Determination of haloacetic acids in aqueous environments by solid-phase extraction followed by ion-pair liquid chromatography-electrospray ionization mass spectrometric detection.

Haloacetic acids (HAAs) were determined in different water samples by a new, fast and simple analysis method based on enrichment of 50-ml water samples at pH 1.8 by solid-phase extraction (SPE) followed by liquid chromatography (LC) separation and electrospray ionization mass spectrometric detection in the negative ionization mode. Deprotonated (M-H)-haloacetates and decarboxylated (M-COOH)- ions were detected. Different polymeric SPE sorbents were tested, and LiChrolut EN was found to be the best material for the extraction. Complete LC separation of all compounds could only be achieved by ion-pair chromatography using triethylamine as volatile ion-pairing reagent. The detection limits were in the low microg/l range. High microg/l concentration levels for the chlorinated and brominated haloacetates were found in drinking water from a drinking water treatment plant in Barcelona, and the corresponding tap water. In swimming pool water samples from Catalonia mg/l levels and in surface river water from Portugal microg/l values were detected. These results confirm other recent reports on the ubiquitous occurrence of HAAs in aqueous environments.     

Determination of fluorescent whitening agents in environmental waters by solid-phase extraction and ion pair liquid chromatography-tandem mass spectrometry

A comprehensive method for the trace determination of four stilbene-type disulfonate and one distyrylbiphenyl-type fluorescent whitening agents (FWAs) in environmental water samples was developed and validated. Various solid-phase extraction (SPE) cartridges were investigated. The newly developed Oasis WAX (weak mixed-mode anion exchange and reversed-phase sorbent) SPE cartridge provides the optimal sample extraction results. The analytes were then identified and quantitated by liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-ESI-MS-MS) in negative ionization mode, applying di-n-hexylammonium acetate (DHAA) as the ion-pairing reagent in mobile phase. Limits of quantitation (LOQs) were established between 4 and 18 ng/l in 50 ml of water samples. Intrabatch and interbatch precision with their accuracy at two concentration levels were also investigated. Precision for these five FWAs, as indicated by RSD, proved to be less than 13 and 11%, respectively, for intra- and interbatch. Accuracy, expressed as the mean recovery, was between 68 and 97%. The method was finally applied to environmental water samples, showing the occurrence of five FWAs in both river water and wastewater treatment plant (WWTP) effluent samples.     

The effects of pH, ionic strength and buffer concentration of mobile phase onR F of acidic compounds in ion-pair TLC

Summary The effects of some factors important in ion-pair, high-performance liquid chromatography were studied in ion-pair, thin-layer chromatography. Tetramethyl and cetyltrimethylammonium salts were used as ion-pairing reagents. As stationary phases, silica gel and chemically bonded reversed-layers (C₁₈) were used. Layers were impregnated with ion-pairing reagent prior to chromatography. In some cases the stationary phase was treated with buffer at different concentrations. The mobile phase contained methanol and water, in one set of experiments buffer, salt for adjustment of ionic strength and ion-pairing reagent were added. The migration behaviour of different benzoic acids was studied. Several problems of ion-pair thin-layer chromatography are discussed. Passed away on 13^th of April, 1998 Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997.     

Separation of stilbenes by capillary electrophoresis and high-performance liquid chromatography

Stilbenes, fluorescence whitening agents (FWAs), are usually added to cleaning agents in household and in industry. Capillary electrophoresis (CE) was often applied to separate various compounds simultaneously for its multinomial advantages. In this paper, we established analytical methods of six diaminostilbenes with CE and ion-pair chromatography (IPC). The optimum mobile phase for IPC was 11.78 mM tetrabutylammonium hydrogen sulfate (TBA) aqueous and acetonitrile. An IPC method has been developed for simple and direct separation for diaminostilbenes, anionic substances, with TBA as ion-pair reagent. Satisfactory linear ranges (7.0 x 10(-3) approximately 3.0 x 10 microg/mL), correlation coefficients (0.9992-0.9999), and detection limits (6-13 ng/mL) were obtained. Separations were also performed by capillary zone electrophoresis (CZE) using a buffer consisting of Tris (pH 10.1), n-tetradecyltrimethylammonium bromide (TTAB) and acetonitrile. A linear range of 5.0 x 10(-1) - 4.0 x 10 microg/mL, correlation coefficients between 0.9975 and 0.9998, and detection limits between 337 and 446 ng/mL were obtained. In particular, the separation of a pair of similar compounds (mass difference of 2) was achieved by addition of TTAB. The optimum analytical methods of CE and high-performance liquid chromatography (HPLC) were applied to commercial household with direct analysis and standard addition. No significant bias were shown between them by t-test at 95% confidence level.     

Hot-water and solid-phase extraction of fluorescent whitening agents in paper materials and infant clothes followed by unequivocal determination with ion-pair chromatography-tandem mass spectrometry

A comprehensive method for the determination of four stilbene-type disulfonate and one distyrylbiphenyl-type fluorescent whitening agents (FWAs) in paper materials (napkin and paper tissue) and infant clothes was developed. FWAs were extracted from paper material and cloth samples using a hot-water extraction, and the aqueous extracts were then preconcentrated with the newly developed Oasis WAX (mixed-mode of weak anion exchange and reversed-phase sorbent) solid-phase extraction cartridge. The analytes were unequivocal determined by ion pair chromatography coupled with negative electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS-MS), applying a di-n-hexyl-ammonium acetate (DHAA) as the ion-pairing reagent in mobile phase. Limits of quantitation (LOQ) were established between 0.2 and 0.9 ng/g in 2 g of samples. Recovery of five FWAs in spiked commercial samples was between 42 and 95% and RSD (n = 3) ranging from 2 to 11%. The method was finally applied to commercial samples, showing that two stilbene-type disulfonates were predominant FWAs detected in napkin and infant cloth samples.     

Simultaneous quantitative trace analysis of anionic and nonionic surfactant mixtures by reversed-phase liquid chromatography

The aim of this work was to simultaneously analyse mixtures of a polydisperse polyethylene oxide (PEO) nonionic surfactant and an anionic surfactant (sodium dodecylsulphate, SDS) in water containing sodium chloride in order to quantify trace amounts of these mixtures after their adsorption at water-solid interfaces. A fractional factorial design was then used to optimise the separation by ion-pair reversed-phase liquid chromatography as a function of six factors: the chain length of the tetraalkylammonium salt used as ion-pairing reagent which varied from methyl (C1) to n-propyl (C3); the concentration of this ion-pairing salt; the acetonitrile percentage in water used as organic modifier; the flow-rate; the temperature of analysis and also the sodium chloride concentration. The factorial design enabled in a limited number of analyses, not only to determine which factors had significant effects on retention times or on resolution between a pair of nonionic oligomers, but also to modelize and then find the interesting and rugged area where this resolution was optimal as well as the conditions where time of analysis was not prohibitive. After optimisation of HPLC analysis, we used a trace enrichment procedure to quantify very low concentrations of SDS and C12E9 polydisperse PEO in water. A C18 cartridge and a strong anionic exchange cartridge were coupled and the conditions of elution were optimised in order to obtain concentrated samples which were injected in the same eluent than the HPLC mobile phase. Under such conditions, we were able to quantify, in a single run, mixtures of anionic and nonionic surfactants at concentrations as low as 3.6 microg l(-1) for SDS and 2.5 microg l(-1) for each PEO oligomer in water.     

Ion-pair chromatography of alkali and alkaline earth ions with the new reagent n-hexylsuccinic acid

Summary Alkali, alkaline earth, zinc and manganese(II) ions are separated by ion-pair chromatography on a LiChrospher RP-18 column with 2 mmol/l n-hexylsuccinic acid as a new ion-pair reagent and 1 mmol/l oxalic acid in the eluent and are detected by conductivity. The separation mechanism is discussed, the applicability for wine and mineral water samples including comparison to AAS results are presented.     

Determination of Fluorescent Whitening Agents in Infant Clothes and Paper Materials by Ion‐Pair Chromatography and Fluorescence Detection

A simple and rapid method was developed to simultaneously determine four stilbene‐type disulfonate and one distyrylbiphenyl‐type fluorescent whitening agents (FWAs) in infant clothes and paper materials by ion‐pair chromatography. FWAs were extracted from cloth and papers samples using a hot‐water extraction. The aqueous extract was then mixed with ion‐pair reagent, extracted with C₁₈‐SPE cartridges and eluted with methanol. The contents of FWAs were determined by an isocratic ion‐pair chromatography with RP‐C₁₈ column and equipped with fluorescence detection. Limits of quantitation were 0.04 to 0.45 ng/g in 10 g of samples. Recovery of FWAs in spiked infant cloth and paper samples was between 76 to 92% and precision (RSD) ranging from 2.0 to 4.0%. Analysis of three infant clothes and six paper materials found concentrations of selected FWAs ranging between n.d. to 24 μg/g and n.d. to 3.8 μg/g, respectively.     

Optimisation of solvent desorption conditions for chemical warfare agent and simulant compounds from Porapak Q using experimental design. Part 2: Extraction of sulphur mustard from steel and glass Porapak tubes

The ion-pair solid-phase extraction (SPE) of 4-alkylphenols followed by derivatization with pentafluoropyridine is demonstrated. Under alkaline conditions, the 4-alkylphenols could be efficiently adsorbed on a C18 SPE cartridge conditioned with an ion-pair reagent, tetra-n-hexylammonium bromide. The ion pairs, ammonium phenolates, formed on the C18 solid phase, were eluted with a solvent containing the derivatizing reagent, pentafluoropyridine, and completely derivatized during the elution. After optimization of the adsorption and derivatization, we established a method for the determination of the 4-alkylphenols in water samples. The method showed good linearity between 20 and 1000 ng (200-10,000 ng for nonylphenol). By processing 20-ml samples, the method detection limits (MDL) were in the range of 5.2-8.9 ng/l for the 4-alkylphenols (76 ng/l for nonylphenol). To evaluate its applicability to a real aqueous matrix, several river water samples were analyzed.     

固相萃取-超高效液相色谱分离测定洗涤用品中4种荧光增白剂

建立了固相萃取净化结合超高效液相色谱-二极管阵列检测器(UPLC-DAD)同时检测洗衣液、洗衣粉等洗涤用品中荧光增白剂351、85、28和71的分析方法。样品经2%（体积分数）甲酸水溶液-甲醇提取,经WAX固相萃取小柱净化后,采用Phenomenex Synergi Max-RP色谱柱(150 mm×2.0 mm),以乙腈-10 mmol/L乙酸铵为流动相实现待测物(包括顺式和反式异构体)的良好分离,以二极管阵列检测器检测,结合保留时间和光谱图定性,以标准曲线定量。结果表明,4种荧光增白剂在0.05～180 mg/L范围内线性关系良好,相关系数均大于0.9993;方法定量限(S/N=10)为1.5～15 mg/kg;添加水平为5～1500 mg/kg时,回收率为84.9%～105%,相对标准偏差(RSD, n=6)为3.2%～6.1%。应用本方法分析了15个样品,阳性样品检出率为53.3%。该法前处理简单,回收率高,精密度好,适用于洗涤用品中4种荧光增白剂的测定。     

Simultaneous determination of nitrite and nitrate by normal phase ion-pair liquid chromatography

Normal phase ion-pair high performance liquid chromatography has been used for simultaneous separation of nitrite and nitrate using tetraethylammonium (TEA)(+) as ion-pairing reagent. The concentration effect of (TEA)(+), buffer salt and pH of the eluent on separation is investigated. The UV detector response at various wavelengths has been optimized. The performance of the proposed method is compared with ion chromatography for quantification of the anions in potable water, wastewater and in food samples, such as spinach and lettuce.     

Regeneration of tetrabutylammonium ion-pairing reagent distribution in a gradient elution of reversed phase ion-pair chromatography

The regeneration of ion-pairing reagent distribution on liquid chromatography columns after gradient elution has been well recognized as the cause for long column equilibration time, a major drawback associated with gradient elution reverse phase ion-pair chromatography. To date, the majority of studies have focused on optimizing the separation conditions to shorten the equilibration time. There is limited understanding of the ion-pairing reagent distribution process between the mobile phase and stationary phase in the course of gradient elution, and subsequent column re-equilibration. The focus of this work is to gain a better understanding of this process. An ion-pair chromatographic system, equipped with a YMC ODS C(18) column and a mobile phase containing tetrabutylammonium (TBA) hydroxide as the ion-pairing reagent, was used in the study. The TBA distribution profile was established by measuring its concentration in the eluent fractions collected during the gradient cycle using different column equilibration times with an ion chromatographic method. Furthermore, the analyte retention time was evaluated as the function of the column equilibration time and TBA concentration in the mobile phase. The column equilibration and its impact on the method robustness will also be discussed.     

The Photoyellowing of Stilbene-derived Fluorescent Whitening Agents—Mass Spectrometric Characterization of Yellow Photoproducts

The application of fluorescent whitening agents (FWAs) significantly accelerates the photoyellowing of wool and silk under exposure to the ultraviolet and visible components of sunlight <500 nm. The photochemistry involved in this process is poorly understood, particularly the role of photoproducts derived directly from the FWA itself. Hydroxylation was identified as the key initial mechanism of photodegradation leading to coloration of the solution in the irradiation of the stilbene-derived FWA 4,4'-bis(2-sulfostyryl)biphenyl (DSBP) in the presence of hydrogen peroxide (H₂O₂). Polyhydroxylated DSBP derivatives were implicated as critical intermediates in the formation of yellow photoproducts under these conditions. The formation of trace quantities of DSBP quinone derivatives subsequent to hydroxylation was identified as the key cause of DSBP photoyellowing. These results are the first successful characterization of yellow photoproducts resulting directly from irradiation of a stilbene-based FWA. Formation of these yellow stilbene-based FWA-derived photoproducts may occur on the surface of FWA-treated wool exposed to simulated sunlight, as previous work has shown that H₂O₂ is photogenerated when wet FWA-treated wool is exposed to light. These results therefore suggest that yellow FWA-derived photoproducts contribute to the accelerated photoyellowing of FWA-treated wool.     

Separation of N-nitrosoamino acids by C18 reversed-phase ion-pair high-performance liquid chromatography and compatible detection by electrospray ionization mass spectrometry.

Four non-volatile N-nitrosoamino acids, namely N-nitrososarcosine, N-nitrosoproline, N-nitrosothiazolidine-4-carboxylic acid and N-nitroso-2-methyl-thiazolidine-4-carboxylic acid were separated by C18 reversed-phase ion-pair high-performance liquid chromatography (HPLC) using 1.4 mM C16-cetyltrimethylammonium chloride in methanol-water-acetonitrile (60:35:5, v/v) as the mobile phase. The N-nitrosoamino acids were sensitively detected by negative electrospray ionization mass spectrometry (ESI-MS) in the form of the deprotonated carboxylate anion, [M-H]-. Compatibility problems associated with HPLC separation and ESI-MS detection, such as formation of solvent cluster ions and the effects of co-eluting anions of the ion-pairing reagent, were systematically investigated. The optimized experimental conditions for separation and detection of N-nitrosoamino acids were described.     

反相离子对色谱-电感耦合等离子体质谱联用技术测定水中痕量Cr(Ⅲ)与Cr(Ⅵ)

建立了反相离子对色谱(RPIPC)与电感耦合等离子体质谱(ICP-MS)联用技术快速分离测定水中痕量Cr(Ⅲ)和Cr(Ⅵ)的方法.通过考察流动相的pH值、离子对试剂及甲醇的浓度和EDTA的添加等对不同形态铬的保留时间及分离度的影响,确定当流动相组成为2.0 mmol/L TBA,5%(V/V)甲醇,pH=5.5时,Cr(Ⅲ)与Cr(Ⅵ)可达最佳分离.ICP-MS测定时选用碰撞池技术以消除40Ar12C+与35Cl16OH+对52Cr+的谱学干扰;进样100 μL时,Cr(Ⅲ)与Cr(Ⅵ)的检出限分别为0.15 μg/L和0.16 μg/L.加标回收率在93.6%～106.2%之间; RSD<4%(n=3).以本方法分析了某市自来水、雨水及某品牌纯净水中Cr(Ⅲ)与Cr(Ⅵ)的含量,结果令人满意.     

Determination of amphetamine in rat brain by in vivo microdialysis and ion-pairing liquid chromatography with electrospray tandem mass spectrometry

An ion-pairing liquid chromatography/electrospray tandem mass spectrometry (LC/ES-MS/MS) method with in vivo microdialysis for the determination of amphetamine in rat brain has been developed. A microdialysis probe was surgically implanted into the striatum of the rat and artificial cerebrospinal fluid (aCSF) was used as the perfusion medium. Samples were collected and then analyzed off-line by LC/ES-MS/MS. A reversed-phase C18 column was employed for LC separation and MS/MS was utilized for detection. Trifluoroacetic acid (TFA) was added to the mobile phase (acetonitrile/water) as an ion-pairing reagent. Detection was by ES-MS/MS directly, and no post-column addition of organic modifier was needed. Dual linear ranges were determined from 0.1-0.5 microg/mL and 0.005-0.1 microg/mL, respectively. The detection limit, based on a signal-to-noise ratio of 3, was 0.001 microg/mL (5 nM). Good precision and accuracy were obtained. The applicability of this newly developed method was demonstrated by continuous monitoring of amphetamine concentrations in rat brain. Amphetamine reached a maximum concentration of 0.086 +/- 0.017 microg/mL over 20-40 min after a single 3.0 mg/kg intraperitoneal administration.     

The photoyellowing of stilbene-derived fluorescent whitening agents--mass spectrometric characterization of yellow photoproducts.

The application of fluorescent whitening agents (FWAs) significantly accelerates the photoyellowing of wool and silk under exposure to the ultraviolet and visible components of sunlight <500 nm. The photochemistry involved in this process is poorly understood, particularly the role of photoproducts derived directly from the FWA itself. Hydroxylation was identified as the key initial mechanism of photodegradation leading to coloration of the solution in the irradiation of the stilbene-derived FWA 4,4'-bis(2-sulfostyryl)biphenyl (DSBP) in the presence of hydrogen peroxide (H2O2). Polyhydroxylated DSBP derivatives were implicated as critical intermediates in the formation of yellow photoproducts under these conditions. The formation of trace quantities of DSBP quinone derivatives subsequent to hydroxylation was identified as the key cause of DSBP photoyellowing. These results are the first successful characterization of yellow photoproducts resulting directly from irradiation of a stilbene-based FWA. Formation of these yellow stilbene-based FWA-derived photoproducts may occur on the surface of FWA-treated wool exposed to simulated sunlight, as previous work has shown that H2O2 is photogenerated when wet FWA-treated wool is exposed to light. These results therefore suggest that yellow FWA-derived photoproducts contribute to the accelerated photoyellowing of FWA-treated wool.     

Retention behaviour of an homologous series of oligodeoxythymidilic acids using reversed-phase ion-pair chromatography

Summary The retention behaviour of an homologous series of phosphorylated oligodeoxythymidylic acid (pd(T)_5–18) oligonucleotides was studied using reversed-phase ion-pair chromatography with isocratic elution conditions. The effects of temperature, pH, eluent ionic strength, percentage organic modifier, concentration and alkyl chain length of the ion-pairing reagent were investigated. The retention behaviour was generally explicable by current theoretical models of ion-pair chromatography. However, the marked effect of mobile phase pH on the retention of the oligonucleotides was unexpected, and this was ascribed to the presence of ionisable residual silanols on the surface of the reversed-phase packing material.     

On-line solid-phase extraction-ion-pair liquid chromatography-electrospray mass spectrometry for the trace determination of naphthalene monosulphonates in water.

This paper presents an HPLC-MS method for the fully automated determination of a group of naphthalene monosulphonates in environmental water samples. The analytical procedure consisted of on-line ion-pair solid-phase extraction using a PLRP-S precolumn and ion-pair LC separation with triethylamine as ion-pair reagent in both cases. A mass spectrometric detector, coupled to LC through an electrospray interface and operated in negative ion mode, was used. Diagnostic ions usually corresponded to [SO3]- and/or [M-SO2H]- together with [M-H] and/or [M-2H+Na]-. The method was applied to the trace determination of several sulphonates present in tap water, seawater and water from the Ebro river. The analytes were determined at a concentration level between 0.05 and 1 microg l(-1) under selected ion monitoring acquisition by preconcentrating just 15 ml of sample. Naphthalene-1-sulphonate and naphthalene-2-sulphonate were identified and quantified in one of the samples of seawater.     

Determination of ceftriaxone in cerebrospinal fluid by ion-pair liquid chromatography

An ion-pair liquid chromatographic assay was developed and validated for the determination of ceftriaxone in cerebrospinal fluid. Chromatographic separation was achieved on a C18 column (125 x 4 mm, 5 microm) with detection at 270 nm, a 1 mL/min flow rate and a 50 microL loop. The mobile phase consisted of 300 mL acetonitrile, 50 mL 0.1M phosphate buffer (pH 7.4), 3.2 g tetrabutylammonium bromide as the ion-pairing agent, and dilution with distilled deionized water to 1 L. Cephradine was used as the internal standard. The assay was linear for ceftriaxone concentrations of 0.5-50 microg/mL. The coefficients of variation for precision were <4.61%. The accuracy ranged from 96.07 to 102.42%. The detection and quantitation limits were 0.019 and 0.065 microg/mL, respectively. This method was used to quantify ceftriaxone in the cerebrospinal fluid of children with meningitis. The results showed that the method described here is useful for the determination of ceftriaxone in cerebrospinal fluid.