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PubMed1987

High-performance liquid chromatography of amino acids, peptides and proteins. LXXIII. Investigations on the relationships between molecular structure, retention and band-broadening properties of polypeptides separated by reversed-phase high-performance liquid chromatography.

The gradient retention behaviour in reversed-phase high-performance liquid chromatography of a series of polypeptides related to human beta-endorphin has been investigated using different n-alkylsilica stationary phases and 0.1% trifluoroacetic acid in water-acetonitrile as mobile phase. In particular, the influence of changes in gradient time and flow-rate on retention parameters has been assessed with five different porous octadecylsilica phases with average particle diameters of 4 microns and 6 microns. Decreasing the pore size from 30 nm to 7.3 nm resulted in decreased S and log k'o values for most solutes. The effect of changes in the gradient steepness parameter, b, on the bandwidth behaviour of these polypeptides has also been investigated. Anomalous band-broadening was observed for very steep and very shallow gradients, i.e. b greater than 0.7 or b less than 0.2. The significance of these results is discussed in relation to the presence of hydrophobic domains in the linear sequence, the probability of the formation of highly stabilised secondary structures and the possible involvement of multiple folded forms of a single solute in the chromatographic performance of these polypeptides.

Amino Acids↗

PubMed1991

Determination of beta-carbolines in foodstuffs by high-performance liquid chromatography and high-performance liquid chromatography-mass spectrometry.

A high-performance liquid chromatographic method combined with fluorimetric detection is described for the determination of beta-carboline (norharman) and 1-methyl-beta-carboline (harman). The analysis of foodstuffs for the identification of beta-carbolines is facilitated by clean-up samples using Bond Elut PRS cartridges. Recoveries were excellent. Further, a high-performance liquid chromatographic-mass spectrometric method was also developed for their identification. The concentration of beta-carboline among the foodstuffs and alcoholic beverages varied greatly. Also, norharman and harman were observed in uncooked foodstuffs, whereas acetaldehyde was found in most fermented food. The toxicological implication of beta-carbolines in foodstuffs is discussed.

Acetaldehyde↗

PubMed1991

Liquid chromatographic analysis of a potential polymeric-pendant drug delivery system for peptides. Application of high-performance size-exclusion chromatography, reversed-phase high-performance liquid chromatography and ion chromatography to the evaluation of biodegradable poly[(chloromethoxytrialanine methyl ester)phosphazenes].

A novel water-soluble polymer, poly[(chloromethoxytrialanine methyl ester)phosphazene] (poly-Tame), was characterized and evaluated using high-performance size-exclusion chromatography, gradient reversed-phase high-performance liquid chromatography and ion chromatography. These novel liquid chromatographic methods were validated for application to in vitro biodegradation experiments of poly-Tame in aqueous solutions. Results from method validation experiments are presented.

Biodegradation, Environmental↗

PubMed1998

Effect of radial gradient of temperature on the performance of large-diameter high-performance liquid chromatography columns. I. Analytical conditions.

The performance of a large-diameter chromatographic column can be drastically reduced when the solvent enters the column at a temperature different from that of the wall of the column. A radial temperature gradient inside the column will affect the physical properties of the solvent and the chromatographic behaviour of the solute resulting in a deformation of the band profile. A mathematical model is proposed to take into account the effect of a radial gradient of temperature in a large-diameter column on the chromatographic peak shape under linear conditions. The model is then compared with experimental results in preparative columns of different sizes. A good agreement between experiment and theory has been found showing a serious effect of thermal conditions on separation quality, depending on the column size. It is also demonstrated that a small difference of temperature can be helpful to compensate practical effect of frits and distribution of the sample at the extremities of the packed bed. Finally, it demonstrates the necessity to perform efficiency measurement under different thermal conditions to have a good comparison between columns.

Chromatography, High Pressure Liquid↗

PubMed2000

Identification of unusual (modified and non-encoded) amino acid residues in peptides by combinations of high-performance liquid chromatography and high-performance capillary electrophoresis with matrix-assisted laser desorption ionization time-of-flight mass spectrometry.

The techniques for micro-level analysis of some widespread unusual amino acids (phosphorylated and hydroxylated ones) as well as of some genetically non-encoded amino acids were developed for their subsequent identification in the peptide and protein amino acid sequence by narrow-bore column high-performance liquid chromatography (approximately 10 pmol of the sample), high-performance capillary electrophoresis (approximately 1-10 pmol), matrix-assisted laser desorption ionization time-of-flight mass spectrometry (approximately 1-10 pmol), and automatic protein gas phase sequencing (approximately 1-50 pmol).

Amino Acid Sequence↗

PubMed2000

Analysis of tea components by high-performance liquid chromatography and high-performance capillary electrophoresis.

Tea is one of the most popular beverages in the world. The number of reports on the analysis of tea components, especially for catechins, has recently been increasing. We review the recent reports on the analysis of tea components using the analytical methods of high-performance liquid chromatography and high-performance capillary electrophoresis.

Chromatography, High Pressure Liquid↗

PubMed2000

Determination of chloroacetanilide herbicide metabolites in water using high-performance liquid chromatography-diode array detection and high-performance liquid chromatography/mass spectrometry.

Analytical methods using high-performance liquid chromatography-diode array detection (HPLC-DAD) and high-performance liquid chromatography/mass spectrometry (HPLC/MS) were developed for the analysis of the following chloroacetanilide herbicide metabolites in water: alachlor ethanesulfonic acid (ESA); alachlor oxanilic acid; acetochlor ESA; acetochlor oxanilic acid; metolachlor ESA; and metolachlor oxanilic acid. Good precision and accuracy were demonstrated for both the HPLC-DAD and HPLC/MS methods in reagent water, surface water, and ground water. The average HPLC-DAD recoveries of the chloroacetanilide herbicide metabolites from water samples spiked at 0.25, 0.5 and 2.0 microg/l ranged from 84 to 112%, with relative standard deviations of 18% or less. The average HPLC/MS recoveries of the metabolites from water samples spiked at 0.05, 0.2 and 2.0 microg/l ranged from 81 to 118%, with relative standard deviations of 20% or less. The limit of quantitation (LOQ) for all metabolites using the HPLC-DAD method was 0.20 microg/l, whereas the LOQ using the HPLC/MS method was at 0.05 microg/l. These metabolite-determination methods are valuable for acquiring information about water quality and the fate and transport of the parent chloroacetanilide herbicides in water.

Acetamides↗

PubMed2001

Analysis of cocaethylene, benzoylecgonine and cocaine in human urine by high-performance thin-layer chromatography with ultraviolet detection: a comparison with high-performance liquid chromatography.

Cocaine and ethanol are frequently used at the same time, resulting in the formation of cocaethylene by transesterification. We studied the capability of high-performance thin-layer chromatography (HPTLC) to simultaneously detect cocaethylene, cocaine and benzoylecgonine in 16 urine specimens of drug addicts, previously tested as positive for benzoylecgonine at immunoenzymatic screening. Accuracy and precision, as well as detection and quantitation limits of the method, were evaluated by comparison with high-performance liquid chromatography (HPLC). HPTLC limit of quantitation was 1.0 microg/ml for the three compounds, whereas HPLC limits were 0.2 microg/ml for benzoylecgonine and cocaine, and 0.1 microg/ml for cocaethylene. The relative standard deviation (RSD) ranged from 1.03 to 12.60% and from 1.56 to 16.6% for intra- and inter-day HPTLC analysis, respectively. In the case of the HPLC method, the RSD for the intra-day precision ranged from 0.79 to 5.05%, whereas it ranged from 1.19 to 10.64% for the inter-day precision. In comparison with HPLC, HPTLC is less expensive and faster, requiring 2-3 h to analyze 10-12 samples on a single plate. In conclusion, HPTLC is suitable for determinations of the three analytes only for samples with high concentrations.

Chromatography, High Pressure Liquid↗

PubMed1986

Detection of digoxin, digitoxin, their cardioactive metabolites and derivatives by high-performance liquid chromatography and high-performance liquid chromatography-radioimmunoassay.

High-performance liquid chromatographic (HPLC) systems are described for the separation of the cardioactive metabolites of the digoxin and digitoxin series that are formed by the splitting of digitoxose sugar residues from the aglycone steroid: isocratic separation of digoxin and its cardioactive metabolites; isocratic separation of digitoxin and its cardioactive metabolites; and gradient elution separation of the digoxin and digitoxin series including beta-acetyl- and beta-methyldigoxin. Separations were performed on a 10-microns bonded octadecyl phase column using various mixtures of acetonitrile--water and acetonitrile--methanol--water as the mobile phase. These methods provide high peak resolution and are well suited for collecting elution fractions, e.g. to link up with sensitive immunological measurements. An HPLC-radioimmunoassay method is described for the quantitation of digoxin, digitoxin and their metabolites in human tissues.

Chromatography, High Pressure Liquid↗

PubMed1997

Microbore high-performance liquid chromatographic method for measuring acetylcholine in microdialysis samples: optimizing performance of platinum electrodes.

A microbore high-performance liquid chromatographic method with electrochemical detection was applied to the measurement of acetylcholine in microdialysis samples. There was an excellent linear relationship (r=0.99998) between the concentration of acetylcholine injected onto the column and the peak height (0.05-10 pmol/5 microl). During the validation of this method, we noticed that the peak height for acetylcholine decreased over time, coupled with the appearance of a brown coating on the surface of the platinum electrode. Repeated measurement of acetylcholine standards which had been stored at 4 degrees C and -20 degrees C before and after cleaning the platinum electrode with ethanol or methanol indicated that the decrease in the peak height of acetylcholine is caused by a decrease in sensitivity of the electrode itself. Results with a second microbore high-performance liquid chromatographic system confirmed these findings. On the basis of these results, we recommend that the platinum electrode is cleaned periodically with ethanol or methanol, and that quantitation is regularly calibrated with external acetylcholine.

Acetylcholine↗

PubMed1999

Simultaneous determination of the urinary metabolites of toluene, xylene and styrene using high-performance capillary electrophoresis. Comparison with high-performance liquid chromatography.

A simple and rapid method using high-performance capillary electrophoresis (HPCE) for the simultaneous determination of the urinary metabolites of toluene, xylene and styrene, plus creatinine and uric acid in human urine specimens and standard solutions is described. The compounds were well separated from each other on a fused-silica capillary utilizing a 20 mM sodium tetraborate buffer (pH 9.65) with 15 mM beta-cyclodextrin and UV detection at 200 and 225 nm. The total analysis time was less than 6 min per sample. The capillary zone electrophoresis (CZE) method shows a good correlation with the high-performance liquid chromatography (HPLC) method with respect to urinary hippuric acid concentrations in the urine specimens of subjects exposed to the vapors of a solvent mixture of toluene and xylene. In comparing these two techniques, HPCE was found to be superior to HPLC because the analysis time is shorter, and the separation of m-MHA and p-MHA takes a long time with HPLC.

Calibration↗

PubMed2000

Item and order information in subject-performed tasks and experimenter-performed tasks.

This study investigated the enactment effect from the perspective of the item-order hypothesis (e.g., M. Serra & J. S. Nairne, 1993). The authors assumed that in subject-performed tasks (SPTs), item encoding is improved but order encoding is disrupted compared with experimenter-performed tasks (EPTs), that order encoding of EPTs is only better in pure lists, and that the item--order hypothesis is confined to short lists. Item information was tested in recognition memory tests, order information in order reconstruction tasks, and both item and order information in free-recall tests. The results of 5 experiments using short (8 items) and long lists (24 items) in a design with list type (pure, mixed) and encoding condition (EPT, SPT) as factors supported the hypotheses.

Adult↗

PubMed2004

Academic performance, career potential, creativity, and job performance: can one construct predict them all?

This meta-analysis addresses the question of whether 1 general cognitive ability measure developed for predicting academic performance is valid for predicting performance in both educational and work domains. The validity of the Miller Analogies Test (MAT; W. S. Miller, 1960) for predicting 18 academic and work-related criteria was examined. MAT correlations with other cognitive tests (e.g., Raven's Matrices [J. C. Raven, 1965]; Graduate Record Examinations) also were meta-analyzed. The results indicate that the abilities measured by the MAT are shared with other cognitive ability instruments and that these abilities are generalizably valid predictors of academic and vocational criteria, as well as evaluations of career potential and creativity. These findings contradict the notion that intelligence at work is wholly different from intelligence at school, extending the voluminous literature that supports the broad importance of general cognitive ability (g).

Career Mobility↗

PubMed2003

Adults' understanding of inversion concepts: how does performance on addition and subtraction inversion problems compare to performance on multiplication and division inversion problems?

Problems of the form a + b - b have been used to assess conceptual understanding of the relationship between addition and subtraction. No study has investigated the same relationship between multiplication and division on problems of the form d x e / e. In both types of inversion problems, no calculation is required if the inverse relationship between the operations is understood. Adult participants solved addition/subtraction and multiplication/division inversion (e.g., 9 x 22 / 22) and standard (e.g., 2 + 27 - 28) problems. Participants started to use the inversion strategy earlier and more frequently on addition/subtraction problems. Participants took longer to solve both types of multiplication/division problems. Overall, conceptual understanding of the relationship between multiplication and division was not as strong as that between addition and subtraction. One explanation for this difference in performance is that the operation of division is more weakly represented and understood than the other operations and that this weakness affects performance on problems of the form d x e / e.

Adolescent↗

PubMed2002

The short DRD4 repeats confer risk to attention deficit hyperactivity disorder in a family-based design and impair performance on a continuous performance test (TOVA).

One particular candidate gene, the dopamine D4 receptor (DRD4), has been the focus of intense study regarding ADHD since the original investigation by La Hoste et al, an observation confirmed by a recent metaanalysis. However, two previous studies from Israel failed to observe this association. We have now recruited an additional sample and, overall, in the combined sample of 178 triads we observe using the transmission disequilibrium test, preferential transmission of the short allele. Additionally, we now report the effect of the DRD4 repeat region on the Test Of Variables of Attention (TOVA), a widely used computerized continuous performance test. Probands with the short exon III repeat performed significantly worse on the TOVA measured both by errors of commission and response time variable. Intriguingly, a 'dose effect' was observed. Increasing repeat size is accompanied by a reduced number of errors of commission and a significant difference is observed between the 2 vs 7 repeats. On the whole, our results lend credence to the notion that the relationship between the DRD4 receptor and ADHD is complex and may be reflecting linkage disequilibrium between the 7 or long DRD4 exon III repeats and a 'true' risk allele in this gene or a neighboring locus.

Adolescent↗

PubMed1990

Analytical methodology for the determination of aflatoxins in peanut butter: comparison of high-performance thin-layer chromatographic, enzyme-linked immunosorbent assay and high-performance liquid chromatographic methods.

High-performance thin-layer chromatography (HPTLC) was applied to the separation and quantification of aflatoxin in 300 jars of "crunchy" peanut butter. A critical evaluation of the proposed HPTLC method has been carried out by statistical comparisons with a commercially available enzyme-linked immunosorbent assay (ELISA) kit and a high-performance liquid chromatographic (HPLC) method. The statistical tests indicated that whilst the distributions of the data sets obtained with each method were similar, the HPLC method was found to be biased. Over-all results indicated that the HPTLC method gave more consistent data, relatively lower standard deviations and lower coefficients of variation. The ELISA kit was found to be less precise than the HPTLC and HPLC methods and prone to some loss of sensitivity caused by matrix interference.

Aflatoxins↗

PubMedDate not supplied

Effect of the feeding level during rearing on performance of Large White gilts. Part 1: Growth, reproductive performance and feed intake during the first lactation.

Fifty pure-bred Large White gilts were allocated to two feeding levels from 28 kg until service. They were fed a standard growing diet (13.4 MJ digestible energy (DE) per kg; 18.1% crude protein, CP; 0.96% lysine) either to appetite (AP) or at 80% of the AP level (R). Growth rate was reduced by about 20% in R gilts, whereas feed conversion ratio was unaffected by rearing treatment. First oestrus was detected earlier in AP gilts (234 versus 247 d of age). At service, AP females had larger body weight (190 versus 150 kg) and thicker backfat (20.9 versus 13.4 mm). After service, the reproductive performances of 30 of these gilts were studied during the first reproductive cycle. All gilts received 2.6 kg/d of a standard diet (12.6 MJ DE/kg; 13.9% CP; 0.59% lysine) during pregnancy and were fed ad libitum a commercial lactation diet (13.1 MJ DE/kg; 17.1% CP; 0.90% lysine) from day five after farrowing. At farrowing, AP females were larger (257 versus 225 kg) and had more backfat (23.7 versus 17.4 mm) than R ones. Reproductive performance during the first lactation was not affected by rearing treatment, and weaning to oestrus interval was similar in both groups (4.8 d, on average). During lactation, R sows consumed significantly more feed (+650 g/d) and lost less backfat depth (1.5 versus 3.8 mm) than AP ones.

Adipose Tissue↗

PubMed2002

The Performance Enhancement Project: improving physical performance in older persons.

OBJECTIVE: To determine the effects of center-based exercise on physical performance in older persons at risk for decline in physical functioning. DESIGN: Randomized controlled trial. SETTING: Senior centers. PARTICIPANTS: A total of 155 community-dwelling persons, 78.7% women, ages 70 years and older (mean +/- standard deviation, 77.0+/-4.5y), with mobility impairments. INTERVENTION: Intervention volunteers (n=80) exercised at a center (endurance, strength, balance, flexibility) 3 times weekly, for months 1 to 6; once weekly, for months 7 to 12 with home exercise 2 sessions a week; and at home only, for months 13 to 18. Home control volunteers (n=75) were instructed in home endurance exercise. MAIN OUTCOME MEASURES: MacArthur battery, Physical Performance Test (PPT-8), and 6-Minute Walk Test (6MWT) at baseline and 3, 6, 12, and 18 months. RESULTS: MacArthur battery scores improved in intervention compared with home control at 3, 6, and 12 months (repeated-measures analysis of variance: group x time, P<.05) but not 18 months. PPT-8 and 6MWT did not improve. Intervention group assignment, younger age, and better baseline physical function and self-perceived health were independent predictors of long-term MacArthur battery score improvement. CONCLUSIONS: Compared with home control, center-based exercise improved gait, chair rise time, and balance over 1 year. Improvements were not sustained with transition to home exercise for months 13 to 18. Classes may be necessary to maintain improvements in older persons attending center-based exercise.

Activities of Daily Living↗