RESUMO

A careful analysis of the typical devices and conditions used during hydrodynamic injection in capillary electrophoresis shows that the Hagen-Poiseuille model for the laminar flow is valid, even during the transitions of pressure. Therefore, the monitoring of pressure becomes a reliable approach to evaluate the effective injected volume, because the volume is proportional to the integral of pressure (IoP) over time. A piezoresistive sensor was used to monitor the air pressure at headspace of the sample vial. A set of 18 injections at 50 mbar and different times were used to evaluate the use of the normalization of the peak areas of the analytes by the IoP to compensate for imperfection during the injection. There was a significant decrease in relative standard deviation (RSD), and the proposed approach presented results similar to the use of internal standard. In addition, a microcontroller was used not only to monitor the pressure but also to command a peristaltic pump and a solenoid valve creating a system that dynamically controls the applied pressure and stops the injection when the desired value of IoP is reached. The system was used in a proof of concept in which different combinations of pressure and time were used: 10 mbar × 50 s, 25 mbar × 20 s, 50 mbar × 10 s, 125 mbar × 4 s, and 250 mbar × 2 s. Despite the constraints posed by the flowrates of the peristaltic pump and the solenoid valve, the microcontroller effectively conducted the injections across this extensive range of conditions, resulting in an IoP RSD of 2.7%.

RESUMO

Over the last two decades, the variable domains from heavy chain-only antibodies in camelids (nanobodies) have emerged as valuable immunoreagents for analytical and diagnostic applications. One prominent use of nanobodies is for the detection of small molecules due to their ease of production, resistance to solvents used in sample extraction, facile genetic manipulation, and small size. These last two properties make it possible to produce biotinylated nanobodies in vivo, which can be loaded in an orientated manner on magnetic beads covered with avidin, creating high-density immunoadsorbenpi twbch ""ts. The method described here details the use of nanobody-based adsorbents to concentrate small molecular weight analytes for subsequent quantitative analysis by MALDI-TOF mass spectrometry. Quantitation requires the inclusion of an internal standard (IS), a compound with properties similar to those of the analyte, enabling compensation for uneven distribution during crystallization of the MALDI-TOF matrix. Since nanobody generation against small compounds requires conjugation to carrier proteins, the same conjugation chemistry can be used to synthesize the IS. By design the IS cross reacts with the capture nanobody and can be preloaded in the immunoadsorbent, facilitating quantitative detection of the target compound.

Assuntos

Anticorpos de Domínio Único , Cadeias Pesadas de Imunoglobulinas , Separação Imunomagnética , Fenômenos Magnéticos , Anticorpos de Domínio Único/metabolismo , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz/métodos

RESUMO

In this work, a principle of flow injection analysis (FIA) was applied for sample introduction to an electrospray ionization - ion trap mass spectrometer (ESI-ITMS) with the aim to quantify chromium(III) picolinate (CrPic3) in commercial supplements by multiple reaction monitoring, and using cobalt(II) picolinate as internal standard (IS). FIA system was operated with ammonium formate 10 mmol L-1 in methanol-water (1:1, v/v) as a carrier solution at a flow rate 200 µL min-1; 100 µL injections were performed in 2-min intervals. Setting ion transitions m/z 419 â†’ 270 and 304 â†’ 260 for the analyte and IS, respectively, and 100 ms integration time, the method detection and quantification limits 12 ng g-1 and 40 ng g-1 of Cr (as CrPic3) in the air-dried powder. Acetonitrile extracts of the real-world samples presented varying from sample-to-sample chemical composition and IS efficiently compensated for ionization interferences. Mean results from triplicate analysis of four different supplements were obtained with relative standard deviation 0.1-4.0%, indicating acceptable precision. Trueness of the proposed FIA-ESI-ITMS/MS procedure was demonstrated by 95.8-108% percentage recoveries attained in the analysis of the CrPic3-spiked samples. For comparative purposes, total Cr was determined by ICP-MS. The quantitative results obtained indicate the necessity of analytical control of Cr(III) supplements commercially available and demonstrate that the proposed FIA-ESI-ITMS/MS procedure is well-suited for the determination of CrPic3 in such products.

Assuntos

Espectrometria de Massas por Ionização por Electrospray , Espectrometria de Massas em Tandem , Cromatografia Líquida de Alta Pressão , Cromo , Cobalto , Suplementos Nutricionais , Ácidos Picolínicos , Reprodutibilidade dos Testes

RESUMO

This paper presents the Outer Plug Standardization - OPS, a novel technique as an alternative for the classic internal standardization using multiple injection in capillary zone electrophoresis is proposed herein. This technique was applied in a new method for the determination of chloride, nitrate and sulfate in rainwater samples. After the injection accuracy was tested and proved to be a minor error source (average 1.26% RSD), the OPS was applied and it improved the intra-day and inter-day precision of the analytical method by 32.5% and 24.7%, respectively. Using a capillary with effective length of 23.5 cm the electrophoretic separation of the three inorganic anions could be achieved in <1 min, with detection limits of 0.05, 0.09 and 0.11 mg L-1 for chloride, nitrate and sulfate, respectively. Also, the statistical t-test was applied to the results obtained for 82 rainwater samples that were collected and analyzed applying both the method developed in this study and the official APHA 4140 method where no statistical difference was noted within a 95% confidence level.

Assuntos

Cloretos , Projetos de Pesquisa , Ânions , Calibragem , Padrões de Referência

RESUMO

In this work a simple and practical method for the determination of Pb and Ni in automotive gasoline by solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry was investigated. In the proposed method, disks of filter paper were used to pre-concentrate and store Pb, Ni and other trace elements from automotive gasoline samples. For this, a volume of sample was deposited and dried out on a filter paper disk previously adapted into a polytetrafluoroethylene mold, and then the gasoline-embedded filter paper was either cut into small pieces or pulverised and introduced directly into the graphite furnace for trace element determination. Temperature program, use of chemical modifier, chromatographic effect and volume of sample were investigated. Calibration curves using organic and inorganic standards of the analytes as well as external and internal calibration methods were evaluated. Using optimised conditions, characteristic masses and limits of detection of 6 and 11 pg, and 0.5 and 2.1 µg L-1 were found for Pb and Ni, respectively. The accuracy of the method was evaluated with spike-recovery tests and a certified reference material of wear lubricant oil. The spike-recovery tests were accomplished for 9 samples and the best results were obtained with the pulverised filter paper. A second method that employs a transversely heated filter atomiser was applied as a comparative one. The filter paper was shown to be a simple and inexpensive tool for storage and transportation of gasoline samples, and it allowed the pre-concentration of the analytes, since a larger volume of sample can be dried out on it.

RESUMO

The application of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is presented for the determination of five sulfonated azo dyes in chili powders. To circumvent problems related to spectral noise and overall poor precision, acid red 88 was used as internal standard and sample cleanup was performed via ion pairing of anionic species with benzyltributylammonium bromide (BTAB) and extraction into chloroform. The key parameters influencing analytical performance were BTAB concentration, pH of the aqueous phase, amount of sample and deposition technique, concentration of 9-aminoacridine (chemical matrix), number of instant spectra per laser shot, and the raster of laser movement. The highest sample load corresponded to 100 µL of water/methanol extract taken for extraction and the method quantification limits for sunset yellow (Y6), ponceau 2R (R5), allura red (R40), and amaranth (R2) were within the range 1.50-3.10 µg g-1 (29.0 µg g-1 for tartrazine, Y5). Two-point standard addition performed in three samples yielded percentage recoveries in the range 86.4-115%; the quantification results were consistent with those obtained by HPLC-DAD. Twelve chili powders were analyzed and the results for nine of them disagreed with information provided by the manufacturers; R40 was determined in seven products at concentrations from 32.5 ± 2.1 µg g-1 to 1125 ± 73 µg g-1; Y6 and Y5 were found at lower concentrations and in fewer samples. The MALDI-TOF MS procedure can be recommended for routine control of sulfonated azo dyes in food products as a memory-free, procedurally simple, high-throughput procedure with minimal costs of instrument operation. Outline of the proposed MALDI-TOF MS procedure.

RESUMO

In this paper, we present the advantages and limitations of the coupling of a ring-oven-based preconcentration technique and surface-enhanced Raman spectroscopy (SERS). Three different methods to promote analyte adsorption on gold nanoparticles using crystal violet as a probe molecule were assessed. The results showed significant improvements in sampling process, selectivity, sensitivity, repeatability (less than ± 10%), and detection limits (nanomolar level) using a sample volume as small as 300 µL. Finally, the standard addition method was successfully applied to the quantitative SERS detection of adenine and guanine in calf thymus DNA after ring-oven preconcentration with a calculated value of (G + C)/(A + T) close to the literature value. This work could therefore pave the way to quantifying a wide variety of biologically relevant compounds in real-world samples via the use of a biodegradable, low-cost and disposable paper platform for SERS.

Assuntos

DNA/química , Nanopartículas Metálicas , Análise Espectral Raman , Animais , Bovinos , Ouro , Propriedades de Superfície

RESUMO

Mycotoxins are secondary fungi metabolites present in foods that cause adverse effects in humans and animals. The aims of this work were to develop and validate a multi-mycotoxin method to determine the presence of aflatoxins, citreoviridin, deoxynivalenol, fumonisins ochratoxin A, zearalenone and some metabolites/derivatives in rice, maize-based products and wheat-based products, and a method to determine total fumonisins (free and bound/hidden forms) in maize-based products. The validated multi-mycotoxin method was based on extraction with acidified acetonitrile and LC-ESI+-MS/MS analysis, with LOQs ranging from 0.5 to 121µg/kg, and proved to be suitable for the multi-mycotoxin analysis in wheat, maize and rice products. Bound/hidden fumonisins were determined after extraction of the free forms using the multi-mycotoxin method, followed by a basic hydrolysis of the unextracted bound/hidden and solid-liquid extraction with low temperature purification (SLE-LTP). The hydrolysis efficiency of the bound/hidden extraction procedure was investigated by analyzing a maize reference material and showed recoveries ranging from 75% (HFB2) to 108% (HFB1). The use of isotope internal standards was crucial for mycotoxins quantification in maize meal and wheat flour, while for rice, external calibration and matrix matched curves gave satisfactory results. All 55 samples of wheat-based products analyzed were contaminated with at least one mycotoxin and 16% of 44 rice samples were also contaminated. The most prevalent mycotoxins were DON and ZON in wheat-based products.

Assuntos

Cromatografia Líquida/métodos , Grão Comestível/química , Fumonisinas/análise , Espectrometria de Massas em Tandem/métodos , Zea mays/química , Marcação por Isótopo , Micotoxinas/análise

RESUMO

The effect of oxidised fatty acids on atherosclerosis progression is controversial. Thus, our objective was to evaluate the effect of long-term consumption of weakly oxidised PUFA from flaxseed oil on oxidative stress biomarkers of LDL-receptor(-/-) mice. To test our hypothesis, mice were separated into three groups. The first group received a high-fat diet containing fresh flaxseed oil (CONT-), the second was fed the same diet prepared using heated flaxseed oil (OXID), and the third group received the same diet containing fresh flaxseed oil and had diabetes induced by streptozotocin (CONT+). Oxidative stress, aortic parameters and non-alcoholic fatty liver disease were assessed. After 3 months, plasma lipid profile, glucose levels, body weight, energy intake and dietary intake did not differ among groups. Likewise, oxidative stress, plasma malondialdehyde (MDA), hepatic MDA expressed as nmol/mg portion (ptn) and antioxidant enzymes did not differ among the groups. Hepatic linoleic acid, α-linolenic acid, arachidonic acid and EPA acid declined in the OXID and CONT+ groups. Aortic wall thickness, lumen and diameter increased only in the OXID group. OXID and CONT+ groups exhibited higher concentrations of MDA, expressed as µmol/mg ptn per %PUFA, when compared with the CONT- group. Our results suggest that ingestion of oxidised flaxseed oil increases hepatic MDA concentration and is potentially pro-atherogenic. In addition, the mean MDA value observed in all groups was similar to those reported in other studies that used xenobiotics as oxidative stress inducers. Thus, the diet applied in this study represents an interesting model for further research involving antioxidants.

Assuntos

Dieta Hiperlipídica , Gorduras na Dieta/farmacologia , Ácidos Graxos/farmacologia , Óleo de Semente do Linho/farmacologia , Malondialdeído/metabolismo , Estresse Oxidativo , Receptores de LDL , Animais , Aorta/efeitos dos fármacos , Aterosclerose/etiologia , Aterosclerose/metabolismo , Aterosclerose/patologia , Biomarcadores/metabolismo , Gorduras na Dieta/metabolismo , Ácidos Graxos/metabolismo , Linho/química , Óleo de Semente do Linho/metabolismo , Fígado/efeitos dos fármacos , Fígado/metabolismo , Masculino , Camundongos Knockout , Modelos Biológicos , Oxirredução , Receptores de LDL/genética , Receptores de LDL/metabolismo

RESUMO

Bismuth was evaluated as internal standard for Pb determination by line source flame atomic absorption spectrometry (LS FAAS), high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS) and line source graphite furnace atomic absorption spectrometry (LS GFAAS). Analysis of samples containing different matrices indicated close relationship between Pb and Bi absorbances. Correlation coefficients of calibration curves built up by plotting A(Pb)/A(Bi)versus Pb concentration were higher than 0.9953 (FAAS) and higher than 0.9993 (GFAAS). Recoveries of Pb improved from 52-118% (without IS) to 97-109% (IS, LS FAAS); 74-231% (without IS) to 96-109% (IS, HR-CS FAAS); and 36-125% (without IS) to 96-110% (IS, LS GFAAS). The relative standard deviations (n=12) were reduced from 0.6-9.2% (without IS) to 0.3-4.3% (IS, LS FAAS); 0.7-7.7% (without IS) to 0.1-4.0% (IS, HR-CS FAAS); and 2.1-13% (without IS) to 0.4-5.9% (IS, LS GFAAS).