Microwave-accelerated derivatization prior to GC-MS determination of sex hormones

A new microwave-accelerated derivatization method was developed for rapid determination of 13 natural sex hormones in feeds. Sex hormones were isolated from the sample matrix by ultrasonic extraction, followed by solid-phase extraction, derivatized under microwave irradiation, and then analyzed directly by gas chromatography-mass spectrometry (GC-MS) in selective ion monitoring (SIM) mode. The key parameters affecting derivatization efficiency, including microwave irradiation time, microwave power, and reaction solvent were studied. Under microwave power of 360 W and microwave irradiation for 3 min, 13 natural sex hormones were simultaneously derivatized using heptafluorobutyric acid anhydride (HFBA) as derivatization reagent. This method was applied to the determination of 13 natural sex hormones in different feed samples, and the obtained results were compared with those obtained by the traditional thermal derivatization. The recoveries from 58.1 to 111% were obtained at sex hormone concentrations of 10-300 μg/kg with RSDs ≤12.0%. The results showed that the proposed method was fast, simple, efficient and can be applied to the determination of 13 natural sex hormones in different feed samples.     

类固醇类环境内分泌干扰物羟基衍生化研究

采用气相色谱-质谱联用技术(GC-MS),以N,O-双三甲基硅基三氟乙酰胺为衍生化试剂,系统研究了4种类固醇类环境内分泌干扰物雌酮(E1)、17β-雌二醇(E2)、雌三醇(E3)、17α-乙炔基雌二醇(EE2)的羟基衍生化行为,考察了BSTFA用量、衍生化温度和时间对类固醇类环境内分泌干扰物衍生化效果的影响以及衍生化产物的稳定性、标准曲线、仪器检出限等,并对衍生化产物特征碎片离子的裂解机理进行了解释.结果表明:对于100 μL 0.01 g/L标准混合溶液,BSTFA的最佳用量为25 μL;衍生化过程不需要加热,常温下(20 ℃)下反应10 min就可取得最佳的衍生化效果;衍生化产物的稳定性较好,在-20 ℃下放置48 h,相对响应因子RRF基本没有降低.在优化的实验条件下,各待测物具有良好的线性相关性,E1和E2的检出限为0.3 μg/L,EE2和E3的检出限为5 μg/L.     

Solid-phase microextraction with on-fiber silylation for simultaneous determinations of endocrine disrupting chemicals and steroid hormones by gas chromatography-mass spectrometry

Based on solid-phase microextraction (SPME) and on-fiber silylation, a method for simultaneous determinations of exogenous endocrine disrupting chemicals (EDCs) and endogenous steroid hormones in environmental aqueous and biological samples by gas chromatography-mass spectrometry (GC-MS) was developed. The selected target compounds were: octylphenol (OP), technical grade nonylphenol (t-NP), diethylstilbestrol (DES), dehydroisoandrosterone (DEHA), estrone (E1), 17beta-estradiol (E2), testosterone (T) and pregnenolone (PREG). The optimization of operating conditions influencing the performances of SPME and derivatization were studied in detail. The average correlation coefficient of the calibration curves of the target compounds was 0.9968 and the linear ranges of most compounds spanned over three orders of magnitude. The LOD/(LOQ) values of the target compounds in river water and blood serum were in the range of 0.002-0.378/(0.008-1.261) microg L(-1) and 0.004-0.474/(0.013-1.579) microg L(-1), respectively, which were a bit higher than those in the pure water due to matrix effects. The developed method was applied to the determinations of target compounds in real samples. Exogenous OP, t-NP and DES were at 0.15, 4.67 and 0.02 microg L(-1) in river water and 3.21, 12.17 and 0.15 microg L(-1) in fish blood serum. Natural steroid hormones E1, E2 and T were at 0.18, 0.10 and 5.55 microg L(-1) in river water, and in female fish serum, E1, E2 and PREG were at 1.61, 1.08 and 4.58 microg L(-1), respectively. The proposed SPME method was compared with traditional SPE procedure and the results found using both methods were in the same order of magnitude and both are quite agreeable.     

Microemulsion electrokinetic chromatography: an application for the simultaneous determination of suspected fragrance allergens in rinse-off products

The feasibility of microwave-accelerated derivatization for capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection was evaluated. The derivatization reaction was performed in a domestic microwave oven. Histidine (His), 1-methylhistidine (1-MH) and 3-methylhistidine (3-MH) were selected as test analytes and fluorescein isothiocyanate (FITC) was chosen as a fluorescent derivatizing reagent. Parameters that may affect the derivatization reaction and/or subsequent CE separation were systematically investigated. Under optimized conditions, the microwave-accelerated derivatization reaction was successfully completed within 150 s, compared to 4-24 h in a conventional water-bath derivatization process. This will remarkably reduce the overall analysis time and increase sample throughput of CE-LIF. The detection limits of this method were found to be 0.023 ng/mL for His, 0.023 ng/mL for 1-MH, and 0.034 ng/mL for 3-MH, respectively, comparable to those obtained using traditional derivatization protocols. The proposed method was characterized in terms of precision, linearity, accuracy and successfully applied for rapid and sensitive determination of these analytes in human urine.     

Dehydration of sodium carbonate monohydrate with indirect microwave heating

In this study, dehydration of sodium carbonate monohydrate (Na₂CO₃·H₂O) (SCM) in microwave (MW) field with silicon carbide (SiC) as an indirect heating medium was investigated. SCM samples containing up to 3% free moisture were placed in the microwave oven. The heating experiments showed that SCM is a poor microwave energy absorber for up to 6 min of irradiation at an 800 W of microwave power. The heat for SCM calcination is provided by SiC which absorbs microwave. The monohydrate is then converted to anhydrous sodium carbonate on the SiC plate by calcining, i.e. by removing the crystal water through heating of the monohydrate temperatures of over 120 °C. The calcination results in a solid phase recrystallization of the monohydrate into anhydrate. In the microwave irradiation process, dehydration of SCM in terms of indirect heating can be accelerated by increasing the microwave field power.     

Microwave-accelerated derivatization processes for the determination of phenolic acids by gas chromatography-mass spectrometry

A rapid method for the derivatization of phenolic antioxidants using microwave irradiation has been developed. Six antioxidatively active phenolic components of wines and fruits, namely gallic acid, gentisic acid, vanillic acid, caffeic acid, ferulic acid and p-coumaric acid were used in the model study. The solution of phenolic acids was evaporated to dryness on a rotary evaporator followed by further drying under microwave irradiation (600 W, 30 s). The resultant residue was dissolved in pyridene and treated with bis(trimethylsilyl)acetamide while irradiated by microwave using high power for 30 s. Controlled reaction was carried out employing bis(trimethylsilyl)trifluoroacetamide under conventional heating for 30 min. The trimethylsilyl derivatives were identified and quantified on a gas chromatography/mass selective detector. The mass spectral fragmentation patterns of the derivatives obtained by microwave irradiation were identical to those prepared by heating. The yields of microwave-assisted silylation were comparable to those from conventional heating. The rsd were less than 8% for six replicates. The linearity in wine matrix was nearly perfect. This method is a useful protocol to examine the phenolic constituents in wines and agricultural products.     

微波消解同时衍生化GC-MS法测定血浆中脂肪酸的研究

研究了利用微波能对样品进行加热, 以Ｈ２ＳＯ４ － 甲苯－ 甲醇体系作衍生化试剂, 在消化的同时对血浆中的脂肪酸进行衍生化, 然后用ＧＣ－ ＭＳ 法测定血浆中脂肪酸。 对微波功率、微波加热时间、消解及衍生化试剂等条件进行了优化, 测定结果较好。该法整个消化及衍生化过程只需２ ｍｉｎ , 与传统方法相比大大缩短了实验操作时间, 特别适用于大量样品的测定。     

Investigation of the species-specific degradation behaviour of methylmercury and ethylmercury under microwave irradiation

The degradation behaviour of methylmercury (MeHg) under microwave irradiation is investigated, as is the (different) degradation behaviour of ethylmercury (EtHg) under similar irradiation. A simple and highly sensitive SPME-GC-pyrolysis-AFS system was used to analyse the aqueous MeHg and EtHg standard solutions after derivatization with sodium tetraphenylborate (NaBPh₄). Samples were irradiated in a microwave digester at microwave powers ranging from 20 to 160 W for durations of 2 to 10 min. The different tolerances towards microwave treatment of the two organomercury species were evident. Practically no degradation was experienced for MeHg for up to 8 minutes of irradiation at 120 W or for up to 4 minutes at 160 W. Significant analyte loss was observed for EtHg after 2 minutes at 40 W of microwave power. Awarded a Poster Prize on the occasion of the European Winter Conference on Plasma Spectrochemistry, February 2005, Budapest, Hungary     

An evaluation of microwave-assisted derivatization procedures using hyphenated mass spectrometric techniques

The potential of microwave-assisted derivatization techniques in systematic toxicological analysis using gas chromatography coupled with mass spectrometry (GC–MS) was evaluated. Special emphasis was placed on the use of dedicated microwave reactors incorporating online temperature and pressure control. The use of such equipment allowed a detailed analysis of several microwave-assisted derivatization protocols comparing the efficiency of microwave and conventional heating methods utilizing a combination of GC–MS and liquid chromatography coupled with mass detection (LC–MS and LC–MS/MS) techniques. These studies revealed that for standard derivatization protocols such as acetylation (exemplified for codeine and morphine), pentafluoropropionylation (for 6-monoacetylmorphine) and trimethylsilylation (for Δ⁹-tetrahydrocannabinol) a reaction time of 5 min at 100 °C in a microwave reactor was sufficient to allow for an effective derivatization. Control experiments using standard operating procedures (30 min at 60 °C conventional heating) indicated that the faster derivatization under microwave irradiation is a consequence of the higher reaction temperatures that can rapidly be attained in a sealed vessel and the more efficient heat transfer to the reaction mixture applying direct in core microwave dielectric heating. The results suggest that microwave derivatization procedures can significantly reduce the overall analysis time and increase sample throughput for GC–MS-based analytical methods.     

Microwave-assisted synthesis of 2-amino and 2-azetidinonyl 5-(2-benzoyl-phenoxymethyl) 1,3,4-oxadiazoles

A simple high yielding method for the integration of heterocyclic rings viz. 1,3,4-oxadiazole and azetidin-2-one at the benzophenone nucleus has been developed starting from substituted 2-hydroxybenzophenones, and by using mild conditions, wet solid surface, and microwave irradiation. A comparison of this microwave-accelerated reaction with conventional heating condition is also illustrated. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 15:37–42, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10210     

Determination of endogenous and synthetic glucocorticoids in human urine by gas chromatography-mass spectrometry following microwave-assisted derivatization

A complete screening and confirmation analytical method for the direct determination of six endogenous (cortisol, cortisone, deoxycorticosterone, tetrahydrocortisol, tetrahydrocortisone, tetrahydro-S) and 17 synthetic (amcinonide, betamethasone, desoximethasone, dexamethasone, fludrocortisone, flumethasone, flunisolide, flucinolone acetonide, flucinonide, fluprednisolone, flurandrenolide, fluorometholone, 6-methylprednisolone, prednisolone, prednisone, triamcinolone, triamcinolone acetonide) glucocorticoids in human urine by gas chromatography with mass spectrometric detection (GC-MS) is presented.The analytical technique comprises a pre-treatment procedure and the instrumental analysis of the trimethylsilyl (TMS) derivatives, performed by GC-MS (quadrupole) with electron impact (EI) ionization. The derivatization yields obtained by two different derivatizing mixtures, namely N-methyl-N(trimethylsilyl)trifluoroacetamide (MTSFA):NH₄I:dithioerythritol (DTE) 1000:2:4 (usually indicated as TMSiodine); and N-trimethylsilylimidazole (TMSim):N,O-bis(trimethylsilyl)acetamide (BSA):trimethylchlorosilane (TMCS) 3:3:2, both under direct thermal heating and with microwave (MW) irradiation, were evaluated, also as a function of the temperature, of the MW power and of the incubation time.The highest yields of the derivatization process were obtained, for most of the compounds here considered, by a two-step procedure: a microwave-assisted derivatization stage (40 min in a microwave oven at 900 W emitted power), followed by a traditional heat transfer derivatization (1.5 h in a thermostated bath at 70 °C) with the derivatization mixture TMSim:BSA:TMCS 3:3:2. In these operating conditions, diagnostic EI-MS spectra of all considered glucocorticoids were obtained. Limits of detection (LOD) of synthetic glucocorticoids in urine ranged from 3 to 25 μg/l. The effectiveness of the method for the determination of glucocorticoids in urine was evaluated on spiked urine samples and on real samples obtained from patients under pharmacological treatment with synthetic glucocorticoids.Apart from the clinical monitoring of glucocorticoids in urine, the method can be applied as a complete screening + confirmation analytical protocol in antidoping tests for the detection of illicit administration of glucocorticoids by the athletes.     

Ionic liquid-based microwave-assisted dispersive liquid-liquid microextraction and derivatization of sulfonamides in river water, honey, milk, and animal plasma

The ionic liquid-based microwave-assisted dispersive liquid-liquid microextraction (IL-based MADLLME) and derivatization was applied for the pretreatment of six sulfonamides (SAs) prior to the determination by high-performance liquid chromatography (HPLC). By adding methanol (disperser), fluorescamine solution (derivatization reagent) and ionic liquid (extraction solvent) into sample, extraction, derivatization, and preconcentration were continuously performed. Several experimental parameters, such as the type and volume of extraction solvent, the type and volume of disperser, amount of derivatization reagent, microwave power, microwave irradiation time, pH of sample solution, and ionic strength were investigated and optimized. When the microwave power was 240 W, the analytes could be derivatized and extracted simultaneously within 90 s. The proposed method was applied to the analysis of river water, honey, milk, and pig plasma samples, and the recoveries of analytes obtained were in the range of 95.0-110.8, 95.4-106.3, 95.0-108.3, and 95.7-107.7, respectively. The relative standard deviations varied between 1.5% and 7.3% (n=5). The results showed that the proposed method was a rapid, convenient and feasible method for the determination of SAs in liquid samples.     

微波消解衍生化气相色谱-质谱法测定鲨鱼软骨中的脂肪酸

 研究了用微波技术消解衍生化气相色谱 质谱法 (GC MS)快速测定鲨鱼软骨中脂肪酸的分析方法。用正交设计试验优化消解衍生化条件 ,以盐酸 甲醇 (体积比为 1∶4)体系作消解衍生化溶液 ,在 60 0W微波功率作用下加热 4min进行样品的前处理 ,将样品的消解、脂肪酸的衍生化及脂肪酸甲酯的萃取融于一体。方法具有灵敏度高、省时、省试剂、操作方便等特点。该法适用于大批量固体样品中脂肪酸的测定。     

Microwave-assisted high-throughput derivatization techniques utilizing silicon carbide microtiter platforms

Parallel microwave-assisted gas chromatography (GC) derivatization protocols utilizing a silicon carbide (SiC)-based microtiter plate platform fitted with screw-capped GC vials were developed. For three selected standard derivatization protocols such as acetylation (exemplified for morphine), pentafluoropropionylation (for 6-monoacetylmorphine) and trimethylsilylation (for Δ⁹-tetrahydrocannabinol) complete derivatization was achieved within 5 min at 100 °C in a dedicated multimode microwave instrument using online temperature monitoring. Microwave irradiation leads to rapid and homogeneous heating of the strongly microwave-absorbing SiC plate, with minimal deviations in the temperature recorded at different positions of the plate. The current platform allows the simultaneous derivatization of 80 reaction mixtures under strictly controlled temperature conditions. Similar results can also be obtained using a standard hotplate as heating source, although heating to the target temperature of 100 °C is slightly slower. The results demonstrate that parallel microwave derivatization procedures can significantly reduce the overall analysis time and increase sample throughput for GC–MS-based analytical methods.     

Rapid determination of volatile constituents in safflower by microwave distillation and simultaneous solid-phase microextraction coupled with gas chromatography-mass spectrometry

In this paper, microwave distillation and solid-phase microextraction coupled with gas chromatography-mass spectrometry (MD-SPME/GC-MS) was developed for the analysis of essential components in safflower. Using the MD-SPME technique, the isolation, extraction and concentration of volatile compounds in safflower were carried out in only one step. Some parameters affecting the extraction efficiency such as SPME fiber coating, microwave power, irradiation time and the volume of water added were optimized. The optimal experiment parameters obtained were: 65 microm CW/DVB SPME fiber, a microwave power of 400 W, an irradiation time of 3 min and water volume of 1 mL. The proposed method has been compared with conventional steam distillation (SD) for extraction of essential oil compounds in safflower. Using MD-SPME followed by GC-MS, 32 compounds in safflower were separated and identified, which mainly included paeonol, alpha-asarone, beta-asarone, 1-methyl-4-(2-propenyl)-benzene and diethenyl-benzene, whereas only 18 compounds were separated and identified by conventional SD followed by GC-MS. The relative standard deviation (R.S.D.) values of less than 10% show that the proposed method has good reproducibility. The results show that MD-SPME/GC-MS is a simple, rapid, effective method for the analysis of volatile oil components in safflower.     

Comparison between the conventional method of extraction of essential oil of Laurus nobilis L. and a novel method which uses microwaves applied in situ, without resorting to an oven

A novel microwave method has been applied to the hydrothermal extraction of essential oil from plants. An insulated microwave coaxial antenna was introduced inside a 1000 ml glass flask containing dry Laurus nobilis L. leaves and tap water. Microwave power up to 800 W at 2450 MHz was emitted in continuous wave regime (CW) or in pulsed regime (PR) at 8 kW peak power. Stirring with a magnetic bar and a Clevenger refrigerator connected to the flask enabled to complete the extraction in 1 h. The results of the in situ microwave extraction were compared with those obtained by heating the same reactor with a conventional electric mantle by gas chromatography-mass spectrometry (GC-MS) analysis. Differences were observed both in the composition of the essential oil and from the energetic point of view. The essential oil obtained with microwave (MW) methods contained substantially higher amounts of oxygenated compounds and lower amounts of monoterpenes than conventional method. The in situ microwave heating is safe and versatile; it presents time and energy saving advantages, and therefore it can be considered useful also for industrial applications.     

甘氨酸母液脱色活性炭的微波法再生研究

脱色甘氨酸母液的废活性炭,是一类吸附有有机胺类聚合物且难以再生的危险固体废弃物。本文探索性地开展了微波法再生脱色甘氨酸母液废活性炭的研究,考察了活性炭在微波炉中的放置方式、含水率以及微波反应条件等对活性炭再生率和炭损率的影响,分别采用红外光谱法、BET法对活性炭进行了分析表征。实验结果表明,在功率640 W、反应时间8 min的条件下,废活性炭的再生率达99%、综合再生率达59.0%,对再生活性碳进行红外光谱分析表明,在微波功率大于480 W后,微波辐射能有效去除废活性炭中的有机物;在微波功率800W条件下,再生活性炭的BET比表面积由废活性炭的128.15 m2/g提高到1398.5437 m2/g,已达到新鲜活性炭的性能。     

Efficient synthesis of functionalized pyrimidones via microwave-accelerated rearrangement reaction

An efficient synthesis of functionalized pyrimidones via microwave-accelerated rearrangement reaction of amidoxime DMAD adducts is described. In most cases, the pyrimidone formation was furnished in reasonable yield after 2 min of microwave irradiation.     

微波辐射活性炭负载磷钨酸催化合成季戊四醇双缩酮(醛)

在微波辐射下，以活性炭负载磷钨酸为催化剂，不用溶剂，合成了8种季戊四醇双缩酮（醛），以环己酮与季戊四缩的缩合为模型反应进行优化，其优化反应条件为：季戊四醇2．0g，催化剂0．3g，环己酮4．0mL，微波输出功率600W，辐射时间3min，产率达95．4％，该条件下的反应速度是常规加热反应速度的30倍，所得产物经元素分析，IR和1H NMR表征。     

Fast Diagnosis of Neonatal Phenylketonuria by Gas Chromatography-Mass Spectrometry Following Microwave-Assisted Silylation

Phenylketonuria (PKU) is a fairly common autosomal recessive disease. Phenylalanine (Phe) and tyrosine (Tyr) are the biomarkers of PKU, and it can be diagnosed by the measurement of Phe and Tyr in neonatal blood samples. A fast diagnostic procedure for neonatal PKU has been developed using microwave-assisted silylation followed by gas chromatography-mass spectrometry. Amino acids extracted from neonatal blood samples are rapidly derivatized with N, O-bis(trimethylsilyl)-trifluoroacetamide under microwave irradiation; the derivatives are then analyzed by GC-MS. The silylation conditions have been optimized, and the method validated for linear range, detection limit, precision and recovery. The proposed method is linear from 20 to 800 µM, detection limit is less than 0.35 µM, relative standard deviation (RSD) is less than 9.0%, and recoveries of 87% and 83% were obtained for Phe and Tyr. The proposed method was tested by the determination of Phe and Tyr in blood spots from eight PKU-positive neonates and twelve control neonates. Microwave irradiation considerably accelerates the derivatization reaction of amino acid with BSFTA, and shortens the whole analysis time. Microwave-assisted silylation coupled to GC-MS is a powerful tool for fast screening of neonatal PKU.