Determination of the antifouling agent zinc pyrithione in water samples by copper chelate formation and high-performance liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry

Zinc pyrithione has recently been incorporated into antifouling paints as a booster biocide, which is slowly released into the water as the paint ages. In order to determine concentrations of zinc pyrithione (ZPT) in aqueous samples, a liquid chromatographic method has been developed. Since ZPT interacts with certain reversed-phase packing materials or stainless steel components of the HPLC system, the method uses transchelation of the ZPT into the stable copper(II) complex before analysis by liquid chromatography coupled to atmospheric pressure chemical ionisation mass spectrometry. ZPT was extracted as copper pyrithione using dichloromethane with adequate recovery (77% +/- 17%, n = 6) from 2-l water samples. The limit of detection was calculated to be 20 ng/l, using selected ion monitoring. The analysis of samples collected from various UK marinas showed no detectable concentrations to be present, whilst a laboratory-based study confirmed that this is probably due to the rapid photodegradation of ZPT in seawater.     

Aqueous phototransformation of zinc pyrithione Degradation kinetics and byproduct identification by liquid chromatography--atmospheric pressure chemical ionisation mass spectrometry

The photochemical behavior of the antifouling agent zinc pyrithione (ZnPT) was studied in aqueous media of different composition under simulated solar irradiation using a xenon light source. The influence of important constituents of natural water (dissolved organic matter and nitrate) was also examined using a multivariate kinetic model. It was found that photodegradation proceeds via a pseudo first-order reaction. Kinetic experiments were monitored by LC-MS and photolytic half-lives ranging between 9.2 and 15.1 min have been observed. The increasing concentration of dissolved organic matter (DOM) accelerates the photolysis reaction, while the effect of nitrate ions was also positive since it increased the degradation rate, but to a lesser extent. Irradiation of the aqueous ZnPT solutions gave rise to several transformation products that were isolated by means of solid-phase extraction using poly(styrene-divinylbenzene) extraction disks. These byproducts were identified using liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry. Besides 2-pyridinesulfonic-acid, other degradation products formed included pyridine-N-oxide, 2-mercaptopyridine, 2,2'-dithiobis(pyridine-N-oxide), 2,2-dipyridyl disulfide and the pyridine/pyrithione mixed disulfide, 2,2'-dithiobispyridine mono-N-oxide (PPMD).     

High performance liquid chromatography determination of chlorophenols in water samples after preconcentration by continuous flow liquid membrane extraction on-line coupled with a precolumn

A continuous flow liquid membrane extraction (CFLME)-C₁₈ precolumn-liquid chromatography system was developed for preconcentration and determination of chlorinated phenols (CPs). After preconcentration by CFLME, which is based on the combination of continuous flow liquid-liquid extraction and supported liquid membrane, CPs were enriched in 960 μl of 0.5 mol l⁻¹ NaOH used as acceptor. This acceptor was on-line neutralized and transported onto the C₁₈ precolumn where analytes were absorbed and focused. Then the focused analytes were injected onto the C₁₈ analytical column for separation and detected at 215 nm with a diode array detector. CFLME related parameters such as flow rates, pH of donor and acceptor concentration were optimized. The proposed method presents detection limits of 0.02-0.09 μg l⁻¹ (S/N=3) when 100 ml samples were enriched. The proposed method was successfully applied to determine CPs in tap water and river water samples with spiked recoveries in the range of 70-121%.     

Determination of alpha-tocopherol in infant foods by liquid chromatography combined with atmospheric pressure chemical ionisation mass spectrometry

A novel, sensitive and specific method for the quantification of alpha-tocopherol in two infant foods (milk and cereals) using liquid chromatography on-line with positive atmospheric pressure chemical ionisation mass spectrometry detection (LC/APCI-MS) has been developed. The samples were first saponified in order to eliminate fats and to transform tocopherol esters into free tocopherol, followed up by a liquid-liquid extraction of the analyte in petroleum benzine/diisopropyl ether (75:25, v/v) prior to injection onto the LC system. For the quantification, deuterium-labelled tocopherol was used as internal standard and the samples were monitored in selected ion monitoring (SIM) mode. Calibration curves between 1-40 microg/mL of alpha-tocopherol showed a good linear correlation (r(2) = 0.99994), and the detection limit was determined to be 2.5 ng/mL. The within-day and between-day precision were determined for several dietetic infant formulae and certified reference samples, and found to be below 3.5%. The accuracy determined on a Nestlé reference sample (milk powder) was calculated to be 115.2 +/- 1.2%, which confirms the robustness of the proposed method. This study shows that single quadrupole LC/MS can be applied for the quantification of vitamins in food and the method offers better sensitivity and selectivity than traditional method such as LC-UV. This would simplify the preparation of the food samples and consequently enhance the vitamin analysis throughput in the food area.     

Characteristic fragmentation of bacteriohopanepolyols during atmospheric pressure chemical ionisation liquid chromatography/ion trap mass spectrometry

Bacteriohopanepolyols (BHPs) fragment via characteristic pathways during atmospheric pressure chemical ionisation liquid chromatography/ion trap mass spectrometry (APCI-LC/MS(n)). Comparison of the MS(2) spectra of bacteriohopane-32,33,34,35-tetrol (BHT) and 2 beta-methylbacteriohopane-32,33,34,35-tetrol has confirmed the previously proposed ring-C cleavage occurring between C-9 and 11 and C-8 and 14. This fragmentation, diagnostic of all hopanoids, also occurs in BHPs containing an amino group (-NH(2)) at C-35 although the higher relative stability of the ion limits this fragmentation to a minor process after protonation of the basic nitrogen function. Studies of a number of cell cultures including a prochlorophyte (Prochlorothrix hollandica) and a cyanobacterium (Chlorogloeopsis LA) demonstrate the power of this technique to detect composite BHPs with a complex biological functionality at C-35. We also report the first observation of intact pentafunctionalised bacteriohopanepolyols using this method.     

Identification of diastereomeric chlorophyll allomers by atmospheric pressure chemical ionisation liquid chromatography/tandem mass spectrometry

Atmospheric pressure chemical ionisation liquid chromatography/mass spectrometry (APCI-LC/MS) has been used for identification of the epimers of hydroxy, methoxy and methoxylactone allomers of chlorophyll a (13(2)-HO-chl a, 13(2)-MeO-chl a and 15(1)-MeO-lact-chl a), the hydroxy allomer of bacteriochlorophyll a (13(2)-HO-bchl a) and the hydroxy and methoxylactone allomers of bacterioviridin a (13(2)-HO-bvir a and 15(1)-MeO-lact-bvir a). The APCI mass spectra show that facile fragmentations involve the methoxyl or hydroxyl groups at the C-13(2) or C-15(1) chiral centres. Losses involving the C-13(2) or C-15(1) hydroxyl or methoxyl groups occur more easily from the S-epimer than from the R-epimer due to the greater relief of the steric strain associated with interaction with the bulky C-17 substituent. The differences in mass spectrometric fragmentation can be used as a diagnostic tool for the assignment of the stereochemical configuration at the C-13(2) or C-15(1) chiral centres.     

A novel approach for sensitivity enhancement in atmospheric pressure chemical ionisation liquid chromatography/mass spectrometry of chlorophylls

Differences in the ionisation efficiency of chlorophylls and their phaeophytin counterparts result in lower sensitivity for atmospheric pressure chemical ionisation mass spectrometric detection of the former. Improvement in the sensitivity of detection of chlorophyll of around an order of magnitude at a concentration of 1 x 10(-6)mol L(-1) has been achieved using post-column addition of methanoic acid during analysis by liquid chromatography/mass spectrometry (LC/MS). The method gives linear response and is a simple strategy to improve sensitivity both for LC/MS and LC/MS/MS without loss of information relating to the precise nature of the tetrapyrrole distributions. Detection levels achieved exceed those obtained by absorbance detection.     

High performance liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry for sensitive determination of bioactive amines in donkey milk

In the present study we report on the optimization and validation of a sensitive high performance liquid chromatography atmospheric pressure chemical ionization mass spectrometry (HPLC–APCI–MS) method for the determination of 8 bioactive amines (histamine, tyramine, tryptamine, 2-phenylethylamine, cadaverine, putrescine, spermidine and spermine) in donkey milk samples. The method involves donkey milk pre-treatment to remove proteins and pre-column dansylation of the amines. HPLC in reversed phase mode has been used for bioactive amines separation and the operating condition of the APCI–MS system proved to be powerful and very efficient for peak assignment. The separation was accomplished in a short time with an excellent resolution for all the amine peaks. Quantification was carried out by monitoring the characteristic [M+H]⁺ ion of each amine derivative. The method sensitivity, linearity and repeatability were assayed with satisfactory results. The detection limits of the analysed amines ranged from 0.5 μg L⁻¹ to 15 μg L⁻¹; the highest LOD was for spermine. Also remarkably good recovery values were obtained; at the lowest spiking level (1 μg L⁻¹) the percent mean recoveries ranged from 77.7 to 109.7. Furthermore, as the investigations relate to a complex matrix as donkey milk, suitable studies on matrix effect were performed. Finally, the developed and validated method was applied to analyse 13 donkey milk samples. Among the identified bioactive amines, putrescine, spermine and spermidine proved to be the main amines in donkey milk. Their concentration levels in the present study were lower than the values determined in mature human, cow and sow milk.     

固相萃取-超高压液相色谱-串联质谱同时分析环境水样中四环素类和喹诺酮类抗生素

应用固相萃取及超高压液相色谱-质谱联用技术,建立了环境水样中4种四环素类和6种喹诺酮类抗生素的同时分析方法。样品经HLB固相萃取柱富集、净化后用甲醇洗脱,以超高压液相色谱-串联质谱仪多反应监测(MRM)离子模式定性、定量分析。以河水和海水为基质,卡巴氧为替代物进行回收率评价,4种四环素类抗生素在加标质量浓度分别为20.0 ng/L和100.0 ng/L时的回收率为94.0%～117.0%,相对标准偏差为2.0%～9.7%(n=4),方法的检出限均为20.0 ng/L;6种喹诺酮类抗生素在加标质量浓度分别为5.0 ng/L和20.0 ng/L时的回收率为63.6%～93.9%,相对标准偏差为1.6%～8.1%(n=4),方法的检出限为0.4 ng/L。结果表明,所建立的方法可成功地应用于近岸海域表层环境水样中目标抗生素残留的分析。     

Determination of chlorantraniliprole residues in crops by liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry/mass spectrometry

An analytical method is presented for the determination of chlorantraniliprole residues in crops. Chlorantraniliprole residues were extracted from crop matrixes with acetonitrile after a water soak. The extracts were passed through a strong anion-exchange (SAX) SPE cartridge stacked on top of a reversed-phase (RP) polymer cartridge. After both cartridges were rinsed and vacuum-dried, the SAX cartridge was removed, and chlorantraniliprole was eluted from the RP polymer cartridge with acetonitrile. The acetonitrile eluate was evaporated to dryness, reconstituted, and analyzed using an LC/MS/MS instrument equipped with an atmospheric pressure chemical ionization source. The method was successfully validated at 0.010, 0.10, and 10 mg/kg for the following crop matrixes: potatoes, sugar beets (tops), lettuce, broccoli, soybeans, soybean forage, tomatoes, cucumbers, oranges, apples, pears, peaches, almonds (nutmeat), rice grain, wheat grain, wheat hay, corn stover, alfalfa forage, cottonseed, grapes, and corn grain. The average recoveries from all crop samples fortified at the method LOQ ranged from 91 to 108%, with an overall average recovery of 97%. The average recoveries from all crop samples fortified at 10 times the method LOQ ranged from 89 to 115%, with an overall average recovery of 101%. For all of the fortified control samples analyzed in this study, the overall average recovery was 99%.     

Quantitative determination of three sulfonamides in environmental water samples using liquid chromatography coupled to electrospray tandem mass spectrometry

An analytical method was developed to detect the three sulfonamides para-toluenesulfonamide (p-TSA), ortho-toluenesulfonamide (o-TSA) and benzenesulfonamide (BSA) in environmental water samples at concentrations down to 0.02 microg/L using liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS). Wastewater, surface water, groundwater and drinking water samples from Berlin (Germany) were analysed for all three compounds which appear to be ubiquitously present in the aquatic environment. p-TSA was found in high concentrations in the wastewater (<0.02-50.8 microg/L) and in groundwater below a former sewage farm (<0.02-41 microg/L), and in lower concentrations in the surface water (<0.02 to 1.15 microg/L) and drinking water (<0.02-0.27 microg/L). o-TSA and BSA were detected in considerably lower concentrations. The study makes clear that p-TSA should be monitored because of its comparatively high concentration in Berlin's drinking water.     

Quantitative on-line preconcentration-liquid chromatography coupled with tandem mass spectrometry method for the determination of pharmaceutical compounds in water

One of the current environmental issues concerns the presence and fate of pharmaceuticals in water bodies as these compounds may represent a potential environmental problem. The characterization of pharmaceutical contamination requires powerful analytical method able to quantify these pollutants at very low concentration (few ng L⁻¹).     

Pressurised hot water extraction coupled on-line with liquid chromatography-gas chromatography for the determination of brominated flame retardants in sediment samples

Pressurised hot water extraction (PHWE) was coupled on-line with liquid chromatography-gas chromatography (LC-GC) to determine brominated flame retardants in sediment samples. After extraction with pressurised hot water the analytes were adsorbed in a solid-phase trap. The trap was dried with nitrogen and the analytes were eluted to the LC column, where the extract was cleaned, concentrated and fractionated before transfer to the GC system. The fraction containing the brominated flame retardants was transferred to the GC system via an on-column interface. The PHWE-LC-GC method was linear from 0.0125 to 2.5 microg with limits of detection in the range 0.70-1.41 ng/g and limits of quantification 6.16-12.33 ng/g.     

Ion suppression in the determination of clenbuterol in urine by solid-phase extraction atmospheric pressure chemical ionisation ion-trap mass spectrometry

Ion suppression effects were observed during the determination of clenbuterol in urine with solid-phase extraction/multiple-stage ion-trap mass spectrometry (SPE/MS(3)), despite the use of atmospheric pressure chemical ionisation. During SPE, a polymeric stationary phase (polydivinylbenzene) was applied. Post-cartridge infusion of analyte to the SPE eluate after the extraction of blank urine was performed to obtain a profile of the suppression. Single and multiple-stage MS were performed to provide insight in the suppressing compounds. The ion suppression was mainly ascribed to two m/z values, but still no identification of the compounds was achieved from the multiple-stage MS data. No ionisable and non-ionisable complexes and/or precipitation of clenbuterol with matrix compounds were observed. A concentration dependence of the percentage of suppression was observed. Up to 70% of the signal was suppressed upon post-cartridge infusion of 0.22 microg/mL (at 5 microL/min) clenbuterol into the eluate, and this decreased to about 4% at infusion of 22 microg/mL clenbuterol. Molecularly imprinted polymers were used to enhance the selectivity of the extraction. Although matrix components were still present after extraction, no interference of these compounds with the analyte was observed. However, the bleeding of the imprint from the polymer (brombuterol) caused significant ion suppression.     

Characterisation of humic substances using atmospheric pressure chemical ionisation and electrospray ionisation mass spectrometry combined with size-exclusion chromatography

Humic substances were analysed by atmospheric pressure chemical ionisation (APCI) and electrospray ionisation (ESI) mass spectrometry in positive and negative modes. Using APCI the average m/z range of humic substances was reduced 5-fold compared to ESI. High-resolution time-of-flight mass spectrometry revealed the formation of multiply charged molecules in the ESI mode. Moreover, it was possible to obtain daughter ion mass spectra of humic substances by nanospray tandem mass spectrometry. The size-exclusion chromatography elution profile of humic substances was highly influenced by the pH of the analyte solution. By contrast, the pH had no significant influence on the observed mass spectra of humic substances.     

Analysis of wax ester molecular species by high performance liquid chromatography/atmospheric pressure chemical ionisation mass spectrometry

High chromatographic resolution of wax esters (WEs) was achieved by non-aqueous reversed-phase liquid chromatography on a Nova-Pak C18 column by optimising the acetonitrile/ethyl acetate mobile phase gradient. The retention behaviour of WEs was studied in this chromatographic system. The WEs eluted according to their equivalent carbon number (ECN) values; within the group of WEs with the identical ECN, the most unsaturated species tended to elute first. The isobaric WEs with different positions of the ester moiety were separated from each other whenever the lengths of the chains were sufficiently different. The methyl-branched esters eluted at shorter retention times than the straight-chained analogues, and the resolution among methyl-branched WEs depended on the position of the branching. The analytes were detected by atmospheric pressure chemical ionisation mass spectrometry (APCI-MS) using data-dependent scanning. WEs provided simple full-scan spectra with abundant protonated molecules and low-intensity fragments. Collision-induced dissociation (CID) promoted identification of the WE molecular species. The responses of WEs were found to be dependent on the number of double bonds and on the alkyl-chain length; the limits of the detection ranged from 20 μmol/L to 200 nmol/L. The HPLC/APCI-MS was applied for the analysis of the WEs isolated from honeycomb beeswax, jojoba oil and human hair. Good agreement between reported results and the literature data was achieved, with several novel polyunsaturated WEs also being found.     

Structural characterisation of unsaturated bacterial hopanoids by atmospheric pressure chemical ionisation liquid chromatography/ion trap mass spectrometry

The production of bacteriohopanepolyols (BHPs) is widespread in many different groups of prokaryotes; however, unsaturated components are less common except amongst the acetic acid bacteria. Here we describe the characterisation of mono- (Delta(6) or Delta(11)) and diunsaturated (Delta(6,11)) bacteriohopanetetrols isolated from the acetic acid bacterium Gluconacetobacter xylinus (formerly Acetobacter aceti ssp. xylinum) by atmospheric pressure chemical ionisation ion trap mass spectrometry (APCI-MS(n)). APCI-MS(2) spectra are compared with equivalent electron ionisation (EI) spectra and differences in fragmentation pathways are discussed. Having established characteristic spectral features for a range of unsaturated BHPs we now have the ability to rapidly detect the presence of unsaturated BHPs in both natural environmental samples (soils, sediments, water columns) as well as in microbial cultures.     

Optimization of the atmospheric pressure chemical ionization liquid chromatography mass spectrometry interface

Use of optimized instrument parameters that result from statistical experimentation revealed that the sensitivity of atmospheric pressure chemical ionization (APCI) liquid chromatography-mass spectrometry (LC/MS) is greater than the sensitivity of an optimized Thermabeam? LC/MS interface by about 3 orders of magnitude, when tested on aromatic compounds. APCI is one of the few LC/MS techniques in which the chromatogram is directly comparable with liquid chromatographs that use ultraviolet detection. The optimum instrument parameters for a Finnigan SSQ-7000 APCI LC/MS interface were found at low flow rates (e. g., 0. 1 mL/min), relatively low capillary heat (e. g., 225 °C), and high sheath-gas pressure (e. g., 60 lb/in²). The optimization was achieved by monitoring the responses of sensitivity, fragmentation, and cluster ion formation. The fine tuning for high sensitivity calls for a high percentage of water in the mobile phase. In contrast, a high percentage of organic content in the mobile phase is required to obtain abundant protonated molecular ions with respect to fragmentation and clustering. This is an important consideration for analyses of unknowns.     

Determination of perfluorooctane sulfonate in river water by liquid chromatography/atmospheric pressure photoionization mass spectrometry by automated on-line extraction using turbulent flow chromatography

A simple, fast and sensitive liquid chromatography/atmospheric pressure photoionization mass spectrometry (LC/APPI-MS) method, with automated on-line extraction using turbulent flow chromatography (TFC), was developed for the determination of perfluorooctane sulfonate (PFOS) in river water. In this method, following an on-line extraction by injection onto a column under TFC conditions, PFOS is back-flushed onto a reversed-phase column via on-line column switching, and resolved chromatographically at a laminar flow rate of 1 mL min(-1). Using this tandem LC-LC/APPI-MS system the extraction, separation and selective detection of PFOS in river water could be achieved with satisfactory selectivity and sensitivity. The limit of detection (LOD) (S/N = 3) and the limit of quantitation (LOQ) (S/N = 10)were 5.35 and 17.86 pg mL(-1). The described procedure was very simple since no off-line sample preparation was required, total analysis time being 18.75 min.