Ozone measurement with silica cartidges and HRGC-MS analysis

Ozone in ambient air is collected onto silica gel cartridges impregnated with pentafluorophenylhydrazine (PFPH) and 1,2-di(4-pyridyl)ethylene (DPE), so that the pyridine-4 aldehyde formed by DPE oxidation is converted into the corresponding PFPH derivative (PPH). The latter product is determined by HRGC/MS. Since the ozonolysis reaction proceeds stoichiometrically on the cartridge, there is no need for calibration in the gas phase with a standardized ozone source. When compared with UV photometry analyzers, this active chromatographic method (ACM) demonstrates a very good accuracy (ACM/UV photometer = 0.97) and precision (12.0-14.0%) under both laboratory and field sampling conditions at ozone concentrations of 20-200 microg m(-3) and exposure times of 1-3 h. The sampling performance was found to be insensitive to relative humidity (r.h.) variations in the 25-90% range and any interference effects could not be observed from various agents, except light, which can be eliminated by using an aluminium shelter. The detection limit for ozone achievable with the ACM in air samples collected at 0.5 L min(-1) for 1 h was found better than 0.5 microg m(-3).     

Ozone analysis by chemiluminescence measurement

Summary Ozone concentrations in ambient air can be determined by measuring light emitted by reaction with the chemiluminescent dye Rhodamine B. The stability of the light emission is increased by protecting the dye by another compound, which reacts with ozone more easily, i.e. gallic acid.The stability of the chemiluminescent surface is also increased by an intermittent sampling procedure. This is accomplished by means of a threeway valve allowing each minute the introduction of ozonized air for about 15 sec in the reaction chamber, followed by the introduction of ozone-free air for about 45 sec. In this way also a check on the stability of the zero-point of the detecting system is obtained.The method is highly selective. No interferences of NO₂, Cl₂, SO₂, H₂S, NH₃, HCl, H₂O₂ and HF have been observed at concentrations up to 2 ppm. The sensitivity of the chemiluminescent surface is decreased by adsorbed moisture. The moisture problem can be eliminated by coating the surface with a hydrophobic compound and by controlling the relative humidity of the ozone-free air, introduced into the reaction chamber between the actual ozone measurements.

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Ozonanalyse, durch Chemiluminescenzmessung

Zusammenfassung Ozon kann in atmosphÄrischer Luft auf Grund der Chemiluminescenzreaktion mit Rhodamin B bestimmt werden. Dabei wird die StabilitÄt der Lichtemission durch Zusatz von GallussÄure, die leichter mit Ozon reagiert, stabilisiert. Die StabilitÄt der leuchtenden FlÄche wird au\erdem durch ein intermittierendes Probenahmeverfahren verbessert. Hierbei wird je Minute 15 sec lang ozonhaltige Luft und 45 sec lang ozonfreie Luft in die Reaktionskammer geleitet. Dadurch wird zugleich eine Kontrolle des Nullpunktes ermöglicht. Das Verfahren ist sehr selektiv. NO₂, Cl₂, SO₂, H₂S, NH₃, HCl, H₂O₂ und HF verursachen bis zu 2 ppm keine Störungen. Da adsorbierte Feuchtigkeit die Empfindlichkeit der leuchtenden FlÄche beeintrÄchtigt, wird diese mit einer hydrophoben Schutzschicht überzogen sowie die relative Feuchtigkeit der ozonfreien Luft, die zwischen den Messungen durch die Kammer geleitet wird, unter Kontrolle gehalten.

     

Solid-phase extraction on silica cartridges as an aid to platelet-activating factor enrichment and analysis

Solid-phase extraction methods using pre-packed silica cartridges and various elution solvents have been developed and evaluated as chromatographic means to enrich biological lipid extracts for platelet-activating factor (PAF). The optimized procedure advanced selectively removed the major tissue/blood neutral lipids and non-choline-containing phospholipids from complex lipid mixtures and yielded thereby a choline phospholipid fraction markedly enriched in bioactive PAF. Some tested solid-phase extraction procedures, while capable of resolving choline phospholipids from other polar and non-polar species, were detrimental to PAF's bioactivity and evidenced considerable loss or degradation of this analyte. It is concluded that, with solvents of appropriate composition, strength and polarity, solid-phase extraction on silica cartridges has several unique advantages over conventional thin-layer and column chromatographic methods presently in use for PAF enrichment from biological sources.     

Spectrofluorimetric determination of formaldehyde in air after collection onto silica cartridges coated with Fluoral P

In the present work, a sensitive and selective fluorimetric method for formaldehyde determination in air samples is described. The method is based in the reaction between formaldehyde and Fluoral P producing 3,5-diacetyl-1,4-dihydrolutidine, which, when excited at 410 nm, emits fluorescence at 510 nm.The Fluoral P was prepared by the reaction of 0.3 ml of acetic acid, 0.2 ml of acetylacetone and 15.4 g of ammonium acetate. Then, the volume was completed to 100 ml with deionized water. The Fluoral P obtained, if stored under refrigeration in the dark, can be used, safely, for 60 days.The calibration curve obtained with concentrations of formaldehyde in the range of 12 to 192 ng ml⁻¹ (n=9) was Intensity=1.11C+0.06 (R²=0.9920). In the quantification of formaldehyde, air samples were passed at 1 l min⁻¹, during 120 min, through glass impingers containing 40 ml of Fluoral P, followed by direct fluorescence measuring, or through two SEP PAK silica cartridges, coated with Fluoral P. The cartridges were eluted with 10 ml of Fluoral P solution and quantified by spectrofluorimetry. Under these conditions, the detection limit (S/N=3) obtained was 2.0 ng ml⁻¹.The new methodology was validated by comparison with a well-known HPLC method in which formaldehyde was collected into SEP PAK C18 cartridges coated with 2,4 dinitrophenylhydrazine. The application of the t_95% test did not show significant differences between the HPLC and either fluorimetric methodologies.This method has been used in the determination of gas phase formaldehyde in both indoor and outdoor sites. For the indoor site, the measured concentrations were in the range of 9.0 to 67.7 μl l⁻¹, while for the outdoor site they were in the range of 16.8 to 38.8 μl l⁻¹. Further, due to the ease of handling in field studies, the SEP PAK cartridges coated with Fluoral P were used. The formaldehyde concentrations thus determined, in outdoor sites, were in the range of 2.09 to 25.1 μl l⁻¹. The main advantage of this analytical procedure is its selectivity for formaldehyde, without interferences from bisulfite and other aldehydes, especially acetaldehyde, and low blank level, resulting in low detection limits. In addition, very little sample preparation is required.     

Perchlorate analysis using solid-phase extraction cartridges

Perchlorate is a compound of increasing concern as an environmental contaminant and is being regulated at increasingly stringent levels. Reliable methods are needed to consistently analyze perchlorate at low concentration levels. This research investigates the use of solid-phase extraction cartridges as an alternative to large-volume injection loops to achieve low-level (microg/L level) perchlorate quantitation. The method involves commercially available strong anion exchange (SAX) cartridges. Water samples are filtered (100 to 1000 mL) using the cartridge, which removes the perchlorate from the solution by anion exchange. Then, after the desired volume is filtered, the perchlorate is extracted using 4 mL of 1% NaOH. In addition, a cleanup method is developed to remove competing anions (chloride, sulfate, and carbonate) that are often found in environmental samples. Analyses are performed with an ion chromatograph using a 10-microL injection loop, yielding a perchlorate method detection limit (MDL) of 210 microg/L. One-liter volumes of a 2-microg/L perchlorate spiked deionized water solution are filtered with SAX SPE. Following extraction and analysis, an MDL of 0.82 microg/L is obtained, comparable to that found for 1-mL injection loop systems (reported as low as 0.53 microg/L). MDL studies are then conducted on perchlorate-amended groundwater (solution concentration of 70 microg/L) and surface water (solution concentration of 10 microg/L) using a filtration volume of 200 mL. The MDLs are 6.7 microg/L for the groundwater and 2.4 microg/L for the surface water.     

Determination of acrolein and other carbonyls in cigarette smoke using coupled silica cartridges impregnated with hydroquinone and 2,4-dinitrophenylhydrazine

A new method for the determination of acrolein and other carbonyls in cigarette smoke using a dual cartridge system has been developed. Each cartridge consists of reagent-impregnated silica particles. The first contains hydroquinone (HQ) for the inhibition of acrolein polymerization, while the second contains 2,4-dinitrophenylhydrazine (DNPH) for the derivatization of carbonyls. Smoke samples were firstly drawn through the cartridge containing HQ-impregnated silica (HQ-silica) and then through the DNPH-impregnated silica (DNPH-silica). Acrolein in the sample was completely trapped in the first HQ-silica cartridge. Some other airborne carbonyls were also trapped by the HQ-silica, and those that pass through were trapped in the second DNPH-silica cartridge. Extraction was performed in the reverse direction to air sampling. When solvent was eluted through the dual-cartridges, excess DNPH was washed into the HQ bed where it reacted with acrolein and other trapped carbonyls to form the corresponding hydrazone derivatives. All of the hydrazones derived from airborne carbonyls were completely separated and measured using high-performance liquid chromatography. This HQ-DNPH-method can be applied for the determination of acrolein and other α,β-unsaturated aldehydes, such as crotonaldehyde, in cigarette smoke.     

Differentiation of strawberry varieties through purge-and-trap HRGC-MS,HRGC-FTIR and principal component analysis

The aroma composition of three different Fragaria anannassa cul-tivars Selva, Chandler, and Osso Grande) is studied by purge-and-trap HRGC and the components identified by MRGC-MS and HRGC-FTIR. The chromatographic aroma profiles from four different maturation stages in each variety are compared and the similarities accessed by principal component analysis (PCA). The contents in n-hexanal and hex-2(Z)-enal are characteristic features of the green stage in the three varieties where the content differences in methyl, ethyl, and butyl acetates act as typifying variables among varieties. Ethyl acetate acts as an important differentiation variable for the Selva variety. In the mature stage, the three cultivars may be distinguished from each other through their relative contents of methyl and ethyl 2-methylbutyrate (Selva), methyl 2-methyl-butyrate, methyl butyrate (Chandler), methyl and ethyl butyrates, and methyl caproate (Osso Grande).     

Stability of fluoroquinolone antibiotics in river water samples and in octadecyl silica solid-phase extraction cartridges

Airborne particulate matter has been sampled at a location close to a metallurgical plant in North-Rhine-Westphalia, Germany, and first results on the chromium(VI) content in the collected dust are presented. A special procedure using a scrubber as sampling device was used to preserve Cr(VI) during the sampling procedure. The scrubber solution which consisted of 0.1 mol L^–1 TRIS-buffer solution was adjusted to a slightly alkaline pH of 8.6 to reduce the oxidation potential of Cr(VI) and to avoid possible oxidation of Cr(III) to Cr(VI), for example by oxygen (or ozone at ambient concentrations). After sampling Cr(VI) was pre-concentrated on an anion-exchange material and eluted with aqueous 0.6 mol L^–1 sodium perchlorate solution. After elution, a species-selective complex of Cr(VI) with diphenylcarbazide (DPC) was prepared; this was extracted into n-hexanol and quantified by UV–visible spectrophotometry. A detection limit of 0.9 ng m^–3 for Cr(VI) in ambient aerosols can be achieved with this method.     

Evaluation of silica gel cartridges coated in situ with acidified 2,4-dinitrophenylhydrazine for sampling aldehydes and ketones in air

A procedure for coating in situ silica gel in prepacked cartridges with 2,4-dinitrophenylhydrazine (DNPH) acidified with hydrochloric acid is described. The coated cartridge was compared with a validated DNPH impinger method for sampling organic carbonyl compounds (aldehydes and ketones) in diluted automotive exhaust emissions and in ambient air for subsequent analysis of the DNPH derivatives by high performance liquid chromatography. Qualitative and quantitative data are presented that show that the two sampling devices are equivalent. The coated cartridge is ideal for long-term sampling of carbonyls at sub to low parts-per-billion level in ambient air or for short-term sampling of carbonyls at low ppb to parts-per-million level in diluted automotive exhaust emissions. An unknown degradation product of acrolein has been tentatively identified as x-acrolein. The disappearance of acrolein in the analytical sample matrix correlates quantitatively almost on a mole for mole basis with the growth of x-acrolein. The sum of the concentration of acrolein and x-acrolein appears to be invariant with time.     

A quantitative extraction method for conjugated bile acids from human serum using reversed-phase octadecyl bonded silica cartridges for HPLC analysis

Summary A method for the quantitative extraction of bile acid conjugates from serum samples using reversed-phase octadecyl bonded silica cartridges for HPLC analysis is described. It is easy to handle, takes only 30 minutes and has a high extraction recovery.     

PCB separation by HRGC-MS. Fourier analysis for characterizing Aroclor chromatograms

Aroclor and Aroclor mixture chromatograms obtained using temperature programmed high resolution capillary GC coupled with mass spectrometric selective detection have been investigated by Fourier analysis developed for the study of multicomponent chromatograms. The experimental autocorrelation function (EACF), i.e. peak shape and position correlation, showed a retention - structure pattern which could be associated with both the type of Aroclor and the ion used for selective ion monitoring (m/z value). In particular, o-m and m-m isomerization effects were singled out by EACF analysis. By fitting EACF with previously developed theoretical models, it was possible to characterize a specific Aroclor in terms of the number of PCB congeners present in it. The results obtained agreed closely with the typical Aroclor content. For the Aroclor mixture, the distribution of inter-distance between successive peaks was derived. The two first distribution moments obtained agreed with those derived from retention data reported in the literature. The consequences on the separation performance, i.e. the number of singlets, doublets, etc. in the chromatogram, are discussed.     

High reliability and stability of enzyme cartridges in flow-injection analysis

For the determination of glucose and lactate by flow-injection analysis enzyme membranes are used, which usually have short operating times and poor reproducibilities. By combining enzyme cartridges and amperometric oxygen electrodes as detectors for the determination of glucose, lactose and maltose, operating time of up to 6 months and high reproducibilities were attained. Details of cartridge preparation and their use for monitoring broth components during cell cultivation and product formation are presented.     

New method for determination of ochratoxin A in beer using zinc acetate and solid-phase extraction silica cartridges

A new method for the determination of ochratoxin A (OTA) in beer has been developed. The new method has been compared with a reference method currently accepted as AOAC official first action. The limits of detection and quantification of the proposed method were 0.0008 and 0.0025 ng/ml, respectively, while they were 0.0025 and 0.0075 ng/ml, respectively, in the AOAC method used as reference. The recovery levels in the 0.025-0.40 ng OTA/ml spiking range for the proposed and the reference methods were 80.6-87.6% and 78.2-83.8%, respectively. The relative standard deviations of recoveries were 2.6-7.5% for the proposed method and 0.7-6.1% for the reference method. Passing and Bablok regression analysis of recovery data obtained by the proposed method versus data obtained by the reference method on an OTA-spiked beer sample showed good correlation (r2 = 0.9993), while the slope and intercept were 1.049 and -0.0013, respectively. The advantage of the proposed method is the low cost of the materials used in sample preparation because expensive immunoaffinity columns are not needed to clean-up samples while it maintains or even increases the good performance of the reference method. The proposed method was applied to 69 beer samples from different geographic origins (national and imported) but purchased in the Spanish market. They were found to be contaminated with OTA in the range from 0.008 to 0.498 ng/ml (average: 0.070 ng/ml). Five samples surpassed the limit recommended by the European Union (0.2 ng OTA/g).     

Gas-liquid chromatographic determination of fatty acid composition of cholesteryl esters in human serum using silica Sep-Pak cartridges

A simple and fast analytical procedure for separation and purification of cholesteryl esters of human serum is described. A single lipid extract, together with spiked cholesteryl pentadecanoate, as an internal standard, was passed through a Silica Sep-Pak cartridge. 1.5% diethyl ester in light petroleum was used to elute cholesteryl esters from the column. The separation was verified with thin-layer chromatography on silica gel using light petroleum-diethyl ether-glacial acetic acid (80:20:1) as a solvent. A very clean thin-layer chromatogram of cholesteryl esters without any additional spots of other lipids was obtained. The cholesteryl esters were quantitated by analyzing their fatty acid composition as methyl esters by gas-liquid chromatography. The coefficients of variation were 0.8--4.9% for the major fatty acids (C16:0, C16:1, C18:1, C18:2, C20:4) and 6.7--30.8% for the minor fatty acids (C18:0 and C20:0). The recoveries for cholesteryl palmitate, cholesteryl oleate and cholesteryl linoleate were 90.7, 92.3 and 91.0%, respectively.     

Preconcentration of trace amounts of beryllium in water samples on octadecyl silica cartridges modified by quinalizarine and its determination with atomic absorption spectrometry

A simple method has been developed for rapid and selective extraction, preconcentration and determination of trace amounts of beryllium. The extraction is carried out by octadecyl silica cartridge, modified with quinalizarine as a chelating agent. The effect of different parameters, such as sample matrix, flowrates of sample solution and eluent, pH, type and least amount of eluent for elution of Be(+2) ions from cartridge, breakthrough volume and limit of detection, were evaluated. Also, the effects of various cationic and anionic interferences on percent recovery of Be(+2) were studied. Be(+2) was extracted from solution at pH 6-6.6 and was eluted from modified cartridge with 5 ml of 0.5 M HNO(3). Extraction efficiencies >99% were obtained by elution of the cartridges with minimal amount of eluent. A preconcentration factor of 200 and a detection limit of 200 ng per 1000 ml were obtained. The method was applied to the recovery and determination of Be(+2) in different water and alloy samples.     

Extraction and fractionation of bile acids and their conjugates using pre-packed microparticulate silica cartridges (Sep-Pak Sil and Bond-Elut C18)

A new method for the extraction of bile acids from human plasma using acetonitrile precipitation of plasma protein and subsequent use of Bond-Elut C18 cartridges is described. After extraction the bile acids can be separated into three fractions: unconjugated, glycine-, and taurine-conjugated, using Sep-Pak SIL cartridges at 4 degrees C, eluting with ethanol--chloroform--water--glacial acetic acid mixtures. These extraction and fractionation procedures were evaluated in terms of recovery, reproducibility and resolution between the fractions. All these parameters were found to be satisfactory. Although the reproducibility of fractionation on Sep-Pak SIL cartridges was found to vary between batches, this did not give rise to significant difficulties. Plasmas from normals and patients with hepatobiliary disease were analysed by capillary gas-liquid chromatography after extraction and fractionation using the procedure described.     

Identification of active compounds in wheat straw extracts with allelopathic activity by HRGC-MS and HRGC-FTIR

The allelopathic effects of decomposing wheat straw have been known for some time. In spite of the ecological and economical importance of the subject, only a limited number of compounds have been asociated with the allelopathic activity of wheat straw. In this study the high resolution, speed of analysis, and sensitivity of capillary gas chromatography coupled with mass spectromtry (HRGC-MS) and Fourier transform infrared spectrometry (HRGC-MS-FTIR) have been used in a systematic study of the composition of biologically active wheat straw extracts. Droplet counter-current chromatography (DCCC) was used for fractionation and isolation of components. The extract components were analyzed as methyl derivatives and free hydroxyl groups were located by means of ethylation with diazoethane. Twenty compounds were identified, most of them being phenolic acids. Naphthoic acid, azelaic acid and 1,2,3,5-tetrabromobenzene were also identified.     

Nicotine-related impurities in e-cigarette cartridges and refill e-liquids

The nicotine used in e-cigarettes and refill e-liquids is extracted from tobacco, and its purity can vary depending upon manufacturer and grade. The US and European Pharmacopoeias make recommendations for the purity of nicotine intended for pharmaceuticals; however, there is no official purity recommendation for nicotine used in e-cigarettes. To date, there are few published reports on nicotine-related impurities in e-cigarettes and refill e-liquids. The objective of this work was to develop a sensitive, selective, and robust analytical method for the quantitation of nicotine-related impurities in e-vapor products and to evaluate the nicotine-related impurities in a variety of commercial e-cigarette cartridges (n?=?10) and refill e-liquids (n?=?10). Nicotine-N-oxide, nornicotine, mysomine, and cotinine were observed to increase with time during stability studies. This method was also applied to estimate the transfer efficiency of nicotine-related impurities to the aerosol. Most of the impurities were observed to transfer efficiently. However, nicotine-N-oxides showed low transfer efficiency and demonstrated thermal degradation. This selective and sensitive method is suitable to provide quantitative data for risk assessments and for use in e-cigarette product and refill e-liquid stability studies as one of the stability-indicating measures.     

Use of prepacked cartridges in the clean-up of plant material in residual pesticide analysis

Summary The results obtained on clean-up of plant material (fruit and leaves) with prepacked cartridges in normal and reverse phase are compared. The samples, which were analyzed by a multi-residue GLC-ECD technique, contained three fungicides (Chlorothalonil, Vinclozolin and Captan) and one insecticide (Endosulfan).     

Ultra-trace analysis of pesticides by solid-phase extraction of surface water with carbopack B cartridges, combined with large-volume injection in gas chromatography

Summary A method has been developed for determination of twenty-four polar pesticides—nine organophosphorus pesticides, thirteen organonitrogen compounds, and two triazine degradation products—in surface water. It entails extraction of the target pesticides from 1-L water samples by solid-phase extraction (SPE), then gas chromatography (GC) with large-volume (40 μL) injection. Filtered surface water, from the St Lawrence River in Canada and the River Loire and its tributaries in France, was extracted on cartridges filled with 500 mg Carbopack B (120–400 mesh). Analysis was performed by gas chromatography with a thermionic specific detector (GC-TSD) and a mass spectrometric (MS) detector. Overall percentage recoveries were satisfactory (>70%) for all target pesticides, with precision below 10%. Detection limits were between 0.5 and 4 ng L⁻¹.