Petra Bajerová

Microextraction by packed sorbent (MEPS) as a suitable selective method for L-ascorbic acid determination in beverages

In this study the modern microextraction by packed sorbent (MEPS) method followed by HPLC-UV analysis was optimised and evaluated for determination of l-ascorbic acid (AA) content in beverages. In this case 300μL of sample was passed through silica BIN (barrel insert and needle assembly) and entrapped AA was eluted by 60μL of methanol-water (10%, v/v) solution. Recovery of the proposed method for three concentration levels ranged between 97.46% and 106.88% with relative standard deviation 8.7% (low conc.), 2.49% (medium conc.) and 1.98% (high). Obtained results of AA contents in real samples were in the ranges 56.5-195.4μg/mL and 130.4-1090.0μg/mL for ice-tea and fruit juice samples, respectively. Proposed method was compared with iodometric titration and DPPH methods, but microextraction method was found to be more selective for AA determination in tested samples.

Comparison of various techniques for the extraction and determination of antioxidants in plants.

The following extraction techniques have been used for extracting antioxidants (apigenin, coumarin, esculetin, umbelliferone, bergapten, quercetin, rutin, scopoletin and xanthotoxin) from plant material: supercritical fluid extraction, pressurized liquid extraction, extraction by means of Soxhlet apparatus, ultrasonic extraction in ultrasonic bath, and by means of ultrasonic probe. The analytical method based on HPLC-UV detection for the determination of selected antioxidants was developed. For all extracts the antioxidant capacity based on the reduction of free 2,2-diphenyl-1-picrylhydrazyl radical was also determined. Comparing all results the ultrasonic probe method using 0.75 g of sample extracted by 50 mL of acetonitrile in water (30%, v/v) for 25 min at room temperature and with amplitude at 60% (equal to 90 W) without pulsation was evaluated as the best tool. The most significant indicator demonstrating this statement is the antioxidant capacity expressed as gallic acid equivalent where the ultrasonic probe method showed the best results in 10 of 16 samples. Also the operability of ultrasonic probe extraction method compared to other tested methods is more favorable.

Unremitting problems with chlorogenic acid Nomenclature: A review

Tento clanek shrnuje problematiku nazvoslovi isomerů patřicich do skupiny chlorogenových kyselin od jejich prvniho výskytu až dosud. Během desetileti bylo publikovano mnoho clanků zabývajicich se touto skupinou. Bohužel výzkumnici, kteři chtěli ziskat informace o tomto tematu, mohli být po přecteni několika clanků silně znechuceni. Kvůli postupným objevům a izolacim jednotlivých isomerů z nejrůznějsich matric a měnici se terminologii po těchto objevech jsou běžne nesrovnalosti mezi jednotlivými clanky. Přicinou těchto nesrovnalosti je hlavni sloucenina teto skupiny, a to 5-kafeoylchinova kyselina (znama jako kyselina chlorogenova) byla jako kyselina 3-kafeoylchinova opravdu nazývana před rokem 1976, kdy byla publikovana nova pravidla pro nazvoslovi. Nicmeně mnoho výzkumniků a take dodavatelů chemikalii zůstalo u použivani „pre UIPAC“ nazvoslovi a chybně nazývaji 3-kafeoylchinovou kyselinu jako kyselinu chlorogenovou, tj. hlavni substituent teto skupiny. Přestože několik praci s touto nesrovnalosti zapasi, tento problem stale přetrvava. Proto byla sepsana tato prace.

Comparison of supercritical fluid and Soxhlet extractions for the isolation of nitro compounds from soils

Supercritical fluid extraction (SFE) with CO(2), a clean and rapid alternative to conventional Soxhlet extraction, was investigated for the extraction of nitro compounds from soil samples. Quantitative extraction by SFE was accomplished at a pressure of 25 MPa and an extraction temperature of 60 degrees C, for 30 min in dynamic mode and using acetonitrile as modifier, and the results were comparable with those obtained by acetonitrile Soxhlet extraction (3 h) for all soil samples. Extracts from these two procedures were analyzed by gas chromatography coupled with mass spectrometry. Quantitative reproducibility for SFE extracts was acceptable (RSD 2-10%), and the quantity of solvent was reduced from 160 mL for Soxhlet extraction to 5 mL in the case of SFE.

Determination of 2-ethylhexyl nitrate in diesel fuel.

The aim of this study was to develop and validate fast and easily applicable GC/MS assay for the quantification of the substance that increases cetane number in diesel fuel (2-ethylhexylnitrate, 2-EHN). These requirements were fulfilled best by a headspace GC-MS assay with negative chemical ionization with methane (HS-GC/MS). Chromatographic separation is achieved using a DB5-MS capillary column after the addition of known amount of internal standard (o-nitrotoluene). The limit of detection was 0.009% v/v for 2-EHN and the limit of quantification was 0.03% v/v. The HS-GC/MS method was applied for the quantification of cetane improver in spiked diesel fuel and real diesel fuel. The method is linear over the studied range (0.03-0.3%, v/v), with satisfactory intra- and inter-assay precision, and the relative standard deviations are lower than 10%. Good accuracy is achieved with bias <10% at all levels tested.

Method validation for the determination of propellant components by Soxhlet extraction and gas chromatography/mass spectrometry.

A fast, sensitive, and accurate GC/MS method for the quantification of aliphatic nitroesters (ethylene glycol dinitrate, nitroglycerin, and triethylene glycol dinitrate) and aromatic amines (diphenylamine, 2-nitrodiphenylamine, and triphenylamine) in propellants was developed and validated. This method comprises a Soxhlet extraction step with dichloromethane, followed by separation on a capillary column MDN-5. Ionization of the analytes is carried out using electron ionization. The limit of quantification of the method was 1% w/w for aliphatic nitroesters and 0.1% w/w for aromatic amines (diphenylamine and triphenylamine). Values of repeatability and reproducibility for analyzed compounds were smaller than values of the maximum allowed tolerances of the Horwitz-equation RSD(max) and 2/3 RSD(max). Values of accuracy for selected compounds were below the acceptable threshold of 15% for all tested levels in the range of calibration curve excepting the lowest concentration of calibration curve for nitroglycerin and aromatic amines. During the validation of method, temperature instability in injection port of gas chromatograph and column was observed for 2-nitrodiphenylamine. Hence, it follows worse results of accuracy and linearity and 2-nitrodiphenylamine was not validated successfully.

On-line monitoring of in-vitro oral bioaccessibility tests as front-end to liquid chromatography for determination of chlorogenic acid isomers in dietary supplements

A novel fully automated in-vitro oral dissolution test assay as a front-end to liquid chromatography has been developed and validated for on-line chemical profiling and monitoring of temporal release profiles of three caffeoylquinic acid (CQA) isomers, namely, 3-CQA,4-CQA and 5-CQA, known as chlorogenic acids, in dietary supplements. Tangential-flow filtration is harnessed as a sample processing approach for on-line handling of CQA containing extracts of hard gelatin capsules and introduction of protein-free samples into the liquid chromatograph. Oral bioaccessibility/dissolution test assays were performed at 37.0±0.5°C as per US Pharmacopeia recommendations using pepsin with activity of ca. 749,000 USP units/L in 0.1mol/L HCl as the extraction medium and a paddle apparatus stirred at 50rpm. CQA release rates and steady-state dissolution conditions were determined accurately by fitting the chromatographic datasets, namely, the average cumulative concentrations of bioaccessible pools of every individual isomer monitored during 200min, with temporal resolutions of ≥10min, to a first-order dissolution kinetic model. Distinct solid-to-liquid phase ratios in the mimicry of physiological extraction conditions were assessed. Relative standard deviations for intra-day repeatability and inter-day intermediate precision of 5-CQA within the 5-40µg/mL concentration range were <3.4% and <5.5%, respectively. Trueness of the automatic flow method for determination of 5-CQA released from dietary supplements in gastric fluid surrogate was demonstrated by spike recoveries, spanning from 91.5-104.0%, upon completion of the dissolution process. The proposed hyphenated setup was resorted for evaluating potential differences in dissolution profiles and content of the three most abundant chlorogenic acid isomers in dietary supplements from varied manufacturers.

Optimization of focused ultrasonic extraction of propellant components determined by gas chromatography/mass spectrometry

A method for focused ultrasonic extraction of nitroglycerin, triphenyl amine and acetyl tributyl citrate presented in double-base propellant samples following by the gas chromatography/mass spectrometry analysis was developed. A face-centered central composite design of the experiments and response surface modeling was used for optimization of the time, amplitude and sample amount. The dichloromethane was used as the extractant solvent. The optimal extraction conditions with respect to the maximum yield of the lowest abundant compound triphenyl amine were found at the 20 min extraction time, 35% amplitude of ultrasonic waves and 2.5 g of the propellant sample. The results obtained under optimal conditions were compared with the results achieved with validated Soxhlet extraction method, which is typically used for isolation and pre-concentration of compounds from the samples of explosives. The extraction yields for acetyl tributyl citrate using both extraction methods were comparable; however, the yield of ultrasonic extraction of nitroglycerin and triphenyl amine was lower than using Soxhlet extraction. The possible sources of different extraction yields are estimated and discussed.

Comparison of Two Ultrasonic Systems with Different Settings for Extraction of Capsaicinoids from Chili Peppers

Abstract Two ultrasonic systems were compared with different settings for extraction of capsaicinoids (capsaicin, dihydrocapsaicin and nordihydrocapsaicin) from chili peppers. The first system was ultrasonic homogenizer using an ultrasonic probe operating at a working frequency of 20 kHz, with variable setting of power output. The second one was ultrasonic cleaner operating at a working frequency of 35 kHz, with fixed power output of 50 W. Determination of the optimum extraction procedures was performed by comparison of the extraction yields. Content of capsaicinoids was determined by high-performance liquid chromatography-mass spectrometry (HPLC-MS). Optimization studies of extractions by both ultrasonic systems were performed. Ten various real samples of chili underwent optimum extraction conditions in both ultrasonic systems. The results were compared with each other and to a conventional Soxhlet extraction. The ultrasonic methods provide the higher extraction efficiency and simple and straightforward operation. System working at higher power of ultrasound resulted in higher extraction yields. An application of ultrasonic system working at lower frequency of ultrasonic waves is slightly advantageous.