the measurement setup, i.e., they have investigated the effects of both the shaft side vibrations and the irregular shape of the targets. On the basis of the theoretical results, the authors propose a measurement method that can reject the effects of these mentioned nonidealities, exploiting the measurements of two or more probes properly positioned around the shaft.

Validated Spectrophotometric Methods for Simultaneous Determination of Food Colorants and Sweeteners

Two simple spectrophotometric methods have been proposed for simultaneous determination of two colorants (Indigotin and Brilliant Blue) and two sweeteners (Acesulfame‐K and Aspartame) in synthetic mixtures and chewing gums without any prior separation or purification. The first method, derivative spectrophotometry (ZCDS), is based on recording the first derivative curves (for Indigotin, Brillant Blue, and Acesulfame‐K) and third‐derivative curve (for Aspartame) and determining each component using the zero‐crossing technique. The other method, ratio derivative spectrophotometry (RDS), depends on application ratio spectra of first‐ and third‐derivative spectrophotometry to resolve the interference due to spectral overlapping. Both colorants and sweeteners showed good linearity, with regression coefficients of 0.9992–0.9999. The LOD and LOQ values ranged from 0.05 to 0.33 μgmL−1 and from 0.06 to 0.47 μgmL−1, respectively. The intraday and interday precision tests produced good RSD% values (<0.81%); recoveries ranged from 99.78% to 100.67% for all two methods. The accuracy and precision of the methods have been determined, and the methods have been validated by analyzing synthetic mixtures containing colorants and sweeteners. Two methods were applied for the above combination, and satisfactory results were obtained. The results obtained by applying the ZCDS method were statistically compared with those obtained by the RDS method.

Simultaneous Determination of Carvedilol and Hydrochlorothiazide in Tablets and Spiked Human Plasma using Derivative Spectrophotometry

Quick and accurate methods for determination of carvedilol and hydrochlorothiazide in tablets and spiked human plasma by using third derivative (3D), fourth derivative (4D) and ratio spectra derivative (1DD) spectrophotometric methods were developed. The zero-crossing technique was employed in measurements, using 3D at 245.9 or 230.2 nm and 4D at 247.4 or 226.9 nm for carvedilol or hydrochlorothiazide, respectively. The first-derivative of ratio spectra (1DD) where the amplitudes were measured at 236.1 nm for carvedilol and 261.1 nm for hydrochlorothiazide. The calibration curves were linear in the ranges of 1.0-20.0 μg mL-1 for each of carvedilol and hydrochlorothiazide using 3D 4D and 1DD methods. The suggested methods were tested using laboratory-prepared mixtures and were successfully applied for the analysis of pharmaceutical formulations. The methods retained their accuracy and precision when the standard addition technique was applied. The results obtained by applying the proposed methods were statistically analyzed and compared with those obtained by reported and official HPLC methods for carvedilol and hydrochlorothiazide, respectively. These methods showed to be appropriate for simultaneous determination of carvedilol and hydrochlorothiazide in human plasma samples with a limit of quantitation (LOQ) is ≤ 0.5 μg mL-1.

IN-VITRO INTERACTION STUDIES OF VERAPAMIL WITH FLUOROQUINOLONES USING FIRST ORDER DERIVATIVE UV SPECTROPHOTOMETRY AND RP-HPLC

Verapamil, a calcium channel blocker, is classified as a class IV anti-arrhythmic agent. It is used in the treatment of hypertension, as an important therapeutic agent for angina pectoris, ischemic heart disease, hypertension and hypertrophic cardiomyopathy. Many in-vivo studies have been carried out to find out the effects on concurrent use of calcium channel blocker with various groups of drugs. In the present paper an in-vitro approach was adapted to study the interaction of verapamil with commonly administered fluoroquinolones i.e. ciprofloxacin, levofloxacin, norfloxacin and sparfloxacin. The interaction studies were carried out in different simulated body fluids pH ranges from 1-9 at 37 oC. To perform these studies first-derivative UV spectrophotometric (using zero-crossing technique) and simultaneous RP-HPLC methods were developed and validated. HPLC analysis was conducted on Shimpack CLC-ODS (6.0 X 150 mm) column. The mobile phase constituted of acetonitrile: water (45:55), whose pH was adjusted to 2.8 and pumped at a flow rate of 1.2 mL min-1 at 230 nm. The results obtained from both methodologies indicated that the availability of verapamil was not affected by simultaneous administration

PHYSICOCHEMICAL STUDIES OF NICKEL AND COPPER COMPLEXES WITH TAR AND SIMULTANEOUS DETERMINATION OF THE METAL IONS IN MIXTURES BY DERIVATIVE SPECTROPHOTOMETRY

Nickel(II) and Copper(II) chelates of 4-(2̀–thiazolylazo)resorcinol (TAR) were reported. The dissociation constants of the ligand and the stability constants of the metal complexes were calculated pH-metrically and spectrophotometrically at 25 ◦C, in 50% (v/v) ethanol and 0.1 M ionic strength. The effects of an acid or a base on the visible absorption behaviour of the ligand and complexes has been investigated. Nickel and copper react with 4-(2̀–thiazolylazo)resorcinol (TAR) to form a binary complexes. The equilibria occurring in solution were established and the basic characteristics of the complexes formed were determined. The complexation reaction in the systems investigated were demonstrated and characterized using graphical logarithmic analysis of the absorbance versus pH graph. The composition of the formed complexes with the reagent have been determined. The molar absorptivity of the binary system is investigated. The binary systems obeyed beer's law up to 0.23 and 0.25 µg/ml for Ni2+ and Cu2+ respectively. A simple and highly sensitive procedure for spectrophotometric determination of Ni2+ and Cu2+ has been developed. A method for the simultaneous determination of nickel and copper in mixtures by first-derivative spectrophotometry is described. Zero-crossing measurement technique is found suitable for the simultaneous determination of the metal ions. The method has been applied to direct determination of copper and nickel in dome synthetic mixtures without any separation.

Simultaneous determination of amoxicillin and potassium clavulanate antibiotics in pharmacueutical sample using derivative spectrophotometric method

Derivatives spectrophotometric techniques were developed for the determination of Amoxicillin Trihydrate (Amox) with Potassium Clavulanate (PC) antibiotic binary mixtures. The simultaneous determination of these compounds was accomplished by derivative (1D, 2D and 3D) spectrophotometric technique and applying zero-crossing technique used for determination of (Amox) and (PC) in tablets. The second order derivative absorption spectra at valley λ=299 nm were used for (Amox) and also the second order derivative spectra at peak λ=239.5 nm were used for (PC). No interferences were found between both determined constituents and those of matrix. A good accuracy and precision of simultaneous determination of (Amox) and (PC) were confirmed by statistical analysis. The recovery of individual constituents under established conditions is very high and ranges for synthetic standards mixture and tablets from 100.11, 99.33 and 96.98, 96.84 respectively. Linearity is maintained within a wide concentration range from 2.0 to 90.0 μg.mL-1 and from 10.0 to 90.0 μg.mL-1 for (Amox) and (PC) and linearity percentage 99.98 and 99.99 respectively. The detection limit is 0.211 μg.mL-1 for (Amox) and 0.259 μg.mL-1 for (PC). The corresponding quantitation limits are 0.704 μg.mL-1 (Amox) and 0.864 μg.mL-1 for (PC).

Simultaneous Spectrophotometric Determination of Metformin Hydrochloride and Glibenclamide in Binary Mixtures Using Combined Discrete and Continuous Wavelet Transforms

In this work, a combined discrete and continuous wavelet transform analysis was developed for simultaneous spectrophotometric determinations of metformin hydrochloride and glibenclamide, two antidiabetic drugs, in binary mixtures without any chemical pretreatment. Absorption spectra were subjected to the 4-level db4 discrete wavelet transform (DWT) for signal de-noising. Selected continuous wavelet transform (CWT) families (rbio3.1 with scaling factor, a = 80, and gaus2, a = 60) were applied on these de-noised signals. Finally, a zero-crossing technique was used for the construction of calibration curves for both drugs. The proposed method was validated by analyzing synthetic mixtures of the investigated drugs with various concentrations. The amount of metformin hydrochloride and glibenclamide were determined by using CWT amplitudes in zero-crossing points. The mean recovery values of metformin hydrochloride and glibenclamide were found between 98.6-102.0 and 97.9-102.4% for rbio3 and 98.3-101.2 and 97.1-101.4% for gaus2 families, respectively. The obtained results showed that the developed method is a simple, rapid and precise procedure for the simultaneous determination of metformin hydrochloride and glibenclamide in binary mixtures.

Time-Domain Quasi-Synchronous Sampling Algorithm for Harmonic Analysis Based on Newton's Interpolation

In the case of asynchronous sampling, spectral leakage has a harmful effect on the accuracy of harmonic analysis. This paper presents a new harmonic analysis algorithm, which successfully adjusts an actual sampling sequence to an ideal sampling sequence synchronized with the original signal. First, a fundamental period is evaluated by a zero-crossing technique, and then, according to this fundamental period, the sampling sequence is reconstructed by the time-domain Newton's interpolation polynomial. Simulation results show that the proposed algorithm has high accuracy in measuring distorted and noisy signals by reducing spectral leakage effectively in the framework of the International Electrotechnical Commission standards. Moreover, the proposed method maintains high measurement accuracy for nonstationary and slow-changing signals even at low-frequency resolution. The results of the field experiment confirm the effectiveness of this algorithm under practical considerations.

Validated stability‐indicating derivative and derivative ratio methods for the determination of some drugs used to alleviate respiratory tract disorders and their degradation products

Derivative and derivative ratio methods are presented for the determination of butamirate citrate, formoterol fumarate, montelukast sodium, and sodium cromoglycate. Using the second derivative ultraviolet (UV) spectrophotometry, butamirate citrate and formoterol fumarate were determined by measuring the peak amplitude at 260.4 and 261.8 nm, respectively, without any interference of their degradation products. Butamirate citrate degradation product, 2-phenyl butyric acid, was determined by the measurement of its second derivative amplitude at 246.7 nm where butamirate citrate displays zero crossing. Formoterol fumarate degradation product, desformyl derivative, could be evaluated through the use of the first derivative at peak amplitude of 264.8 nm where interference of formoterol fumarate is negligible. In the first mode, the zero-crossing technique was applied at 305 nm for the determination of montelukast sodium in the presence of its photodegradation product, cis-isomer. The derivative of ratio spectra of montelukast sodium and its cis- isomer were used to determine both isomers using the first derivative of the ratio spectra by measuring the amplitudes of the trough at 305 nm and the peak at 308 nm, respectively. The later technique was also used for the determination of a ternary mixture of sodium cromoglycate and its two degradation products using zero-crossing method. In the derivative ratio spectra of the ternary mixture, trough depths were measured at 271.6, 302.8 and 302.2 nm, using the second, the first, and the second mode to evaluate sodium cromoglycate, degradation product (1) and degradation product (2), respectively. All the methods were applied successfully to the pharmaceutical preparation and were validated according to ICH guidelines.

DETERMINATION OF MONTELUKAST SODIUM AND LEVOCETIRIZINE DIHYDROCHLORIDE IN COMBINED TABLET DOSAGE FORM BY HPTLC AND FIRST-DERIVATIVE SPECTROPHOTOMETRY

Two simple, rapid, precise, and reproducible methods were developed for the simultaneous determination of montelukast sodium and levocetirizine dihydrochloride in combined tablet dosage form. The first method was based on high performance thin layer chromatography using paracetamol as an internal standard. In this method, the precoated silica gel 60F254 aluminium plate was selected as the stationary phase and the mixture of ethyl acetate: methanol:triethylamine (5:5:0.02 v/v/v) was used as mobile phase. The detection was carried out at 240 nm. Beer's law was obeyed in the range of 400–1200 ng/spot for montelukast sodium and 200–600 ng/spot for levocetirizine dihydrochloride, respectively. The second method involved first derivative spectrophotometry. In this method, the zero-crossing technique was applied for the determination of montelukast sodium at 291.60 nm and for levocetirizine dihydrochloride at 238.20 nm. Both method passes f tests and t test. The proposed methods were validated statistically and by performing recovery study.

Determination of energizers in energy drinks

The method of UV/VIS derivative spectrophotometry for the determination of caffeine and B vitamins in energy drinks after solid phase extraction has been developed. Caffeine has been determined in the mixture with B2 vitamin with zero-crossing technique from the I derivative spectra (λ = 266.8 nm), and B3 in mixture with B6 vitamin from the II derivative spectra (λ = 280.1 nm). B12 vitamin has also been determined in a three-component mixture with vitamins B3 and B6. Taurine in drinks has been determined from the basic spectra after derivatization with ninhydrin (λ = 570 nm).