Standard Addition Technique Research Articles

Trace impurities analysis in UF4 via standard addition and 103Rh internal standardization techniques combined with ICP-MS

In order to determine trace impurities in the nuclear grade UF4, an analysis method based on the standard addition and 103Rh internal standardization techniques combined with ICP-MS has been established. The examination tests, including comparison with the quantity of trace impurities assigned in a certified reference uranium oxide and determination of the standard addition recovery, were performed to validate the accuracy and precision of the method. Total 42 trace impurity elements from Li to Bi were determined, with the method detection limit for the 42 impurities were found in the range of 0.0004–0.072 μg g−1. The recoveries were varied from 92% to 111%, and the relative deviations for most of the impurity elements were less than 10%. The method has been verified to meet the requirements of quality control for the UF4 and will be used in the molten salt reactor.

Analytical Determination of the Oxazolidinone Antibiotic Linezolid at a Pencil Graphite and Carbon Paste Electrodes

AbstractElectrochemical properties of linezolid, an antibiotic drug, using unmodified renewable pencil graphite and carbon paste electrodes, were investigated from pH 2 to 10 in Britton‐Robinson buffer solution. Experimental studies were examined by square‐wave (SW) and cyclic voltammetry (CV). Firstly, parameters affecting the performance of both electrode, such as electrode activation, support electrolyte selection, pH effect, interval of potentials, scan rates and voltammetric method parameters were investigated in detail by using square wave voltammetry. Linezolid was not reversibly oxidized in supporting electrolytes solutions, yielding well‐defined peaks in the oxidation potential interval. Using the pencil graphite electrode (PGE), a linearity range between peak current and concentration was obtained between 0.01 and 0.2 μg mL−1 (2.96×10−8‐5.93×10−7 M), other one, at carbon paste electrode (CPE), a linearity range between 0.1 and 7.5 μg mL−1 (2.96×10−7‐2.22×10−5 M) was obtained by SWV. The selectivity, sensitivity, precision, and other validation parameters of the developed voltammetric method was evaluated. Lastly, the concentration of linezolid was examined in pharmaceutical and biological samples with standard addition technique.

A Comparison of ETV and LA for the Determination of Trace Elements in Solid Samples by MIP OES

AbstractThe performance of electrothermal vaporization (ETV) and laser ablation (LA) of dry aerosols as sample introduction systems for microwave induced plasma optical emission spectrometry (MIP OES) are compared and evaluated in terms of detection limits, precision and accuracy for the determination of trace elements (Ca, Cd, Cu, Fe, Mg, Mn, Sr, Zn) in the same solid micro samples. In MIP OES both radiation sources can be independently adjusted to optimize the sampling process and then its subsequent excitation. A univariate approach and simplex optimization procedure were used to obtain the best signal/noise (S/N) ratio and derive analytical figures of merit. A comparison using a Student’st-test between the results obtained by both ETV/LA-MIP OES methods for trace elements, and concentrations in standard reference material (SRM) and certified reference materials (CRMs) showed that there was no significant differences on a 95 % confidence level. The detection limits of the tested elements in solid samples by ETV/LA-MIP OES were in the range of 0.1 to 11 µg g−1for all elements determined, while the corresponding absolute values in the range of ng. The precision of the results for ETV-MIP OES and LA-MIP OES varied between 2 and 4 % and 3 and 7 %, respectively. The linear dynamic ranges in the ETV/LA-MIP OES are extend over three decades of concentration. The methods were validated by the analysis of NIST SRM 2711Montana Soil, NRCC CRM PACS-2 Marine Sediment and NRCC CRM TORT-2 Lobster Hepatopancreas of different matrix composition and by the standard addition technique.

Determination of Trace Amount of Iron with as-Triazine Containing Ferroin- Functional Group

The as-triazines containing iron(II) methine chromophoric group; 3-(2-pyridyl)-5,6-diphenyl-as-triazine (PDT), and 3-(2- pyridyl)-5,6-bis(p-methoxyphenyl)-as-triazine (PBMPT) have been prepared from commercially available relatively cheaper reagents. The absorptiometric characteristics of the iron(II) complexes with PDT and PBMPT have been re-evaluated. The interference of copper ion on the determination of iron with these selective reagents and its masking has also been studied. The application of these spectrophotometric reagents for determination of iron in water samples based on the formation of extractable PDT-iron(II) and PBMPT-iron(II) complexes in chloroform medium has been described. Standard addition technique was used to verify the reliability of the method. Repeated determinations gave results with a very small standard deviation.
 Dhaka Univ. J. Sci. 67(2): 145-150, 2019 (July)

High‐precision Determination of Gold Mass Fractions in Geological Reference Materials by Internal Standardisation

Determination of gold abundances in natural rock is critical for applications, but very challenging. Here, we report a method for determining gold with a very low mass fraction (> 0.01 ng g−1) in rocks. The method involves Carius tube digestion with reverse aqua regia, chromatographic separation to remove most of the sample matrix and measurement by high‐sensitivity ICP‐MS. The mono‐isotopic element gold was quantified by external calibration using an internal standardisation of gold to platinum that was precisely determined by isotope dilution. The method is robust and the obtained results are indistinguishable (< 5–10%, 2s) from those independently obtained by a standard addition technique on the same solution. The results from reference materials TDB‐1 and GPt‐2 are consistent with the certified values and those determined by HF‐aqua regia digestion, confirming the validity of the method. TDB‐1 (n = 20), GPt‐2 (n = 6), BHVO‐2 (n = 9) and other mafic RMs are homogenous for gold (10–20%, 2s) at the 2 g test portion level; however, sample heterogeneity affects some RMs. Gold and platinum‐group elements also display different extents of sample heterogeneity for different RMs. Given the homogeneity observed for TDB‐1, GPt‐2 and BHOV‐2, they are recommended as well‐suited RMs for inter‐laboratory comparison studies of gold.

Two-wavelength manipulation stability-indicating spectrophotometric methods for determination of meropenem and ertapenem: greenness consolidation and pharmaceutical product application

Green assessed, UV-spectrophotometric methods were developed and validated for estimation of meropenem (MP) and ertapenem (EP), categorized to be non-classical β-lactam antibiotics, in the presence of their corresponding oxidative and hydrolytic degradants. The methods were successful to be used as stability-indicating ones and be applied for determination of the cited compounds in drug product and in pharmaceutical formulations. Three different spectrophotometric methods concerning two wavelengths manipulation for drug-degradant mixture resolution were adopted, namely; dual and induced dual wavelength, ratio difference, and advanced amplitude centering for partially overlapping spectra. Testing of the methods selectivity was achieved by successful analysis of synthetic mixtures of the studied drugs with different degradants. Validation was performed according to the USP guidelines. Application to pharmaceutical formulations and standard addition technique proved the methods’ analytical performance. Statistical comparison of the obtained results with those of the official or reported HPLC methods was performed using student t test, F test, and one-way ANOVA, where no significant differences with respect to accuracy and precision were observed. The greenness evaluation of the developed methods was assessed by applying two metrics to ensure environmental and personnel safety. No prior separation or long preparation steps were required for the proposed methods. The developed methods were specific, cost effective, and environmentally safe, less time-consuming methods for the quantitative determination of MP and EP in quality control laboratories with acceptable ultra-micro-linearity ranges and a promising wider applicability.

Validated Spectrophotometric Determination of Rizatriptan Benzoate in Pharmaceutical Formulations using Alizarin Derivatives

Two simple, sensitive, accurate, precise and economical spectrophotometric methods have been developed and validated for the determination of rizatriptan benzoate (RZT) in pure form and pharmaceutical formulations. These methods were based on the formation of charge transfer complex between RZT as n-electron donor and alizarin red S (ARS) or quinalizarin (Quinz) as π-acceptor in methanol to form highly colored chromogens which showed an absorption maximum at 532 and 574 nm using ARS and Quinz, respectively. The optimization of the reaction conditions such as the type of solvent, reagent concentration and reaction time were investigated. Under the optimum conditions, Beer’s law is obeyed in the concentration ranges 1.0-16 and 2.0-20 g mL-1 using ARS and Quinz, respectively with good correlation coefficient (r2 ≥ 0.9996) and with a relative standard deviation (RSD% ≤ 1.16). The molar absorptivity, Sandell sensitivity, detection and quantification limits were also calculated. The methods were successfully applied to the determination of RZT in its pharmaceutical formulations and the validity assesses by applying the standard addition technique. Results obtained by the proposed methods for the pure RZT and commercial tablets agreed well with those obtained by the reported method.

Discrete sampling based-flow injection as an introduction system in ICP-MS for the direct analysis of low volume human serum samples

Discrete sampling based on the flow injection options offered by advanced autosamplers has been tested and applied for the direct analysis of low volume samples (human serum) for multi-elemental purposes (simultaneous Al, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Ni, Pb, Rb, Se, V, and Zn assessment). Serum samples (200 µL aliquots) were directly diluted to 2.0 mL with 1% (v/v) HNO3, and discrete sampling operating conditions were optimized to allow cleaning, loading (300 µL injection loop), and measuring steps by using a volume lower than 2.0 mL (diluted serum sample). Matrix effect has been overcome by using the standard addition technique, and accurate results implied the use of kinetic energy discrimination (KED) mode (He as a collision gas) for measurements. The proposed method has been found to be reliable for serum samples analysis because of the low sample volume requirements, the minimal sample preparation required, and high sampling rate (each replicate analysis takes 2.50 min). In addition, validation results show good precision and accuracy (both analytical recovery and analysis of certified reference materials), and acceptable sensitivity. Applicability of the proposed method has been finally demonstrated by analysing several serum samples from healthy adults.

Validated Chromatographic Methods for Simultaneous Determination of Calcipotriol Monohydrate and Betamethasone Dipropionate in the Presence of Two Dosage Form Additives.

Two chromatographic methods were developed, optimized and validated for simultaneous determination of calcipotriol monohydrate (CPM) and betamethasone dipropionate (BMD) in the presence of two dosage form additives named; butylated hydroxytoluene (BHT) and alpha-tocopherol (TOCO). The proposed methods were accurate, sensitive and specific. The first method based on using aluminum thin-layer chromatographic plates precoated with silica gel GF254 as a stationary phase and chloroform-ethyl acetate-toluene (5:5:3, by volume) as a developing system. This was followed by densitometric measurement of the separated bands at 264 nm. Whereas the second method is RP-HPLC where OnyxMonolithic C18® column was used with a gradient profile using methanol, water and acetic acid at flow rate 2.0 mL min-1. Detection was carried out at 264 nm. The methods were validated according to ICH guidelines. The specificity of the developed methods was investigated by analyzing the pharmaceutical dosage form. The validity of the proposed methods was assessed using the standard addition technique. The obtained results were statistically compared with those obtained by the official methods, showing no significant difference with respect to accuracy and precision at P = 0.05.

Microwave-assisted extraction of the gallic acid biomarker from Acacia arabica bark followed by HPLC analysis

An efficient and fast microwave-assisted extraction (MAE) technique was developed for extracting gallic acid as an indicative biomarker for the quality control of Acacia arabica bark. The MAE technique was optimized and compared with other conventional extraction techniques. The optimal conditions of MAE were 20% methanol as solvent, solid/liquid ratio 1:40 (g/mL), irradiation power 20% and two extraction cycles, 5 min each. The proposed extraction technique produced a maximum yield of 10.59 (mg/g) gallic acid in 10 min, which was 1.03 and 1.15 times more efficient than 6 h of heat reflux and 24 h of maceration extraction, respectively. This high yield, along with saving of time, energy, and solvent would position MAE as a valuable and cost-effective technology suitable for today's highly competitive industries, with growing demand for increased productivity, improved efficiency, and reduced cycle time. Moreover, a new high-performance liquid chromatography method was developed and validated for the determination of gallic acid in Acacia arabica bark extract. The method was found to be rapid, sensitive, accurate, precise, and robust. The method showed good linearity over concentration range 1-100 (µg/mL) with LOD 16.08 (ng/mL) and LOQ 48.73 (ng/mL). The average recovery obtained using standard addition technique was 100.36% with a low value of RSD% (1.19%) indicating the accuracy of the proposed method for determination of gallic acid in Acacia arabica bark extract.

Forensic electrochemistry: Electrochemical study and quantification of xylazine in pharmaceutical and urine samples

Xylazine is marketed as a veterinary drug and used for sedative and analgesic purposes; it is not approved for human use due to various side effects. In recent years, xylazine has emerged as a drug of abuse and has been associated with drug-facilitated sexual assaults. Herein, we describe, for the first time, the electrochemical study of xylazine in aqueous and organic media and proposed a quantification method using glassy carbon electrode. The simple and accurate quantification method was performed using differential pulse voltammetry. Under the optimized experimental conditions, a linear analytical curve was obtained for xylazine concentrations ranging from 0.5 to 256 μmol L−1, with an estimated detection limit of 120 nmol L−1. The proposed method was applied to determination of xylazine in pharmaceutical formulation. Furthermore, to forensic scenario, a standard addition technique on urine samples exhibited recovery values in the range of 93–103%, demonstrating the potentiality to forensic and clinical analysis of xylazine intoxication.

Venlafaxine Determination in Pharmaceutical Formulation and Serum by Ion-Selective Electrodes.

The application of an ion selective technique for the determination of analyte concentrations is considered one of the most economical techniques for quality control purposes. To elaborate and investigate the construction and general performance characteristics of potentiometric PVC membrane sensors for venlafaxine cation (Ven+). The sensors are based on the use of the ion association complexes of the venlafaxine cation with phosphotungstate (PT) and silicotungstate (ST) counter anions as ion exchange sites in the plasticized PVC matrix. They are characterized by potentiometric and conductimetric measurements, performed under various conditions. The electrodes showed a fast (response time around 15 s), stable (life span 45 days) and linear (r2 0.995) response for venlafaxine over the concentration range of 5x10-5 - 1x10-2 M venlafaxine hydrochloride. The solubility product of the ion pair and the formation of the precipitation reaction leading to the ion pair, were determined conductimetrically. The electrodes were found to be very selective, precise (RSD < 1%) and applicable to the potentiometric determination of venlafaxine hydrochloride in pure solutions or in pharmaceutical preparation and in biological fluid (serum), without any interference. Validation of the method shows the suitability of the proposed electrodes for use in the quality assessment of venlafaxine hydrochloride. Using only a pH meter in combination with the selective electrodes, drug substance or drug product could be determined accurately in a few seconds. In addition, the in-house made electrodes were tested to monitor venlafaxine in serum. Acceptable results were achieved using the standard addition technique.

Use of multiple lines for improving accuracy, minimizing systematic errors from spectral interferences, and reducing matrix effects in MIP OES measurements

Bismuth-based medicines, which are generally available without prescription, are used for a variety of purposes including stomach relief, diarrhea, and cold sores. The determination of Bi in these types of medicines using MIP OES is considered easy, due to the relatively high concentrations of this element. However, high dilution factors can lead to systematic errors and thus low precision. Furthermore, the drugs, excipients, and other active pharmaceutical ingredients (APIs) present in these products can cause spectral and matrix interferences. The present study evaluates the use of multiple spectral lines as a strategy to avoid analytical difficulties. For comparative purposes, hydride generation and standard additions techniques were also evaluated. The results demonstrated the feasibility of using the sum of the intensities of multiple lines to improve accuracy, minimizing systematic errors from spectral interferences and matrix effects, employing simple calculations in a data spreadsheet. The accuracies, calculated based on labeled values, varied from 89.2 to 98.8% and from 72.2 to 124% for direct analysis without and with standard additions, respectively, from 73.2 to 114% for hydride generation, and from 89.8 to 101% for the multiple lines sum method.

Efficient UPLC and CE methods for the simultaneous determination of azelastine hydrochloride and its genotoxic impurity.

A novel stability-indicating UPLC and CE method was established and validated for the determination of azelastine hydrochloride (AZL) and its genotoxic impurity, benzohydrazide, in the presence of benzalkonium chloride. The developed UPLC method was based on chromatographic separation using a C18 column as a stationary phase and acetonitrile-(0.1% w/v) aqueous sodium lauryl sulfate (55:45, v/v, pH 5 with phosphoric acid) as a mobile phase with a flow rate of 1.2 mL/min and UV detection at 215 nm. The chromatographic run time was ~2 min. The developed CE method depended on using a stationary phase of Standard Bare Fused Silica Capillaries (75 μm i.d. × 59 cm and 50 cm detection length) and the applied voltage was 30 kV using 40 mm phosphate buffer (pH 2 with aqueous H3 PO4 ); the detection wavelength was 225 nm. The analysis time was about 6 min. The suggested methods were successfully applied for the analysis of AZL in a pharmaceutical preparation. The validity of the developed methods was assessed by applying the standard addition technique and no interference from excipients was observed. The results obtained by the proposed methods were statistically analyzed and compared with the manufacturer's method and no significant difference was found between the compared methods.

Different Spectrophotometric Methods Applied for the Determination of Aclidinium in Duaklir ® Genuair ® Inhalation Powder

Three simple, accurate and selective spectrophotometric methods were developed to determine aclidinium in the presence of formoterol as interferent compound in Duaklir ® Genuair ® inhalation powder. The methods under study are absorbance subtraction, area under the curve and simultaneous equation. The methods were linear over the concentration range of 5-50 μg/mL for aclidinium and validated according to the ICH guidelines. The accuracy and precision were found to be within the acceptable limits. The specificity of the proposed methods was tested using laboratory prepared mixtures and assessed by applying the standard addition technique. Furthermore, the methods were statistically compared to the RP-HPLC method and good results were obtained.

Different Spectrophotometric Methods Manipulating Ratio Spectra Applied for the Analysis of Aclidinium in Duaklir® Genuair® Inhalation Powder

Two simple, accurate, and selective spectrophotometric methods were developed to determine aclidinium in the presence of formoterol as interferent compound in Duaklir Genuair inhalation powder. The methods under study are ratio derivative and ratio subtraction spectrophotometric methods. These methods are based on different mathematical processing of the obtained ratio spectra. The methods are linear over the concentration range of 5–50 µg/mL for aclidinium and validated according to the ICH guidelines. The accuracy and precision are found to be within the acceptable limits and assessed by applying the standard addition technique. The specificity of the proposed methods was tested using laboratory-prepared mixtures. Furthermore, the methods were statistically compared to the reported RP-HPLC method, and good results were obtained.

Multivariate Validated Models for Simultaneous Determination of Ibuprofen and Famotidine in the Presence of Related Substances.

Two multivariate validated spectrophotometric methods, namely partial least-squares (PLS) and principal component regression (PCR), were developed and validated for the determination of ibuprofen and famotidine in presence of famotidine degradation products and ibuprofen impurity (4-isobutylacetophenone). A calibration set was prepared in which the two drugs together with the degradation products and impurity were modeled using a multilevel multifactor design. This calibration set was used to build the PLS and PCR models. The proposed models successfully predicted the concentrations of both drugs in validation samples, with low root mean square error of cross validation (RMSECV) percentage. The method was validated by the estimate of the figures of merit depending on the net analyte signal. The results of the two models showed that the simultaneous determination of both drugs could be performed in the concentration ranges of 100-500 µg/mL for ibuprofen and 5-25 µg/mL for famotidine. The proposed multivariate calibration methods were applied for the determination of ibuprofen and famotidine in their pharmaceutical formulation, and the results were verified by the standard addition technique.

THE ANALYSIS OF ZIRCONIUM DIOXIDE STABILIZED WITH YTTRIUM OXIDE BY ATOMIC-EMISSION SPECTROMETRY WITH INDUCTIVELY COUPLED PLASMA

A method of aluminum, hafnium, iron, yttrium, calcium, magnesium, and titanium determination in yttria-stabilized zirconia (YSZ) by inductively coupled plasma atomic emission spectrometry (ICP-AES) is described. Conditions for the decomposition of two modifications of the analyzed material — unburned and subjected to stabilizing firing — were studied. It was found that the unburnt zirconia dissolves well in sulfuric acid, and the conversion to the solution of the burnt sample is possible only with fusion with potassium pyrosulfate or potassium bifluoride, but using of these reagents leads to high values of the control experiment correction for trace impurities (at the level of tenths and hundredths of a percent). In this connection, we studied the possibility of acid dissolution of a burnt sample under microwave decomposition, varying the qualitative and quantitative composition of the acid mixture, the reaction temperature, the time to reach and to maintain the required temperature. It was found that the decomposition in the mixture of hydrofluoric and sulfuric acids (2:1) in the microwave system with stepwise heating of the reaction mixture ensures quantitative dissolution of the burnt sample and sufficiently low values of the control experiment correction for microimpurities. The analytical lines were chosen taking into account their relative intensity, possible spectral overlaps, and the matrix effect in the analysis of model solutions containing 1.3 mg/cm 3 Zr, 0.2 mg/cm 3 Y and from 0.2 to 20 mg/cm 3 impurities. As a result, the following analytical lines were chosen: Al II 167.079 nm and Al I 308.215 nm; Ca II 184.006 nm and 393.366 nm; Fe II 238.204 nm; Mg II 279.553 nm, Ti II 334.941 nm, Y II 371.030 nm and Hf II 232.247 nm. The developed method for the analysis of yttria-stabilized zirconia (YSZ) by the ICP-AES allows simultaneously determining aluminum, iron, magnesium and titanium in the range of 0.01 – 1.0%, calcium — 0.02 – 1.0%, hafnium — 0.1 – 5.0% and yttrium — 2.0 – 15% with a % rel. (Y). The correctness of the method is confirmed by the standard addition technique.

Use of continuous wavelet transform approach for simultaneous quantitative determination of multicomponent mixture by UV–Vis spectrophotometry

In the present paper, a multicomponent analysis approach based on spectrophotometry method was developed for simultaneous determination of Guaifenesin (GU), Chlorpheniramine (CHL) and Pseudoephedrine (PSE) without any separation steps. The method under study is signal processing method based on Continuous Wavelet Transform (CWT) coupled with zero cross point technique. In this paper, CWT method was tested by synthetic ternary mixtures and was applied to the commercial cough syrup as a real sample and assessed by applying the standard addition technique. For demonstrate the accuracy of the results, other applications of signal processing, such as Derivative Transform (DT), Partial Least Squares (PLS) regression and Principal Components Regression (PCR) were used as comparative methods. Afterwards, the obtained results from analyzing the cough syrup by all methods were compared to the High-Performance Liquid Chromatography (HPLC) as a reference method. One-way analysis of variance test at 95% confidence level showed no significant differences between CWT and other applications.

Diffusion profile simulations and enhanced iron sensing in generator-collector mode at interdigitated nanowire electrode arrays

Gold interdigitated nanowire electrode arrays (INEAs) (∼100 nm wide, ∼50 nm high, ∼45 μm long and ∼500 nm spacing) on a Si/SiO2 chip substrate were fabricated and characterised. Arrays were employed in both non-generator-collector (non-GC) mode (one array electrically connected) and in generator-collector (GC) mode (both arrays electrically connected). In non-GC mode, the individual arrays were confirmed to behave as microelectrodes arising from linear diffusion to the total area of the array. By contrast, in GC-mode, arrays displayed steady-state electrochemical behaviour arising from enhanced diffusion to the nanowires and redox cycling (RC) between adjacent electrodes. Finite element simulations were investigated to explore the effect of altering connected and non-connected electrodes on the diffusional behaviour of the arrays with 500 nm separations. They correlated well with the experimental observations for the influence of the collector electrode potential on redox reactions taking place at the generator for a range of scan rates. The suitability of the gold INEAs towards iron sensing in water is also reported. A calibration curve is obtained for 0.5–40 μM (28–2234 μg L−1) Fe2+ with a limit of detection (LOD) of 0.01 μM (0.6 μg L−1) well below the permitted level in drinking water. Finally, iron determination in tap water using a standard addition technique is presented.