Selective determination of amino acids using flow injection analysis coupled with chemiluminescence detection

The determination of the amino acids proline, histidine, tyrosine, arginine, phenylalanine and tryptophan using flow injection analysis (FIA) with chemiluminescence detection is described. Proline was the only amino acid to exhibit chemiluminescence with the tris(2,2-bipyridyl)ruthenium(III) reaction at pH 10. While, histidine was found to selectively enhance the reaction of luminol with Mn(II) salts in a basic medium. Acidic potassium permanganate chemiluminescence was able to selectively determine tyrosine at pH 6.75. Low pressure separations using a C18 guard column allowed the simultaneous determination of tyrosine and tryptophan or phenylalanine and tryptophan with acidic potassium permanganate and copper(II)-amino acid-hydrogen peroxide chemiluminescence, respectively. Precision for each method was less than 3.9% (R.S.D.) for five replicates of a standard (1×10⁻⁵ M) and the detection limits ranged between 4×10⁻⁹ and 7×10⁻⁶ M. Preliminary investigations revealed that the methodology developed was able to selectively determine the individual amino acids in an equimolar mixture of the 20 naturally occurring amino acids.     

Determination of trivalent europium using flow injection chemiluminescence method

A simple flow injection chemiluminescence (CL) analysis method for the determination of europium in mineral samples is reported. It is based on luminescence produced by NaIO₄-H₂O₂ CL system sensitized by [Eu(EDTA)]⁻. The relative chemiluminescence intensity of the Eu³⁺-EDTA-NaIO₄-H₂O₂ system is proportional to the amount of Eu³⁺. The optimized experimental conditions were investigated. The linear range and detection limit for Eu³⁺ are 2.0×10⁻⁷ to 1.0×10⁻⁵ and 6.2×10⁻⁸ M, respectively. The sample throughput of the method is 80 samples/h. This method was successfully applied to the determination of europium in rare earth oxides. And the mechanism of chemiluminescence is proposed.     

鲁米诺-铁氰化钾化学发光体系测定双嘧达莫

在碱性条件下,铁氰化钾氧化鲁米诺产生化学发光,双嘧达莫对该体系的化学发光有显著的增强作用。基于此并结合流动注射技术建立了测定双嘧达莫的新方法。该方法检出限为5.7×10-11g mL(IUPAC),线性范围为1.0×10-10～5.0×10-8g mL,对5.0×10-9g mL双嘧达莫平行测定11次,其相对标准偏差为1.9%。     

Determination of nanomolar concentrations of phosphate in freshwaters using flow injection with luminol chemiluminescence detection

A simple and rapid flow injection (FI) method is reported for the determination of phosphate (as molybdate reactive P) in freshwaters based on luminol chemiluminescence (CL) detection. The molybdophosphoric heteropoly acid formed by phosphate and ammonium molybdate in acidic conditions generated chemiluminescence emission via the oxidation of luminol. The detection limit (3× standard deviation of blank) was 0.03 μg P l⁻¹ (1.0 nM), with a sample throughput of 180 h⁻¹. The calibration graph was linear over the range 0.032–3.26 μg P l⁻¹ (r²=0.9880) with relative standard deviations (n=4) in the range 1.2–4.7%. Interfering cations (Ca(II), Mg(II), Ni(II), Zn(II), Cu(II), Co(II), Fe(II) and Fe(III)) were removed by passing the sample through an in-line iminodiacetate chelating column. Silicate interference (at 5 mg Si l⁻¹) was effectively masked by the addition of tartaric acid and other common anions (Cl⁻, SO₄²⁻, HCO₃⁻, NO₃⁻ and NO₂⁻) did not interfere at their maximum admissible concentrations in freshwaters. The method was applied to freshwater samples and the results (26.1±1.1–62.0±0.4 μg P l⁻¹) were not significantly different (P=0.05) from results obtained using a segmented flow analyser method with spectrophotometric detection (24.4±4.45–84.0±16.0 μg P l⁻¹).     

New method for simultaneous determination of Fe(II) and Fe(III) in water using flow injection technique

The method exploits the possibilities of flow injection gradient titration in a system of reversed flow with spectrophotometric detection. In the developed approach a small amount of titrant (EDTA) is injected into a stream of sample containing a mixture of indicators (sulfosalicylic acid and 1,10-phenanthroline). In acid environment sulfosalicylic acid forms a complex with Fe(III), whereas 1,10-phenanthroline forms a complex with Fe(II). Measurements are performed at wavelength λ = 530 nm when radiation is absorbed by both complexes. After injection EDTA replaces sulfosalicylic acid and forms with Fe(III) more stable colourless complex. As a result, a characteristic “cut off” peak is registered with a width corresponding to the Fe(III) concentration and with a height corresponding to the Fe(II) concentration. Calibration was performed by titration of four two-component standard solutions of the Fe(II)/Fe(III) concentrations established in accordance with 2² factorial plan. The method was tested with the use of synthetic samples and then it was applied to the analysis of water samples taken from artesian wells. Under optimized experimental conditions Fe(II) and Fe(III) were determined with precision less than 0.8 and 2.5% (RSD) and accuracy less than 3.2 and 5.1% (relative error) within the concentration ranges of 0.1-3.0 and 0.9-3.5 mg L⁻¹ of both analytes, respectively.     

Ultratraces analysis of organochlorine pesticides in drinking water by solid phase extraction coupled with large volume injection/gas chromatography/mass spectrometry

This study describes an SPE coupled with large volume injection (LVI) analytical method for the analysis of organochlorine pesticides, BHC (alpha, beta, delta), aldrin, endosulfan (alpha, beta), endrin, dieldrin, and DDT, from aqueous samples. Determination was carried out by GC with MS. The LODs of organochlorine pesticides were determined at 10 ng/L concentration levels, and the results show that SPE-LVI-GC/MS has the potential to accurately determine organochlorine pesticides in water, as it avoids analyte classes in the various steps of a typical extraction procedure.     

Sensitive determination of captopril by flow injection analysis with chemiluminescence detection based on the enhancement of the luminol reaction

This work reports a novel flow injection (FI) method for the determination of captopril, 1-[(2S)-3-mercapto-2-methylpropionyl]-l-proline (CPL), based on the enhancement CPL affords on the chemiluminescence (CL) reaction between luminol and hydrogen peroxide. For this purpose alkaline luminol and hydrogen peroxide solutions were mixed online, the sample containing CPL was injected into an aqueous carrier stream, mixed with the luminol-hydrogen peroxide stream and pumped into a glass flow cell positioned in front of a photomultiplier tube (PMT). The increase in the CL intensity was recorded in the form of FI peaks, the height of which was related to the CPL mass concentration in the sample. Different chemical and instrumental parameters affecting the CL response were investigated. Under the selected conditions, the log-log calibration curve was linear in the range 5-5000 μg l⁻¹ of CPL, the limit of detection was 2 μg l⁻¹ (at the 3σ level), the R.S.D., s_r was 3.1% at the 100 μg l⁻¹ level (n=8) and the sampling rate was 180 injections h⁻¹. The method was applied to the determination of CPL in pharmaceutical formulations with recoveries in the range 100±3%.     

Determination of iodide by detection of iodine using gas-diffusion flow injection and chemiluminescence

This work describes development of a flow injection (FI) system for determination of iodide, based on the chemiluminescence (CL) reaction between iodine and luminol. Iodide in the sample zone is oxidized to iodine. Employment of a gas-diffusion (GD) unit allows for selective detection of the generated CL (425 nm). Preliminary results showed for concentrations of less than 2 mg L⁻¹, that signals were irreproducible and that the calibration was not linear.In order to solve these problems, a method of ‘membrane conditioning’ was investigated, in which iodide stream was continuously merged with oxidant to generate I₂ that conditioned the GD membrane and tubing. This minimized surface interaction between the active surface and the I₂ generated from the samples, thus improving both precision and sensitivity. By employing membrane conditioning, it has been possible to reliably detect concentrations down to 0.1 mg L⁻¹.At the optimized condition, an excellent linear calibration (r² = 0.999) was obtained from 0.1 to 1.0 mg L⁻¹. The method was successfully applied to determine iodide in some pharmaceutical products such as potassium iodide tablets and a liquid patent medicine. However, for vitamin tablets, ascorbic acid was found to interfere seriously by causing a negative signal.     

Sensitive and selective determination of molybdenum by flow injection chemiluminescence method combined with controlled potential electrolysis technique

A sensitive and selective flow injection chemiluminescence (CL) method combined with controlled potential electrolysis technique was described for the determination of molybdenum. The method is based on the chemiluminescence reaction of luminol with unstable molybdenum(III) in alkaline solution. The molybdenum(III) was on-line reduced from molybdenum(VI) via controlled potential electrolysis technique using a homemade flow-through carbon electrolytic cell at the potential of −0.6 V (versus Ag/AgCl). The method allows the determination of molybdenum in the 5.0×10⁻¹⁰ to 5.0×10⁻⁷ g ml⁻¹ range with a limit of detection (3σ) of 5×10⁻¹¹ g ml⁻¹ molybdenum. The relative standard deviation is 2.6% for the 1.0×10⁻⁹ g ml⁻¹ molybdenum solution in 11 repeated measurements. This method was successfully applied to the determination of molybdenum in water samples.     

Sensitive determination of phenothiazines in pharmaceutical preparation and biological fluid by flow injection chemiluminescence method using luminol-KMnO4 system

A flow injection chemiluminescence method was described for the determination of four phenothiazine drugs, namely, chlorpromazine hydrochloride, perphenazine hydrochloride, fluphenazine hydrochloride and thioridazine hydrochloride. Strong Chemiluminescence (CL) signal was produced when above-mentioned drug was injected into the mixed stream of luminol with KMnO₄. The linear ranges of the method were 0.0020-1.0 μg/mL chlorpromazine hydrochloride, 0.0040-3.0 μg/mL perphenazine hydrochloride, 0.0020-5.0 μg/mL fluphenazine hydrochloride and 0.0050-1.0 μg/mL thioridazine hydrochloride. The detection limits were 0.4 ng/mL chlorpromazine hydrochloride, 0.7 ng/mL perphenazine hydrochloride, 2 ng/mL fluphenazine hydrochloride and 0.7 ng/mL thioridazine hydrochloride. The proposed method was applied to the determination of chlorpromazine hydrochloride in injections and in mental patient's urine samples and the satisfactory results were achieved. The possible CL reaction mechanism was also discussed briefly.     

A multi-pumping flow system for chemiluminescent determination of ammonium in natural waters

Abstract

This paper presents a novel technique for measuring soluble inorganic monophosphate in water based on high performance liquid chromatography and flow injection detection (IC-FI). The IC-FI technology was applied to irrigation water from the Macalister Research Farm in South Eastern Australia. Overland flow was measured exiting two irrigation bays. Inorganic monophosphate constituted over 97% of the DRP component and between 86–93% of the total phosphorus. Similar results were obtained from a channel that drained the excess irrigation water from the farm. This work supports the findings of others that show DRP contributes a large portion of the P in runoff from grazing systems. Additionally, it confirms this fraction is dominated by immediately bioavailable inorganic monophosphate, something that previously could only be inferred due to the limitations of the chemistry applied.     

New strategy for the biosorption of atrazine after magnetic solid‐phase extraction from water followed by high‐performance liquid chromatography analysis

We describe a rapid and simple microextraction of atrazine from water samples. This method is based on the use of magnetic nanoparticles as sorbents and bioaggregates that are applied to the extraction and preconcentration of atrazine. The resulting magnetic nanoparticles possess a fast adsorption kinetics and high adsorption capacity. Bioaggregates made up of rhaminolipid biosurfactant were assessed as a new strategy for the sample treatment. The extractant was obtained from magnetic nanoparticles using the magnetic solid‐phase extraction method. Then the target analyte was rapidly transferred from the sorbent surface to bioaggregates, which have a low toxicity and are green and ecofriendly. Finally, the extract is centrifuged and transferred to micro‐syringe for analysis by high‐performance liquid chromatography. Experimental parameters affecting the extraction efficiency were studied and optimized. Under optimum conditions the enrichment factor was 268. The linear dynamic range and limit of detection were 0.1–50 and 0.033 μg/L, respectively. The relative standard deviation for six replicate measurements was 5.3%. The results demonstrate good applicability of biosorption‐assisted magnetic solid‐phase extraction method for the determination of atrazine from water samples.     

Improved methods for urinary atrazine mercapturate analysis--assessment of an enzyme-linked immunosorbent assay (ELISA) and a novel liquid chromatography-mass spectrometry (LC-MS) method utilizing online solid phase extraction (SPE)

Elimination of interfering substances in urine by solid phase extraction (SPE) prior to analysis resulted in 10-fold improvement in the sensitivity of atrazine mercapturate (AM) enzyme-linked immunosorbent assay (ELISA) compared to previous reports. Of the two tested SPE systems, Oasis^® HLB and MCX, the mixed-mode MCX gave good recoveries (82%) of AM in spiked samples measured by ELISA, whereas the reverse-phase HLB phase was not compatible with the immunochemical method. At relatively high concentrations of urinary AM (>20 ng mL⁻¹), sample dilution was effective enough for the elimination of interfering substances. The new liquid chromatography-mass spectrometry (LC-MS) method developed for AM utilizes online-SPE with Oasis^® HLB, column switching and a stable-isotope internal standard. The limit of quantification (0.05 ng mL⁻¹) indicates improved sensitivity compared with most previously published LC-MS methods for AM. Validation of all three methods, LC-MS, ELISA + SPE and ELISA + dilution with spiked urine samples showed good correlation between the known and measured concentrations with R² values of 0.996, 0.957 and 0.961, respectively. When a set (n = 70 plus 12 blind duplicates) of urine samples from farmers exposed to atrazine was analyzed, there was a good agreement (R² = 0.917) between the log normalized data obtained by ELISA + SPE and LC-MS. High correlation among the data obtained by the two tested methods and the LC-MS method by the Center of Disease Control and Prevention (CDC), together with low variability among the blind duplicates, suggests that both methods reported here would be suitable for the analysis of urinary AM as a biomarker for human exposure of atrazine.     

流动注射阻抑化学发光法测定己烯雌酚

基于在碱性介质中,己烯雌酚对N-溴代丁二酰亚胺-鲁米诺化学发光体系的阻抑作用,建立了测定己烯雌酚的流动注射化学发光分析新方法,探讨并优化了流动注射化学发光的分析条件。该方法测定己烯雌酚的线性范围为1.5×10-8~2.6×10-7g/mL,检出限为5.0×10-9g/mL,对1.0×10-7g/mL的己烯雌酚标准溶液进行11次测定,相对标准偏差为2.6%。并应用于饲料、己烯雌酚片剂中的己烯雌酚的测定。     

Determination of psilocin and psilocybin using flow injection analysis with acidic potassium permanganate and tris(2,2'-bipyridyl)ruthenium(II) chemiluminescence detection respectively

A simple, rapid and sensitive method for the determination of psilocin and psilocybin is described. This is the first report on the determination of psilocin and psilocybin using flow injection analysis with acidic potassium permanganate and tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence. The limits of detection (signal-to-noise ratio = 3) are 9 × 10⁻¹⁰ M and 3 × 10⁻¹⁰ M for psilocin and psilocybin, respectively.A concise synthetic route for psilocin in three steps from readily available starting materials is also described. The structures were elucidated on the basis of spectroscopic data.     

Highly sensitive flow analysis determination of orthophosphate using solid phase enrichment of phosphomolybdenum blue without need for organic solvents in elution

In a flow analysis configuration, orthophosphate has been enriched as phosphomolybdenum blue on reversed phase polymers (styrene-divinylbenzene (DVB), methacrylate, dextran), recovered by an alkaline solution without added organic solvent, and measured photometrically at 700 nm. It was found that phosphomolybdenum blue is bound to those polymers mainly by fast adsorption but also partly by slow diffusion (which causes some carryover); the relative extent of both processes depends on the chemical nature of the polymer. With the enrichment column placed near the detector to minimize transport dispersion and an enrichment time of 120 s; a signal improvement factor of 30–50 was obtained using styrene-DVB.     

Post-column detection of benzenediols and 1,2,4-benzenetriol based on acidic potassium permanganate chemiluminescence

Based on the sensitizing effect of formic acid on the chemiluminescence (CL) reaction of polyhydroxylbenzenes with acidified potassium permanganate and the combination technique of high-performance liquid chromatography (HPLC), a sensitive, selective and simple post-column CL detection method for simultaneously determining catechol, resorcinol, hydroquinone and 1,2,4-benzenetriol is described. The optimal conditions for the CL detection and HPLC separation were carried out. The linear ranges were: 6.0 × 10⁻³-1.5 mg/L for hydroquinone, 8.0 × 10⁻³-1.5 mg/L for 1,2,4-benzenetriol, 1.0 × 10⁻²-2.0 mg/L for resorcinol and 1.0 × 10⁻²-2.5 mg/L for catechol, respectively. The detection limits are: 3.2 × 10⁻³ mg/L for hydroquinone, 3.9 × 10⁻³ mg/L for 1,2,4-benzenetriol, 4.7 × 10⁻³ mg/L for resorcinol and 5.2 × 10⁻³ mg/L for catechol, respectively. Combining with solid phase extraction, the proposed method has been successfully applied to the determination of the polyhydroxylbenzenes in river water. The recoveries for three benzentriols were 92.1-95.4% and 82.0% for 1,2,4-benzenetriol, respectively.     

Flow injection on-line displacement/solid phase extraction system coupled with flame atomic absorption spectrometry for selective trace silver determination in water samples

A novel flow injection (FI) on-line displacement solid phase extraction preconcentration and/or separation method coupled with FAAS in order to minimize interference from other metals was developed for trace silver determination. The proposed method involved the on-line formation and subsequently pre-sorption of lead diethyldithiocarbamate (Pb-DDTC) into a column packed with PTFE-turnings. The preconcentration and/or separation of the Ag(I) took place through a displacement reaction between Ag(I) and Pb(II) of the pre-sorbed Pb-DDTC. Finally, the retained analyte was eluted with isobutyl methyl ketone (IBMK) and delivered directly to nebulizer for measuring. Interference from co-existing ions with lower DDTC complex stability in comparison with Pb-DDTC, was eliminated without need for any masking reagent. With 120 s of preconcentration time at a sample flow rate of 7.6 mL min−1, an enhancement factor of 110 and a detection limit (3 s) of 0.2 μg L−1 were obtained. The precision (RSD, n = 10) was 3.1% at the 10 μg L−1 level. The developed method was successfully applied to trace silver determination in a variety of environmental water samples and certified reference material.     

流动注射分光光度法快速测定水样中的铬

建立了用流动注射分光光度法快速检测水样中铬含量的方法.测定耗时140 s,测定频率25样/h.本法利用Cr(Ⅵ)和二苯碳酰二肼显色反应,Cr(Ⅵ)标准溶液的质量浓度在0.05～0.8 mm/L之间与吸光度呈线性.该法的检出限是4.0 μg/L,低于国家对Ⅰ类水的相关标准.应用此法分别测定了北京城区一些地表水中铬的含量,加标回收率在90.1%～113%之间.     

Detection of L‐phenylalanine using molecularly imprinted solid‐phase extraction and flow injection electrochemiluminescence

A novel flow injection electrochemiluminescence method combined with molecularly imprinted solid‐phase extraction was developed for the determination of L ‐phenylalanine, in which was used as the luminophor and indium tin oxide glass was modified as the working electrode. Molecularly imprinted polymers, synthesized by self‐assembly with functional monomer and crossing linker, were used for the selective extraction of L ‐phenylalanine. In order to overcome the drawbacks of traditional electrochemiluminescence cells such as high IR drop, high over‐potential and so on, a novel electrochemiluminescence cell was developed. The enhanced electrochemiluminescence intensity was linearly related with the concentration of L ‐phenylalanine in the range from 1.0×10^?7 to 5.0×10^?5 g/mL with a detection limit of 2.59×10^?8 g/mL. The relative standard deviation for the determination of 1.0×10^?6 g/mL L ‐phenylalanine was 1.2% (n=11). The method showed higher sensitivity and good repeatability, and was successfully applied for the determination of L ‐phenylalanine in egg white, chicken and serum samples. A possible mechanism for the enhanced electrochemiluminescence response on indium tin oxide glass is proposed.