Gas chromatography-mass spectrometry and high-performance liquid chromatography-tandem mass spectrometry in quantifying fatty acids

This critical overview covers current analytical methods and future developments in quantitative determination of fatty acids (FAs), emphasizing sample extraction, derivatization and instrumental analysis with gas chromatography/mass spectrometry (GC/MS) and high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS²). We compare the benefits and the drawbacks of these two analytical techniques.We consider the well-established GC/MS method with pre-derivatization to be a traditional technique in terms of highly standardized sample-preparation procedures, affordability and readily available library searching for compound identification. However, the complicated derivatization steps required prior to instrumental analysis with GC/MS take a long time, with loss and transformation of FAs, low recovery and poor reproducibility.HPLC/MS² without derivatization shows the benefits of simple, mild sample-processing conditions, satisfactory recovery, short running time and high selectivity and sensitivity, which may allow it to become a viable alternative to GC/MS for the analysis of FAs in the years ahead.     

Elucidation of urinary metabolites of fluoxymesterone by liquid chromatography-tandem mass spectrometry and gas chromatography-mass spectrometry

The suitability of liquid chromatography tandem mass spectrometry (LC-MS/MS) and gas chromatography mass spectrometry (GC-MS) for the elucidation of fluoxymesterone metabolism has been evaluated. Electrospray ionization (ESI) and collision induced dissociation (CID) fragmentation in LC-MS/MS and electron impact spectra (EI) in GC-MS have been studied for fluoxymesterone and two commercially available metabolites. MS(n) experiments and accurate mass measurements performed by an ion-trap analyser and a QTOF instrument respectively have been used for the elucidation of the fragmentation pathway. The neutral loss scan of 20 Da (loss of HF) in LC-MS/MS has been applied for the selective detection of fluoxymesterone metabolites. In a positive fluoxymesterone doping control sample, 9 different analytes have been detected including the parent compound. Seven of these metabolites were also confirmed by GC-MS including 5 previously unreported metabolites. On the basis of the ionization, the CID fragmentation, the accurate mass of the product ions and the EI spectra of these analytes, a tentative elucidation as well as a proposal for the metabolic pathway of fluoxymesterone has been suggested. The presence of these compounds has also been confirmed by the analysis of five other positive fluoxymesterone urine samples.     

稻谷副产品中脂肪酸的气相色谱-质谱分析

对稻谷副产品脂肪酸的组成和含量进行分析测定. 采用索氏提取法提取了稻谷副产品中的脂肪油, 再进行甲酯化处理, 利用气相色谱-质谱法对其脂肪酸组成及含量进行了分析测定. 结果表明, 从稻糠、稻叶、稻秆中鉴定出的脂肪酸分别占其总检出量的96.72%、 71.77%和92.63%, 不饱和脂肪酸含量分别为72.88%、 45.26%和66.96%.     

Analysis of steroids in environmental water samples using solid-phase extraction and ion-trap gas chromatography-mass spectrometry and gas chromatography-tandem mass spectrometry

This paper describes an improved method for the extraction and determination of three steroids, oestrone, 17beta-oestradiol, and the synthetic contraceptive steroid 17alpha-ethinyloestradiol in aqueous matrices. Samples of wastewater and environmental water were spiked with internal standards, comprising isotopically labelled analogues of the steroids to be determined. The samples were extracted using solid-phase extraction disks and the extracts were then derivatized to form tert.-butyldimethylsilyl derivatives. The derivatised steroids were determined in the final extracts by GC-MS or GC-MS-MS allowing an operational detection limit for each steroid in effluent samples of 1 ng l(-1).     

Carbohydrate profiling of bacteria by gas chromatography-mass spectrometry and their trace detection in complex matrices by gas chromatography-tandem mass spectrometry.

Bacterial cellular polysaccharides are composed of a variety of sugar monomers. These sugars serve as chemical markers to identify specific species or genera or to determine their physiological status. Some of these markers can also be used for trace detection of bacteria or their constituents in complex clinical or environmental matrices. Analyses are performed, in our hands, employing hydrolysis followed by the alditol acetate derivatization procedure. Substantial improvements have been made to sample preparation including simplification and computer-controlled automation. For characterization of whole cell bacterial hydrolysates, sugars are analyzed by gas chromatography-mass spectrometry (GC-MS). Simple chromatograms are generated using selected ion monitoring (SIM). Using total ion GC-MS, sugars can be readily identified. In more complex clinical and environmental samples, markers for bacteria are present at sufficiently low concentrations that more advanced instrumentation, gas chromatography-tandem mass spectrometry (GC-MS-MS), is preferred for optimal analysis. Using multiple reaction monitoring, MS-MS is used (replacing more conventional SIM) to ignore extraneous chromatographic peaks. Triple quadrupole and ion trap GC-MS-MS instruments have both been used successfully. Absolute chemical identification of sugar markers at trace levels is achieved, using MS-MS, by the product spectrum.     

Evaluation of gas chromatography-tandem quadrupole mass spectrometry for the determination of organochlorine pesticides in fats and oils

A gas chromatography-tandem quadrupole mass spectrometry multi-residue method for the analysis of 19 organochlorine pesticides in fats and oils has been developed. Gel permeation chromatography was employed to remove lipid material prior to GC-MS/MS analysis. Average recoveries of the pesticides spiked at 10 and 50 microg kg(-1) into fish oil, pork fat, olive oil and hydrogenated vegetable oil were typically in the range 70-110% with relative standard deviations generally less than 10%. Calculated limits of detection are between 0.1 and 2.0 microg kg(-1) and results obtained for the analysis of proficiency test materials are in good agreement with assigned values. The higher selectivity of the GC-MS/MS compared to electron capture detection and GC-MS in selective ion monitoring mode allowed unambiguous identification and confirmation of all the target pesticides at low microg kg(-1) levels in fats and oils in a single analysis.     

气相色谱-串联质谱法测定土壤中的邻苯二甲酸酯

建立了土壤中6种邻苯二甲酸酯的气相色谱-串联质谱(GC-MS/MS)分析方法。土壤样品用超声提取,以二氯甲烷-丙酮(1:1, v/v)混合溶液为提取溶剂,提取液经Florisil小柱净化后,经HP-5MS色谱柱(30 m×0.25 mm×0.25 μm)分离,利用MS/MS的多反应监测(MRM)模式进行定性和定量。结果表明本方法可对样品中的邻苯二甲酸酯进行分析,在10～1000 μg/L质量浓度范围内,线性关系良好,相关系数为0.9973～0.9976;6种邻苯二甲酸酯的相对标准偏差(RSD)不大于14.3%, 2 μg/kg和10 μg/kg两个加标水平的回收率为72.9%～106.2%; 6种目标化合物的检出限为0.1～0.5 μg/kg。该方法快速准确、背景干扰较少、分析灵敏度较高,适用于土壤样品中邻苯二甲酸酯的分析。     

Liquid chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry determination of N-methylpyrrolidinone in riverine biofilms

A rugged procedure utilizing reversed-phase liquid chromatography with positive-ion electrospray ionization mass spectrometry (LC-MS) along with tandem MS is described for the quantification and confirmation of N-methylpyrrolidinone (NMP) in methanolic extracts of riverine biofilm. The LC-MS method provided a 100-fold improvement in detection limits (2 ng g(-1) with a repeatability of 80-95% based on triplicate analyses) compared to a conventional LC-UV detection procedure and was applicable to quantitative analysis of biofilm samples with little or no clean up. Under low-energy collision induced dissociation (CID) conditions (17 V, laboratory frame of reference, with argon as the collision gas), two product-ions of the [M+H]+ ion were formed at m/z 69 [MH-CH3NH2]+ and m/z 58 [MH-CH3NCH]+ with relative abundances of 30% and 5%, respectively. These CID transitions were used to demonstrate that biofilm uptake of a photocatalytically-generated mixture of NMP was rapid once acclimation was achieved.     

Rapid identification of fatty acid methyl esters using a multidimensional gas chromatography-mass spectrometry database

A multidimensional approach for the identification of fatty acid methyl esters (FAME) based on GC/MS analysis is described. Mass spectra and retention data of more than 130 FAME from various sources (chain lengths in the range from 4 to 24 carbon atoms) were collected in a database. Hints for the interpretation of FAME mass spectra are given and relevant diagnostic marker ions are deduced indicating specific groups of fatty acids. To verify the identity of single species and to ensure an optimized chromatographic resolution, the database was compiled with retention data libraries acquired on columns of different polarity (HP-5, DB-23, and HP-88). For a combined use of mass spectra and retention data standardized methods of measurement for each of these columns are required. Such master methods were developed and always applied under the conditions of retention time locking (RTL) which allowed an excellent reproducibility and comparability of absolute retention times. Moreover, as a relative retention index system, equivalent chain lengths (ECL) of FAME were determined by linear interpolation. To compare and to predict ECL values by means of structural features, fractional chain lengths (FCL) were calculated and fitted as well. As shown in an example, the use of retention data and mass spectral information together in a database search leads to an improved and reliable identification of FAME (including positional and geometrical isomers) without further derivatizations.     

Gas chromatography-tandem mass spectrometry analysis of gabapentin in serum

A new highly sensitive analytical method for determining gabapentin [1-(aminomethyl) cyclohexaneacetic acid; Neurontin] in serum using gas chromatography/tandem mass spectrometry (GC-MS/MS) was developed. GC-MS/MS was applied to determine the levels of gabapentin in serum samples of mice at 1 and 6 h after oral or intraperitoneal treatment (300 mg/kg). At 1 h, the concentrations of the drug were 4.02 +/- 0.42 and 4.32 +/- 0.28 microg/mL in mice treated orally and intraperitoneally, respectively. At 6 h, drug levels decreased by about 66% in both groups. The method, coupling two stages of mass analysis, could be very useful in identifying the drug in complex mixtures such as blood and urine. Moreover, it is easy and rapid to perform, and sensitive enough to allow the presence of the drug to be determined at very low detection limits. It is a very reliable method for both clinical and experimental monitoring of gabapentin.     

顶空气相色谱-质谱联用法测定胶粘剂中的残余单体

建立了一种测定胶黏剂中6种丙烯酸酯和甲基丙烯酸酯类残余单体的分析方法。样品经100 ℃、30 min顶空加热后,通过DB-WAX色谱柱(30 m×0.25 mm×0.25 μm)分离和质谱选择离子模式检测,内标法定量。结果表明,6种残余单体能达到良好的分离,检出限(信噪比为3)为0.069～0.096 mg/kg,定量限(信噪比为10)为0.23～0.32 mg/kg,平均回收率为96.0%～104.6%,相对标准偏差(RSD)小于7.2%。该方法操作简便、准确、重复性好、灵敏度高,可用于胶黏剂中丙烯酸酯和甲基丙烯酸酯类残余单体的快速测定。     

Validation of a confirmatory method for the determination of melamine in egg by gas chromatography-mass spectrometry and ultra-performance liquid chromatography-tandem mass spectrometry

A sensitive and reliable method was developed and validated for detection and confirmation of melamine in egg based on gas chromatography-mass spectrometry (GC-MS) and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Trichloroacetic acid solution was used for sample extraction and precipitation of proteins. The aqueous extracts were subjected to solid-phase extraction by mixed-mode reversed-phase/strong cation-exchange cartridges. Using ultra-performance liquid chromatography and electrospray ionization in the positive ion mode, melamine was determined by LC-MS/MS, which was completed in 5 min for each injection. For the GC-MS analysis, extracted melamine was derivatized with N,O-bis(trimethylsilyl)trifluoracetamide prior to selected ion monitoring detection in electron impact mode. The average recovery of melamine from fortified samples ranged from 85.2% to 103.2%, with coefficients of variation lower than 12%. The limit of detection obtained by GC-MS and UPLC-MS/MS was 10 and 5 μg kg⁻¹, respectively. This validated method was successfully applied to the determination of melamine in real samples from market.     

Rapid discrimination of fatty acid composition in fats and oils by electrospray ionization mass spectrometry.

Fatty acids in 42 types of saponified vegetable and animal oils were analyzed by electrospray ionization mass spectrometry (ESI-MS) for the development of their rapid discrimination. The compositions were compared with those analyzed by gas chromatography-mass spectrometry (GC-MS), a more conventional method used in the discrimination of fats and oils. Fatty acids extracted with 2-propanol were-detected as deprotonated molecular ions ([M-H]-) in the ESI-MS spectra of the negative-ion mode. The composition obtained by ESI-MS corresponded to the data of the total ion chromatograms by GC-MS. The ESI-MS analysis discriminated the fats and oils within only one minute after starting the measurement. The detection limit for the analysis was approximately 10(-10) g as a sample amount analyzed for one minute. This result showed that the ESI-MS analysis discriminated the fats and oils much more rapidly and sensitively than the GC-MS analysis, which requires several tens of minutes and approximately 10(-9) g. Accordingly, the ESI-MS analysis was found to be suitable for a screening procedure for the discrimination of fats and oils.     

Simultaneous determination of 405 pesticide residues in grain by accelerated solvent extraction then gas chromatography-mass spectrometry or liquid chromatography-tandem mass spectrometry

A new method has been established for simultaneous determination of 405 pesticide residues in grain, using accelerated solvent extraction (ASE), solid-phase extraction (SPE), and GC-MS and LC-MS-MS. The method was based on appraisal of the GC-MS and LC-MS-MS characteristics of 660 pesticides, their efficiency of extraction from grain, and their purification. Samples of grain (10 g) were mixed with Celite 545 (10 g) and the mixture was placed in a 34-mL cell of an accelerated solvent extractor and extracted with acetonitrile in the static state for 3 min with two cycles at 1,500 psig and at 80°C. For the 362 pesticides determined by GC-MS, half of the extracts were cleaned with an Envi-18 cartridge and then further cleaned with Envi-Carb and Sep-Pak NH₂ cartridges in series. The pesticides were eluted with acetonitrile-toluene, 3:1, and the eluates were concentrated and used for analysis after being exchanged with hexane twice. For the 43 pesticides determined by LC-MS-MS the other half of the extracts were cleaned with Sep-Pak Alumina N cartridge and further cleaned with Envi-Carb and Sep-Pak NH₂ cartridges. Pesticides were eluted with acetonitrile-toluene, 3:1. After evaporation to dryness the eluates were diluted with acetonitrile-water, 3:2, and used for analysis. In the linear range of each pesticide the linear correlation coefficient r was equal to or greater than 0.956 and 94% of linear correlation coefficients were greater than 0.990. At low, medium, and high fortification levels, at the limit of detection (LOD), twice the LOD and ten times LOD, respectively, recoveries ranged from 42 to 132%; for 382 pesticides, or 94.32%, recovery was from 60 to 120%. The relative standard deviation (RSD) was always below 38% and was below 30% for 391 pesticides, or 96.54%. The LOD was 0.0005–0.3000 mg kg⁻¹. The proposed method is suitable for determination of 405 pesticide residues in grain such as maize, wheat, oat, rice, and barley, etc.      

气相色谱-串联质谱法测定婴儿奶粉中16种邻苯二甲酸酯类化合物

建立了气相色谱-串联质谱（GC-MS/MS）测定复杂基体婴儿奶粉中16种邻苯二甲酸酯类塑化剂的分析方法。奶粉样品以水溶解均质,乙腈提取,乙二胺-N-丙基硅烷（PSA）类型玻璃固相萃取柱净化,DB-5 MS UI气相色谱柱（30 m×0.25 mm×0.25 μm）分离,同位素稀释质谱法（IDMS）定量。比较了氧化铝/PSA和PSA两种固相萃取柱在不同洗脱条件下萃取16种塑化剂的回收率。最终选择PSA固相萃取柱,以正己烷-丙酮（60：40,v/v）作为洗脱溶剂,实现奶粉基体中16种塑化剂的净化。采用基质匹配同位素内标法定量,16种塑化剂在0.01~2.0 mg/kg范围内线性良好,线性相关系数（R²）大于0.9996,检出限和定量限分别是0.15~2.50 μg/kg和0.50~8.33 μg/kg,加标回收率为96.1%~104.0%,相对标准偏差（RSD）小于3.3%（n=5）,该方法灵敏度好、精密度高,适用于婴儿奶粉基体中16种塑化剂的痕量分析。     

Direct analysis of fatty acid profile from milk by thermochemolysis-gas chromatography-mass spectrometry

The fatty acid composition of milk is of considerable interest due to their nutritional and functional properties. Although rapid milk fat separation and transesterification procedures have been developed, the overall procedure remains time consuming, specially, for the analysis of a large number of samples. In this work, a fast and simple method for direct profiling of fatty acids from milk using thermochemolysis has been developed. This method has the capability of directly analyse fatty acids from one drop of milk without fat extraction or cleanup. Our approach for thermochemolysis is based on thermal desorption integrated with a cold trap inlet. The optimized method does not present isomerisation/degradation of polyunsaturated fatty acid and shows milk fatty acid profiles comparable to the conventional method based on fat extraction and alkaline transesterification. Overall, this method has demonstrated significant potential for high throughput analysis of fatty acids in milk.     

Comparative study of analytical methods involving gas chromatography-mass spectrometry after derivatization and gas chromatography-tandem mass spectrometry for the determination of selected endocrine disrupting compounds in wastewaters

Two GC-MS methods, based on the application of N,O-bis(trimethylsilyl)trifluoroacetamide-derivatization-GC-MS (selected-ion monitoring) and GC-MS-MS without derivatization, respectively, were optimised and applied to the determination of a group of five selected endocrine disrupting compounds (EDCs) in wastewaters. Both methods included solid-phase extraction with Oasis HLB cartridges allowing an enrichment factor for wastewater samples of 100-fold. The investigated EDCs were estrone, 17beta-estradiol, 17alpha-ethynylestradiol, 4-tert-octylphenol and bisphenol A. Results obtained from the validation studies yielded comparable results in both cases. Recoveries in spiked wastewaters at 50 ng/l were higher than 90% for all the compounds, except for 4-tert-octylphenol (75%). Repeatability and reproducibility were adequate, varying from 1.6 to 14%, except for estrone which reproducibility was 28% when the derivatization-GC-MS method was applied. Limits of detection calculated ranged from 2.5 to 27.5 ng/l with differences between both methods from 1.1 (estrone) to 10.4 (bisphenol A) times. Both methods were successfully applied to the analysis of the target compounds in sewage treatment plant influents and effluents. Traces of bisphenol A, 4-tert-octylphenol, estrone and 17beta-estradiol were detected at concentration levels ranging from 13.3 to 1105.2 ng/l.     

Simultaneous analysis of fourteen tertiary amine stimulants in human urine for doping control purposes by liquid chromatography-tandem mass spectrometry and gas chromatography-mass spectrometry

A method for the simultaneous screening and confirmation of the presence of fourteen tertiary amine stimulants in human urine by gas chromatography-mass spectrometry (GC-MS) in combination with liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed and validated. Solid phase extraction (SPE) and liquid-liquid extraction (LLE) approaches were utilized for the pre-treatment of the urine samples. The study indicated that the capillary temperature played a significant role in the signal abundances of the protonated molecules of cropropamide and crotethamide under positive ion electrospray ionization (ESI) conditions. In addition, comparison studies of two different pre-treatment approaches as well as the two ionization modes were conducted. The LODs of the developed method for all the analytes were lower than the minimum required performance limit (MRPL) as set forth in the World Anti-Doping Agency (WADA) technical document for laboratories. The human urine sample obtained after oral administration of prolintane·HCl was successfully analyzed by the developed method, which demonstrated the applicability and reliability of the method for routine doping control analysis.     

固相萃取结合超高效液相色谱-串联质谱法及气相色谱-负化学源质谱法测定人血清中的四溴双酚A、六溴环十二烷和多溴联苯醚

建立了固相萃取同时提取、净化血清中四溴双酚A(TBBPA)、α, β, γ-六溴环十二烷(HBCD)和8种多溴联苯醚(PBDEs)同系物的样本前处理方法,并结合色谱-质谱分离分析技术检测人血清样本中该类化合物的含量。试样在加入各自的同位素内标物后以甲基叔丁基醚/正己烷(1:1, v/v)混合溶剂进行萃取,再经浓硫酸去除脂肪后,以LC-Si固相萃取柱分离HBCD/TBBPA和PBDEs。采用分步检测的方式,在50 mm长BEH C18反相色谱柱上以超高效液相色谱-串联质谱(UPLC-MS/MS)的多反应监测模式(MRM)检测HBCD和TBBPA,在15 m长的毛细管柱上以气相色谱-负化学源质谱(GC-NCI/MS)的选择离子监测模式(SIM)检测PBDEs。以胎牛血清为空白基质,当HBCD、TBBPA和BDE-209的加标水平为0.5 ng/g和5 ng/g、三溴至七溴联苯醚的加标水平为0.05 ng/g和0.5 ng/g时,它们的平均加标回收率为80.3%～108.8%,相对标准偏差为1.02%～11.42%(n=5);以信噪比(S/N)为3计算,方法的检出限(LOD)为1.81～42.16 pg/g。采用该方法对实际样品进行测定,结果表明,本方法快速、准确、灵敏度高,能够满足血清中HBCD、TBBPA和PBDEs残留的同时提取及测定的要求。