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PubMed2000

Selenium speciation in enriched and natural samples by HPLC-ICP-MS and HPLC-ESI-MS with perfluorinated carboxylic acid ion-pairing agents.

Selenium-enriched plants, such as hyperaccumulative phytoremediation plants (Astragalus praleongus, 517 micrograms g-1 Se, and Brassica juncea, 138 micrograms g-1 Se in dry sample), yeast (1200, 1922 and 2100, micrograms g-1 Se in dry sample), ramp (Allium tricoccum, 48, 77, 230, 252, 405 and 524 micrograms g-1 Se in dry sample), onion (Allium cepa, 96 and 140 micrograms g-1 Se in dry sample) and garlic (Allium sativum, 68, 112, 135, 296, 1355 micrograms g-1 Se in dry sample) were analyzed by HPLC-ICP-MS for their selenium content and speciation after hot water and enzymatic extractions. Reference samples with natural selenium levels, such as onion and garlic controls, cooking garlic powder, baking yeast powder and a commercial garlic supplement were also analyzed. Selected samples were also examined by HPLC-electrospray ionization (ESI)-MS. HPLC was mostly carried out with 0.1% heptafluorobutanoic acid (HFBA) as ion-pairing agent in 1 + 99 v/v methanol-water solution, but 0.1% trifluoroacetic acid (TFA) in 1 + 99 v/v methanol-water solution was also utilized to permit chromatography for compounds that did not elute with HFBA. More than 75% of the total eluting selenium compounds, based upon element specific detection, were identified from retention time data and standard spiking experiments, and between 60 and 85% of compounds were identified by MS, with up to 25% of the total eluting molecular selenium species being unidentified as yet. Limits of quantification (LOQ, defined as the concentration giving an S/N of 10) for HPLC-ICP-MS were in the range 2-50 ng mL-1 Se in the injected extracts for the selenium-enriched samples and 2-10 ng mL-1 Se for the natural selenium level samples. LOQ values for HPLC-ESI-MS were ca. 100 times higher than those measured by HPLC-ICP-MS.

Chromatography, High Pressure Liquid↗
PubMed2003

Diffusive sampling of methyl isocyanate using 4-nitro-7-piperazinobenzo-2-oxa-1,3-diazole (NBDPZ) as derivatizing agent.

A diffusive sampling method for the determination of methyl isocyanate (MIC) in air is introduced. MIC is collected using a glass fiber filter impregnated with 4-nitro-7-piperazinobenzo-2-oxa-1,3-diazole (NBDPZ). The urea derivative formed is desorbed from the filter with acetonitrile and analyzed by means of high-performance liquid chromatography (HPLC) using fluorescence detection (FLD) with lambdaex = 471 nm and lambdaex = 540 nm. Additionally, a method was developed using tandem mass spectrometric (MS-MS) detection, which was performed as selected reaction monitoring (SRM) on the transition [MIC-NBDPZ + H]+ (m/z 307) to [NBDPZ + H]+ (m/z 250). The diffusive sampler was tested with MIC concentrations between 1 and 35 microg m(-3). The sampling periods varied from 15 min to 8 h, and the relative humidity (RH) was set from 20% up to 80%. The sampling rate for all 15 min experiments was determined to be 15.0 mL min(-1) (using HPLC-FLD) with a relative standard deviation of 9.9% for 56 experiments. At 80% RH, only 15 min sampling gave acceptable results. Further experiments revealed that humidity did not affect the MIC derivative but the reagent on the filter prior to and during sampling. The sampling rate for all experiments (including long term sampling) performed at 20% RH was found to be 15.0 mL min(-1) with a relative standard deviation of 6.3% (N = 42). The limit of quantification was 3 microg m(-3) (LC-MS-MS: 1.3 microg m(-3)) for 15 min sampling periods and 0.2 microg m(-3) (LC-MS-MS: 0.15 microg m(-3)) for 8 h sampling runs applying fluorescence detection.

Absorption↗
PubMed2005

Aspiration and sampling efficiencies of the TSP and louvered particulate matter inlets.

An experimental system was developed for the rapid measurement of the aspiration/transfer efficiency of aerosol samplers in a wind tunnel. We attempted to measure the aspiration and particle transfer characteristics of two inlets commonly used for sampling airborne Particulate Matter (PM): the 'Total Suspended Particulate' or TSP inlet, and the louvered 'dichotomous sampler inlet' typically used in sampling PM10 or PM2.5. We were able to determine the fraction of the external aerosol that enters the inlet and is transferred through it, and hence is available for collection by a filter, or further size fractionation into PM10 or PM2.5. This 'sampling efficiency' was analysed as a function of dimensionless aerodynamic parameters in order to understand the factors governing inlet performance. We found that for the louvered inlet the sampling efficiency increases as the external wind increases. Under all conditions expected in practical use the louvered inlet aspirates sufficient PM to allow either PM10 or PM2.5 to be selected downstream. The TSP inlet's sampling efficiency decreases with increasing external wind, and the TSP inlet is likely to under-sample the coarse end of the PM10 fraction at moderate and high external winds. As this inlet is generally not used with a downstream size fractionator, changes in sampling efficiency directly affect the measured aerosol concentration. We also investigated whether it is possible to dimensionally scale the PM inlets to operate at either higher or lower flow rates, while preserving the same sampling characteristics as the current full-scale, 16.67 L min(-1) versions. In the case of the louvered inlet, our results indicate that scaling to lower flow rates is possible; scaling to higher flow rates was not tested. For the TSP sampler, the sampling efficiency changes if the sampler is scaled to operate at smaller or larger flow rates, leading to unreliable performance.

Aerosols↗
PubMed1997

Cervex brush versus vaginal-cervical-endocervical (VCE) triple smear techniques in cervical sampling.

Cervex brush sampling was compared with the conventional triple vaginal-cervical-endocervical (VCE) smear technique. Nine hundred and fifty-nine Cervex brush smears and 1064 VCE smears were studied. All smears with both methods were technically satisfactory for evaluation. Endocervical cells were found in 90.7% and metaplastic cells in 73.3% of Cervex brush samples and in 92.5% and 64.1% of VCE samples, respectively. There were significantly more metaplastic cells in smears from premenopausal women. Low grade squamous intraepithelial lesion (SIL) was found in three Cervex brush samples and in two VCE samples. High-grade SIL was found only in one Cervex brush sample. Benign cellular changes were found in 142 Cervex brush samples and in 144 VCE samples. Sampling with the Cervex brush is efficient, simple and fast and gives high quality cervical smears for cytological evaluation.

Adolescent↗
PubMed2002

Prevalence of and resistance to anti-microbial drugs in selected microbial species isolated from bulk milk samples.

The prevalence of strains of Staphylococcus aureus, coagulase-negative (CN) staphylococci, Listeria monocytogenes, Escherichia coli, Enterococcus faecalis, E. faecium and Bacillus cereus, was investigated in 111 bulk milk samples. Staphylococcus aureus was isolated from 38 samples, CN staphylococci from 63 samples, E. coli from 49 samples, E. faecalis or E. faecium from 107 samples, and L. monocytogenes from two samples. Bacillus cereus was not found in any of the samples and three samples were free of any of the selected species. Sensitivity to the anti-microbial drugs amikacin, ampicillin, ampicillin + sulbactam, cephalothin (CLT), cephotaxime, clindamycin, chloramphenicol (CMP), co-trimoxazole, erythromycin (ERY), gentamicin, neomycin, norfloxacin, oxacillin, penicillin, streptomycin (STR), tetracycline (TTC) and vancomycin was tested using the standard dilution technique. Minimum inhibitory concentration (MIC) characteristics (MIC50, MIC90, MIC range) were determined for each microbial species. Resistance against one or more anti-microbial drugs was found in 93% of S. aureus, 40% of CN staphylococci, 73% of E. coli, 88% of E.faecalis, 55% of E.faecium, and one L. monocytogenes strain. Most of the strains, particularly enterococci, were resistant to STR, TTC, and ERY (MIC50 4 microg/ml). A high percentage of staphylococci were resistant to beta-lactam antibiotics. High resistance to CLT was found in 11 strains of E. coli (MIC 256 microg/ml) and strains resistant to CMP (MIC90 16 microg/ml) were detected. The highest numbers of resistance phenotypes were found in E. coil (16) and CN staphylococci (12). Eighteen identical resistance phenotypes were demonstrated in indicator bacteria (E. coli, E. faecalis, E. faecium) and pathogens (S. aureus, CN staphylococci) isolated from the same bulk milk sample. The obtained resistance data were matched against the herd owners' information on therapeutic use of the drugs. This confrontation could not explain the findings of strains resistant to ERY or CMP. Our findings are evidence of selection of resistant strains among not only pathogenic agents, but also among indicator bacteria which can become significant carriers of transmissible resistance genes.

Animals↗
PubMed2001

Accuracy of predonation Hct sampling affects donor safety, eligibility, and deferral rates.

BACKGROUND: Safe blood donation depends upon reliable predonation Hct screening. Earstick (ES) capillary samples are frequently used, but they may not be accurate. STUDY DESIGN AND METHODS: Predonation ES and fingerstick (FS) and postdonation venous Hct results were compared in 1960 whole-blood and 210 apheresis donors. The validity of using postdonation venous samples to evaluate predonation ES and FS Hct was assessed in 20 whole-blood donors. The impact of Hct screening method on donor Hct deferrals was examined during periods when either ES or FS sampling was used exclusively. RESULTS: All donors were eligible to donate on the basis of a predonation capillary Hct of > or = 38 percent. In venous samples obtained immediately after donation, 36 percent of whole-blood donors had a Hct <38 percent. With correction for a decrease of approximately 2 Hct units during donation, 20 percent of these donors had a predonation Hct <38 percent. The lowest venous Hct was 23.1 percent. FS samples showed better correlation with venous Hct. Hct discrepancies were similar for apheresis donors. Hct deferrals were significantly higher with FS sampling, especially among women. CONCLUSION: Hct determinations from ES samples overestimate venous Hct. Fingerstick samples are more sensitive in detecting anemia. The accuracy of predonation Hct sampling has implications for donor safety, eligibility, and deferral rates.

Blood Component Removal↗
PubMed2001

Caval backflow: a potential problem during blood sampling from the hepatic vein.

A proper measurement of splanchnic metabolism involves sampling blood from the hepatic vein without backflow contamination of blood from the caval vein. We have investigated the potential problem of caval backflow in human volunteers with an indwelling hepatic vein catheter by sampling blood with different amounts of suction on the syringe (ie, sampling speeds). We also investigated the potential problem in pigs in which a balloon catheter was inserted in the hepatic vein. Pure hepatic vein samples were obtained with the balloon inflated and compared with samples obtained from the same catheter in the conventional manner. In overnight fasted humans, drawing blood samples from the hepatic vein with minimal suction ("slow" drawing) resulted in glucose values 9.6% higher than drawing the samples with greater suction ("fast" drawing). The calculated arterial-venous balance across the splanchnic bed was 4.8 times greater with "slow" blood drawing as compared with "fast" drawing. Values obtained from the pigs showed no concentration differences between pure hepatic vein samples and "slow" drawing from the hepatic vein. The current study indicates that it is possible to obtain a "true" hepatic vein sample, but backflow from the caval vein is a potential pitfall that can have a physiologically significant impact on calculated balance data.

Adult↗
PubMed2000

Heparin neutralization is essential for accurate measurement of factor VIII activity and inhibitor assays in blood samples drawn from implanted venous access devices.

The purpose of this study was to determine the prevalence and effect of heparin contamination in samples drawn from implanted venous access devices (VADs, ports) on factor VIII activity and Bethesda inhibitor assay (BU) and the efficacy of heparinase to neutralize heparin. Plasma samples containing 85, 45, and 2 U/dL factor VIII were spiked in vitro with heparin from 0 to 3 U/mL. Factor VIII activity was assayed with a one-stage clotting assay on paired samples before and after heparinase, 25 mg/mL plasma. Paired patient samples drawn from VADs were assayed for heparin concentration, factor VIII, and BU before and after heparinase. At all three concentrations of factor VIII in vitro, the addition of heparin at 0.12 to 0.25 U/mL decreased assayed factor VIII activity. Heparinase neutralized up to 2 U/mL heparin and resulted in accurate factor VIII determination. Of 105 VAD samples, 47 (45%) had heparin contamination >0.05 U/mL. Of 47 heparin-contaminated samples, 42 showed decreased factor VIII activity in before/after comparisons. False-positive BU results were detected in 6 of 47 heparin-contaminated samples. Heparin contamination occurs frequently in samples drawn from VADs and could increase costs through excessive factor concentrate use. We recommend that all VAD samples be pretreated with heparinase before the assay of factor VIII activity or Bethesda inhibitor titers.

Antibodies↗
PubMed1990

Effects of blood sampling on plasma concentrations of corticosterone and glucose in laying hens caged in groups.

1. The effects of taking a blood sample from one bird in a caged group on plasma concentrations of corticosterone and glucose in birds from its own group and birds from other groups were investigated. 2. Two blood sampling protocols were used: successive (all birds within a group were sampled one immediately after another) and alternative (birds from different groups were sampled one after another until all birds in all groups had been sampled). 3. Neither sampling protocol nor between or within group sampling rank was related to plasma concentrations of corticosterone and glucose. 4. The time taken to remove a blood sample (generally more than 45 s but less than 2 min) did not influence circulating corticosterone and glucose. 5. In individual birds plasma concentrations of corticosterone and glucose were poorly correlated with one another. 6. It is concluded that it is possible to take blood samples from a bird, kept in a group, without affecting plasma concentrations of corticosterone and glucose in other birds from that group or in birds from other groups in other cages.

Analysis of Variance↗
PubMed2006

Residues of DDT and HCH in wheat samples collected from different states of India and their dietary exposure: A multicentre study.

Under a multicentre study conducted by the Indian Council of Medical Research, 1712 samples of wheat grain/flour were collected from urban and rural areas in 11 states representing different geographical regions of India. These samples were analysed for residues of DDT (2,2-bis (p-chlorophenyl)-1,1,1-trichloro ethane) and different isomers of HCH (1,2,3,4,5,6-hexachloro cyclohexane, a mixture of isomers) by gas-liquid chromatography. Residues of DDT were detected in 59.4% of 1080 samples of wheat grain and in 78.2% of 632 samples of wheat flour. Different isomers of HCH were present in about 45-80% of the samples of wheat grain/flour. Medians of DDT and total HCH, respectively, for pooled samples of wheat grain were 0.013 and 0.035 mg kg(-1), while those for wheat flour were 0.01 and 0.02 mg kg(-1). Estimated daily intakes of DDT and different isomers of HCH through the consumption of wheat contaminated at their median and 90th percentiles constituted a small proportion of their acceptable daily intakes. Amongst the pesticide residues analysed, statutory maximum residue limits have been fixed only for gamma-HCH in wheat in India, as 0.1 mg kg(-1) in wheat grain and zero in wheat flour. Residue levels of gamma-HCH exceeded these maximum residue limits in five of 1080 samples of wheat grain and in 340 of 632 samples of wheat flour. The failure to meet the requirement of the gamma-HCH maximum residue limit in large number of wheat flour samples was attributed to the fixation of practically unachievable zero limit. Comparing the previous studies and the present one, the levels of residues of DDT and HCH in wheat were significantly decreased.

Adult↗
PubMedDate not supplied

Estimation of menthol in Pan Masala samples by a spectrophotometric method.

Recently, the Prevention of Food Adulteration Act of India has fixed the level of menthol addition to Pan Masala at 0.1%, therefore good manufacturing practice (GMP) should be adopted so that the samples do not exceed 0.1% menthol (1 mg/g). The estimation of menthol in Pan Masala samples involves steam distillation followed by reaction with p-dimethyl amino benzaldehyde (DMAB) in acidic medium to give a red colour which is read at 550 nm. The sensitivity of this procedure is 75 micrograms menthol per g sample. Using this method, 130 branded and 53 non-branded samples of Pan Masala were analysed for menthol content. Almost 25% of branded samples contained less than 1 mg menthol per g while 75% of samples contained 1.1-6.5 mg menthol per g Pan Masala. Non-branded Pan Masala contained 1 mg menthol per g in only 7.6% of samples. However, 92% of samples contained 1.1-6.5 mg menthol per g, suggesting that the addition of menthol is relatively higher in non-branded Pan Masala samples than in branded ones.

Areca↗
PubMed2001

Surface sampling for a pesticide in dust and small spills of a solid dye.

The aim was to determine whether a published sampling technique for loose soil on hard surfaces achieved acceptable efficiency at surface dust/soil coverages of 10-20 mg/ 100 cm2. The sampler was a cordless personal sampling pump operated at 4.0 L/min connected to a cassette containing a filter, the cassette being also connected to a Tygon sampling probe that was moved manually on the surface to be sampled. Rhodamine 6G dye dust was evaluated at 10 mg/100 cm2 coverage at flow rates of 1.0-4.0 L/min. Two National Institute of Standards and Technology (NIST) standard reference materials (SRMs) were used for pesticide experiments: SRM 2711 Montana Soil, and SRM 1649a Urban Dust. The efficiencies for these SRMs were determined uncoated, and coated with 1300 microg chlorpyrifos/g as a Lorsban 4E emulsifiable concentrate formulation. The 3-pass technique sampled both the pesticide-coated and uncoated dust and soil at >79 percent efficiency and at better than 16 percent coefficient of variation (CV) above 15 mg collected mass. Sampling at 20 mg/100 cm2 coverage lowered the CV to < or = 7.1 percent. The dye was sampled with similar efficiency > or = 1.5 L/min, but the CV for the 3-pass technique was <10 percent at 1.5-2.0 L/min, and <20 percent at 1.5-4.0 L/min. The efficiency for a 5-pass technique for the dye exceeded 90 percent at > 1.5 L/min with CVs < 10 percent at 1.5, 2.0, 2.5, and 3.5 L/min. The weight change of the sampling probe and the cassette must be measured for accurate determination of low surface coverages rather than just the weight change of the filter alone. The method allows use of personal sampling equipment for aerosols to measure low coverages of loose dust, soil, and chemical solids on hard surfaces.

Coloring Agents↗
PubMed1998

Sensitivity of phylogeny estimation to taxonomic sampling.

Recent studies have shown that addition or deletion of taxa from a data matrix can change the estimate of phylogeny. I used 29 data sets from the literature to examine the effect of taxon sampling on phylogeny estimation within data sets. I then used multiple regression to assess the effect of number of taxa, number of characters, homoplasy, strength of support, and tree symmetry on the sensitivity of data sets to taxonomic sampling. Sensitivity to sampling was measured by mapping characters from a matrix of culled taxa onto optimal trees for that reduced matrix and onto the pruned optimal tree for the entire matrix, then comparing the length of the reduced tree to the length of the pruned complete tree. Within-data-set patterns can be described by a second-order equation relating fraction of taxa sampled to sensitivity to sampling. Multiple regression analyses found number of taxa to be a significant predictor of sensitivity to sampling; retention index, number of informative characters, total support index, and tree symmetry were nonsignificant predictors. I derived a predictive regression equation relating fraction of taxa sampled and number of taxa potentially sampled to sensitivity to taxonomic sampling and calculated values for this equation within the bounds of the variables examined. The length difference between the complete tree and a subsampled tree was generally small (average difference of 0-2.9 steps), indicating that subsampling taxa is probably not an important problem for most phylogenetic analyses using up to 20 taxa.

Animals↗
PubMedDate not supplied

Effect of temperature on the breakthrough of a charcoal tube during vinyl chloride monomer sampling.

This study evaluated the effects of temperature on breakthrough of two standard collection media at various concentrations during vinyl chloride monomer (VCM) sampling. The National Institute for Occupational Safety and Health (NIOSH) and Occupational Safety and Health Administration (OSHA) methods were evaluated. To determine whether breakthrough of VCM would occur at the extremes of exposure and temperature that might be encountered in some workplaces, air samples containing 4 ppm (10.24 mg/m3), 8 ppm (20.45 mg/m3), 16 ppm (40.98 mg/m3), and 32 ppm (81.80 mg/m3) of VCM were collected at temperatures of 4, 22, and 40 degrees C. Five liters of air was sampled at the rate of 0.05 L/min for 100 min using the activated charcoal tube recommended by NIOSH. A second tube was added to the sampling train to collect any VCM that might not have been absorbed in the first tube. To collect VCM air samples by the OSHA method, two carbon molecular sieve tubes were connected serially and 3 L of air was sampled at the rate of 0.05 L/min for 60 min. A gas chromatograph with a flame ionization detector and ultra 2 capillary column was used to analyze VCM. Significant breakthrough was found when sampling at higher temperatures with the NIOSH method. No breakthrough was found when samples were collected using the OSHA media at different temperatures and concentrations. Therefore, under hot ambient conditions (>22 degrees C), the possibility of breakthrough should be considered when sampling VCM by the NIOSH method.

Air Pollutants, Occupational↗
PubMed1980

Validation of gas and vapor sampling methods under field insult conditions.

A technique has been developed to validate gas and vapor sampling methods under field insult conditions. Laboratory validation, a necessary aspect of good laboratory practices, only tests the feasibility of a sampling method. "Field validation" determines the effectiveness of a given sampling method in the actual workplace environment where potentially interfering components may exist. A simple and inexpensive means is shown for introducing a known addition spike onto the sampling device during sampling. The validation sample is subject to the same field conditions as area or personnel samples. Upon analysis, recovery of the known addition spike within specified limits, verifies validity of the day's samples. Insufficient known addition spike recovery alerts the hygienist that something has caused sample failure, resulting in an invalid measurement of worker exposure.

Air Pollutants↗
PubMed1995

A field method for sampling benzene in end-exhaled air.

A simple and reliable field method is presented for sampling and analysis of benzene in end-exhaled air. The sample is collected directly on an adsorbent tube while the subject exhales through a sampling device consisting of a modified peak expiratory flow meter. To ensure sampling of end-exhaled air, the temperature of the breath is monitored during expiration. The analytes subsequently are thermally desorbed and analyzed by gas chromatography. No sample preparation before analysis is needed, and therefore sample loss is minimized, shipping is easy, storage is possible, and clean up is unnecessary. All these steps have been major problems in earlier methods for breath analysis. The presented method has been applied to the monitoring of benzene. The separation of benzene from other components of exhaled air was good and the detection limit low (0.5 microgram/m3), and therefore benzene could be monitored in occupationally nonexposed nonsmokers. No carry-over in the sampling device or breakthrough could be detected. The samples were stable for at least a week. The combined precision in sampling and analysis was excellent, with a coefficient of variation of 13%.

Adsorption↗
PubMed2004

Comparison of ECG-gated rectilinear vs. real-time radial K-space sampling schemes in cine True-FISP cardiac MRI.

PURPOSE: To compare three k-space sampling schemes in cine True-FISP cardiac magnetic resonance imaging and to evaluate changes in calculated quantitative functional cardiac parameters as a function of underlying k-space sampling techniques. MATERIAL AND METHODS: Using a 1.5 T MR imaging system (Magnetom Sonata, Siemens Medical Solutions, Erlangen, Germany), three k-space data-sampling schemes: rectilinear (2.96 ms/1.58 ms/70 degrees /12 s TR/TE/FA/AcquisitionTime), and two radial k-space acquisitions, with filtered back-projection (RADIAL) (2.45 ms/1.25 ms/ 50 degrees /3.3 s TR/TE/FA/AT), and steady-state projection imaging with dynamic echotrain readout (SPIDER) (3.39 ms/1.62 ms/55 degrees /1.8 s TR/TE/FA/AT) of a True-FISP sequence were applied in 10 healthy volunteers. Long- and short-axis breath-hold series were acquired and signal-to-noise ratios (SNR) for blood and myocardium were determined, as was contrast-to-noise ratios (CNR). Quantitative cardiac functional analysis included: determination of end-systolic/end-diastolic volumes, ejection fraction, and left ventricular mass. Functional analysis was performed by two independent readers three times for each volunteer and k-space sampling strategy. Statistical analysis evaluated the accuracy of the measurements obtained from each of the three sampling techniques and the intra- and interobserver reliability. RESULTS: Intraobserver and interobserver reliability measures of functional data were homogeneous without statistically significant differences. Intraobserver correlation coefficients ranged from 0.94-0.99; interobserver correlation coefficients ranged from 0.97-0.99. Direct comparison of SPIDER- and RADIAL-sampled True-FISP sequences showed no statistically significant differences in measured functional parameters with interstudy correlation coefficients from 0.88-0.98. RADIAL and SPIDER images had better temporal resolution and were qualitatively judged to provide superior wall/blood border definition. Statistically significant differences were identified in each volumetric functional parameter when results from the rectilinear sampling acquisitions were compared with either radial or SPIDER sampling techniques. RADIAL and SPIDER results were consistently higher than volumetric measures obtained from the rectilinear data set. CONCLUSION: Employing faster sampling schemes led to enhanced signal homogeneity while maintaining the necessary CNR for estimation of functional cardiac parameters. Enhanced signal homogeneity and maintained CNR will most likely improve the accuracy of the cardiac functional parameter determination.

Adult↗
PubMed1999

The effect of humidity on samples of microcrystalline cellulose taken from the extrusion/marumerization process.

The purpose of this work was to examine the sorption and desorption of water by various samples of microcrystalline cellulose, MCC (Avicel PH-101), taken from the extrusion/marumerization process, and to provide data that may explain how water affects the MCC polymer matrix during the formation of beads. Two isopiestic (humidity) studies were conducted: the first used samples exposed directly to controlled humidity conditions, whereas the second used samples that were freeze-dried before being exposed to controlled humidity conditions. Water sorption and desorption were determined gravimetrically. When both sets of samples were initially exposed to low-humidity conditions, they reached equilibrium by desorbing water. When these samples were initially exposed to high-humidity conditions, the high moisture content samples desorbed water, whereas the low moisture content and the freeze-dried samples sorbed water to reach equilibrium. When the first set of samples was initially exposed to high- and then to low-humidity conditions, they reached the same water content achieved by being equilibrated directly at the low-humidity condition. However, samples that were initially exposed to low- and then to high-humidity conditions had equilibrium water contents that were lower than those achieved by being equilibrated directly at the high-humidity condition. The original MCC systems exhibit a hysteretic effect above 85%, whereas the freeze-dried systems have a broader range hysteretic effect starting at 20% relative humidity. The results suggest that the internal structure of the MCC polymer fibers must change with the sorption and desorption of water, supporting the autohesion theory.

Adsorption↗