Linear Calibration Range Research Articles

A label-free ratiometric immunoassay using bioinspired nanochannels and a smart modified electrode

Labeling with redox reporter is often required in developing electrochemical bioassay for most proteins or nucleic acid biomarkers. Herein, a label-free ratiometric immunosensing platform is firstly developed by integrating the antibody-conjugated nanochannels with a smart modified electrode. The electrode modifier is the composite of C60, tetraoctylammonium bromide (TOA+) and Prussian blue (PB). Cyclic voltammograms of the ultimate C60-TOA+/PB modified electrode exhibited two pairs of peaks at 0.15 V and −0.13 V, ascribing to the redox of PB and C60, respectively. With the addition of K3[Fe(CN)6] in the electrolyte solution, the peaks of PB decreased due to the adsorption of [Fe(CN)6]3− while the peaks of C60 increased because of the formation of the ternary complex (TC) C60-TOA+-[Fe(CN)6]3−. As a result, the peak current ratio IPB/ITC decreased gradually with the increment of the concentration of [Fe(CN)6]3−. For the nanochannels-based immunosensing platform, the steric hindrance of the bioconjugated nanochannels varied with the loading amount of the target CA125, and thus [Fe(CN)6]3− passing through the channels was quantitatively affected. And the higher CA125 level was, the less [Fe(CN)6]3− concentration was. And thus, the ratio IPB/ITC monitored at the C60-TOA+/PB modified electrode increased with the increase of the concentration of CA125. The ratiometric immunoassay featured a linear calibration range from 1.0 U mL−1 to 100 U mL−1 with a low detection limit of 0.86 U mL−1. In addition, the ratiometric immunosensing platform demonstrated good specificity and stability as well as acceptable accuracy in overcoming the effect of electrode passivation which was an inherent problem of electroanalysis.

Reagent free electrochemical-based detection of silver ions at interdigitated microelectrodes using in-situ pH control

• Applying 1.65 V to a protonator electrode lowered the pH at the sensor electrode to pH 3, optimal for silver ion detection. • In-situ pH control eliminated the need for the addition of mineral acids to a solution before analysis. • Chlorine present in tap water helped in detection, causing a sharpening of the silver stripping peak due to formation of silver chloride. • Detection of 250 nM of silver ions in tap water in less than 3 min was possible without the need for additional electrolytes. Herein we report on the development of an electrochemical sensor for silver ions detection in tap water using anodic sweep voltammetry with in-situ pH control; enabled by closely spaced interdigitated electrode arrays. The in-situ pH control approach allowed the pH of a test solution to be tailored to pH 3 (experimentally determined as the optimal pH) by applying 1.65 V to a protonator electrode with the subsequent production of protons, arising from water electrolysis, dropping the local pH value. Using this approach, an initial proof-of-concept study for silver detection in sodium acetate was undertaken where 1.25 V was applied during deposition (to compensate for oxygen production) and 1.65 V during stripping. Using these conditions, calibration between 0.2 and 10 μM was established with the silver stripping peak ∼0.3 V. The calculated limit of detection was 13 nM. For the final application in tap water, 1.65 V was applied to a protonator electrode for both deposition and stripping of silver. The chloride ions, present in tap water (as a consequence of adding chlorine during the disinfection process) facilitated silver detection and caused the striping peak to shift catholically to ∼0.2 V. The combination of the complexation of silver ions with chloride and in-situ pH control resulted in a linear calibration range between 0.25 and 2 μM in tap water and a calculated limit of detection of 106 nM without the need to add acid or supporting electrolytes.

Simple and Equipment-Free Paper-Based Device for Determination of Mercury in Contaminated Soil.

This work presents a simple and innovative protocol employing a microfluidic paper-based analytical device (µPAD) for equipment-free determination of mercury. In this method, mercury (II) forms an ionic-association complex of tetraiodomercurate (II) ion (HgI42−(aq)) using a known excess amount of iodide. The residual iodide flows by capillary action into a second region of the paper where it is converted to iodine by pre-deposited iodate to liberate I2(g) under acidic condition. Iodine vapor diffuses across the spacer region of the µPAD to form a purple colored of tri-iodide starch complex in a detection zone located in a separate layer of the µPAD. The digital image of the complex is analyzed using ImageJ software. The method has a linear calibration range of 50–350 mg L−1 Hg with the detection limit of 20 mg L−1. The method was successfully applied to the determination of mercury in contaminated soil and water samples which the results agreed well with the ICP-MS method. Three soil samples were highly contaminated with mercury above the acceptable WHO limits (0.05 mg kg−1). To the best of our knowledge, this is the first colorimetric µPAD method that is applicable for soil samples including mercury contaminated soils from gold mining areas.

Characterizing the Performance of a Compact BTEX GC-PID for Near-Real Time Analysis and Field Deployment.

In this study, we test the performance of a compact gas chromatograph with photoionization detector (GC-PID) and optimize the configuration to detect ambient (sub-ppb) levels of benzene, toluene, ethylbenzene, and xylene isomers (BTEX). The GC-PID system was designed to serve as a relatively inexpensive (~10 k USD) and field-deployable air toxic screening tool alternative to conventional benchtop GCs. The instrument uses ambient air as a carrier gas and consists of a Tenax-GR sorbent-based preconcentrator, a gas sample valve, two capillary columns, and a photoionization detector (PID) with a small footprint and low power requirement. The performance of the GC-PID has been evaluated in terms of system linearity and sensitivity in field conditions. The BTEX-GC system demonstrated the capacity to detect BTEX at levels as high as 500 ppb with a linear calibration range of 0–100 ppb. A detection limit lower than 1 ppb was found for all BTEX compounds with a sampling volume of 1 L. No significant drift in the instrument was observed. A time-varying calibration technique was established that requires minimal equipment for field operations and optimizes the sampling procedure for field measurements. With an analysis time of less than 15 min, the compact GC-PID is ideal for field deployment of background and polluted atmospheres for near-real time measurements of BTEX. The results highlight the application of the compact and easily deployable GC-PID for community monitoring and screening of air toxics.

Development of QuEChERS extraction method for the determination of pesticide residues in cereals using DART-ToF-MS and GC-MS techniques. Correlation and quantification study

Cereal crops comprise more than 60 % of agricultural production worldwide. To ensure high production, the extensive use of pesticides is common practice. Analysis of pesticide residues in food and particularly cereals has become an essential requirement for consumers, producers, food inspectors and authorities. However, the determination of pesticides in cereal samples is not an easy task due to the complexity of the matrices and the trace levels of pesticides. In this study, a simple and high-throughput method was validated for the determination of multi-residue pesticide in 30 different types of cereals which are commonly consumed around the world. QuEChERS procedure has been developed, a mixture of primary-secondary amine and C18 proved better performance for the reduction of the interfering substances from the cereal grains than multiwalled carbon nanotubes. For a comprehensive investigation, the pesticide cereals contents were purified following the established cleanup method and detected by DART-ToF-MS and GC-MS. As “soft” and “hard” MS ionization methods, DART-ToF-MS and GC-MS are strong nominated for comprehensive studies of the unknown molecules. The results showed that 19 pesticides were successfully identified by both techniques in all samples, 16 by DART-ToF-MS and 13 using GC-MS. Regarding the correlation between the developed methods, 10 pesticides were detected as a commonality between the two techniques, this indicates that a single MS technique is not sufficient to detect all of the existing pesticides in cereals. The findings exposed that the two MS techniques are complementary, and both can be used for comprehensive identification of the pesticides presented in cereals. Quantitative analysis was performed using GC-MS under the selective ion monitoring mode by external and internal standard methods. Tributyl phosphate has been used as an internal standard. The measured limits of detection ranged between 4 and 9 μg kg−1 for all pesticides, while the limit of quantification values was <34.8 μg kg−1, which were below the regulatory maximum residue limits. The coefficient of determination was >0.9980 within the calibration linearity range of 15–6250 μg kg−1 for the detected pesticides. The recovery of all detected pesticides was in the range 75.28–122.02 % (n = 3) with associated RSDs <14 % indicating satisfactory accuracy.

Kynurenic Acid Electrochemical Immunosensor: Blood-Based Diagnosis of Alzheimer's Disease.

Alzheimer’s disease (AD) is a neurodegenerative disorder, characterized by a functional deterioration of the brain. Currently, there are selected biomarkers for its diagnosis in cerebrospinal fluid. However, its extraction has several disadvantages for the patient. Therefore, there is an urgent need for a detection method using sensitive and selective blood-based biomarkers. Kynurenic acid (KYNA) is a potential biomarker candidate for this purpose. The alteration of the KYNA levels in blood has been related with inflammatory processes in the brain, produced as a protective function when neurons are damaged. This paper describes a novel electrochemical immunosensor for KYNA detection, based on successive functionalization multi-electrode array. The resultant sensor was characterized by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The proposed biosensor detects KYNA within a linear calibration range from 10 pM to 100 nM using CA and EIS, obtaining a limit of detection (LOD) of 16.9 pM and 37.6 pM in buffer, respectively, being the lowest reported LOD for this biomarker. Moreover, to assess our device closer to the real application, the developed immunosensor was also tested under human serum matrix, obtaining an LOD of 391.71 pM for CA and 278.8 pM for EIS with diluted serum.

Optimization and method validation for the quantitative analysis of a monoclonal antibody and its related fab fragment in human plasma after intravitreal administration, using LC–MS/MS

As biologic based drugs become an increasingly important sector of the pharmaceutical industry, accurate and precision techniques for bioanalysis are required to support clinical trials and beyond. Ranibizumab, a fab therapeutic, is an FDA approved drug to treat wet age-related macular degeneration (AMD), as well as other eye related diseases. Ranibizumab’s mAb counterpart, bevacizumab, is often also used off-label to treat wet AMD. Ranibizumab and bevacizumab target circulating VEGF-A in the eye, reducing unwanted angiogenesis. Since these drugs are designed for local intravitreal administration, concentration levels in human plasma are expected to be significantly lower compared to vitreous fluid concentrations, presenting bioanalytical challenges. However, this is important for assessment of drug toxicity. In this manuscript, we describe the development, optimization, and validation of an LC-MS/MS method designed for quantitative bioanalysis of ranibizumab and bevacizumab in human plasma following intravitreal administration. In order to fully develop this method, evaluations were conducted to optimize the conditions, including selection of the surrogate peptide by in-silico experiments, optimizations of the immunocapture, denaturation, reduction, alkylation, and digestion extraction steps, as well as optimization of the LC-MS/MS conditions, and evaluation of a dissociation step to determine if there was interference from VEGF or ADAs. Once the method was fully optimized, it was then validated, following the 2018 FDA guidance on bioanalytical method validations. This method is now available for use during clinical trials and precision medicine, for the quantitative evaluation of systemic exposure of ranibizumab or bevacizumab in human plasma after intravitreal administration, with a linear calibration range of 0.300–100 ng/mL.

DNAzyme-Au nanoprobe coupled with graphene-oxide-loaded hybridization chain reaction signal amplification for fluorometric determination of alkaline phosphatase.

A sensing platform is presentedfor the determination of alkaline phosphatase (ALP) activity based on the cooperation of DNAzyme-Au spherical nucleic acid nanoprobe with the graphene-oxide-loaded hybridization chain reaction (HCR/GO) system to achieve good detection sensitivity and specificity. This assay takes advantage of the strong affinity of pyrophosphate (PPi) to Cu2+ ions and the fact that ALP can hydrolyze pyrophosphate (PPi) to release free Cu2+ ions. In the presence of ALP, the released Cu2+ can promote the Cu2+-dependent DNAzyme to cleave the substrate that generates a shorter DNA fragment, which is responsible for further triggering the HCR/GO system to form a long fluorescence dsDNA and thereby giving an amplified fluorescence signal. Linear calibration range was obtained from 0.2 to 10UL-1, and the limit of detection (LOD) is about 0.14UL-1. The feasibility of the proposed method was validated by spiking ALP standards in bovine serum. The recovery ranged from 97.2 to 104.6%, and a coefficient of variation (CV) of less than 8% (n = 3) was obtained. This assay strategy was also applied to evaluate the ALP inhibitor efficiency, which indicates that the assay has potential for drug screening.

Optimization of 204 veterinary drug residues method and establishing their mass spectrum library

ABSTRACT A multi-class multi-residue analytical method was validated in this paper for simultaneously identifying 204 veterinary drugs in pork by UPLC-QTRAP MS/MS, including sulfonamides, quinolones, β-agonists, and nitroimidazoles. MRM-IDA-EPI mode of QTRAP was used to establish a secondary mass spectrum library of these 204 veterinary drugs, which could enhance the qualitative analysis of suspect substances. The separation of substances was performed on a C18 column, with a gradient elution of 0.1% formic acid solution in water and methanol. Electrospray ionization (ESI), fast polarity switching, and scheduled MRM mode were used to collect the characterization results. Factors that affected the recovery were delicately optimized, such as solvent proportion, formic acid content, and purification method. We finally determined the extracting method with formic acid-acetonitrile-water (0.1:90:10, v:v:v) and purifying method with Cleanert LipoNo as a package for dispersive solid-phase extraction. Matrix effects on the quantitative results were also investigated. Some compounds had strong matrix inhibition or enhancement, and the matrix matching external standard method was used to quantify the compounds accurately. The correlation coefficient R2 was over 0.99 within the calibration linearity range for the detected 204 veterinary drugs. The limit of quantification (LOQ) was 0.5 ~ 5 μg/kg. The recoveries ranged from 61.4% to 118.8% with RSDs of 3.1% to 19.2% (n = 6).

Fluorometric probe for the lipase level: Design, mechanism and biological imaging application

To realize accurate regulation for fluorescent substrate of lipase, two series compounds (I, II) with similar structure were designed and synthesized. The flexible diphenylmethane was permitted I to go deep into the catalytic site of lipase, while rigid structure of 9H-fluoren makes itself difficult to approach the center. Series I could be effectively hydrolyzed by porcine pancreatic lipase (PPL), and the product emitted fluorescence based on aggregation-induced emission (AIE) mechanism, meanwhile different substituent groups (–Br, –Cl, –Ph, –H) on I induced the tunable hydrolysis rate. The limit of detection (LOD) was 0.05 U/mL, and linear calibration range was 0.1–4.0 U/mL, this would be effectively applied to biological detection. This result was well supported by theories calculation and molecular docking. Moreover, substrate 1 was selected to describe the distribution of lipase in many living biology such as zebrafish, Locusta migratoria and Helianthus annuus seeds coat. It was found that lipase and lipid droplets (LDs) coexist in biological systems, but there is no lipase in LDs. The designed probe gives us an opportunity to describe lipase distribution in many important tissues, including biology and medical science.

Flow injection-chemiluminescence determination of cetirizine dihydrochloride in pharmaceuticals using tris(2,2'-bipyridyl)ruthenium (II)-Ag(III) complex reaction.

A simple and sensitive flow injection-chemiluminescence (FI-CL) method was developed for determination of cetirizine dihydrochloride (CTZH) in pharmaceuticals. The method is primarily based on the enhancement effect of CTZH on the tris(2,2'-bipyridyl)ruthenium (II)-diperiodatoargentate (III) ([Ru(bpy)3 ]2+ -Ag(III) complex) CL system in an acidic medium. The optimum investigated variables of the CL reaction were: [Ru(bpy)3 ]2+ , 50 × 10-6 mol/L; sulfuric acid, 1.0 × 10-3 mol/L; Ag(III) complex, 100 × 10-6 mol/L; potassium hydroxide, 1.0 × 10-3 mol/L; flow rate, 3.0 ml/min and sample loop volume, 300 μl. The detection and quantification limits were 2.0 × 10-4 and 5.0 × 10-4 mg/L (S/N of 3 and 10) respectively with a linear calibration range of 5.0 × 10-4 to 7.5 mg/L (R2 = 0.9999, n = 11), injection throughput of 110/h and the relative standard deviations of 1.5-3.5% over the range studied. The methodology was successfully applied to determine CTZH in different pharmaceutical samples and validated with a high-performance liquid chromatography method, and resulted in the recovery of 94.6-108.6%. The probable CL reaction mechanism is described in brief.

Fluorescent and electrochemical bimodal bioplatform for femtomolar detection of microRNAs in blood sera

Noncoding RNAs such as miRNAs (miRs) are extensively researched as a novel class of cancer biomarkers. Herein, we describe a new method to sensitively determine the levels miRNAs via dual signal readout involving competitive hybridization between the miR-21 target and its biotinylated analog towards the same thiolated DNA probe attached onto the surface of gold nanoparticles. Hybridization of the DNA probes by the biotinylated miRs followed by conjugation with streptavidin-horseradish peroxidase, which catalyzes the oxidation of o-phenylenediamine into 2,3-diaminophenazine, allows detecting the target using fluorescence and electrochemistry. The two signals varied in a miRNA concentration-dependent manner. The bioplatform has limits of detection of 15 fmol/L and 19 fmol/L (0.15 and 0.19 attomol in 20 μL, respectively). Furthermore, it displays a wide linear calibration range varying from 19 fmol/L to 100 pmol/L and 15 fmol/L to 100 pmol/L using voltamperometry and fluorescence, respectively. The bioplatform is able to provide very low detection limits without any DNA/RNA amplification step, an excellent selectivity toward non-complementary miRs along with an acceptable distinction with a single nucleotide mismatched sequence. Finally, the method was used to determine miR-21 expression levels in blood sera from patients diagnosed with breast cancer.

Environmentally friendly liquid medium for a cost-effective long-path absorption liquid core waveguide with a gas diffusion flow analysis system

An environmentally friendly modified flow analysis carrier with a high refractive index liquid to perform a total internal refrection phenomenon in a typical Teflon tube was achieved as a cost-effective long-path liquid core waveguide (LCW) for absorption spectrophotometry. A home-built LED-photodiode based long-path colorimeter was demonstrated to enhance the sensitivity of chemical analysis without using a preconcentration unit. A low toxicity carrier such as syrup or ethanol was selected to improve the sensitivity for NH4+ ion determination via butterfly pea flower extract reagent in a gas-diffusion flow injection (GD-FI) system. A linear calibration range of NH4+ ion determination in the GD-FI based on syrup modified LCW (mLCW) system of 10–500 µmol L−1 can be obtained with a detection limit of 9.8 µmol L−1, repeatability of <2% RSD, and 12 injections h−1 sample throughput. The proposed cost-effective and environmentally friendly mLCW shows the potential to apply with other natural/synthetic chromogenic reagents for the green chemical analysis approach.

Liquid chromatography-tandem mass spectrometric assay for TPN171 in human plasma

A simple, rapid and accurate method for quantitative analysis of a highly selective phosphodiesterase-5 inhibitor (PDE5), TPN171 by high performance liquid chromatography and tandem mass spectrometry in human plasma was proposed and validated successfully using D3-TPN171 as internal standards (ISTD). An aliquot of 100 μL of plasma was mixed with internal standard and was precipitated with acetonitrile. Gradient elution was performed on a ACQUITY HSS T3 column (50 × 2.1 mm, 1.8 μm) coupled with a ACQUITY column in-line filter at 40℃, by 5 mM ammonium acetate in water containing 0.1 % formic acid and 0.1 % formic acid in acetonitrile as the mobile phase. The total analytical run time was 3.5 min. The analyte was monitored using multiple reaction monitoring (MRM) scan in positive polarity mode. The ion transition was m/z 442.2→113.2 and 445.2→116.2 for TPN171 and D3-TPN171 respectively. The method was validated for specificity, sensitivity, precision, accuracy, and other analytical parameters. The results found were satisfactory over the linear calibration range of 1−500 ng/mL. Within-day precisions ranged from 1.8 to 7.3 %, and between-day precisions from 2.3 to 4.9 %, accuracies were 95.5–99.8 %.The validated method was successfully applied to determine the plasma concentration after oral administration of 10 mg TPN171 in six healthy volunteers.

Gold nanoparticles decorated bimetallic CuNi-based hollow nanoarchitecture for theenhancement ofelectrochemical sensing performance of nitrite.

Gold nanoparticles (AuNPs) decorated bimetallic CuNi-based hollow nanoarchitecture (CNHN) are reported for the first timeas a nonenzymatic sensor for the quantification of nitrite in neutral solution . The CNHN was prepared via a convenient calcining routine using the bimetallic CuNi-MOFs as a coprecursor. The unique chemical structure of hollow CNHN with high specific surface area and abundant terminal amino groups effectively avoid the aggregation of AuNPs and facilitate the subsequent adsorption of nitrite. The Au/CNHN exhibited high electrocatalytic activity towards nitrite oxidation due to the synergetic catalytic effect of AuNPs and CNHN. Chronoamperometric detection of nitrite at the Au/CNHN/GCE achieved a lower linear calibration range of0.05 to 1.15mM, with an LOD of 0.017μM compared with previous reports. Theproposed method obtained satisfactory recoveries for nitrite determination in practical applications, which was verified by UV-Vis spectrophotometry. Theprepared sensor based on Au/CNHN featured favorable selectivity and stability, which providesa promising approach for real sample analysis. Graphical abstract.

Development and Validation of an HPLC-UV Detection Assay for the Determination of Clonidine in Mouse Plasma and Its Application to a Pharmacokinetic Study.

An accurate and simple HPLC-UV method has been developed for the determination of clonidine in mouse plasma. A reversed phase C18 Nova Pack® column (125 mm × 4.6 mm i.d., × 3 μm particle size) was used as stationary phase. The mobile phase composition was a mixture of 0.1% diethylamine/acetonitrile (70:30, v/v) at pH 8 in an isocratic mode at flow rate was 1.0 mL/min. Detection was set at 210 nm. Tizanidine was used as an internal standard. The clonidine and tizanidine were extracted from plasma matrix using the deproteinization technique. The developed method exhibited a linear calibration range 100.0–2000 ng/mL and the lower limit of detection (LOD) and quantification (LOQ) were 31.0 and 91.9 ng/mL, respectively. The intra-day and inter-day accuracy and precision of the method were within 8.0% and 3.0%, respectively, relative to the nominal concentration. The developed method was validated with respect to linearity, accuracy, precision, and selectivity according to the US Food and drug guideline. Minimal degradation was demonstrated during the determination of clonidine under different stability conditions. The suggested method has been successfully applied during a pharmacokinetic study of clonidine in mouse plasma.

Amperometric assay of hydrazine utilizing electro-deposited cobalt hexacyanoferrate nanocrystals on graphene oxide sheets

In-situ electrochemical deposition of cobalt hexacyanoferrate (CoHCF) on graphene oxide (GO) and its application for the electrocatalytic hydrazine determination in real samples are described in this research study. Co2+ is immobilized on GO and the resulting material, GO-Co2+ is coated on the surface of glassy carbon (GC) electrode. The fabricated electrode (GC/GO-Co2+) is subjected to a continuous potential cycling in the range of 0.0–1.0 V which results in the formation of a thin CoHCF film on the surface of GO coated on the GC electrode (abbreviated as GC/GO-CoHCF). The synthesized GO-CoHCF composite material is characterized by Fourier transform infrared and scanning electron microscopy. GC/GO-CoHCF electrode electrocatalytically oxidizes hydrazine at low overpotential (0.63 V) and this phenomenon is subsequently utilized for the sensitive determination of hydrazine in aqueous solutions. It exhibits a wide linear calibration range (0.1–400 µM), high sensitivity (0.93 µA µM−1 cm−2) and low limit of detection (17.5 nM) for the determination of hydrazine. Further, this electrode is employed for hydrazine determination in real samples.

Two-step separation and determination of inorganic As species in water, soil and sediment samples by implementing two ionic liquids in dispersive liquid–liquid microextraction with electrothermal atomic absorption spectrometry detection

A highly efficient liquid–liquid microextraction method based on two magnetic ionic liquids (MILs) as extraction solvents for the determination of inorganic As species in water, soil and sediment samples, with electrothermal atomic absorption spectrometry detection, was developed. First, As(III) species was separated by chelation with ammonium pyrrolidine dithiocarbamate and then extracted by the MIL trihexyl(tetradecyl)phosphonium hexachlorodisprosiate ([P6,6,6,14]3DyCl6). The As(V) species remaining in the aqueous phase was preconcentrated by extraction in the MIL trihexyl(tetradecyl)phosphonium tetrachloroferrate ([P6,6,6,14]FeCl4) at 2 mol L-1 HCl. The MIL phase containing As(V) was separated by a magnetic rod and diluted in chloroform. Then, an aliquot was injected into the graphite furnace for As determination. Total inorganic As was determined using the MIL [P6,6,6,14]FeCl4 as the extraction solvent at 0.5 mol L-1 HCl to achieve the same extraction efficiency for both species. The concentration of As(III) was calculated by the difference between total inorganic As and As(V) concentration. An extraction efficiency of 99% for As(V) and an enhancement factor of 35 were obtained with 5 mL of sample. The method detection limits were 17 ng L-1, 0.11 ng g−1 and 0.13 ng g−1 for As(V) and 20 ng L-1, 0.13 ng g−1 and 0.14 ng g−1 for As(III) in water, soil and sediment samples, respectively. The relative standard deviations for six replicate measurements of 3 µg L-1 for As(V) and As(III) were 3.1% and 3.9% respectively. The calibration linear range was 0.05–13 µg L-1. The method was successfully applied for inorganic As species determination in water, soil and sediment samples.

Determination of sulfamethoxazole adulterated in traditional Chinese medicine

In this study, three kinds of traditional Chinese medicine obtained from a traditional Chinese physician's clinic for curing herpes were analyzed. Each kind of medicine was dispensed for use after breakfast, lunch and dinner. For each meal, 11, 11 and 12 doses were collected, respectively. The weight distribution ranges and their coefficient of variation among doses of each kind of medicine were 2.822-4.420 g, 13.2%, 2.808-3.782 g, 9.2% and 2.654-3.723 g, 9.2%, respectively. Sulfamethoxazole was detected in the doses dispensed for breakfast and lunch but not found in the dose for dinner. Sulfamethoxazole in the samples were assayed by high performance liquid chromatography on C 18 column. The linear calibration range was 0.1-0.8 mg/ml (r = 0.9999) and recovery was 93.9-97.0%. The relative standard deviations for intraday and interday analysis were 1.2% and 0.2% (n = 5), respectively. The average content of sulfamethoxazole in the dose for breakfast and lunch were 395 mg and 345 mg, respectively.

Determination of phenylpropanolamine in pharmaceutical preparations by second derivative spectrophotometry

Phenylpropanolamine (PPA) hydrochloride used as nasal decongestant agent was determined by second derivative spectrophotometry after derivatization with 2-hydroxynaphthaldehyde. The absorbance was measured between minimum-maximum of 386 nm-392 nm. The linear calibration range was obtained within 0.5∼2.0 μg/mL. The method was applied for the determination of phenylpropanolamine from pharmaceutical preparations Tavegyl-D and Sinutab with coefficient of variation of 0.8∼1.6%. Paracetamol present together with phenylpropanolamine could also be determined by spectrophotometry in aqueous phase after extraction of PPA in chloroform.