Spectrophotometric resolution of ternary mixtures of pseudoephedrine hydrochloride, dextromethorphan hydrobromide, and sodium benzoate in syrups using wavelength selection by net analyte signals calculated with hybrid linear analysis

Hybrid linear analysis (HLA), as a recent factor-based multivariate calibration technique, was applied for the spectrophotometric determination of ternary mixtures of pseudoephedrine hydrochloride (PSU), dextromethorphan hydrobromide (DXT), and sodium benzoate (BNZ). The utilized HLA was assisted by a wavelength selection procedure which was based on the calculation of the net analyte signal (NAS) regression plot in any considered wavelengths window for each test sample, in addition to a moving window strategy for searching the region with maximum linearity of NAS regression plot (minimum error indicator (EI)). HLA was applied because it was simpler to adapt to the NAS regression plot methodology, and also used less factors than partial least squares (PLS). An orthogonal array design was applied for formation of calibration and prediction sets in the concentration ranges 0-7500 μmol L⁻¹ for PSU, 0-300 μmol L⁻¹ for DXT, and 0-1400 μmol L⁻¹ for BNZ. The method had the ability to select wavelength regions that minimize the effect of non-linearity of the spectral data, in addition to that of non-modeled interferences. The application of the selected wavelength regions improved the obtained relative standard error of predictions for PSU, DXT, and BNZ, respectively, from 5.24, 8.67, and 5.48% to 2.19, 5.21, and 3.62% (using lower number of factors). To check the ability of the proposed method in selection of linear regions of spectra, a test for detecting non-linear regions of spectral data in multivariate spectroscopic assays was also described. Additives in the commercial syrup samples did not interfere with their determinations. The method was successfully applied for the determination of pseudoephedrine HCl, dextromethorphan HBr, and sodium benzoate in cough suppressant syrup samples.     

Application of Quartz Crystal Nanobalance for Simultaneous Determination of Vanillylmandelic and Homovanillic Acids by a Net Analyte Signal-Based Method

Homovanillic acid (HVA) and vanillylmandelic acid (VMA) were selectively determined by quartz crystal nanobalance sensor in conjunction with net analyte signal (NAS)-based method called HLA/GO. An orthogonal design was applied for the formation of calibration and prediction sets including HVA, VMA, and some common and structurally similar urine compounds. The selection of the optimal time range involved the calculation of the NAS regression plot in any considered time window for each test sample. The searching of a region with maximum linearity of NAS regression plot (minimum error indicator) and minimum of predicted error sum of squares value was carried out by applying a moving window strategy. Based on the obtained results, the differences on the adsorption profiles in the time range between 1 and 300 s were used to determine mixtures of compounds by HLA/GO method. Several figures of merit like selectivity, sensitivity, analytical sensitivity, and limit of detection were calculated for both compounds. The results showed that the method was successfully applied for the determination of VMA and HVA.     

Use of 2-mercaptopyridine for the determination of alkylating agents in complex matrices: application to dimethyl sulfate

A rapid and sensitive method for the determination of alkylating agents in complex reaction mixtures was developed and characterized. Analyses are based on the alkylation of 2-mercaptopyridine by the analyte; the derivative is separated by RP-HPLC and measured by fluorescence detection. When applied to the determination of dimethyl sulfate, the method is linear over four orders of magnitude: 0.01-10 μg mL⁻¹. By using recrystallized 2-mercaptopyridine, quantitation limits of 10 ng mL⁻¹ can be achieved. Precision of the assay is 2% R.S.D. in the 1-10 μg mL⁻¹ range and about 15% R.S.D. at 10 ng mL⁻¹. Studies on the pH dependence of the derivatization reaction were key to minimizing interference from the dimethyl sulfate degradation product, monomethyl sulfate, in quenched reaction samples.     

Determination of copper,iron, nickel and zinc in ethanol fuel by energy dispersive X-ray fluorescence after pre-concentration on chromatography paper

This paper presents an alternative analytical method employing energy dispersive X-ray fluorescence (EDXRF) to determine copper, iron, nickel and zinc ions in ethanol fuel samples after a pre-concentration procedure. Our pre-concentration strategy utilizes analyte retention on cation exchange chromatography paper, a convenient substrate for direct EDXRF measurements. The repeatability, expressed in terms of RSD of standard solutions containing 0.25 μg mL⁻¹ of Cu, Fe, Ni and Zn, and calculated from fifteen consecutive measurements, was 2.5, 2.8, 3.0, and 2.7%, respectively. The limits of detection (LOD), defined as the analyte concentration that gives a response equivalent to three times the standard deviation of the blank (n = 10), were found to be 13, 15, 15 and 12 μg L⁻¹ for Cu, Fe, Ni and Zn, respectively. The proposed method was applied to Cu, Fe, Ni and Zn determination in hydrated ethanol fuel samples collected from different gas stations.     

Development of a validated liquid chromatographic method for the quality control of Prunellae Spica: Determination of triterpenic acids

A simple and rapid reversed-phase HPLC-UV method was developed for the determination of triterpenic acids in the crude extract of Prunellae Spica. Five triterpenic acids were extracted and isolated from P. Spica as marker compounds for use in the quality control of herbal medicines. Various solvent extraction techniques were evaluated, and the greatest efficiency was observed with sonication in 100% ethanol. Elemental compositions of the five marker compounds were determined by high-resolution mass spectroscopy. The dynamic range of the HPLC-UV method depended on the specific analyte, and acceptable quantitation was obtained between 10 and 250 μg mL⁻¹ for oleanolic acid, between 10 and 300 μg mL⁻¹ for ursolic acid, between 3 and 75 μg mL⁻¹ for 2α,3α,24-trihydroxyolean-12en-28oic acid, between 5 and 100 μg mL⁻¹ for euscaphic acid, and between 5 and 100 μg mL⁻¹ for 2α,3α-dihydroxyurs-12en-28oic acid. The method was deemed satisfactory by inter- and intra-day validation and exhibited both high accuracy and precision (relative standard deviation <9.4%). Overall limits of quantitation and detection were approximately 0.5-2.5 μg mL⁻¹ at a signal-to-noise ratio (S/N) of 3 and were about 3.0-10.0 μg mL⁻¹ at a S/N of 10. In addition, principal component analysis (PCA) was performed on the analytical data of 15 different P. Spica samples in order to classify samples collected from different regions.     

Ligandless-dispersive liquid-liquid microextraction of trace amount of copper ions

In the present work, a new ligandless-dispersive liquid-liquid microextraction (LL-DLLME) method has been developed for preconcentration trace amounts of copper as a prior step to its determination by flame atomic absorption spectrometry. In the proposed approach 1,2-dicholorobenzene and ethanol were used as extraction and dispersive solvents, respectively. Some factors influencing on the extraction efficiency of copper and its subsequent determination were studied and optimized, such as the extraction and dispersive solvent type and volume, pH of sample solution, extraction time and salting out effect. Under the optimal conditions, the calibration curve was linear in the range of 1.0 ng mL⁻¹-0.6 μg mL⁻¹ of copper with R² = 0.9985. Detection limit was 0.5 ng mL⁻¹ in original solution (3S_b/m) and the relative standard deviation for seven replicate determination of 0.2 μg mL⁻¹ copper was ±1.4%. The proposed method has been applied for determination of copper in standard and water samples with satisfactory results.     

Ligandless dispersive liquid-liquid microextraction for the separation of trace amounts of silver ions in water samples and flame atomic absorption spectrometry determination

In this article, a new ligandless dispersive liquid-liquid microextraction method has been developed for preconcentration of trace quantities of silver as a prior step to its determination by flame atomic absorption spectrometry. In the proposed approach, carbon tetrachloride and ethanol were used as extraction and dispersive solvents. Several factors that may be affected on the extraction process, like, extraction solvent, disperser solvent, the volume of extraction and disperser solvent, pH of the aqueous solution and extraction time were optimized. Under the optimal conditions, the calibration curve was linear in the range of 5.0 ng mL⁻¹ to 2.0 μg mL⁻¹ of silver with R² = 0.9995 (n = 9) and detection limit based on three times the standard deviation of the blank (3S_b) was 1.2 ng mL⁻¹ in original solution. The relative standard deviation for eight replicate determination of 0.5 μg mL⁻¹ silver was ±1.5%. The high efficiency of dispersive liquid-liquid microextraction to carry out the determination of silver in complex matrices was demonstrated. The proposed method has been applied for determination of trace amount of silver in standard and water samples with satisfactory results.     

Flow injection chemiluminescence determination of nitrofurazone in pharmaceutical preparations and biological fluids based on oxidation by singlet oxygen generated in N-bromosuccinimide-hydrogen peroxide reaction

A simple flow injection chemiluminescence (FI-CL) method was proposed for the determination of nitrofurazone. Strong CL signal was generated during the reaction of nitrofurazone with H₂O₂ and N-bromosuccinimide (NBS) in alkaline condition. The CL signal was proportional to the nitrofurazone concentration in the range 1.0 × 10⁻⁷ to 1.0 × 10⁻⁵ g mL⁻¹. The detection limit was 2 × 10⁻⁸ g mL⁻¹ nitrofurazone and the relative standard deviation was less than 4% (6.0 × 10⁻⁶ g mL⁻¹ nitrofurazone, n = 11). The proposed method was successfully applied to the determination of nitrofurazone in compound furacillin nasal drops, human plasma and urine samples. The CL reaction mechanism was also discussed briefly. Singlet oxygen generated in the reaction between H₂O₂ and NBS was suggested to be participated in the CL reaction.     

Usefulness of gold nanoparticles as labels for the determination of gliadins by immunoaffinity chromatography with light scattering detection

A simple and fast immunoaffinity method is proposed for the determination of gliadins for the first time using gold nanoparticles (AuNPs) as labels. The tracer used consists in a gliadin-AuNP conjugate prepared by the adsorption of gliadins onto the nanoparticle surface. Two AuNP sizes with diameters of 10 nm and 20 nm were assayed to compare the behaviour of the corresponding tracer in the assay. The method relies on the injection in a commercial Protein G column of a preincubated mixture containing gliadins, polyclonal anti-gliadin antibodies, and the gliadin-AuNP tracer. This approach allows the separation of free and bound tracer fractions without any additional elution step, and the direct measurement of the resonance light scattering intensity of the free tracer through the peak height of the immunochromatogram, which is proportional to the analyte concentration. The immunocolumn can be used up to 25 times without eluting and it can be regenerated for at least 20 times. The dynamic ranges of the calibration graphs and the detection limits are 0.5-15.0 and 1.5-15.0 μg mL⁻¹ gliadins, and 0.2 μg mL⁻¹ and 0.8 μg mL⁻¹ gliadins, using 20-nm and 10-nm Au-NPs as labels, respectively. The precision, expressed as relative standard deviation, ranges between 2.7% and 2.9% using 20-nm AuNPs and 4% and 6.1% for 10-nm AuNPs. The method has been applied to the determination of the prolamin fraction in beer samples, obtaining recovery values in the range 71.2% and 101.7%.     

Simultaneous determination of salbutamol sulphate, bromhexine hydrochloride and etofylline in pharmaceutical formulations with the use of four rapid derivative spectrophotometric methods

Four simple, rapid, accurate, precise, reliable and economical spectrophotometric methods have been proposed for simultaneous determination of salbutamol sulphate (SS), bromhexine hydrochloride (BH) and etofylline (ET) in pure and commercial formulations without any prior separation or purification. They were first derivative zero crossing spectrophotometry (method 1), simultaneous equation method (method 2), derivative ratio spectra zero crossing method (method 3) and double divisor ratio spectra derivative method (method 4). The ranges for SS, BH and ET were found to be 1-35 μg mL⁻¹, 4-40 μg mL⁻¹ and 5-80 μg mL⁻¹. For methods 1 and 2, the values of limit of detection (LOD) were 0.2314 μg mL⁻¹, 0.4865 μg mL⁻¹ and 0.2766 μg mL⁻¹ and the values of limit of quantitation (LOQ) were 0.7712 μg mL⁻¹, 1.6217 μg mL⁻¹ and 0.9221 μg mL⁻¹ for SS, BH and ET, respectively. For method 3, LOD values were 0.3297 μg mL⁻¹, 0.2784 μg mL⁻¹ and 0.7906 μg mL⁻¹ and LOQ values were 0.9325 μg mL⁻¹, 0.9282 μg mL⁻¹ and 2.6352 μg mL⁻¹ for SS, BH and ET, respectively. For method 4, LOD values were 0.3161 μg mL⁻¹, 0.2495 μg mL⁻¹ and 0.2064 μg mL⁻¹ and LOQ values were 0.9869 μg mL⁻¹, 0.8317 μg mL⁻¹ and 0.6879 μg mL⁻¹ for SS, BH and ET. The precision values were less then 2% R.S.D. for all four methods. The common excipients and additives did not interfere in their determinations. The results obtained by the proposed methods have been statistically compared by means of Student t-test and by the variance ratio F-test.     

Ultrasound-assisted dispersive liquid–liquid microextraction combined with high-performance liquid chromatography-fluorescence detection for sensitive determination of biogenic amines in rice wine samples

Ultrasound-assisted dispersive liquid–liquid microextraction coupled with high-performance liquid chromatography-fluorescence detection was used for the extraction and determination of three biogenic amines including octopamine, tyramine and phenethylamine in rice wine samples. Fluorescence probe 2,6-dimethyl-4-quinolinecarboxylic acid N-hydroxysuccinimide ester was applied for derivatization of biogenic amines. Acetonitrile and 1-octanol were used as disperser solvent and extraction solvent, respectively. Extraction conditions including the type of extraction solvent, the volume of extraction solvent, ultrasonication time and centrifuging time were optimized. After extraction and centrifuging, analyte was injected rapidly into high-performance liquid chromatography and then detected with fluorescence. The calibration graph of the proposed method was linear in the range of 5–500 μg mL⁻¹ (octopamine and tyramine) and 0.025–2.5 μg mL⁻¹ (phenethylamine). The relative standard deviations were 2.4–3.2% (n = 6) and the limits of detection were in the range of 0.02–5 ng mL⁻¹. The method was applied to analyze the rice wine samples and spiked recoveries in the range of 95.42–104.56% were obtained. The results showed that ultrasound-assisted dispersive liquid–liquid microextraction was a very simple, rapid, sensitive and efficient analytical method for the determination of trace amount of biogenic amines.     

A reversed-phase high performance liquid chromatography coupled with resonance Rayleigh scattering detection for the determination of four tetracycline antibiotics

A new reversed-phase high performance liquid chromatography with resonance Rayleigh scattering detection (HPLC-RRS) was developed for simultaneous separation and determination of four tetracycline antibiotics (TCs). A good chromatographic separation among the compounds was achieved using a Synergi Fusion-RP column (150 mm × 4.6 mm; 4 μm) and a mobile phase consisting of methanol-acetonitrile-oxalic acid (5 mM) at the flow rate of 0.8 mL min⁻¹. Column temperature was 30 °C. The RRS signal was detected at λ_ex = λ_em = 370 nm. The recoveries of sample added standard ranged from 95.3% to 103.5%, and the relative standard deviation was below 2.79%. A detection limit of 2.12-5.12 μg mL⁻¹ was reached and a linear range was found between peak height and concentration in the range of 10.36-518.0 μg mL⁻¹ for oxytetracycline (OTC), 12.11-605.5 μg mL⁻¹ for tetracycline (TC), 11.79-589.5 μg mL⁻¹ for chlortetracycline (CTC) and 10.32-516.0 μg mL⁻¹ for doxycycline (DC). The linear regression coefficients were all above 0.999. The method has been applied successfully to the determination of OTC, TC, CTC, DC in pharmaceutical formulations and in honey. The method was simple, rapid and showed a better linear relation and high repeatability.     

Determination of some phthalate acid esters in artificial saliva by gas chromatography-mass spectrometry after activated carbon enrichment

The determination of six phthalate acid esters was achieved in artificial saliva using gas chromatography-mass spectrometry following activated carbon enrichment of samples. Central composite experimental design was applied to optimize method parameters, such as pH, adsorption time and amount of activated carbon. The best compromise of analytical conditions for the simultaneous determination of analytes from spiked artificial saliva were found to be: pH (3), adsorption time (30 min), activated carbon amount (1.8 g L⁻¹) and elution solvent (chloroform). These conditions were applied to study the migration of phthalate acid esters from different children's toys into saliva. A horizontal agitation method was applied to extract the analytes from plastic toys into saliva for 2 h at 37 °C. The detection limits of the method were in the range of 1.3-5.1 μg L⁻¹, while the relative standard deviation (%) values for the analysis of 100 μg L⁻¹ of the analytes were below 3.0% (n = 5). Di-2-ethylhexyl phthalate was the main analyte found in these samples.     

Determination of simazine in water samples by HPLC after preconcentration with diatomaceous earth

A sensitive and selective batch adsorption method is proposed for the preconcentration and determination of simazine. Simazine was preconcentrated on diatomaceous earth as an adsorbent and then determined by high-performance liquid chromatography (HPLC). Several parameters on the recovery of the analyte were investigated. The experimental results showed that it was possible to obtain quantitative analysis when the solution pH was 2 using 100 mL of validation solution containing 1.5 μg of simazine and 5 mL of ethanol as an eluent. Recovery of simazine was 89.0 ± 1.6% with a relative standard deviation for seven determinations of 1.5% under optimum conditions. The maximum preconcentration factor was 100 for simazine when 500 mL of sample solution volume was used. The linear range of calibration curve was 1-200 ng mL⁻¹ with a correlation coefficient of 0.996 and the detection limit (3S/N) was 0.3 ng mL⁻¹. The capacity of the adsorbent was also examined and found to be 1.1 mg g⁻¹ for simazine. The proposed method was successfully applied to the determination of simazine in river water with high precision and accuracy.     

Flow injection chemiluminescence determination of naproxen based on KMnO4-Na2SO3 reaction in neutral aqueous medium

A simple, rapid and sensitive flow injection chemiluminescence (CL) method is described for the determination of naproxen. It was found that strong CL signal was generated when naproxen was mixed with KMnO₄ and Na₂SO₃ in neutral aqueous medium. Under the optimum experimental conditions, the CL intensity was linearly related to the concentration of naproxen from 4.0 × 10⁻⁹ to 1.0 × 10⁻⁶ g mL⁻¹ (r = 0.9993). The detection limit was 2 × 10⁻⁹ g mL⁻¹ naproxen, the relative standard deviation for 1.0 × 10⁻⁷ g mL⁻¹ naproxen solution was 1.5% (n = 11) and the sampling frequency was 120 h⁻¹. The method was applied to the determination of naproxen in pharmaceutical preparation with satisfactory results. The mechanism of CL reaction was discussed briefly.     

Approaches for application of sub and supercritical fluid extraction for quantification of orbifloxacin from plasma and milk: Application to disposition kinetics

Since its extensive development in the early 1980s, SFE has attracted considerable attention as a sample-preparation procedure. However, other different sample preparation procedures, including precipitation, liquid- and/or solid-phase extraction in biological fluids, also remain in use. In this investigation, SFE was introduced to isolate and identify orbifloxacin from plasma and milk. Four parameters, including the temperature and the pressure of supercritical fluid, modifier ratios, and dynamic extraction time, were evaluated and optimized to obtain the best yield of the analyte from the biological fluids. Determinations of the orbifloxacin (OBFX) in the extracts were carried out using HPLC-FLD. The optimum conditions of the extraction process that yielded the maximum analyte extraction efficiencies were 150 °C vs. 60 °C, 250 kg cm⁻², 30% vs. 35% methanol, and 40 min vs. 20 min, for plasma and milk, respectively. The linearity of the calibration curves as well as the instrument LODs/LOQs were evaluated. Good linearity (at least r² ≥ 0.999) of the calibration curves was obtained over the range from 0.2 to 0.01 μg mL⁻¹. The method showed a good recovery rate (74.2-127.73%) and precision (RSDs: 1.64-20%). The instrumental LOD and LOQ values were 0.004 μg mL⁻¹ vs. 0.01 μg mL⁻¹ or 0.006 μg mL⁻¹ vs. 0.02 μg mL⁻¹, for plasma and milk, respectively. The method was successfully applied to estimate the pharmacokinetic variables of orbifloxacin in lactating does. To the best of our knowledge, this is the first time that SFE has been applied to isolate an antimicrobial agent from biological fluids. This method is promising for clinical applications and for pharmacokinetic studies of various pharmaceuticals in biological fluids.     

Modified iron oxide nanoparticles as solid phase extractor for spectrophotometeric determination and separation of basic fuchsin

This study presents a novel separation, preconcentration and determination of basic fuchsin (BF) in an aqueous solution by sodium dodecyl sulfate (SDS)-bounded iron oxide nanoparticles (S-IONPs). It is shown that the novel magnetic nano-adsorbent is quite efficient for the adsorption and desorption of BF at 25 °C. Different parameters such as pH, temperature, ionic strength and composition of desorbent solvent were optimized. The effect of some co-existing ions on the determination was investigated. The nanoparticles were analyzed by transmission electron microscopy (TEM) and the sizes of S-IONPs were in the range of 20-100 nm. The method showed good linearity for the determination of BF in the range of 10-300 ng mL⁻¹ with a regression coefficient of 0.9989. The limit of detection (LOD) (signal-to-noise ratio of 3:1) was 0.0073 μg L⁻¹ and the relative standard deviation (RSD) for 0.03 μg mL⁻¹ and 0.2 μg mL⁻¹ of BF were 4.53% and 4.73%, respectively. The BF was determined successfully in spiked samples of Karoon River water.     

An ultrasensitive post chemiluminescence reaction of ammonium in NBS-dichlorofluorescein system and its application

A strong post chemiluminescence (PCL) phenomenon was observed when ammonium was injected into the reaction mixture after the finish of CL reaction of N-bromosuccinimide (NBS) and dichlorofluorescein. Based on this, a sensitive flow injection PCL method was established for the determination of ammonium. The possible CL mechanism of the reaction was proposed based on a series of experiments. The PCL intensity responded linearly to the concentration of ammonium in the range 3.0 × 10⁻¹¹-1.0 × 10⁻⁷ g mL⁻¹ with a detection limit of 1 × 10⁻¹¹ g mL⁻¹. The relative standard deviation (R.S.D.) was 1.4% for 1.0 × 10⁻⁹ g mL⁻¹ ammonium (n = 11). This method had been applied to the determination of ammonium in samples of mineral water, tap water and river water.     

Determination of osthole in rat plasma by high-performance liquid chromatograph using cloud-point extraction

A new straightforward method based on cloud-point extraction (CPE) was developed to determine osthole in rat plasma by reversed phase high-performance liquid chromatography with ultraviolet detection using a photodiode array detector. The non-ionic surfactant Triton X-114 was chosen as the extract solvent. Variable parameters affecting the CPE efficiency were evaluated and optimized. A Zorbax SB-C₁₈ column was used for elution separation at 25 °C with detection wavelength at 322 nm. Under the optimum conditions, the method was shown to be reproducible and reliable with intra-day precision below 7.62%, inter-day precision below 6.37%, and accuracy within ±5.02% and mean extraction recovery more than 90.4%, which were all calculated using a range of spiked samples at three concentrations of 0.5, 5.0 and 15.0 μg mL⁻¹ for osthole in plasma. The calibration curve for the analyte was linear in the range from 0.1 to 20 μg mL⁻¹ with the correlation coefficients greater than 0.9981. Limit of detection (S/N = 3) was less than 0.03 μg mL⁻¹and limit of quantification (S/N = 10) was less than 0.1 μg mL⁻¹. After strict validation, the method was successfully applied to the pharmacokinetic study of osthole in rats after oral and intravenous administration, respectively.     

Application of a novel co-enzyme reactor in chemiluminescence flow-through biosensor for determination of lactose

A novel enzyme reactor with co-immobilization of β-galactosidase and glucose oxidase in calcium alginate fiber (CAF) and amine modified nanosized mesoporous silica (AMNMS) was prepared which incorporate the adsorption and catalysis of AMNMS with the cage effect of the polymer to increase catalytic activity and stability of immobilized enzyme. The enzyme reactor was applied to prepare a chemiluminescence (CL) flow-through biosensor for determination of lactose combined with a novel luminol-diperiodatonickelate (DPN) CL system we reported. It shows that the CL flow-through biosensor possesses long lifetime, high stability, high catalytic activity and sensitivity. The relative CL intensity was linear with the lactose concentration in the range of 8 × 10⁻⁸-4 × 10⁻⁶ g mL⁻¹ with the detection limit of 2.7 × 10⁻⁸ g mL⁻¹ (3σ). It has been successfully applied to the determination of lactose in milk.