Solid-phase microextraction in combination with GC/MS for quantification of the major volatile free fatty acids in ewe cheese

This work describes a method for quantification of the major free fatty acids of ewe cheese that contribute to its distinct and strongly marked flavor. A headspace SPME method in combination with GC/MS was used for the extraction, identification, and quantification of butanoic, hexanoic, octanoic and decanoic acids in ewe cheeses. The method used for sample preparation was simple. A fiber coated with 85-microm polyacrylate film was chosen to extract the free fatty acids. To perform a reliable quantification, several factors were taken into consideration for reliable quantification, namely, (i) the influence of addition of water, of an electrolyte or of a hygroscopic salt, on the release of free fatty acids from the matrix; (ii) the linear relationship between the amount of analyte adsorbed by the SPME polymer film and the initial concentration of the analyte in the cheese sample; and (iii) the competition for adsorption by fiber. Water removal with sodium sulfate promoted a more efficient extraction of volatile free fatty acids; biases due to competition or linear range excesses were controlled by choosing the appropriate amount of sample for each ewe cheese. The method of standard additions was used with success for the quantification of free fatty acids. Calibration curves that were constructed for the major short-chain free fatty acids (butanoic, hexanoic, octanoic, and decanoic acids) spiked into cheese followed linear relationships with highly significant (p < 0.001) correlation coefficients (r > 0.999). Coefficients of variation of <7.9% indicated that the technique was reproducible. A marked increase in concentration of short-chain free fatty acids was observed during cheese ripening, ranging from 0.35 to 9.33 mg/100 g for butanoic acid, 0.363 to 4.34 mg/100 g for hexanoic acid, 0.343 to 2.0 mg/100 g for octanoic acid, and 1.291 to 3.85 mg/100 g for decanoic acid. The limits of quantification were registered at levels of parts per million. The absolute quantification of butanoic acid was also carried out by using isotope dilution assays (IDA). The levels of acid obtained with this method were similar to those obtained by the standard additions method.     

Synthesis of molecularly imprinted polymer as a sorbent for solid phase extraction of citalopram from human serum and urine

This paper describes a new method for the determination of citalopram in biological fluids using molecularly imprinted solid-phase extraction as the sample cleanup technique combined with high performance liquid chromatography. The molecularly imprinted polymers were prepared using methacrylic acid as functional monomer, ethylene glycol dimethacrylate as crosslinker, chloroform as porogen and citalopram hydrobromide as the template molecule. The novel imprinted polymer was used as a solid-phase extraction sorbent for the extraction of citalopram from human serum and urine. Effective parameters on citalopram retention were studied. The optimal conditions for molecularly imprinted solid-phase extraction consisted of conditioning with 1 mL methanol and 1 mL of deionized water at neutral pH, loading of citalopram sample (50 μg L(-1)) at pH 9.0, washing using 1 mL acetone and elution with 3 × 1 mL of 10 % (v/v) acetic acid in methanol. The MIP selectivity was evaluated by checking several substances with similar molecular structures to that of citalopram. Results from the HPLC analyses showed that the calibration curve of citalopram using MIP from human serum and urine is linear in the ranges of 1-100 and 2-120 μg L(-1) with good precisions (2.5 and 1.5 % for 10.0 μg L(-1)), and recoveries (between 82-86 and 83-85 %), respectively.     

Redox hydrogel-based amperometric bienzyme electrodes for fish freshness monitoring

This work presents the design and optimization of amperometric biosensors for the determination of biogenic amines (e.g., histamine, putrescine, cadaverine, tyramine, cystamine, agmatine, spermidine), commonly present in food products, and their application for monitoring of freshness in fish samples. The biosensors were used as the working electrodes of a three-electrode electrochemical cell of wall-jet type, operated at -50 mV vs Ag/AgCl, in a flow injection system. Two different bienzyme electrode designs were considered, one based on the two enzymes [a newly isolated and purified amine oxidase (AO) and horseradish peroxidase (HRP)] simply adsorbed onto graphite electrodes, and one when they were cross-linked to an Os-based redox polymer. The redox hydrogel-based biosensors showed better biosensors characteristics, i.e., sensitivity of 0.194 A M-1 cm-2 for putrescine and 0.073 A M-1 cm-2 for histamine, and detection limits (calculated as three times the signal-to-noise ratio) of 0.17 microM for putrescine and 0.33 microM for histamine. The optimized redox hydrogel-based biosensors were evaluated in terms of stability and selectivity, and were used for the determination of total amine content in fish samples kept for 10 days in different conditions.     

A selective optode membrane for histidine based on fluorescence enhancement of meso-meso-linked porphyrin dimer

A plasticized polymer film, poly(vinyl chloride) (PVC) incorporated with a specific porphyrin dimer, is shown to exhibit significant and analytical usefulness for optical response toward histidine. The porphyrin dimer containing a free-base porphyrin and a covalently linked metalloporphyrin is shown to be weakly fluorescent as a result of the photoinduced intramolecular electron transfer from the inner free-base porphyrin in singlet excited state to a low-spin cobalt(II). The fluorescence enhancement of the membrane by histidine is based on favorable extraction of histidine into the bulk organic membrane and complexation with the inner metallopophyrin moiety and inhibiting the electron transfer process. With the optode membrane described, histidine in a sample solution from 0.0045 to 1.53 mM can be determined. The calibration curve of the optode membrane for histidine shows a good correlation with the mathematically derived formalism and, thus, confirms the theoretically expected behavior. The sensor presented exhibits high selectivity toward histidine over several amino acids and common inorganic anions. The optical selectivity coefficients obtained for histidine over other biologically relevant amino acids and anions are shown to meet the selectivity requirements for the monitoring concentration levels of histidine in biological samples. The selective characteristic of the sensor has been discussed in the view of the coordination chemistry of metalloporphyrin.     

Selected reaction monitoring LC-MS determination of idoxifene and its pyrrolidinone metabolite in human plasma using robotic high-throughput, sequential sample injection

The generation of large numbers of samples during early drug discovery has increased the demand for rapid and selective methods of analysis. Liquid chromatography-tandem mass spectrometry (LC-MS-MS), because of its sensitivity, selectivity, and robustness, has emerged as a powerful tool in the pharmaceutical industry for many analytical needs. This work presents a high-throughput selected reaction monitoring LC-MS bioanalytical method for the determination of idoxifene, a selective estrogen receptor modulator, and its pyrrolidinone metabolite in clinical human plasma samples. The described method uses short, small-bore columns, high flow rates, and elevated HPLC column temperatures to perform LC separations of idoxifene and its metabolite within 10 s/sample. Sequential injections were accomplished with a 215/889 multiple probe liquid handler (Gilson, Inc.), which aspirates eight samples simultaneously and performs its rinse cycle parallel to sample injection, resulting in minimum lag time between injections. This high-throughput method was applied to the determination of idoxifene and its metabolite in clinical human plasma samples. Sample preparation employed liquid/liquid extraction in the 96-well format. Method validation included determination of intra- and interassay accuracy and precision values, recovery studies, autosampler stability, and freeze-thaw stability. The LOQ obtained was 10 ng/mL for idoxifene and 30 ng/mL for the metabolite. Using idoxifene-d5 as an internal standard, idoxifene showed acceptable accuracy and precision values at QC level 1 (QC1, 15 ng/mL), level 2 (QC2, 100 ng/mL), and level 3 (QC3, 180 ng/mL) (85.0% accuracy +/- 12.0% precision, 95.1 +/- 4.9%, and 90.3 +/- 4.7%, respectively). The pyrrolidinone metabolite also showed acceptable accuracy and precision values (using no internal standard for quantitation) at QC1 (60 ng/mL), QC2 (100 ng/mL), and QC3 (180 ng/mL) (104.9 +/- 14.4%, 91.1 +/- 13.0%, and 90.8 +/- 12.2%, respectively). The validated method was applied to the analysis of 613 human clinical plasma samples. An average run time of 23 s/sample (approximately 37 min/ 96-well plate or over 3,700 sample/day) was achieved. The successful validation presented indicates that rapid methods of analysis can efficiently and reliably contribute to the fast sample turnaround required for high sample number generating processes.     

Analysis of neuroactive amines in fermented beverages using a portable microchip capillary electrophoresis system

A portable microfabricated capillary electrophoresis (CE) instrument is used for the determination of neurologically active biogenic amines, especially tyramine and histamine, in fermented beverages. The target molecules are labeled on their primary amino groups with fluorescamine in a 10-min reaction, and the samples analyzed directly, producing a detailed electropherogram in only 120 s on a microfabricated glass CE device containing 21.4-cm-long separation channels. Tyramine was found mainly in red wines at <1-3.4 mg/L, while the histamine content of these samples ranged from 1.8 to 19 mg/L. The highest levels of histamine (20-40 mg/L) were found in sake. The analysis of samples drawn from grape crush through malolactic fermentation in four varieties of zinfandel red wines revealed that histamine and tyramine are produced during yeast and malolactic fermentation, respectively. Following malolactic fermentation, the histamine content in these samples ranged from 3.3 to 30 mg/L, and the tyramine content ranged from 1.0 to 3.0 mg/L. This highly sensitive and rapid lab-on-a-chip analysis method establishes the feasibility of monitoring neurologically active amine content and potentially other chemically and allergenically important molecules in our food supply.     

高效液相色谱法测定食品中姜黄素

本文研究建立了食品中姜黄素的高效液相色谱测定方法。样品中的姜黄索经乙醇：氨水（3：1）提取后,聚酰胺吸附,再经甲醇氨水洗脱、浓缩,液相色谱二级管阵列检测器检测。姜黄索标准在0．5μg／mL-50μg／mL范围内具有良好的线性,该方法回收率高,样品定量检测限（LOQ）为0．2mg／kg,可作为糖果、糕点、面制品等食品的定量检测方法。     

纳氏试剂比色法测定高浓度有机废水中氨氮预处理方法的研究

目的:建立一种测定高浓度工业有机废水中氨氮含量的纳氏试剂比色法。方法:利用干扰纳氏试剂比色反应的有机物和三氯甲烷互溶,用三氯甲烷萃取弃去消除干扰。结果:工作曲线在0.10-2.0mg/L氨氮浓度范围内线性关系良好,线性相关系数为0.9993,平均加标回收率为93.6%--105.8%,相对标准偏差小于2.58%,方法的检出限为0.029mg/L。结论:该方法操作简便、去干扰效果好、灵敏、结果可靠。     

In-tube moleculary imprinted polymer solid-phase microextraction for the selective determination of propranolol

A molecularly imprinted polymer (MIP) material was synthesized for use as an in-tube solid-phase microextraction (SPME) adsorbent. The inherent selectivity and chemical and physical robustness of the MIP material was demonstrated as an effective stationary-phase material for in-tube SPME. An automated and on-line MIP SPME extraction method was developed for propranolol determination in biological fluids. This simplified the sample preparation process and the chromatographic separation of several beta-blocker compounds. The method developed for propranolol showed improved selectivity in comparison to alternative in-tube stationary-phase materials, overcoming the limitations of existing SPME coating materials. Preconcentration of the sample by the MIP adsorbent increased the sensitivity, yielding a limit of detection of 0.32 microg/mL by UV detection. Excellent method reproducibility (RSD < 5.0%) and column reusability (> 500 injections) were observed over a fairly wide linear dynamic range (0.5-100 microg/mL) in serum samples. To our knowledge, this is the first report on the automated application of a MIP material for in-tube SPME. The method was inexpensive, simple to set up, and simplified the choice of SPME adsorbent for in-tube extraction. The approach can potentially be extended to other MIPs for the determination of a wide range of chemically significant analytes.     

Analysis of free hormone fractions by an ultrafast immunoextraction/displacement immunoassay: studies using free thyroxine as a model system

A system was developed for measuring the noncomplexed or free fraction of a hormone in serum based on the combined use of ultrafast immunoextraction with a chromatographic displacement immunoassay. This approach was tested using L-thyroxine as a model analyte. Items considered in the development of this technique included the choice of immunoassay format and the selection of conditions for removal of thyroxine's free fraction from samples without significant interference from its protein-bound fraction. The final method had an effective extraction time of 90 ms and allowed the amount of free thyroxine to be determined within 30 s after sample injection. The limit of detection was 6 pM (S/N = 3) for a 100-microL sample, and the linear response extended up to at least 100 pM. This technique gave good correlation versus reference methods when used for the determination of free thyroxine in serum samples. Advantages of this method included its speed and its ability to analyze a sample with no pretreatment other than standard filtration. The same approach could be adapted for other hormones or drugs by using appropriate antibodies and labeled analogues for such agents.     

醒脑再造胶囊中淫羊藿甙含量测定方法的研究

目的:建立醒脑再造胶囊中淫羊藿甙含量测定的方法。方法:采用超声提取样品,聚酰胺柱吸附,用HPLC法测定淫羊藿甙的含量。色谱柱为HypersilBDS(250mm×4.0mm,5μm),流动相为乙腈-水(30:70),检测波长为270nm。结果:淫羊藿甙进样量在0.06-2μg范围内线性关系良好,R=0.9996,平均回收率为95.79%,RSD=1.0%(n=9)。结论:本法重现性好、准确度高、回收率较高。     

Quantitative analysis of amoxycillin and its major metabolites in animal tissues by liquid chromatography combined with electrospray ionization tandem mass spectrometry

A sensitive and specific method for the quantitative determination of amoxycillin and its major metabolites (amoxycilloic acid, amoxycillinpiperazine-2',5'-dione) in animal tissue samples using liquid chromatography combined with positive electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) is presented. A liquid extraction using an aqueous 0.01 M potassium dihydrogenphosphate solution as the extraction solvent was performed for a preliminary sample cleanup. The extracts were further purified by a solid-phase extraction using an octadecyl (C18) column. Ampicillin was used as the internal standard. Chromatographic separation of the analytes of interest was achieved on a reversed-phase Hypersil column (100 x 3 mm i.d., dp, 5 microm), using a mixture of 9.6 mM pentafluoropropionic acid in water and acetonitrile as the mobile phase. Gradient elution was performed. To obtain as high sensitivity and selectivity as possible, the mass spectrometer was operated in the multiple reaction monitoring mode. The method was validated for the analysis of amoxycillin and its investigated metabolites in various porcine tissues, kidney, liver, muscle, and fat, according to the requirements defined by the European Community. Calibration graphs were prepared for all tissues, and good linearity was achieved over the concentration range tested (25-500 ng/g, r > or = 0.9974, and goodness of fit < or = 9.6). A limit of quantification of 25 ng/g was obtained for amoxycillin and its metabolites in all tissues, which corresponds to half the maximum residue limit for amoxycillin. Limits of detection ranged from 2.3 to 12.0 ng/g for amoxycillin and from 1.1 to 15.1 ng/g and 0.2 to 2.4 ng/g for amoxycilloic acid and amoxycillinpiperazine-2',5'-dione, respectively. The results for the within-day precision and the trueness fell within the ranges specified. The method has been successfully used for the quantitative determination of amoxycillin and its major metabolites in tissue samples from pigs medicated via the drinking water, proving the usefulness of the developed method for application in the field of residue analysis.     

Determination of parabens and triclosan in indoor dust using matrix solid-phase dispersion and gas chromatography with tandem mass spectrometry

A simple sample preparation method for the determination of four parabens and triclosan in indoor dust is presented. Analytes were extracted from the sample and isolated from interfering species using the matrix solid-phase dispersion technique. After that, they were silylated and determined by gas chromatography combined to tandem mass spectrometry (GC/MS/MS). The influence of several factors on the yield and selectivity of the extraction was evaluated in detail. Under final working conditions, samples (0.5 g) were mixed with the same amount of anhydrous sodium sulfate and dispersed on 1.25 g of C18. This blend was transferred to the top of a polypropylene cartridge containing 2 g of Florisil. After removing less polar species with 10 mL of dichloromethane, analytes were recovered using 10 mL of acetonitrile. This extract was concentrated to 1 mL, derivatized, and injected in the GC/MS/MS system. Derivatization was carried out at 45 degrees C in 5 min using 100 microL of N-methyl-N-(tert-butyldimethylsilyl) trifluoroacetamide. Quantification limits from 0.6 to 2.6 ng/g and absolute recoveries between 80 and 114% were achieved. Analysis of dust samples demonstrated the presence of the target species in indoor dust from private houses. The highest average concentration (702 ng/g) corresponded to triclosan.     

Quantitative analysis of fuel-related hydrocarbons in surface water and wastewater samples by solid-phase microextraction

Solid-phase microextraction (SPME) parameters were examined on water contaminated with hydrocarbons including benzene and alkylbenzenes, n-alkanes, and polycyclic aromatic hydrocarbons (PAHs). Absorption equilibration times ranged from several minutes for low molecular weight compounds such as benzene to 5 h for high molecular weight compounds such as benzo[a]pyrene. Under equilibrium conditions, SPME analysis with GC/FID was linear over 3-6 orders of magnitude, with linear correlation coefficients (r(2)) greater than 0.96. Experimentally determined FID detection limits ranged from ～30 ppt (w/w hydrocarbon/sample water) for high molecular weight PAHs (e.g., MW > 202) to ～1 ppb for low molecular weight aromatic hydrocarbons. Experimental distribution constants (K) were different with 100- and 7-μm poly(dimethylsiloxane) fibers, and poor correlations with previously published values suggest that K depends on the fiber coating thickness and the sorbent preparation method. The sensitivity of SPME analysis is not significantly enhanced by larger sample volumes, since increasing the water volume (e.g., from 1 to 100 mL) has little effect on the number of analyte molecules absorbed by the fiber, especially for compounds with K < 500. Water sample storage should utilize silanized glassware, since hydrocarbon losses up to 70% could be attributed to unsilanized glassware walls when samples were stored for 48 h. Hydrocarbon losses at part-per-billion concentrations also occurred with surface waters due to partitioning onto part-per-thousand concentrations of suspended solids. Quantitative determinations of aromatic and aliphatic hydrocarbons (e.g., in gasoline-contaminated water) can be performed using GC/MS with deuterated internal standard or standard addition calibration as long as the target components or standards had unique ions for quantitation or sufficient chromatographic resolution from interferences. SPME analysis gave good quantitative performance with surface waters having high suspended sediment contents, as well as with coal gasification wastewater which contained matrix organics at 10(6)-fold higher concentrations than the target aromatic hydrocarbons. Good agreement was obtained between a 45-min SPME and methylene chloride extraction for the determination of PAH concentrations in creosote-contaminated water, demonstrating that SPME is a useful technique for the rapid determination of hydrocarbons in complex water matrices.     

高效液相色谱法快速测定小麦粉中过氧化苯甲酰

目的:用高效液相色谱准确、快速测定小麦粉中过氧化苯甲酰。方法:小麦粉直接以水溶解,经振荡及超声提取,滤膜过滤后上高效液相色谱进行测定。结果:苯甲酸在0.2μg/ml～100μg/ml范围内呈良好线性,检出限为0.3mg/kg。平均回收率在94.1%～99.0%范围内。相对标准偏差小于2%。经检验,本法对CNCA能力验证剩余样品的检测结果与CNCA公布结果基本一致。结论:本法简单快捷,结果准确,重现性好,适用于小麦粉中过氧化苯甲酰的测定。     

Assessment of cellulose acetate/manganese oxide thin film as adsorbent for selective extraction of flavone

The present study depicts the efficiency of cellulose acetate/manganese oxide thin films as adsorbents for selective extraction and detection of flavone in environmental waters. The selectivity of thin films (CA/Mn-1 and CA/Mn-2) was evaluated towards several organic compounds. Based on selectivity study results, CA/Mn-2 thin film was the most selective towards flavone among other compounds. In addition, the effect of other parameters such as contact time and initial concentration of flavone was investigated to optimize adsorption conditions. The adsorption capacity of flavone was experimentally obtained as \(57.96\hbox { mg}\hbox { g}^{-1}\) and theoretically calculated from Langmuir equation as \(58.48\hbox { mg}\hbox { g}^{-1}\), which indicates the high agreement of the results. Moreover, data obtained from kinetic study suggested that the adsorption of flavone onto CA/Mn-1 phase followed a pseudo-second-order kinetic model. Finally, validation of this method has attained reasonable results for determination of flavone in real water samples.     

QuEChERS/高效液相色谱测定食品中15种多环芳烃

建立了检测食品中15种多环芳烃(PAHs)的QuEChERS/高效液相色谱分析方法。样品经正己烷超声萃取,浓缩后用乙腈溶解,采用含100 mg PSA和100 mg C18填料粉进行净化。净化后,采用高效液相色谱-荧光检测器进行分析测定。在最优化色谱条件下,15种PAHs在1.0~100μg/L范围内,线性关系良好,方法检出限(S/N=3)为0.1~0.9μg/kg,方法的定量限(S/N=10)为0.3~3.0μg/kg。回收率在65~120%,相对标准偏差(RSD)小于15%。该方法具有数据可靠、简便快速,灵敏度高,适合于食品中多环芳烃的测定。     

Determination of alkylphenols after derivatization to ferrocenecarboxylic acid esters with gas chromatography-atomic emission detection

A method is described for the rapid determination of alkylphenols in nonpolar matrixes. The alkylphenols are derivatized with ferrocenecarboxylic acid chloride so that every phenol molecule is labeled with one iron atom. The resulting esters are analyzed by gas chromatography with atomic emission detection (AED) in the iron-selective detection mode. This method utilizes the AED's low detection limit (0.05 pg/s) for iron and the high selectivity versus carbon (3.5 x 10(6)) for the detection of the alkylphenols. Because the derivatization is performed before the first step of sample preparation, the risk of analyte loss by adsorption or volatilization is minimized. The total recoveries in the lower ppm concentration range vary between 79 and 125%. The quantification of 20 C0-C3-alkylphenols in crude oils is demonstrated by analyzing a shale oil (SRM 1580) and a petroleum crude oil (SRM 1582). The complete workup is easily carried out in only 45 min/sample.     

HG-AFS测定四种禽蛋各组分中硒含量

硒元素是人体必须的重要微量元素,而禽蛋正是人们生活中获取硒元素的重要途径,准确分析禽蛋中硒含量将有助于做到科学补硒。使用混合酸湿法消解禽蛋,采用氢化物发生-原子荧光光谱法(hydride generation-atomic fluorescence spectrometry,HG-AFS)测定四种禽蛋各组分中的硒含量。通过对湿法消解条件以及HG-AFS测定禽蛋中硒含量的最佳仪器工作参数进行探讨,建立分析方法。硒标准曲线浓度在1.00~20.0μg/L时,相关系数为0.99998。方法检出限(LOD)为0.001 mg/kg,定量限(LOQ)为0.004 mg/kg(称样量为1 g,定容体积为25 mL)。样品加标回收率在94.1%~103.4%之间,相对标准偏差(RSD,n=6)在2.1%~4.6%之间。比较4种禽蛋中硒含量,从高到低依次为:鹅蛋、鹌鹑蛋、鸭蛋、鸡蛋。