LC Determination of Chloramphenicol in Honey Using Dispersive Liquid–Liquid Microextraction

A novel method, dispersive liquid–liquid microextraction coupled with liquid chromatography-variable wavelength detector (LC-VWD), has been developed for the determination of chloramphenicol (CAP) in honey. A mixture of extraction solvent (30 μL 1,1,2,2-tetrachloroethane) and dispersive solvent (1.00 mL acetonitrile) were rapidly injected by syringe into a 5.0 mL real sample for the formation of cloudy solution, the analyte in the sample was extracted into the fine droplets of C₂H₂Cl₄. After extraction, phase separation was performed by centrifugation and the enriched analyte in the sedimented phase was determined by LC-VWD. Some important parameters, such as the kind and volume of extraction solvent and dispersive solvent, extraction time, sample solution pH, sample volume and salt effect were investigated and optimized. Under the optimum extraction condition, the method yields a linear calibration curve in the concentration range from 3 to 2,000 μg kg^?1 for target analyte. The enrichment factor for CAP was 68.2, and the limit of detection (S/N = 3) were 0.6 μg kg^?1. The relative standard deviation (RSD) for the extraction of 10 μg kg^?1 of CAP was 4.3% (n = 6). The main advantages of method are high speed, high enrichment factor, high recovery, good repeatability and extraction solvent volume at μL level. Honey samples were successfully analyzed using the proposed method.     

A gravity driven micro flow injection wetting film extraction system on a polycarbonate chip

A micro flow injection wetting film liquid-liquid extraction system has been developed for trace analyte concentration and on-chip detection. A hydrophobic channel fabricated on a polycarbonate chip was used to support the wetting film, and hydrostatic pressure generated by the difference in liquid levels was employed to drive the fluids. Sequential injection of segments of aqueous sample solution and organic solvent was conducted by switching the sample- or solvent-containing vials to an on-chip sampling probe, and detection was performed by a co-focused, laser induced fluorescence detector. Using butyl rhodamine B as a model analyte and butanol as the solvent for both film-coating and elution, various experimental conditions such as hydrostatic pressure, coating time, channel length, sampling volume, and sample acidity were investigated. Under optimized conditions, a 24-fold enrichment factor was obtained with the consumption of about 3 μL sample solution, and a detection limit (3σ) of 6.0 × 10⁻⁹ M butyl rhodamine B was achieved at the sampling rate of 19 h⁻¹. Eleven consecutive runs of a 1.0 × 10⁻⁵ M butyl rhodamine B solution produced a relative standard deviation of 1.5% for the detected fluorescence signals.     

Rapid flow-injection sandwich-type immunoassays of proteins using an immobilized antibody reactor and adenosine deaminase-antibody conjugates

A rapid flow-injection sandwich enzyme immunoassay suitable for the direct determination of proteins in biological samples is described. The proposed system utilizes highly active adenosine deaminase—antibody conjugates in conjunction with a flow-through immunoreactor and an ammonium ion-selective potentiometric detector. After appropriate sample/reagent injection steps, the enzyme activity bound to the reactor is measured by diverting a coninuously flowing stream of substrate (adenosine) through the packed immunocolumn and detecting liberated ammonium ions downstream with a tubular ammonium ion-selective electrode. The bound enzyme activity is directly proportional to the concentration of analyte in the original sample. By using non-equilibrium flow-rates of sample and reagent slugs, a single protein assay takes less than 12 min, including regeneration of the reactor. The proposed method is shown to be selective, reproducible and capable of determining accurately the model protein (human IgC) at sub-μg ml^?1 concentrations.     

Detector Systems in Capillary Gas Chromatography

Expressions for the minimum detectable amount Q_o and the minimum analyte concentration C_o as functions of the chromatographic parameters are derived for both mass and concentration sensitive detectors. The effects of pressure drop, column inner diameter, and film thickness are given. The minimum analyte concentration for mass flow sensitive detectors, C_o^m, can be reduced considerably by selecting the carrier gas velocity well above its optimum value (related to H_min), however, at the cost of long columns and long analysis times. For Q_o the improvements can be neglected, and so the analysis can best be performed at u_opt. When the flow rate in the detector, F_d, is equal to the column flow rate F_c, the maximum permissible detector volume of concentration sensitive detectors is proportional to d_c² up to d_c³, and so narrow bore columns require detectors of extremely small volume. Make-up gas has to be added when the actual volume is too large, thus worsening the detectability. Another approach, vacuum operation of the detector cell, appears to be very attractive. On the other hand, when wide bore columns are used in combination with small volume concentration sensitive detectors, very small values of Q_o^c and C_o^c are obtainable when the abundant carrier gas can be removed before entering the detector cell. Digital noise filtering can further reduce the obtainable Q_o and C_o values, especially for broad peaks and thus for wide bore columns.     

Quantitative ion mobility spectroscopy based on molecular collision rate theory

Atmospheric pressure chemical ionization and ion mobility spectrometry (IMS) have traditionally been viewed as a qualitative analytical technique for identifying specific chemicals in the atmosphere. This work employs a nonlinear model based on molecular collision rate theory for quantitative modeling of chemical analyte concentrations. The collision rate between any two molecules depends on the relative populations of each chemical species in the volume of air analyzed where most collisions between ions, or neutral molecules and ions, result in no charge transfer. The rate constants for formation of product ions and consumption of source ions are estimated using empirical data over a wide concentration range for several analytes and reagent gases. The rate constants are unique to the analyte and the reagent gas as well as the sensitivity of the particular IMS instrument and provide a quantitative model to relate the mobility peak amplitudes to the analyte concentration. The rate constants can also be normalized by the reaction ion consumption rate constant to remove the IMS instrument sensitivity and provide a qualitative metric for analyte identification independent of a particular IMS instrument. A quantitative example is given for an acetic acid plume measured by a hand-held IMS detector outdoors has the plume passes. The quantitative rate constants provide a reasonable basis for estimating analyte concentration from the ion mobility spectra over a wide range of analyte concentrations.     

Simultaneous determination of silicate and phosphate in boiler water at power plants based on series flow cells by using flow injection spectrophotometry

A new flow injection spectrophotometric method is described for the simultaneous determination of silicate and phosphate. Effects on the sensitivity of the method of the wavelength, temperature, length of reaction coils, pump rates, acidity, sampling volume, concentration of the chromogenic reagent, etc. were also investigated. The optimum conditions were ascertained.The principle of the method is that total concentration of silicate plus phosphate is determined when a injected sample plug is passing through the first flow cell and then the concentration of silicate is serially) determined at a second flow cell of the same detector after continuously masking the yellow molybdophosphate in the sample zone. Finally, the concentration of phosphate is obtained by difference.Silicate and phosphate are determined in boiler water at power plants; 60-120 samples h⁻¹ be analyzed. Determination ranges are 0.05-22 mg l⁻¹ for silicate and 0.1-24 mg l⁻¹ for phosphate. Relative standard deviations for metasilicate and orthophosphate were ≤1.2 and 1.3%, respectively. Recovery ranges of silicate and phosphate in the samples are 98-103%.     

FLOW - Injection Determination of Traces of Sulfide by the Brilliant Green - Sulfide Reaction with Spectrophotometry Detection

Abstract

A flow injection system is proposed for the rapid and sensitive determination of trace amounts of sulfide based on the addition reaction of sulfide with Brilliant Green at pH 7 and 25 C°. The effect of important parameters, such as reagent concentration, pH, reagent flow rate, sample volume, temperature and length of the reaction coil are reported. Sulfide in the range of 40 - 2000 ng·ml^?1 can be determined at a rate of 40 ± 5 samples per hour. The limit of detection was obtained as 2.0 ng of sulfide. The relative standard deviation for the determination of 100 ng·ml^?1 of sulfide is 0.8%. A system is proposed for elimination of potential interferences. The method was applied to the determination of sulfide in synthetic samples and in spring water.     

ByT-FAS (Bypass trapped-flow analysis system)

A new semi-automated flow analysis system called bypass trapped flow analysis system (ByT-FAS), is described. ByT-FAS gives an analyst the ability to inject sample and reagent volumes of 50-100 mul or more, into flowing streams and attain physical steady state concentrations in the detection cell within a few seconds (<1 min) after the insertion of the sample and/or reagent. After physical steady state is attained, the system flow is diverted around the detection cell and the reaction mixture is trapped in the detector. The concentration of the analyte and the reagent in the detection cell can be readily computed from knowledge of the original concentrations of the analyte sample and reagents and knowledge of the flow rates of the streams propelling the analyte and the reagents. ByT-FAS was demonstrated to be useful for direct measurements of analytes in liquid solutions and for assays which utilize equilibrium and/or kinetic chemistries to create measurable product(s) using ultraviolet/visible spectrophotometry. Enzyme activities and fundamental enzyme kinetic parameters (K(M)s, K(I)s, k(cat)s, etc.) were determined directly. The ByT-FAS instrumentation, as described, can be used interchangeably for either equilibrium or kinetic assays. It is believed that this new type of instrumentation will be of significant use for the analytical chemical, biochemical, molecular biology, biotechnology, environmental, pharmaceutical and medical communities.     

Investigation and quantification of spectroscopic interferences from polyatomic species in inductively coupled plasma mass spectrometry using electrothermal vaporization or pneumatic nebulization for sample introduction

A new method for quantification of spectral interferences based on analyte isotope ratio measurements in the presence of various concentrations of a specific matrix is presented. Within the method, a tolerance level is used, defined as the matrix concentration at which the ratio between analyte isotopes with and without interferences is altered by 10% compared to a pure water reference standard, normalized with respect to the analyte concentration in the solutions. This can be used to estimate the lowest analyte concentration which can be determined with a defined accuracy in the presence of a known concentration of a specific matrix. Regarding spectroscopic interference effects, comparative results for sample introduction into the ICP–MS by electrothermal vaporization, ETV, and nebulization are presented for common matrix — (Ca, Na, K, Cl, P, O) and analyte (Cr, Ni, Cu, As, Se) elements. With the exception of the spectral overlap of ³¹P₂⁺ on ⁶²Ni⁺, spectroscopic interferences were reduced by 1–2.5 orders of magnitude when using ETV for sample introduction. Reasons for the increase in the spectral interference of ³¹P₂⁺ on ⁶²Ni⁺ are discussed. For sample introduction by nebulization, it was found that spectral interferences from CaO⁺ on ⁵⁸Ni⁺ and ⁶⁰Ni⁺ were reduced in the presence of phosphate.     

Multipumping flow system for improving hydride generation atomic fluorescence spectrometric determinations

The advantages of using membrane micropumps rather than peristaltic pumps to introduce both sample and reagent solutions for hydride generation atomic fluorescence spectrometry are discussed. Arsenic was used as a test analyte to check the performance of the proposed manifold. Sample and reagent consumption was reduced 8–9 fold compared with continuous mode measurements made with peristaltic pumps, with no deterioration in sensitivity. The calibration graph was linear in the 0.05 to 2.5 μg l^− 1 As range using peak area as the analytical signal and maximum gain in the detector setting. A limit of detection (3σ) of 0.02 μg l^− 1 and relative standard deviation values close to 2% for 10 independent measurements of a 1 μg l^− 1 As solution were obtained. The sampling frequency increased from 45 to 102 h^− 1 with the subsequent saving in carrier gas used and reduction in wastes generated. The instrumental modification, which could be used for other elements currently determined by atomic fluorescence spectrometry, will permit hydride generators of more reduced dimensions to be constructed.     

Flow-injection extraction with a microvolume module based on integrated conduits

A self-contained module for liquid—liquid extractions is described. The module contains engraved conduits for mixing of sample and ragent, an engraved segmentor, a detachable extraction coil, a membrane separator, and a rinsing system for the flow cell. The membrane in the separator is supported by a teflon-coated steel grid and can be replaced rapidly. The segmented stream enters at the centre of the circular membrane and travels through an engraved, coiled channel in contact with the membrane before leaving the membrane area at the periphery. The volume of the receptor chamber for the organic phase is 10 μl. For a detector flow-cell volume of 8 μl, an aqueous flow rate of 2.0 ml min^?1 and an organic flow rate of 1.2 ml min^?1, the “loss factors” caused by analyte dispersion are 3.2 and 1.5 for caffeine sample volumes of 40 μl and 100 μl, respectively, compared with batch extraction. The system is also tested for extraction of anionic surfactants as their ion-pairs with methylene blue.     

Gas-chromatographic determination of airborne monoethanolamine using reagent-coated adsorbent tubes

A sampling and analytical procedure was developed for the monitoring of airborne monoethanolamine (MEA). The analyte is collected by drawing air through the adsorbent tubes containing XAD-4 resin coated with cyclohexanone as a derivatising reagent. Derivatisation takes place during sampling. After desorption with methanol, the MEA derivative was quantified by gas chromatography using a thermionic specific detector (TSD) in the nitrogen mode. Application of cyclohexanone as a derivatising reagent gives a more stable product and TSD allows subsequent GC analysis in the presence of excess reagent. The structure of the MEA derivative was confirmed by mass spectrometry. The lower limit of detection for MEA was 1 g and the detector response was linear between 5 and 200 g. The working range of the method is 0.5 to 20 mg/m³ in a 10 l air sample. Collected samples were stable for at least 2 weeks at 4°C and room temperature. The efficiency of sampling was evaluated using a Test Atmosphere Generation System.Presented at the Lab-Ex 1990 Conference in Palais de Congres, Montreal, during October 23–24, 1990     

An enzymatic-fluorimetric method for monitoring of ethanol in ambient air

A method is described for the continuous monitoring of ethanol in ambient air. The system consists of a scrubber coil for enrichment of the analyte from air in an aqueous solution and a directly connected fluorescence detector. Because of using a reagent solution containing alcohol dehydrogenase (ADH) and nicotinamide adenine dinucleotide (NAD⁺) for absorption, ethanol can react directly with ADH and NAD⁺ during air sampling, producing NADH, which can be measured by fluorescence detection. The influence of reagent concentrations, gas flow rate and scrubber solution flow rate on the performance of the instrument was tested. Possible ozone interferences can be avoided by placing a KI coated filter in front of the scrubber inlet. The response time of the system was found to be 2.3 min and the detection limit about 1 ppb_V. The applicability of the developed method was demonstrated during a field campaign in Brazil.     

Simple, stable and sensitive electrogenerated chemiluminescence detector for high-performance liquid chromatography and its application in direct determination of multiple fluoroquinolone residues in milk

A simple, stable and sensitive electrogenerated chemiluminescence (ECL) detector was developed. It was based on tris(2,2-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) immobilized on the surface of a Pt wire with Nepem-105D ion exchange solution. The detector was prepared by inserting a Pt wire with immobilized Ru(bpy)₃²⁺ (working electrode) into a capillary tube, followed by inserting another Pt wire (counter electrode) in this tube and sealing. ECL behavior was investigated using ofloxacin as an analyte. Under optimal conditions, stable ECL intensity was obtained. This detector has been used in HPLC-ECL for the determination of multiple target fluoroquinolone residues in milk. There is no post column reagent addition, which would dilute the analytes, potentially leading to chromatographic band-broadening. The system is very simple with low dead volume, low baseline and background noise, together with high sensitivity and stability. The as-prepared ECL detector, when was used for the determination of ofloxacin, pefloxacin, enrofloxacin and difloxacin in milk, demonstrated adequate sensitivity to allow quantification of trace FQ levels in commercial milk samples. One or more of the target FQ analytes were present at levels above the LOD of the new ECL detector in each and every one of the 22 milk samples analysed.     

Investigation of polar organic solvents compatible with Corona Charged Aerosol Detection and their use for the determination of sugars by hydrophilic interaction liquid chromatography

A range of organic solvents (ethanol, isopropanol and acetone) has been investigated as alternatives to acetonitrile and methanol when used in conjunction with Corona Charged Aerosol Detection (Corona CAD). These solvents have been evaluated with regard to their effect on the response of the Corona CAD. Three dimensional response surfaces were constructed using raw data showing the relationship between detector response, analyte concentration and percentage of organic solvent in the mobile phase, using sucralose or quinine as the test analyte. The detector response was non-linear in terms of analyte concentration for all solvents tested. However, detector response varied in an approximately linear manner with percentage of organic solvent over the range 0–40% for ethanol or isopropanol and 0–80% for acetone and methanol. The chromatographic performance of the various solvents when used as aqueous–organic mobile phases was evaluated for isocratic and gradient separations of sugars and sugar alcohols by hydrophilic interaction liquid chromatography (HILIC) using an Asahipak NH2P-504E column coupled with Corona CAD detection. It was found that whilst acetonitrile provided the highest column efficiencies and lowest detection limits of the solvents studied, acetone also performed well and could be used to resolve the same number of analytes as was possible with acetonitrile. Typical efficiencies and detection limits of 5330 plates m⁻¹ and 1.25 μg mL⁻¹, respectively, were achieved when acetone was used as the organic modifier. Acetone was utilised successfully as an organic modifier in the HILIC separation of carbohydrates in a beer sample and also for a partially digested dextran sample.     

Determination of citric acid by means of competitive complex formation in a flow injection system

A photometric method for the determination of citrate and other organic acids based on their ability to complex Fe³⁺-ions is presented. The red colored complex of [Fe(SCN)₂]⁺, used as reagent, is destroyed upon contact with the sample because the organic acid complexes the Fe³⁺-ion. The decrease in absorption is monitored at 460 nm. The reaction is carried out in a simple flow injection system either in single or preferably double channel configuration.The influence of pH was investigated. Best results were obtained by adjusting the carrier stream to pH 2.0–2.5 with a KCl/HCl-buffer. With an increasing concentration of reagent the linear range is shifted to higher citrate concentrations. The slope of the calibration graph and the linear range are influenced by the sample volume. Other variations of parameters include flow rate, reactor volume and diameter of tubing. Generally speaking, optimum conditions for the flow system are not specified because they vary with the application.The typical conditions for a calibration graph from 1 to 8 mmol/l citrate were a reagent concentration of 2.6 mmol/l [Fe(SCN)₂]⁺, a flow rate of 2.4 ml/ min, a reactor length of 50 cm with tubing of 0.97 mm inner diameter and a sample volume of 100 l. At these system settings the coefficients of variation were 2.5% and 1.6% for eight replicate measurements of samples containing 4 mmol/l and 8 mmol/l citrate, respectively. Up to 180 samples can be analyzed per hour.Naturally the method is disturbed by all other ions that form complexes or precipitates with Fe³⁺-ions. Therefore its application is limited to samples with a known matrix, which was given in the analysis of citrate in lemon flavored soft drinks, where the citric acid usually accounts for 95 to 99% of the total acidity and other interfering ions are absent.     

LC Determination of 4-Bromoaniline in Green Algae Chlamydomonas reinhardtii After Continuous-Flow Microextraction

In this study, the determination of 4-Bromoaniline (4-BA) in green algae Chlamydomonas reinhardtii (C. reinhardtii) was investigated by applying continuous-flow microextraction (CFME) combined with high-performance liquid chromatography (HPLC). Continuous-flow microextraction was conducted in a homemade glass chamber, i.e. the sample solution flowed through a constant volume drop of solvent in the chamber at a constant flow rate. The effects of different factors on extraction efficiencies were also investigated and these factors included the kind of extraction solvent, solvent drop volume, sample flow rate, extraction time and addition amount of salt. Under the optimum extraction conditions (extraction solvent, carbon tetrachloride; solvent drop volume, 3.5 μL; sample flow rate, 1.0 mL min⁻¹; extraction time, 10 min; no addition of salt), the calibration plot was set up by plotting peak area against a series of 4-Bromoaniline concentrations (0.01–10 μg mL⁻¹) in aqueous solution. The correlation coefficient (r) was 0.9990. The limit of detection (LOD) was 0.6 ng mL⁻¹. The precision of this method was obtained by successive five time analyses of 100-ng mL⁻¹ standard solution of 4-Bromoaniline, and the relative standard deviation (RSD) was 3.5%. The concentration factor was calculated by the ratio of peak area of the analyte obtained after and before extraction and found to be 10.6. 4-Bromoaniline residues in Chlamydomonas. reinhardtii cells and tap water samples were satisfactorily analyzed according to the method described above.     

Substitution–dilution method to correct the matrix effect in multi-element quantitative analysis by X-ray fluorescence

A mathematical model based on the dilution–addition method (DAM) for multi-elemental analysis using an X-ray fluorescence technique is proposed. The conditions for sample preparation do not require both the unknown and standard samples to be similar in composition and mineralogy, and the unknown sample is replaced quantitatively by the standard sample, hence the denomination substitution–dilution method (SDM). This method makes it possible to correct the matrix effect in multi-elemental quantitative analysis by X-ray fluorescence for each analyte. The proposed model presents hyperbolic behaviour of the experimental data when the X-ray fluorescence intensities are represented versus the substitution factor (h) for each analyte. After calculating the A/B parameter relations, which depend on the X-ray fluorescence intensity of each analyte (I_i^ns) and the substitution factor (h) and determining the analyte concentration in the multi-element standard sample (C_i^p), it is possible to calculate the analyte concentration in the multi-element unknown using an algorithm suggested for this purpose. This work studies the substitution–dilution phase proposed in the method, and the factors arising from incorporation of the standard and diluent are established according to the nature of the samples and the modifications. These factors make it possible to establish the experimental interval of analyte concentration, generally narrow, which corresponds to a section of the hyperbolic function which is so short that it can be accepted as linear. This linear model can be accepted for a wide variety of samples with a diluent/sample ratio greater than 10. The proposed linear method provides satisfactory results which are comparable to those calculated by applying the hyperbolic method. The proposed method (SDM) has been applied to two different types of matrices, a binary alloy (without diluent, using the hyperbolic model) and a geological sample (with diluent, using both hyperbolic and linear models). In all cases the results were satisfactory.     

A method for direct,semi-quantitative analysis of gas phase samples using gas chromatography–inductively coupled plasma-mass spectrometry

A new and complete GC–ICP-MS method is described for direct analysis of trace metals in a gas phase process stream. The proposed method is derived from standard analytical procedures developed for ICP-MS, which are regularly exercised in standard ICP-MS laboratories. In order to implement the method, a series of empirical factors were generated to calibrate detector response with respect to a known concentration of an internal standard analyte. Calibrated responses are ultimately used to determine the concentration of metal analytes in a gas stream using a semi-quantitative algorithm. The method was verified using a traditional gas injection from a GC sampling valve and a standard gas mixture containing either a 1 ppm Xe + Kr mix with helium balance or 100 ppm Xe with helium balance. Data collected for Xe and Kr gas analytes revealed that agreement of 6–20% with the actual concentration can be expected for various experimental conditions.To demonstrate the method using a relevant “unknown” gas mixture, experiments were performed for continuous 4 and 7 hour periods using a Hg-containing sample gas that was co-introduced into the GC sample loop with the xenon gas standard. System performance and detector response to the dilute concentration of the internal standard were pre-determined, which allowed semi-quantitative evaluation of the analyte. The calculated analyte concentrations varied during the course of the 4 hour experiment, particularly during the first hour of the analysis where the actual Hg concentration was under predicted by up to 72%. Calculated concentration improved to within 30–60% for data collected after the first hour of the experiment. Similar results were seen during the 7 hour test with the deviation from the actual concentration being 11–81% during the first hour and then decreasing for the remaining period. The method detection limit (MDL) was determined for the mercury by injecting the sample gas into the system following a period of equilibration. The MDL for Hg was calculated as 6.8 μg · m^− 3. This work describes the first complete GC–ICP-MS method to directly analyze gas phase samples, and detailed sample calculations and comparisons to conventional ICP-MS methods are provided.     

Headspace in-drop derivatization of carbonyl compounds for their analysis by high-performance liquid chromatography-diode array detection

A simple and rapid method has been reported for the determination of carbonyl compounds involving sample preparation by headspace single drop microextraction using 1-butanol as extraction solvent containing 2,4-dinitrophenylhydrazine for hydrazone formation, and direct transfer of the drop into the injector for high-performance liquid chromatography with diode array detection. An angle-cut polytetrafluoroethylene sleeve, 3 mm × 0.5 mm, was fixed at the tip of the syringe needle and this allowed the use of 7 μL drop of solvent drop for extraction and derivatization. The procedure has been optimized with respect to suitable solvent for headspace drop formation, drop volume, concentration of reagent, sample temperature, reaction time, and headspace-to-sample volume ratio. The method has been validated when rectilinear relationship was obtained between the amount of analyte and peak area ratio of hydrazones in the range 0.01-15 mg L⁻¹, the correlation coefficient over 0.996-0.999, and the limit of detection in the range 1.7-24.1 μg L⁻¹. Spiked real samples have been analyzed with adequate accuracy, and application has been demonstrated of the method for analysis of carbonyl compounds formed as oxidation products.