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PubMed2006

High-throughput analysis of catechins and theaflavins by high performance liquid chromatography with diode array detection.

Increased interest in potential health-protective activities of flavonoid-rich tea has created the need to take advantage of HPLC column and system advances in order to optimize methodologies for flavonoid analysis. Two new RP-C18 methods for HPLC-DAD analysis of tea flavonoids were developed to facilitate separation of catechins within 5 min and separation of catechins and theaflavins within 10 min total analysis time. Calibration results indicate that these methods have on-column limits of detection on the order of 1-10 pmol for most tea catechins, and method replication generally resulted in intraday and interday peak area variation of <5% for catechins and <9% for theaflavins in green and black tea infusions. These new methods are therefore sensitive, reproducible, and represent a 2-4-fold reduction in HPLC analysis time from existing analytical methods. These improvements are readily achievable with commonly used HPLC equipment, thus facilitating increased sample throughput and efficiency across a broad range of experimental applications.

Biflavonoids↗
PubMed1987

Matching impedance of a nonuniform transmission line: application to cochlear modeling.

A generalization of the concept of characteristic impedance to nonuniform transmission lines leads to an impedance having a local character. This matching impedance depends on the solution of the transmission line equations, and cannot generally be obtained in analytical form. However, when the propagation properties of the line vary only slowly (as is the case in cochlear macromechanics), a convenient analytical approximation of the matching impedance can be derived by means of the Liouville-Green method.

Acoustic Impedance Tests↗
PubMed1978

New automated dye-binding method for serum albumin determination with bromcresol purple.

We describe a new automated dye-binding method for serum albumin determination with bromcresol purple (BCP) that has several advantages over an existing bromcresol green (BCG) method. The continuous-flow method is sensitive, linear, and precise, with negligible sample interaction at an analytical rate of 60 samples per hour. Unlike BCG, BCP did not react with an albumin-free serum globulin preparation or pure human transferrin solutions. Reaction with serum was instantaneous; in contrast, BCG exhibits a slow nonspecific reaction with some specimens. The specificity of BCP was demonstrated by good agreement with results of "rocket" immunoelectrophoresis (EIA) where y(BCP) = 0.95X(EIA) + 1.72. The BCG method overestimated serum albumin concentration where y(BCG) = 1.01X(EIA) + 6.77. Precipitation, which affects the BCG method, was not observed with BCP. Blank corrections were negligible, salicylate did not interfere, and bilirubin affected the method only if present in very high concentration. The method offers a solution to the poor accuracy of existing BCG methods while retaining many of their desirable features.

Autoanalysis↗
PubMed2001

Simultaneous determination of twelve tea catechins by high-performance liquid chromatography with electrochemical detection.

A high-performance liquid chromatographic method with electrochemical detection was developed for the determination of twelve tea catechins including four major catechins: epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG) and epigallocatechin gallate (EGCG); four of their epimers at the C-2 position, C, GC, CG and GCG; and four methylated catechin derivatives, epigallocatechin-3-O-(3-O-methyl)gallate, gallocatechin-3-O-(3-O-methyl)gallate, epigallocatechin-3-O-(4-O-methyl)gallate and epicatechin-3-O-(3-O-methyl)gallate. These catechins were separated on an ODS C18 reversed-phase column by isocratic elution with 0.1 M NaH2PO4 buffer (pH 2.5)-acetonitrile (87:13) containing 0.1 mM EDTA.2Na. The detection limits (S/N = 3) of these catechins were approximately 10-40 pmol ml-1 at an applied voltage of 600 mV. Extracting these catechins from tea leaf powder with H2O-acetonitrile (1:1) at 30 degrees C for 40 min inhibited the epimerization at C-2 significantly from these epicatechins compared to extraction with hot water at 90 degrees C. This analytical method is sensitive to and appropriate for the simultaneous determination of various biologically active catechins in green tea.

Catechin↗
PubMed2001

Dielectrophoretic manipulation of macromolecules: the electric field.

The use of dielectrophoresis is fast becoming a proven technique for manipulating particles and macromolecules in microfluidic systems. Here an analytic solution for the gradient in the electric field strength, delta (E . E) [corrected] produced by a two-dimensional array of parallel electodes is derived using the method of Green's functions. The boundary condition for the potential between electrodes is estimated by using a linear approximation. While the Green's function used here is somewhat different from Wang et al., J. Phys. D 29, 1649 (1996), the resulting analytic expression for the potential field is in exact agreement with their result. Selected results for equispaced electrodes with equal widths are compared with Wang et al., J. Phys. D 29, 1649 (1996). The analytic solution is employed to study the effects of electrode spacing and electrode width on the gradient in electric field intensity. Results show that the magnitude in the gradient in the electric field intensity exhibited the expected dependence on the applied voltage; however, the dependence on electrode width was found to be on the order of the electrode width squared. Results to explore the effects of electrode spacing show that as the spacing is reduced below two electrode widths the magnitude of the gradient increases exponentially.

Journal Article↗
PubMed1999

Formation and identification of azaarene transformation products from aquatic invertebrate and algal metabolism.

The metabolism of two azaarenes, viz. acridine and phenanthridine, by aquatic organisms was studied in short-term and chronic laboratory tests. The identity of metabolites observed in the test waters was investigated with different analytical methods, including HPLC, GC and hyphenated LC- or GC-MS. The Zebra mussel (Dreissena polymorpha), one green alga species (Selenastrum capricornutum) and periphyton or bacteria transformed acridine into 9[10H]-acridinone. Phenanthridine was transformed into 5[6H]-phenanthridinone by midge (Chironomus riparius) larvae. The findings indicate that closely related isomers may undergo species-specific biotransformation. It was concluded that keto-metabolites are major products in the aquatic fate of benzoquinolines, which may be overlooked in the risk assessment of parent compounds. This study illustrates the typical problems with, as well as the potency of, chromatographic methods in the elucidation of metabolic routes of organic contaminants.

Acridines↗
PubMed2006

Analysis of amino acids and carbohydrates in green coffee.

The analysis of carbohydrates and amino acids in green coffee is of the utmost importance since these two classes of compounds act as precursors of the Maillard reaction during which the colour and aroma are formed. During the course of the Maillard reaction potentially harmful substances like acrylamide or 5-hydroxymethyl-furfural accrue as well. The carbohydrates were analysed by anion-exchange chromatography with pulsed amperometric detection and the amino acids by reversed phase chromatography after derivatization with 6-amino-quinolyl-N-hydroxysuccinimidyl carbamate and fluorescence detection. Both methods had to be optimized to obtain a sufficient resolution of the analytes for identification and quantification. Sucrose is the dominant carbohydrate in green coffee with a concentration of up to 90 mg/g (mean = 73 mg/g) in arabica beans and significantly lower amounts in robusta beans (mean=45 mg/g). Alanine is the amino acid with the highest concentration (mean = 1200 microg/g) followed by asparagine (mean = 680 microg/g) in robusta and 800 microg/g and 360 microg/g in arabica respectively. In general, the concentration of amino acids is higher in robusta than in arabica.

Amino Acids↗
PubMed2003

A method of images for a penetrable acoustic waveguide.

In this paper the complex-image approximation to the reflection coefficient for water over a seabed half-space is used to generate an image representation for a bounded acoustic waveguide with an underlying layered seabed. The images are true point sources; they have constant amplitudes which are raypath independent and, in the case of a Pekeris waveguide, frequency-independent. This image representation is ideal for constructing the Green's function kernel of the boundary integral equation method for target scattering in a waveguide. The singular behavior of the Green's function for an infinitesimal source/receiver separation, possibly with the target adjacent to one of the interfaces, is modeled correctly and the image expansion has a simple analytic form which can be analytically differentiated. The method is also accurate for significant source/receiver separations, which means that it can be used in the modeling of scattering from large-sized objects and can also be used as an efficient and accurate short-range propagation model for harmonic and broadband propagation in a penetrable waveguide.

Journal Article↗
PubMed1989

pros-methylimidazoleacetic acid in rat brain: its regional distribution and relationship to metabolic pathways of histamine.

pros-Methylimidazoleacetic acid (p-MIAA; 1-methylimidazole-5-acetic acid), an isomer of the histamine metabolite, tele-methylimidazoleacetic acid (t-MIAA), is present in brain and CSF. Its relationship to histamine synthesis and catabolism was assessed in brains of rats. p-MIAA distribution in brain regions was heterogeneous although the concentrations in regions with the highest (hypothalamus) and the lowest (medulla-pons) levels differed less than four-fold. There was no significant correlation between the regional distributions of p-MIAA with those of histamine or its metabolites. pros-Methylhistidine (1 g/kg, i.p.) produced a 20-fold increase in mean levels of p-MIAA and up to a 50-fold increase in levels of pros-methylhistamine (p-MH), a putative intermediate; levels of histamine and its metabolites were unaltered. L-Histidine (1 g/kg, i.p.) or alpha-fluoromethylhistidine (100 mg/kg, i.p.), the irreversible inhibitor of histamine synthesis, did not alter the levels of p-MIAA in brain. Like the levels of t-MIAA, the levels of p-MIAA were unaltered after probenecid administration. Contrary to its effects in lowering t-MIAA levels, pargyline (75 mg/kg, i.p.) produced a slight rise in levels of p-MIAA in all regions. These findings suggest that, in brain, the metabolic pathways of histamine are independent of pathways that generate p-MIAA. Further, since brain is capable of p-MH formation, its use as an internal standard in analytical methods merits caution.

Animals↗
PubMed2003

Characterization of nonstarch polysaccharides content from different edible organs of some vegetables, determined by GC and HPLC: comparative study.

Content and composition of dietary fiber as nonstarch polysaccharides (NSP) was determined in vegetables belonging to different types of edible organs, using GC and HPLC. Samples analyzed were subterranean organs (radish and leek), leaves (celery, swiss chard, and lettuce), stalks (celery, swiss chard, and asparagus), inflorescence (broccoli), and fruits (tomato, green pepper, and marrow). The results indicate that though the monomeric profile is similar in all these samples quantitative differences were found for neutral sugars and uronic acids among samples of the same type of vegetal organ. The NSP values determined using CG method were in good agreement with HPLC method (R(2) = 0.9005). However, arabinose, mannose, and galactose plus rhamnose are more influenced by the analytical method used than the rest of the monomers in nearly all the samples analyzed. Final values of NSP depend on the method used in celery stalks, broccoli, and green pepper.

Chromatography, Gas↗
PubMed1997

Evaluation of different solid-phase traps for automated collection and clean-up in the analysis of multiple pesticides in fruits and vegetables after supercritical fluid extraction.

This study was designed to determine which combination of sorbent-trap and elution solvent provided the most efficient automated method of collection in supercritical fluid extraction (SFE), elution of analytes, and clean-up of orange, sweet potato and green bean extracts for analysis of 56 diverse pesticides using GC-ion-trap MS. The solid-phase traps evaluated consisted of octyldecylsilane (ODS), diol, Tenax and Porapak-Q, and the elution solvents compared were acetone, ethyl acetate, acetonitrile and methanol. SFE collection by bubbling into each organic solvent was also compared. Recoveries, elution volumes, limits of detection and clean-up aspects were determined for each combination of commodity, trap and solvent tested. High trapping efficiencies were achieved in each case, and acetone usually eluted the pesticides in the least volume (< 1 ml) from the traps. The few matrix components that interfered in GC-ion-trap MS continued to interfere in all trap/solvent pairs, and limits of detection were independent of trap/solvent combination. The use of the ODS trap and acetone elution solvent gave the most consistently high recoveries of the traps and solvents tested.

Autoanalysis↗
PubMed2005

[Determination of nine life elements in brick tea by ICP-AES].

ICP-AES was used for the direct determination of nine life elements (Ca, Mg, K, Al, P, Cu, Zn, Fe and Mn) in brick tea. The RSDs of the method were between 2.11% and 8.68%, and the analytical results of the tea reference samples were consistent with the certified values. The method was simple and accuracy. The analytical results of brick tea were compared with those of the ordinary leaf tea (green tea, scent tea and oolong tea). The Al, Fe, Mn, Ca and Mg contents of brick tea were about 5.78, 3.26, 2.19, 2.11 and 1.64 times higher than those of the ordinary leaf tea respectively. The P, K, Zn and Cu contents of brick tea were 48.70%, 85.68%, 78.19% and 98.78% times lower than those of the ordinary leaf tea respectively.

Aluminum↗
PubMed2000

Quantitative analysis of tyrosinase transcripts in blood.

BACKGROUND: Tyrosinase is an enzyme unique to pigment-forming cells. Methods using this transcript for detection of melanoma cells in blood have given divergent results. Quantitative analytical procedures are therefore needed to study the analytical performance of the methods. METHODS: Mononucleated cells were isolated by Percoll centrifugation. RNA was isolated by each of three methods: Ultraspec(TM)-II RNA isolation system, FastRNA(TM) GREEN Kit, and QIAamp RNA Blood Mini Kit. cDNA was synthesized using random hexamer primers. A tyrosinase-specific product of 207 bp was amplified by PCR. As an internal standard (and competitor) we used a 207-bp cDNA with a base sequence identical to the tyrosinase target except for a 20-bp probe-binding region. The PCR products were identified by 2, 4-dinitrophenol (DNP)-labeled probes specific for tyrosinase (5'DNP-GGGGAGCCTTGGGGTTCTGG-3') and internal standard (5'DNP-CGGAGCCCCGAAACCACATC-3') and quantified by ELISA. RESULTS: The calibration curves were linear and had a broad dynamic measuring range. A detection limit (2 SD above zero) of 48 transcripts/mL of blood was obtained from a low control. The analytical imprecision was 50% and 48% at concentrations of 1775 and 17 929 transcripts/mL (n = 12 and 14, respectively). With the cell line SK-Mel 28 added to blood and RNA extracted with the Ultraspec, Fast RNA, and QIAamp RNA methods, we found (mean +/- SD) 1716+/-1341, 2670+/-3174, and 24 320+/-5332 transcripts/mL of blood. Corresponding values were 527+/-497, 2497+/-1033, 14 930+/-1927 transcripts/mL of blood when the cell line JKM86-4 was added. One high-risk patient was followed by repeated analysis of tyrosinase transcripts in blood. The melanoma marker 5-S-cysteinyldopa in serum and urine was within reference values, but tyrosinase mRNA was slightly increased (120-168 transcripts/mL of blood). The tyrosinase mRNA increased to 1860 transcripts/mL concomitant with the increase in 5-S-cysteinyldopa; later a spleen metastasis was found. CONCLUSIONS: The results obtained with different RNA extraction methods illustrate the importance of quantitative methods for validation of methods. The use of QIAamp RNA improved the extraction efficiency considerably. Data from a case study suggest the assay is suitable in the follow-up of patients with high risk of developing metastases.

Cell Line↗
PubMed1995

Determination of benzoic and sorbic acids in packaged vegetable products. Comparative evaluation of methods.

Three analytical methods for determining sorbic and benzoic acids in various packaged vegetable products were evaluated, with special attention being paid to green olives. Two of these methods used a simple, isocratic, reversed-phase HPLC technique for separating and detecting the preservatives, but differed in the preparation of the sample (extraction with 60% methanol or steam distillation). The third method was based on separation by steam distillation and determination of the acids in the distillate by spectrophotometry. For the olives, while this method proved to be excellent (total error < 25%) for high concentrations (> 100 ppm), the HPLC methods were more efficient for the whole range of concentrations studied (5-500 ppm). Both HPLC methods had detection limits of approximately 1 ppm for the two preservatives. With other sample matrices (tomatoes, cucumbers, caperberries, silver-skinned onions and hot peppers), the three methods proved to be excellent for high concentrations of preservatives (500 ppm), but at low levels (20 ppm), the spectrophotometric method and the HPLC method with extraction by 60% methanol proved to be unacceptable (total error > 50%) in some cases.

Benzoates↗
PubMed2004

Monitoring multi-class pesticide residues in fresh fruits and vegetables by liquid chromatography with tandem mass spectrometry.

A new analytical method was developed using liquid chromatography with tandem mass spectrometry for the routine analysis of 31 multi-class pesticide residues and applied to approximately 50 fresh fruit and vegetable samples (green bean, cucumber, pepper, tomato, eggplant, watermelon, melon and zucchini). Extraction of the pesticides with ethyl acetate was carried out. The optimal ionisation conditions were selected for each pesticide in the same run. The procedure was validated and the values of some merit figures, such as recovery, precision, linear range, detection limit and quantification limit for each pesticide were calculated together with its calculated expanded uncertainty (U). The average recoveries in cucumber obtained for each pesticide ranged between 74 and 105% at two different fortification levels (n = 10 each) that ranged between 9 and 250 ng g(-1) (depending on the pesticide). The uncertainty associated to the analytical method was lower than 23% for all compounds tested. The calculated limits of detection and quantitation were typically <1 ng g(-1) that were much lower than the maximum residue levels established by European legislation.

Capsicum↗