Ultrasonic extraction and LC determination of linear alkylbenzene sulfonate in plant tissues

Summary A new method has been developed for the extraction and determination of linear alkylbenzene sulfonate (LAS) in plant tissues (rice stems and leaves). It consists of methanol-ultrasonic extraction followed by clean-up with aluminum oxide, enrichment with C₁₈ solid-phase extraction column and determination by HPLC. Both efficiency and accurracy of the overall method were high, i.e. mean recovery of: 89% (84 to 93% for LAS concentrations ranging from 1 to 100 mg kg⁻¹) and repeatability of: 3% relative standard deviation for 6 replicate analyses. With a 2 g sample for analysis, LAS levels of 0.5 mg kg⁻¹ in plants could be detected with the proposed method. Further advantages were: it was less time consuming (1 h for extraction), less solvent consumption, and smaller samples (2 to 3 g) required when compared with Soxhlet extraction.     

Evaluation of eggshell membrane-based bio-adsorbent for solid-phase extraction of linear alkylbenzene sulfonates coupled with high-performance liquid chromatography

The potential of eggshell membrane (ESM) as a novel solid-phase extraction bio-adsorbent was investigated in the present study. The ESM with a unique structure of intricate lattice network showed a predominant ability to capture linear alkylbenzene sulfonates (LAS) as a model of organic pollutants by the hydrophobic interactions between ESM and LAS molecular at pH very close to the isoelectric point of ESM, which was similar to the most widely used trapping mechanism for SPE. Under the optimal conditions, the breakthrough capacities of the ESM packed cartridge for C10–C13 LAS homologues were found to be 30, 53, 50, and 43 μg g⁻¹, respectively. On the basis of high-performance liquid chromatography separation and UV detection of LAS homologues, the proposed system could respond down to 0.027 ng mL⁻¹ of LAS with a linear calibration range from 0.2 to 100 ng mL⁻¹, showing a good LAS enrichment ability of eggshell membrane biomaterial with high sensitivity, and could be successfully used for the detection of residual LAS in environmental water samples. The reproducibility among columns was satisfactory (RSD among columns is less than 10%). A comparison study with ESM, C8 and C18 as adsorbents for LAS demonstrated that ESM-based bio-adsorbent was advantageous over C8 and C18, the widely used traditional adsorbents.     

New rapid methods for determination of total LAS in sewage sludge by high performance liquid chromatography (HPLC) and capillary electrophoresis (CE)

Linear alkylbenzene sulfonates (LAS) are the most common synthetic anionic surfactant used in domestic and industrial detergents, with a global production of 2.4 × 10⁶ t year⁻¹. After use and disposal, LAS may enter the environment by one of the several routes, including by direct discharge to surface water or discharge to water from sewage treatment plants. Sewage treatment plants break down LAS only partly: some of them remain in effluent and other fraction is adsorbed in sewage solid.New and rapid methods for determination of total LAS from sewage sludge based on microwave assisted extraction and HPLC-FL and CE-DAD determination are proposed. The extraction of total LAS is carried out by using microwaves energy, an extraction time of 10 min and 5 mL of methanol. For HPLC-FL determination, mobile phase acetonitrile-water was used, comprising 60% (v/v) from 0 to 1 min and a flow rate of 1 mL min⁻¹ programmed to 100% acetonitrile between 1 and 2 min and a flow rate of 2 mL min⁻¹. The final composition was maintained for a further 5 min. The determination of total LAS by CE-DAD was performed in a phosphate buffer (10 mM, pH 9). The separation voltage was 25 kV and the temperature of the capillary was 30 °C. Injections were performed in the pressure mode and the injection time was set at 12 s. The determination of total LAS is carried out in less than 5 min. The methods did not require clean-up or preconcentration steps. Detection limit for total LAS in the sludge was 3.03 mg kg⁻¹ using HPLC-FL and 21.0 mg kg⁻¹ using CE-DAD, and recoveries were >85% using both determination methods. Concentrations of total LAS obtained using both methods were compared with the sum of concentrations of homologues LAS C-10, LAS C-11, LAS C-12 and LAS C-13 obtained using microwaves assisted extraction and HPLC-FL and CE-DAD determination.     

Determination of photodegradation and ozonation by products of linear alkylbenzene sulfonates by liquid chromatography and ion chromatography under controlled laboratory experiments

A Suntest solar simulator with arc xenon lamp was used to irradiate pure linear alkylbenzene sulfonates (LAS) standard and some commercial LAS solutions. The ozonation treatment was carried out in a pilot plant air-lift type reactor. Kinetic degradation curves were obtained showing an apparent first order reaction in both cases. Extraction and preconcentration of samples was carried out by off-line SPE using polymeric an RP-18 cartridges with recoveries varying from 77 to 93% for the LAS compounds. For LC chromatographic elution of LAS and degradation products an ion pair based on 5 mM triethylamine and 5 nM acetic acid had to the acetonitrile-water or methanol-water mobile phases. Fluorescence detection was achieved at 225 and 295 nm as excitation and emission radiation wavelength, respectively. Degradation by products were identified by liquid chromatography electrospray mass spectrometry detection (LC-ESI-MS). Ion chromatography (IC) was used to analyze refractory species such as oxalate, formate and acetate ions which were present in the treated solution even after 3 h of ozone treatment. The LAS mixture was almost totally degraded in less than 20 min using O₃/H₂O₂, the reaction being faster than in the case of catalyzed photodecomposition. TOC removal reached 84% after 3 h of ozonation process.     

Improved sample treatment for the determination of insoluble soap in sewage sludge samples by liquid chromatography with fluorescence detection

A new selective and sensitive method for the determination of insoluble fatty acid salts (soap) in sewage sludge samples is proposed. The method involves a clean up of sample with petroleum ether, the conversion of calcium and magnesium insoluble salts into soluble potassium salts, potassium salts extraction with methanol, and a derivatization procedure previous to the liquid chromatography with fluorescence detection (LC-FLD) analysis. Three different extraction techniques (Soxhlet, microwave-assisted extraction and ultrasounds) were compared and microwave-assisted extraction (MAE) was selected as appropriate for our purpose. This allowed to reduce the extraction time and solvent waste (50 mL of methanol in contrast with 250 mL for Soxhlet procedure). The absence of matrix effect was demonstrated with two standards (C_13:0 and C_17:0) that are not commercials and neither of them has been detected in sewage sludge samples. Therefore, it was possible to evaluate the matrix effect since both standards have similar environmental behaviour (adsorption and precipitation) to commercial soaps (C_10:0-C_18:0). The method was successfully applied to samples from different sources and consequently, with different composition.     

Determination of linear alkylbenzene sulfonates by ion-pair solid-phase extraction and high-performance liquid chromatography

In this paper, the potential use of multiwalled carbon nanotubes (MWCNTs) as solid phase extraction (SPE) adsorbent was evaluated for preconcentration of linear alkylbenzene sulfonates (LAS) using ion-pair (IP)-SPE with tetrabutylammonium hydroxide (TBAH). The LAS homologues present in the aqueous sample were ion-paired with TBAH and the solution was passed through the MWCNT cartridges. The analytes retained in the cartridge were eluted with methanol and the concentrated methanol extract was analysed by HPLC-UV. In order to obtain the satisfactory recovery of LAS homologues, various parameters including the type and amount of the ion-pair reagents, the desorption and enrichment conditions such as the effect of eluent and its volume, pH, the flow rate, the ultrasonic time of sample, and the volume of sample solution were systematically optimized. Under the optimal conditions, LAS homologues could be easily extracted by the proposed SPE cartridge. The favorable limits of detection (LOD) for LAS homologues were in the range from 0.02 to 0.03 μg L⁻¹, and the relative standard deviations (RSDs) were 1.55-2.54% for 10 μg L⁻¹ LAS (n = 6). The proposed method has been successfully applied for the analysis of LAS homologues in aqueous environmental samples. A comparison study with ion-pair solid extraction on MWCNTs, C8 and C18 as adsorbents for LAS demonstrated that ion pair-based solid extraction on MWCNTs adsorbent was advantageous over C8 and C18, the widely used traditional adsorbents.     

Application of probe sonication extraction for the determination of linear alkylbenzene sulfonates from sewage sludge. Comparison with other extraction methods

A new method based on probe sonication extraction (USP) prior to high performance liquid chromatography (HPLC) has been developed for the determination of linear alkylbenzene sulfonates (LAS) from sewage sludge. The optimized method was designed to be cost effective compared to existing extraction methods (ultrasonic assisted extraction, Soxhlet or pressurized liquid extraction) which may require large quantities of organic solvents, or costly instrumentation or equipment.The main factors affecting the extraction efficiency (extractant volume, ultrasounds power and extraction time) were optimized using compost sludge. The detection limit of total LAS in the sludge was 10 mg kg^− 1. The extraction of C₁₀-C₁₃ homologues is carried out using an extraction time of 7 min with 10 mL of methanol. Liquid chromatography with fluorescence (FL) detector is used for determination of LAS homologues. A mobile phase acetonitrile-water containing 0.1 M NaClO₄ (65:35) and isocratic elution was used. Compounds were eluted over 6 min at a flow rate of 1 mL/min. Polar interferences are eluted between 0 and 2 min and no purification of the samples is required prior to the final determination by high performance liquid chromatography (HPLC). The recoveries of LAS in spiked sewage sludge were between 84.0% and 97.0%, which reflect the efficiency of the method for extraction of these analytes from sewage sludge. Concentration levels found were between 11,858 mg kg^− 1 for digested sludge and 2379 mg kg^− 1 for compost sludge.     

Carboxyl modified multi-walled carbon nanotubes as solid-phase extraction adsorbents combined with high-performance liquid chromatography for analysis of linear alkylbenzene sulfonates

Recently, multi-wall carbon nanotubes (MWCNTs) as adsorbents of solid-phase extraction are attractive because they can be used for enrichment of organic compounds and metal ions at trace levels. In this study, we use the carboxyl modified multi-wall carbon nanotubes (CMMWCNTs) as adsorbents of solid-phase extraction for extraction of linear alkylbenzene sulfonates (LAS), which are widely used anion surfactant with different homologues, and detected by HPLC-UV. The effect of eluent and its volume, sample pH and flow rate, sample volume and the ultrasonic time of sample, the content of the electrolyte (NaCl) were investigated and optimized. The detection limit for LAS homologues was 0.02-0.03 μg L⁻¹ with R.S.D. (n = 6) ranging from 2.04 to 10.03%. The recoveries of LAS homologues in the spiked environmental water samples ranged from 84.8 to 106.1%. The proposed method has been applied successfully to the analysis of LAS in aqueous environmental samples, which demonstrates that CMMWCNTs-based solid-phase extraction is a precision and convenient enrichment method and can be used for analysis of LAS homologues in water samples.     

A new method for the routine analysis of LAS and PAH in sewage sludge by simultaneous sonication-assisted extraction prior to liquid chromatographic determination

Linear alkylbenzene sulphonates (LAS) and polycyclic aromatics hydrocarbons (PAH) are organic pollutants in sewage sludge which will have to be monitored in the European Union according to the third draft of a future sludge directive. In the present work, an analytical method for the simultaneous extraction of 4 LAS homologues and 16 PAH congeners in sludge from wastewater treatment plants is proposed to improve the routine analysis of these compounds in sludge samples. The method involves sonication assisted extraction, clean-up and preconcentration by solid phase extraction, and determination by high-performance liquid chromatography with ultraviolet diode array (UV-DAD) and fluorescence (FLD) detectors. Average recoveries were 87% for LAS and 76% for PAH, with relative standard deviations below 13%. Limits of quantification of LAS and PAH were in the range from 13 to 56 mg kg⁻¹ and from 80 to 650 μg kg⁻¹, respectively, when using UV-DAD. Limits of quantification of LAS and PAH were in the range 5-18 mg kg⁻¹ and from 1 to 150 μg kg⁻¹, respectively, when using FLD. The applicability of the proposed method was evaluated by the determination of these compounds in sludge from wastewater treatment plants in Seville (South Spain).     

鸡肉中11种喹诺酮类药物多残留的高效液相色谱检测

建立了用荧光检测器同时测定11种喹诺酮类药物(包括诺氟沙星、培氟沙星、环丙沙星、恩诺沙星、氧氟沙星、达氟沙星、洛美沙星、二氟沙星、沙拉沙星、恶喹酸和氟甲喹)在鸡肉中的多残留的高效液相色谱检测方法。鸡肉样品用10%三氯乙酸-乙腈(体积比为7∶3)提取两次并稀释,随后用反相固相萃取柱净化。采用Hypersil BDS-C18色谱柱分离,以乙腈和水为流动相梯度洗脱,荧光检测器用程序编程检测波长检测。11种喹诺酮类药物标准曲线的线性范围为5～1200 μg/L,相关系数大于0.998。在高、中、低三个添加水平下的回收率为56%～119%,批内相对标准偏差为0.4%～16.1%,批间相对标准偏差为1.4%～23.0%。检出限和定量限分别为1～23 μg/kg和4～40 μg/kg。该方法快速、灵敏,达到了兽药残留检测的要求。     

Multiple headspace extraction-capillary gas chromatography (MHE-CGC) for the quantitative determination of volatiles in contaminated soils

A multiple headspace extraction-capillary gas chromatographic method for the quantitative, accurate, and rapid determination of volatiles in multicontaminated soil samples has been developed. A thick film fused silica column has been used and a nine-step multiple headspace extraction (MHE) determination performed. Calibration was achieved by introducing 1 μl of a standard solution of mixed volatiles into empty headspace vials, the presence of the matrix being unnecessary in multiple headspace extraction. Accuracy of determination by MHE-CGC and a simple method employing standard additions have been compared.     

Determination of linear alkylbenzene sulfonates in water samples by liquid chromatography-UV detection and confirmation by liquid chromatography-mass spectrometry

A high-performance liquid chromatographic (HPLC) method was developed for the separation and determination of individual (C₁₀-C₁₃) linear alkylbenzene sulfonates (LAS). New sets of conditions have been established for routine analysis of individual chemical forms of four LAS surfactants, i.e. C₁₀-C₁₃ LAS. Under a condition set using a mobile phase containing 1.5 mM ammonium acetate in methanol/water 80:20 (v/v) mixture, detection limits obtained were in the range 1.5 ppb (for C₁₀ LAS) to 11.5 ppb (for C₁₃ LAS). This offers the advantages of significant improvement in resolution, short separation time and using less amount of common salt under isocratic condition. In addition, the use of simple mobile phase containing a simple low amount of salt cannot deposit at the entrance of mass spectrometric detector. The method is applicable to the simultaneous determination of LAS surfactants in various water samples. LAS surfactants presented in these samples were also successfully confirmed by using electrospray mass spectrometry.     

Determination of pharmaceuticals in soils and sediments by pressurized liquid extraction and liquid chromatography tandem mass spectrometry

The present work describes the development of a sensitive analytical method based on pressurized liquid extraction (PLE) and pre-concentration by solid-phase extraction (SPE), followed by liquid chromatography–electrospray tandem mass spectrometry (LC–ESI-MS/MS) for the determination of seventeen pharmaceuticals in soils and sediments. The method is based on sample homogenisation using Na₂–EDTA washed sand and extraction with water at 90 °C. Special emphasis was placed on the optimization of the extraction procedure to develop a green method that reduces, at a maximum, the use of organic solvents in order to eliminate matrix components during the clean-up. The proposed method was linear in a concentration range from 0.3 to 333 ng g⁻¹, with correlation coefficients higher than 0.993. Method detection (MDLs) and quantification (MQLs) limits ranged from 0.1 to 6.8 ng g⁻¹ and from 0.25 to 23 ng g⁻¹, respectively. Absolute recoveries were analyte dependent, varying between 50% and 105% at the MQL level, except for fenofibrate (40%) and diclofenac (34%). The intra-day and inter-day precision was given by RSD values from 0.7% to 7.9% and from 1.6% to 14.5%, respectively. Acetaminophen, carbamazepine, ciprofloxacin, clofibric acid, codeine, diazepam, fenofibrate, metropolol, ofloxacin and propanolol were detected at concentrations from MDL to 35.62 ng g⁻¹ in soils and sediments from marsh areas. Due to the low recoveries, results for fenofibrate and diclofenac can only be considered as semi-quantitative. The method was fully suitable for the other 15 pharmaceuticals.     

Homogeneous liquid–liquid extraction combined with high performance liquid chromatography–fluorescence detection for determination of polycyclic aromatic hydrocarbons in vegetables

In this article, homogeneous liquid–liquid extraction (HOLLE), combined with HPLC-fluorescence detector (HPLC-FLD), has been developed for the extraction and determination of polycyclic aromatic hydrocarbons (PAHs) in vegetables. ACN was used as extraction solvent for the extraction of target analytes from vegetables. When the previous extraction process was over, the ACN extract was transferred to the water-immiscible organic phase, tetrachloroethane, used as extraction solvent in HOLLE procedures. Under the optimum conditions, repeatability was carried out by spiking PAHs at concentration level of 12.5 μg/kg, the RSDs varied between 1.1 and 8.5% (n = 3). The LODs, based on S/N of 3, ranged from 0.025 to 0.25 μg/kg. Relative recoveries of PAHs from cucumber and long crooked squash samples were in the range of 72.4–104.9% and 65.5–119.3%, respectively. Compared with the conventional extraction method, the proposed method has the advantage of being quick, easy to operate, and having low consumption of organic solvent.     

Ion-pair extraction and GC-MS determination of linear alkylbenzene sulphonates in aqueous environmental samples

A GC-MS method was developed for the determination of linear alkylbenzene sulphonates (LAS) and sulphophenylcarboxylic acids (SPC) in aqueous environmental samples. LAS and SPC were isolated from aqueous samples using methylene green (MG) as ion-pair reagent and derivatised with diazomethane for their chromatographic analysis. LAS and SPC were then analysed with GC-MS in EI mode as their methyl esters. The method eliminates positive and negative interferences found by the methylene blue method and considered to be selective and sensitive for the determination of LAS and SPC in aqueous samples. The recovery of LAS was 98% with a relative standard deviation (R.S.D.) of 2.0% and the detection limit obtained from calculations by using GC-MS results based on S/N:3 was lower than 10 ppb. Obtained results revealed that the method can also be employed in the analysis of organic compounds bearing sulphate and sulphonate groups.     

High-performance liquid chromatography determination of nitrated polycyclic aromatic hydrocarbons by indirect fluorescence detection

A high-performance liquid chromatography (HPLC) method for the analysis of nitrated polcyclic aromatic hydrocarbons (NPAHs) is reported. NPAH mixtures were pre-concentrated using solid-phase extraction and well resolved on a C(18) column. They were detected using an indirect method involving the quenching of the emission from the fluorophores 5,6,7,8-tetrahydronaphthol (5,6,7,8-THN-1-OH), 7-amino-4-methyl coumarin (Coumarin 120, COU-120) and 3-hydroxy-4-(2-hydroxy-4-sulfo-1-naphthylazo)2-naphthalene carboxylic acid (Calcon carboxylic acid, CCA). Linear calibration curves were obtained in the range 1.1 x 10(-9) to 1.1 x 10(-8) mol/L. Using COU 120 as the fluorophore, the detection limit was 2.9 x 10(-10) mol/L for 1-nitronaphthalene and 2.1 x 10(-11) mol/L for 2-nitrofluorene. Recoveries of NPAHs from spiked tap water samples were between 88 and 100%.     

十六烷基三甲基溴化铵修饰P型沸石吸附水中直链烷基苯磺酸钠的研究

通过使用碱液对天然斜发沸石(Z)进行处理制得P型沸石(PZ), 再用十六烷基三甲基溴化铵(CTMAB)对Z和PZ进行修饰, 制得有机改性沸石ZC和PZC, 对比考察了ZC和PZC对直链烷基苯磺酸钠(LAS)的吸附性能. 实验结果表明, 制得的PZ硅/铝比为2, 比Z(4.85)降低58.8%; PZ的零净电荷点、 比表面积、 孔径和孔容均高于Z; 吸附平衡时间为4 h. 当pH=2时, ZC和PZC对LAS吸附量达到最高, 吸附数据符合Langmuir准二级动力学方程和Langmuir等温吸附方程, 饱和吸附量(q_m)分别为12.658和27.100 mg/g, 吸附过程主要为单分子层的化学吸附, PZC的吸附速率常数大于ZC, 具有更好的动力学性能.     

Determination of phenols in water by on-line solid-phase disk extraction and liquid chromatography with electrochemical detection

Poly(styrene-divinylbenzene) (PS-DVB) membrane extraction disks were used as sorbents for the on-line solid phase extraction of 13 phenols (nitro and chlorophenols) in river and tap waters. Determination was performed by liquid chromatography with electrochemical detection (LC-ED). An acetate buffer-acetonitrile-methanol mixture as mobile phase and amperometric detection at +1100 mV were used. High water volumes, up to 250 ml, can be preconcentrated without loss of phenols (recoveries between 80% and 100%) except for the more polar ones. Moreover, detection limits between 0.01 and 0.1 μg l⁻¹ in tap water and between 0.1 and 1.0 μg⁻¹ in river water were obtained. The method has been applied to the analysis of two river water samples.     

Simultaneous determination of eleven quinolones in animal feed by liquid chromatography with fluorescence and ultraviolet absorbance detection

A rapid and simple multi-residue procedure is described for assaying eleven quinolones (cinoxacin, ciprofloxacin, danofloxacin, difloxacin, enrofloxacin, flumequine, marbofloxacin, nalidixic acid, norfloxacin, oxolinic acid and sarafloxacin) in feeds at sub-additive levels (1–5 mg kg⁻¹). Five grams of sample were extracted by a metaphosphoric acid/acetonitrile mixture (70/30, v/v) and purified onto OASIS HLB cartridges. The determination was achieved by liquid chromatography (LC) using a GEMINI C18 analytical column both with fluorescence detection (FD) and photodiode-array (DAD). Limits of detection for each drug were in the range 0.04–0.8 mg kg⁻¹. Above the limit of quantification (LOQ), in poultry feed the recoveries were from 69 to 98% with relative standard deviations less than or equal 10%. Finally the measurement uncertainty was estimated using the bottom-up approach.     

Quantitative determination of low concentrations of DHETX m. s. in human plasma by high performance liquid chromatography with fluorescence detection

A method is described for separation of low amounts of DHETX m. s. from human plasma, based on extraction and determination by high performance liquid chromatography with fluorimetric detection.