Extraction of formic and acetic acids from aqueous solution by dynamic headspace-needle trap extraction temperature and pH optimization

A combined method of dynamic headspace-needle trap sample preparation and gas chromatography for the determination of formic and acetic acids in aqueous solution was developed in this study. A needle extraction device coupled with a gas aspirating pump was intended to perform sampling and preconcentration of target compounds from aqueous sample before gas chromatographic analysis. The needle trap extraction (NTE) technique allows for the successful sampling of short chain fatty acids under dynamic conditions while keeping the headspace (HS) volume constant. Two important parameters, including extraction temperature and effect of acidification, have been optimized and evaluated using the needle trap device. The method detection limits for the compounds estimated were 87.2microg/L for acetic acid and 234.8microg/L for formic acid in spite of the low flame ionization detection response for formic acid and its low Henry's law constant in aqueous solution. Precision was determined based on the two real samples and ranged between 4.7 and 10.7%. The validated headspace-needle trap extraction method was also successfully applied to several environmental samples.     

Solid phase extraction of petroleum carboxylic acids using a functionalized alumina as stationary phase

Petroleum essentially consists of a mixture of organic compounds, mainly containing carbon and hydrogen, and, in minor quantities, compounds with nitrogen, sulphur, and oxygen. Some of these compounds, such as naphthenic acids, can cause corrosion in pipes and equipment used in processing plants. Considering that the methods of separation or clean up the target compounds in low concentrations and in complex matrix use large amounts of solvents or stationary phases, is necessary to study new methodologies that consume smaller amounts of solvent and stationary phases to identify the acid components present in complex matrix, such as crude oil samples. The proposed study aimed to recover acid compounds using the solid phase extraction method, employing different types of commercial stationary ion exchange phases (SAX and NH(2)) and new phase alumina functionalized with 1,4-bis(n-propyl)diazoniabicyclo[2.2.2]octane chloride silsesquioxane (Dab-Al(2)O(3)), synthesized in this work. Carboxylic acids were used as standard mixture in the solid phase extraction for further calculation of recovery yield. Then, the real sample (petroleum) was fractionated into saturates, aromatics, resins, and asphaltenes, and the resin fraction of petroleum (B1) was eluted through stationary ion exchange phases. The stationary phase synthesized in this work showed an efficiency of ion exchange comparable to that of the commercial stationary phases.     

Application of purge and trap extraction and gas chromatography for determination of minor esters in cider

The validation of a method based on the purge and trap technique combined with gas chromatography-mass spectrometry-flame ionization detection has been carried out in order to apply it to the analysis of ciders. Although 49 compounds were identified, our work was focused on the study of nine minor esters, obtaining recoveries ranging between 93% for ethyl decanoate and 117% for ethyl 3-methylbutyrate, and a precision (RSDs) ranging between 2.2% for hexyl acetate and ethyl decanoate and 10.9% for isopentyl acetate. To demonstrate the feasibility of the procedure, the method was applied to the analysis of commercial ciders.     

Development of continuous on-line purge and trap analysis

An on-line purge and trap system for continuous monitoring of Volatile Organic Compounds (VOC) is presented. The purge chamber was designed for continuous extraction of VOC from water with nitrogen. The analytes were preconcentrated on a microtrap prior to analysis by GC with flame ionization detection. The microtrap served as a fast injection device for carrying out analysis at high frequency. Continuous monitoring was accomplished by performing injections at fixed intervals. This system showed high sensitivity, high precision, detection limits at the ppb level, and stable response over long periods of continuous operation. Factors affecting system performance were studied. A predictive model based on gas-liquid partitioning is also presented.     

Hyphenated gas chromatography-mass spectrometry analysis of 3-mercaptohexan-1-ol and 3-mercaptohexyl acetate in wine: Comparison with results of other sampling procedures via a robust regression

This work describes a new purge and trap gas chromatography electron impact mass spectrometry (PT-GC-EIMS) method for quantifying 3-mercaptohexan-1-ol (3-MH) and 3-mercaptohexyl acetate (3-MHA), two molecules able to characterize some wines with their tropical scents. Firstly the experimental conditions of the purge and trap extraction (sample temperature, extraction time, trap temperature, flow rate) following a multivariate approach were optimized. Then the method through the construction of the calibration curves and the establishment of the detection limits was validated. The purge and trap procedure appears faster and more sensitive than both the headspace solid phase microextraction (HS-SPME) and the solid phase extraction (SPE) procedures, reaching detection limits for the two thiols closer to their sensory thresholds. Evidence of similar performances of the three sampling methods considered was gained comparing the results relevant to same wine samples. The Theil's regression method was used for purpose of comparison.     

Comparison of purge and trap GC/MS and spectrophotometry for monitoring petroleum hydrocarbon degradation in oilfield produced waters

Results of using a field spectrophotometer and its appropriate protocols as a surrogate method for an oilfield produced water treatment process is presented. Methylene chloride extractions of the produced water before and after treatment maintained a yellow color pigment that was directly proportional to the hydrocarbon concentration. From this, an absorption spectrum and standard curve were developed. A resultant linear plot of the standard curve indicated that there is an excellent correlation (r²=0.9847) between the varying concentrations and the associated absorbance values at a wavelength of 400 nm. Total n-alkane concentration comparisons between the laboratory GC/MS analysis and the spectrophotometry analysis generated data of similar accuracy and precision at concentrations ranging from 1 to 137 mg/l (alpha=0.05). Linear comparisons between GC/MS and spectrophotometric coefficients were near unity, with the constant being near zero, with a correlation coefficient (r²) of 0.99. Based on this study, spectrophotometry is a complimentary method to GC/MS for determining total n-alkane concentrations in oilfield produced water samples.     

Phenylboronic acid modified solid‐phase extraction column: Preparation,characterization, and application to the analysis of amino acids in sepia capsule by removing the maltose

Maltose, a common auxiliary material of pharmaceutical preparation, may disturb the analysis of total amino acids in sepia capsule by aldolization. Therefore, it is necessary to remove the maltose through a convenient method. In this work, a phenylboronic acid modified solid‐phase extraction column has been synthesized and used to remove the maltose. The materials were synthesized by one step “thiol‐ene” reaction and the parameters of the column such as absorption capacity, recovery, and absorption specificity have been investigated. The results showed the column (0.5 cm of length × 0.5 cm of inner diameter) can absorb 4.6 mg maltose with a linear absorption and absorption specificity. Then this technique was applied in the quantification of amino acids in sepia capsule. After the optimization of the method, four kinds of amino acids, which were the most abundant, were quantified by high‐performance liquid chromatography with diode array detection. The amounts of the four kinds of amino acids are 1.5～2 times more than that without the treatment of solid‐phase extraction column, which almost overcomes the influence of the maltose. All the results indicate that the phenylboronic acid modified solid‐phase extraction column can successfully help to accurately quantify the total amino acids in sepia capsule.     

The analysis of light aromatics in aqueous effluent by gas chromatography

Summary A quantitative method is described for the analysis of trace quantities of benzene, toluene and the C₈ aromatics in aqueous effluents. The light aromatics are pre-concentrated using a purge and trap technique and are separated into individual components on a gas chromatographic system. The limit of detection is 10 ppb. The sampling, transportation, and storage of the effluent in order to obtain a representative sample and to prevent losses are discussed. The need for the analysis to be carried out as quickly as possible after sampling is stressed.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Effective sorbents for solid-phase extraction in the analysis of quinolones in animal tissues by capillary electrophoresis

In this work, several commercial sorbents (Zorbax C18, Bond Elut C18, Isolute ENV+, Oasis HLB, Oasis MAX, SDB-RPS, and MPC-SD) were compared for the solid-phase extraction of the series of quinolones regulated by the European Community in chicken tissues in order to establish a method for the determination of this series of quinolones by capillary electrophoresis and diode array detection. Sorbents were chosen in order to achieve maximum recoveries and optimal clean-up efficiency. Better results were obtained using SDB-RPS and Oasis MAX which would provide suitable limits of detection, below of the maximum residue limits (MRLs) regulated.     

Potential sources of background contaminants in solid phase extraction and microextraction

A study to identify the sources of background contamination from SPE, using a C-18 sorbent, and solid-phase microextraction (SPME), using a 70 microm carbowax/divinylbenzene (CW/DVB) fiber, was carried out. To determine the source of contamination, each material used in the procedure was isolated and examined for their contribution. The solid-phase column components examined were: sorbent material and frits, column housings and each solvent used to elute analytes off the column. The components examined in the SPME procedure were: SPME fiber, SPME vials, water (HPLC grade), and salt (sodium chloride) used to increase the ionic strength. The majority of the background contaminants from SPE were found to be from the SPE sorbent material and frits. The class of contaminants extracted during a blank extraction were phthalates and other plasticizers used during the manufacturing process. All had blank levels corresponding to measured concentrations below 2 ng/ mL, except for undecane, which had a concentration of 5.4 ng/mL. The most prevalent contaminants in the SPME blank procedure are 1,9-nonanediol, a mixture of phthalates and highly bis-substituted phenols. All the concentrations were below 2 ng/mL, with the exception of bis (2-ethylhexyl) phthalate, which had concentrations ranging from 5 to 20 ng/mL.     

Rapid extraction of codeine and morphine in whole blood for HPLC analysis

Summary A rapid and efficient procedure is described for the extraction and analysis of codeine and morphine in whole blood. Red blood cells were fragmented by sonication and the blood sample extracted by passing through a bonded silica column (Bond Elute^?). The adsorbed drugs were washed and eluted followed by analysis by HPLC. Recoveries were between 95–100% at 5 ng/ml concentrations.     

Rapid magnetic solid‐phase extraction of Congo Red and Basic Red 2 from aqueous solution by ZIF‐8@CoFe2O4 hybrid composites

Core–shell metal–organic framework materials have attracted considerable attention mainly due to their enhanced or new physicochemical properties compared with their single‐component counterparts. In this work, a core–shell heterostructure of CoFe₂O₄‐Zeolitic Imidazolate Framework‐8 (ZIF‐8@CoFe₂O₄) is successfully fabricated and used as an solid‐phase extraction adsorbent to efficiently extract Congo Red and Basic Red 2 dyes from contaminated aqueous solution. Vibrating sample magnetometry indicates that the saturated magnetization of ZIF‐8@CoFe₂O₄ is 3.3 emu/g, which is large enough for magnetic separation. The obtained hybrid magnetic metal‐organic framework based material ZIF‐8@CoFe₂O₄ can remove the investigated dyes very fast within 1 min of the contact time. The adsorbent ZIF‐8@CoFe₂O₄ also shows a good reusability. After regeneration, the adsorbent can still exhibit high removal efficiency (～97%) toward Congo Red for five cycles of desorption–adsorption. This work reveals the great potential of core–shell ZIF‐8@CoFe₂O₄ sorbents for the fast separation and preconcentration of organic pollutants in aqueous solution before high‐performance liquid chromatography analysis.     

Evaluation of needle trap micro‐extraction and solid‐phase micro‐extraction: Obtaining comprehensive information on volatile emissions from in vitro cultures

Volatile organic compounds (VOCs) emitted from in vitro cultures may reveal information on species and metabolism. Owing to low nmol L⁻¹ concentration ranges, pre‐concentration techniques are required for gas chromatography–mass spectrometry (GC–MS) based analyses. This study was intended to compare the efficiency of established micro‐extraction techniques – solid‐phase micro‐extraction (SPME) and needle‐trap micro‐extraction (NTME) – for the analysis of complex VOC patterns. For SPME, a 75 μm Carboxen®/polydimethylsiloxane fiber was used. The NTME needle was packed with divinylbenzene, Carbopack X and Carboxen 1000. The headspace was sampled bi‐directionally. Seventy‐two VOCs were calibrated by reference standard mixtures in the range of 0.041–62.24 nmol L⁻¹ by means of GC–MS. Both pre‐concentration methods were applied to profile VOCs from cultures of Mycobacterium avium ssp. paratuberculosis. Limits of detection ranged from 0.004 to 3.93 nmol L⁻¹ (median = 0.030 nmol L⁻¹) for NTME and from 0.001 to 5.684 nmol L⁻¹ (median = 0.043 nmol L⁻¹) for SPME. NTME showed advantages in assessing polar compounds such as alcohols. SPME showed advantages in reproducibility but disadvantages in sensitivity for N‐containing compounds. Micro‐extraction techniques such as SPME and NTME are well suited for trace VOC profiling over cultures if the limitations of each technique is taken into account.     

Application of NaClO-treated multiwalled carbon nanotubes as solid phase extraction sorbents for preconcentration of trace 2,4-dichlorophenoxyacetic acid in aqueous samples

Multiwalled carbon nanotubes functionalized by oxidation of original multiwalled carbon nanotubes with NaClO were prepared and their application as solid phase extraction sorbent for 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated systemically, and a new method was developed for the determination of trace 2,4-D in water samples based on extraction and preconcentration of 2,4-D with solid phase extraction columns packed with NaClO-treated multiwalled carbon nanotubes prior to its determination by HPLC. The optimum experimental parameters for preconcentration of 2,4-D, including the column activating conditions, the amount of the sorbent, pH of the sample, elution composition, and elution volume, were investigated. The results indicated 2,4-D could be quantitatively retained by 100 mg NaClO-treated multiwalled carbon nanotubes at pH 5, and then eluted completely with 10 mL 3:1 (v/v) methanol-ammonium acetate solution (0.3 mol/L). The detection limit of this method for 2,4-D was 0.15 μg/L, and the relative standard deviation was 2.3% for fortified tap water samples and 2.5% for fortified riverine water sample at the 10 μg/L level. The method was validated using fortified tap water and riverine water samples with known amount of 2,4-D at the 0.4, 10, and 30 μg/L levels, respectively.     

Fundamentals and applications of needle trap devices: A critical review

The needle trap device (NTD) is an extraction trap that contains a sorbent inside a small needle, through which fluid can be actively drawn into and out of by a gas-tight syringe or pump, or analytes can be introduced passively to the trap by diffusion. The needle trap (NT) is a potentially solventless sampling technique/sample preparation and introduction device. Both fluid-borne analytes and particles can be trapped inside the needle and then adsorbed analytes are desorbed in an inlet of analytical instrument and introduced for identification and quantification. The fluid may be either gaseous or liquid. The objectives of this critical review are to summarize the theory of the sampling process for both active and passive time-average extraction modes in addition to outlining the evolution of the technology and main applications.     

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.     

Determination of benzene,toluene, ethylbenzene,and xylenes in urine by purge and trap gas chromatography

A method for determination of benzene, toluene, ethylbenzene, and xylenes (BTEX) in urine is described. Determination is performed by dynamic headspace (purge and trap) gas chromatography with photoionization detection. The features of the described method, i.e. detection limits of 15–35 ng L^–1, relative standard deviations of 0.2–10%, accuracy of 80–100%, removal of interference of many compounds present in urine, sharp chromatographic peaks because of cryogenic refocusing, no sample preparation, make it convenient for biological monitoring of exposure to low levels of BTEX. However, the method is time‐consuming and sophisticated.     

吹扫捕集-GC-MS-SIM法测定水中挥发性硫化合物

建立了水中的二硫化碳(CS2)、甲硫醚(DMS)和二甲二硫醚(DMDS) 3种挥发性硫化合物分析方法.采用吹扫-捕集对水中的被测成分进行预富集,然后导入GC-MS系统中在选择离子模式(SIM)下进行检测.CS2、DMS和DMDS 3种硫化合物分别在0.03～3.42 μg/L,0.17～2.72 μg/L和0.04～3.41 μg/L范围内线性关系良好,相关系数r分别为0.9967、0.9930和0.9959;在不同的浓度下,平行测定5次后的相对标准偏差均小于6.0%;方法检出限为3.75,11.33和2.10 ng/L.     

Novel application of modified multiwalled carbon nanotubes as a solid phase extraction adsorbent for the determination of polyhalogenated organic pollutants in aqueous solution

This paper describes a novel application of pristine and chemically modified multiwalled carbon nanotubes (MWCNTs) as the packing materials for the determination of different polyhalogenated organic pollutants, pentachlorophenol, 2,4,5-trichlorophenol, 3,3′,4,4′-tetrachlorobiphenyl and 2,2′,5,5′-tetrabromobiphenyl, from aqueous solution based on solid phase extraction. The modified MWCNTs were characterized using different techniques and the results revealed the successful modification of the MWCNTs with octadecyl amine and poly(ethylene glycol), separately. Factors that maybe influence the preconcentration efficiency, such as sample flow rate, adsorbent mass, sample pH and sample volume, were studied. Desorption of the target analytes was studied using different solvents and the results showed that acetone was the best solvent for all the analytes compared with methanol and hexane. All the results indicated that the proposed method could be used for the simultaneous determination of different pollutants in environmental water samples at trace levels.     

Determination of polar analytes in aqueous matrices by purge and trap

(not readable) fully autimated purge and trap system has been developed for (not readable) detemination of volatile wine components. The proposed system consists of sampler, a purge and trap instrument, and a GC, (not readable) steps, from the uptake of the infiltrated wine from the sampler (not readable) to the printout of the intergrated chromatograms, proceed(not readable), Typical problems occurring when analyzing polar analytes by the classical purse and trap approach have been specifically addressed. The system has been desiggned to handle such difficult (not readable) analytes. Efforts have been made to improve the reproducibility and the carry-over of these analytes. The measures adopted include: thorough rinsing and subsequent conditioning of the P + T parger; elimination of matrix effects by dilution and high salt (not readable); tight specification of purge relevant parameters; split-inter-(not readable) to improve GC retention time reproducibility.