Determination of formaldehyde and acetaldehyde in air by HPLC with fluorescence detection

Summary Sensitive detection of atmospheric formaldehyde and acetaldehyde can be achieved by use of silica-gel cartridges impregnated with 2-diphenylacetyl-1,3-indandione-1-hydrazone (DAIH) to form fluorescent DAI hydrazones. The hydrazones are extracted with acetonitrile and separated by reversed-phase HPLC with fluorimetric detection. The low detection limits achieved (0.25 ppb CH₂O or CH₃CHO for sampling periods of 1 h) means that the sensitivity of the method is better than that of the classical dinitrophenylhydrazine (DNPH) method. Several experimental conditions, such as collection and reaction efficiency, interference by ozone and storage stability of blank and sampled cartridges have been investigated. There were no significant differences between ambient concentrations of CH₂O and CH₃CHO measured concurrently with the DAIH and DNPH techniques (10–20% in the 0–5 ppb range).     

A highly sensitive method for the determination of adriamycin and adriamycinol in human plasma using HPLC with fluorimetric detection

Summary A simple and very sensitive HPLC method, for the simultaneous determination in human plasma of adriamycin and its metabolite adriamycinol, is described. Plasmas from patients were stored frozen. Thawed samples were extracted by absorption of anthracyclin onto a small C18 column. After evaporation of the eluate and reconstitution of the residue with methanol (100L), 30 to 40L of the mixture were injected into the chromatograph. Separation was obtained using an RP 8 column with a mobile phase of formate buffermethanol-acetonitrile (502327, v/v). A spectrofluorimeter was used as detector. The limit of sensitivity of the assay was 50 pcg/ml of plasma.     

On-line determination of trace sulfur dioxide in air by integrated microchip coupled with fluorescence detection

A microchip-based method was developed for on-line determination of trace sulfur dioxide (SO₂) in air. Gaseous SO₂, which diffused through the porous glass materials on the microchip, was absorbed into an absorption solution of triethanolamine (TEA) as sulfite ions and reacted with N-(9-acridinyl)maleimide (NAM), which was used as a fluorescent reagent. The fluorescence of NAM-sulfite in micro-fluidic channel was detected. The calibration curve of sulfite ions in the range of 1.5-30 μmol/L (SO₂ 3-60 ppbv) showed a linear relation R² = 0.995, and the relative standard deviation (R.S.D.) was 1.9% for 10 μmol/L sulfite ions in five measurements. The entire measurement procedure was achieved by the integrated microchip, and the consumption of reagents was drastically reduced. It was satisfactory to apply this method to determine on-line the SO₂ level in the air.     

On-line coupling of solid-phase extraction and gas chromatography with atomic emission detection for analysis of trace pollutants in aqueous samples

Summary An on-line, solid-phase extraction gas chromatography atomic-emission detection (SPE-GC-AED) system has been set up using an on-column interface to transfer 100 l of desorbing solvent to the GC part of the system. Analytical characteristics such as recovery, precision and linearity of calibration plots were comparable with those of the off-line combination of SPE-GC-AED using organophosphorus pesticides as test compounds. The fully on-line set-up causes a marked improvement in detection because of the quantitative transfer of the analytes from the SPE module to the GC: detection limits are as low as 5–20 ng l^–1 for the analysis of 10 ml raw and spiked surface water samples using the phosphorus channel. Detection levels can be further enhanced by processing up to 100 ml samples. The integrated analytical system is robust. The potential of the on-line set up has been demonstrated for the analysis of surface water and waste water.     

A novel spectrofluorimetric method for the ultra trace analysis of nitrite and nitrate in aqueous medium and its application to air, water, soil and forensic samples

A highly sensitive and virtually specific method has been developed for the trace and ultra trace 5 ng ml⁻¹-1 μg ml⁻¹ fluorimetric analysis of nitrite. The method is based on the quenching action of nitrite on the native fluorescence of murexide (ammonium purpurate) [λ_ex=349.0 nm, λ_em=444.5 nm] in the acid range of 0.045-0.315 (M) H₂SO₄. The method is very precise and accurate (S.D.=±0.4877 and R.S.D.=0.4878% for the determination of 0.1 μg ml⁻¹ of nitrite in 11 replicates). Relatively large excesses of over 35 cations and anions do not interfere. The proposed technique has been successfully applied for the determination of nitrite and nitrate in ground water, surface water and sea water, nitrite in soil and nitrate in forensic samples. The method has also been extended for the analysis of NO_x in air.     

Monitoring of pesticides in surface water: Off-line SPE followed by HPLC with UV detection and confirmatory analysis by mass spectrometry

Summary The presence of 16 of the most widely used pesticides in southern Italy (plus atrazine, the use of which is currently restricted in Europe) has been monitored in ten surface waters of the Calabria Region. The analytes were extracted from water by off-line solid-phase extraction with a Carbograph cartridge. Base-neutral, and acid pesticides were then isolated by differential elution. Analyte fractionation and quantification were performed by liquid chromatography (HPLC) with UV detection. Recoveries of analytes from 0.5 L river water (200 ngL⁻¹ spike level) were ≥84%. Confirmatory analysis was performed by HPLC coupled with ion-spray mass spectrometry (LC-ESI-MS).     

Determination of sulbutiamine and its disulfide derivatives in human plasma by HPLC using on-line post-column reactors and fluorimetric detection

Summary A new direct HPLC procedure for the simultaneous determination of sulbutiamine (Arcalion) and other thiamine disulfides in human plasma has been developed. The method involves an automated solidphase extraction on octadecylsilyl (C18) cartridges and chromatographic separation of the compounds on an RP Select B column with gradient elution using methanol and phosphate buffer. Detection was by fluorescence of the resulting thiochromes obtained from two on-line post-column reactors. Optimization of post-column reaction parameters has been achieved. This method has been proved to be highly selective for the determination of the thiamine disulfide derivatives and quantitation limits of 5 ng·ml^–1 were obtained for each compound in human plasma. Linearity was in the range 5–200 ng·ml^–1. Precision and accuracy were also demonstrated by within-day and between-day assays, and showed the good reliability of the method.     

Occurrence and behavior of system peaks in RP HPLC with solely aqueous mobile phases

System peaks are important but often also disturbing phenomena occurring in separation systems. Behavior of system peaks was studied in reversed phase high performance liquid chromatography (RP HPLC) systems consisting of an RP Amide C16 column and aqueous solutions of organic acids with alkaline metal hydroxides as mobile phases. Binary mobile phases, composed of benzoic acid and lithium hydroxide (LiOH) or cesium hydroxide (CsOH), yielded two system peaks. The first peak was stationary and the second one moved with dilution of the mobile phase or with changes of the alkaline metal hydroxide concentration. The latter changes affected dissociation of the benzoic acid present in the mobile phase and thereby its retention. The presumption that the first system peak is not influenced by the type of alkaline metal cation and that it is related to the non‐adsorbed component of the mobile phase was confirmed by a cyclic procedure. Three‐component mobile phases composed of benzoic acid, tropic acid, and a hydroxide gave rise to three system peaks as expected. The first peak was again stationary and the two others shifted depending on the concentration variation of both acids. Resonance causing a zigzag peak, well described in capillary zone electrophoresis (CZE), was observed if 1‐pentanol was injected into a chromatographic system with one‐component mobile phase.     

Molecularly imprinted polymer for the determination of trace ractopamine in pork using SPE followed by HPLC with fluorescence detection

In this study, a molecularly imprinted functionalized polymer for the selective separation of ractopamine (RAC) was prepared by combining a surface molecular imprinting technique with a sol–gel method process. The polymer was evaluated by static, kinetic adsorption, and selective experiments. Results indicated that the molecularly imprinted polymer had high adsorption capacity, selective ability, and fast mass transfer rate. The polymer was applied for the determination of trace RAC through online SPE‐HPLC. With a sample loading flow rate of 2 mL/min, the enhancement factor of 516.26 and the LOD (S/N = 3) of 4.6 ng/L were achieved, respectively, and the linear range of the calibration curve was 0.04–18 μg/L with r² >0.99. The RAC in pork was determined at three spiked levels (0.5, 1, and 2 ng/g) with recoveries ranging from 55.86 to 67.28%.     

Determination of eleven priority EPA phenolics at ng L−1 levels by on-line solid-phase extraction and liquid chromatography with UV and electrochemical detection

Summary The eleven priority, EPA phenolic pollutants were determined by liquid chromatography followed by two detectors in series; UV and electrochemical. Three different adsorbents, Envi-Carb (a carbon black) and two functionalized polymeric resins, Bond Elut PPL and another synthesized in our laboratory with an ocarboxybenzoyl moiety, were compared for solid-phase extraction (SPE) to detect lower concentrations of the eleven phenolics in natural waters. Higher recoveries were obtained using the functionalized polymeric adsorbents compared with Envi-Carb. When real samples were analysed, the synthetic adsorbent gave lower interference than Bond Elut PPL and phenol was determined at low levels with no humic and fulvic acid inter-ference when Na₂SO₃ was added. The linearity range for most compounds in tap water was 0.05–20 μg L⁻¹ and the limits of detection were <35 ng L⁻¹. Repeatability and reproducibility between days for real samples spiked at 0.1 μg L⁻¹, expressed as relative standard deviation, were <8% and 10%, respectively.     

Screening and confirmation of PAHs in vegetable oil samples by use of supercritical fluid extraction in conjunction with liquid chromatography and fluorimetric detection

A fast, simple, non-destructive method for the direct screening of polycyclic aromatic hydrocarbons (PAHs) in vegetable oil samples is proposed. The method uses a supercritical fluid extraction (SFE) system coupled on-line with a fluorimetric detector to determine PAHs. This special assembly avoids the main problems encountered in the determination of PAHs in complex matrices such as vegetable oils. PAHs are selectively extracted by using silica gel in the thimble and cleaned up by passage through a C18 column. Interferences are preferentially retained by the silica gel during the SFE process while PAHs are adsorbed in the C18 column and the remainder of the matrix is sent to waste. Finally, the C18 column is purged to remove residual CO₂ gas and adsorbed PAHs are recovered by desorption with a solvent. The extracts from positive samples are subsequently analyzed by liquid chromatography (LC) with fluorescence detection. The proposed method allows the confirmation of vegetable oil safety and hence provides a new tool for consumer protection.     

Chemiluminescence determination of carbofuran at trace levels in lettuce and waters by flow-injection analysis

A simple, fast chemiluminescence (CL) flow-injection (FI) method based on the reaction of luminol with KMnO₄ in alkaline medium has been described for the direct determination of carbofuran. The method is based on the enhancing effect in the emission light from the oxidation of luminol produced in presence of carbofuran. The optimisation of instrumental and chemical variables influencing the CL response of the method has been carried out by applying experimental design, using the proposed flow-injection manifold. Under the optimal conditions, the CL intensity was linear for a carbofuran concentration over the range of 0.06-0.5 μg ml⁻¹, with a detection limit of 0.02 μg ml⁻¹. The method has been successfully applied to the determination of carbofuran residues in spiked water and lettuce samples.     

Determination of olefinic aldehydes and other volatile carbonyls in air samples by DNPH-coated cartridges and HPLC

Summary The collection of low-boiling olefinic aldehydes on 2,4-dinitrophenylhydrazine (DNPH)-coated adsorbents (silica cartridges and glass denuders) is examined. Concurrent formation of two different hydrazones by both acrolein and crotonaldehyde is reported and discussed. Identification and quantitation of these compounds do not represent a problem in HPLC analysis, because of their separation from other C₃ and C₄ carbonyl derivatives present in airborne sample extracts.     

Elaboration and use of a double channel detection ion chromatographic method for determination of ions in aqueous samples

Summary In this paper we report our research in developing a simple and reliable method for determination of various anions in aqueous samples. Among the several methods existing for determining ions in aqueous samples, ion chromatography is becoming more and more important, due to its reliability and ability to determine the concentration of more ions from one sample. Although several detection methods are available, in this work we used conductivity detection, and indirect UV photometric detection. Because in some cases it can be important to gather more detailed information on the composition of a sample, we present a way to meet this demand by using double channel detection. Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September, 1–3, 1999     

Determination of trace amounts of chromium (VI) by flow injection analysis with chemiluminescence detection

A new sensitive chemiluminescence (CL) method combined with continuous flow injection analysis is described for the determination of Cr(VI). Strong CL signals were generated by Cr(VI)-catalysed oxidation of gallic acid in the presence of potassium permanganate and hydrogen peroxide. Effects of reagent concentrations, temperature, pH, flow rates, mixing coil length and mixing flow sequences on the chemiluminescence intensity were studied. Under the optimised experimental conditions, the relationship between the logarithm of concentration (log?C) of Cr(VI) and the logarithm of intensity (log?I) is linear over the range of 2?×?10^?11 – 5?×?10^?4?mol?L^?1, with the detection limit (3σ) of 4?×?10^?12?mol?L^?1. Relative standard deviation of ten measurements of 1?×?10^?9?mol?L^?1 Cr(VI) is 1.7%. This flow injection analysis (FIA) system proved to be able to analyse up to 40 samples h^?1. Effects of various interferences possibly present in the water samples were investigated. Most cations and anions, as well as organic compounds, did not interfere with the determination of Cr(VI) in water samples. The experimental results obtained for chromium in reference materials were also in good agreement with the certified values.     

Quantitative analysis of trace levels of surface contamination by X‐ray photoelectron spectroscopy. Part I: Statistical uncertainty near the detection limit

We discuss the problem of quantifying common sources of statistical uncertainties for analyses of trace levels of surface contamination by using X‐ray photoelectron spectroscopy. We examine the propagation of error for peak‐area measurements by using common forms of linear and polynomial background subtraction including the correlation of points used to determine both background and peak areas. This correlation has been neglected in previous analyses, but we show that it contributes significantly to the peak‐area uncertainty near the detection limit. We introduce the concept of relative background subtraction variance (RBSV) that quantifies the uncertainty introduced by the method of background determination relative to the uncertainty of the background area itself. The uncertainties of the peak area and atomic concentration and of the detection limit are expressed using the RBSV, which separates the contributions from the acquisition parameters, the background‐determination method, and the properties of the measured spectrum. These results are then combined to find acquisition strategies that minimize the total measurement time needed to achieve a desired detection limit or atomic‐percentage uncertainty for a particular trace element. Minimization of data‐acquisition time is important for samples that are sensitive to X‐ray dose and also for laboratories that need to optimize throughput.     

Monitoring of vitamin C species in aqueous solution by flow injection analysis coupled with an on-line separation with reversed-phase column

Two vitamin C species of ascorbic acid and dehydroascorbic acid in aqueous solution were monitored by flow injection analysis. Ascorbic acid and dehydroascorbic acid were resolved by a reversed-phase column, and dehydroascorbic acid was reduced to ascorbic acid by an on-line post-column reaction with dithiothreitol. Both natural and reduced ascorbic acids were photometrically detected at 260 nm, and the two vitamin C species were simultaneously determined. The determination range was from 0 to 8 × 10⁻⁵ M with a limit of detection of 1.7 × 10⁻⁶ M. The proposed method was applied to the conversion monitoring of ascorbic acid and dehydroascorbic acid in weakly acidic to weakly alkaline aqueous solutions, as well as to the determination of the vitamin C in some beverage samples.     

Determination of aminopolycarboxylic acids at ultra-trace levels by means of online coupling ion exchange chromatography and inductively coupled plasma-mass spectrometry with indirect detection via their Pd-complexes

A new indirect IC-ICP-MS method for the determination of aminopolycarboxylic acids in water samples is described. It is based on the addition of an excess of Pd(II) to water samples. The analytes are forced into very strong and negatively charged palladium complexes, separated by ion exchange chromatography and detected by their palladium content, utilizing an on-line coupled ICP-MS. This method is suitable to determine the concentration of 8 aminopolycarboxylic acids (nitrilotriacetic acid (NTA), (2-carboxyethyl) iminodiacetic acid (β-ADA), methylglycinediacetic acid (MGDA), 2-hydroxyethyl) ethylenediamine triacetic acid (HEDTA), diethylene triamine pentaacetic acid (DTPA), ethylendiamine tetraacetic acid (EDTA), 1,3-diaminopropane tetraacetic acid (1,3-PDTA) and 1,2-diaminopropane tetraacetic acid (1,2-PDTA) at the ng kg⁻¹ level. The method is faster and easier than the established gas chromatography (GC)-method ISO 16588:2002 [1] and up to two orders of magnitude more sensitive than the ion pair chromatography based method of DIN 38413-8. Analytic performance is superior to ISO 16588:2002 and the comparability is good.     

Selective and sensitive detection of organic contaminants in water samples by on-line trace enrichment–gas chromatography–mass spectrometry

Liquid chromatographic (LC) type trace enrichment is coupled online with capillary gas chromatography (GC) with mass spectrometric (MS) detection for the analysis of aqueous samples. A volume of 1–10 ml of an aqueous sample is preconcentrated on a trace-enrichment column packed with a polymeric stationary phase. After cleanup with HPLC-grade water the precolumn is dried with nitrogen and subsequently desorbed with ethyl acetate. A fraction of 60 μl is introduced on-line into a diphenyltetramethyldisilazane-deactivated retention gap under partially concurrent solvent evaporation conditions and using an early solvent vapor exit. The analytes are separated and detected by means of GC–MS. The potential of the LC–GC–MS system for monitoring organic pollutants in river and drinking water is studied. Target analysis is carried out with atrazine and simazine as model compounds; the detection limits achieved under full-scan and multiple ion detection conditions are 30 pg and 5 pg, respectively. Identification of unknown compounds (non-target analysis), is demonstrated using a river water sample spiked with 168 pollutants varying in polarity and volatility.     

应用SPE柱净化HPLC/UV法测定乳制品及其原料中的硫氰酸盐

采用SPE柱净化、高效液相反相离子对色谱分离、紫外检测器(HPLC/UV)测定乳制品及其原料中的硫氰酸盐。试样经乙酸沉淀蛋白、Oasis WAX SPE柱净化和浓缩,以甲醇和磷酸盐缓冲液加离子对试剂为流动相,经Symmetry C18色谱柱分离,在231 nm波长处进行检测,外标法定量。结果表明,硫氰酸盐浓度在0.2～50 mg/L范围内线性良好,相关系数大于0.999,方法检出限为0.05 mg/kg,定量下限为0.15 mg/kg,在加标量为1、5、25 mg/kg时的回收率为77%～104%。该方法重现性好、检测时间短,灵敏度高,为乳制品及其原料中硫氰酸盐的定量检测提供了较为理想的方法。