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At least 19 recordsLinked to original sources
PubMedDate not supplied

Sampling almonds for aflatoxin, part I: estimation of uncertainty associated with sampling, sample preparation, and analysis.

Domestic and international regulatory limits have been established for aflatoxin in almonds and other tree nuts. It is difficult to obtain an accurate and precise estimate of the true aflatoxin concentration in a bulk lot because of the uncertainty associated with the sampling, sample preparation, and analytical steps of the aflatoxin test procedure. To evaluate the performance of aflatoxin sampling plans, the uncertainty associated with sampling lots of shelled almonds for aflatoxin was investigated. Twenty lots of shelled almonds were sampled for aflatoxin contamination. The total variance associated with measuring B1 and total aflatoxins in bulk almond lots was estimated and partitioned into sampling, sample preparation, and analytical variance components. All variances were found to increase with an increase in aflatoxin concentration (both B1 and total). By using regression analysis, mathematical expressions were developed to predict the relationship between each variance component (total, sampling, sample preparation, and analysis variances) and aflatoxin concentration. Variance estimates were the same for B1 and total aflatoxins. The mathematical relationships can be used to estimate each variance for a given sample size, subsample size, and number of analyses other than that measured in the study. When a lot with total aflatoxins at 15 ng/g was tested by using a 10 kg sample, a vertical cutter mixer type of mill, a 100 g subsample, and high-performance liquid chromatography analysis, the sampling, sample preparation, analytical, and total variances (coefficient of variation, CV) were 394.7 (CV, 132.4%), 14.7 (CV, 25.5%), 0.8 (CV, 6.1%), and 410.2 (CV, 135.0%), respectively. The percentages of the total variance associated with sampling, sample preparation, and analytical steps were 96.2, 3.6, and 0.2, respectively.

Aflatoxin B1↗
PubMedDate not supplied

Comparison of Cytobrush sampling, spatula sampling and combined Cytobrush-spatula sampling of the uterine cervix.

Since the introduction of the Cytobrush for sampling the uterine cervix, some practitioners have ceased taking a concomitant cervical scraping using a spatula. To examine whether Cytobrush sampling alone is adequate for the diagnosis of cervical lesions, the Cytobrush and spatula samples in 444 smears (most with original diagnoses of at least mild dysplasia) were analyzed separately for the presence of diagnostic cells, endocervical cells and squamous cells. Of the 412 smears showing pathologic findings (mild to severe dysplasia or worse), diagnostic cells were present in 400 Cytobrush samples and in 369 spatula samples; the combination of both samples thus gave a 3% gain in correct diagnoses as compared to use of the Cytobrush samples alone. Another 18 smears would have been underdiagnosed based only on the Cytobrush samples. Endocervical cells were present in 95.3% of the Cytobrush samples and 83.8% of the spatula samples; squamous cells were present in 93.9% of the Cytobrush samples and 96.8% of the spatula samples. Analysis confirmed that it is important that the smear should contain both endocervical and squamous cells. A positive relationship between the absence of squamous cells in the Cytobrush sample and the probability of a false-negative assessment was suggested. It thus seems inadvisable to replace the combination sampling method by Cytobrush sampling alone, which may lead to a false-negative diagnosis.

Adult↗
PubMed1994

Human monitoring behavior in a multiple-instrument setting: independent sampling, sequential sampling or arrangement-dependent sampling.

This study aims at contributing to the understanding of human monitoring behavior in multiple instrument settings. Eye movements were recorded so as to test whether sampling behavior is more consistent with traditional normative models (Senders, 1983) or with alternative approaches that emphasize heuristics and strategies rather than quantitative modelling. A core assumption of normative modelling concerns the premise that sampling one instrument is independent of the other instruments in an array. This assumption was tested in three experiments. In a first experiment, subjects monitored four independent continuous stochasts so as to detect critical situations. In a fast condition, two instruments were paired with two relatively fast changing instruments. In a slow condition, the two instruments were paired with two relatively slow changing instruments. Sampling one instrument appeared to be independent of the rates of change of the other instruments in the array. Furthermore, sampling was a function of the information generation rates of the individual instruments. This is in accordance with normative modelling. However, the spatial arrangement of the instruments on the display as well as the presence of a central fixation point strongly affected sampling behavior. In a second experiment, subjects monitored six instruments. In addition, there was no central fixation point. The results indicated again that a perceptual heuristic was used in that the spatial arrangement of the instruments on the display affected sampling behavior. Horizontal transitions occurred more often than would be predicted on the basis of independent sampling. Diagonal transitions occurred less often than would be predicted. Finally, a third experiment tested whether this preference for sampling by means of horizontal eye movements at the expense of diagonal eye movements would, under conflict situations, affect the mean sampling interval of specific instruments. In a four-instrument monitoring task, sampling intervals of two slow and two fast independent instruments were compared in different spatial arrangements. Sampling intervals strongly depended on the arrangement of the instruments on the display. Human monitoring seems to be biased by a tendency towards sampling by means of horizontal transitions at the cost of diagonal transitions. Under certain conditions, this tendency might make sampling intervals unrelated to the information generation rates of the individual instruments.

Adolescent↗
PubMedDate not supplied

Sampling hazelnuts for aflatoxin: uncertainty associated with sampling, sample preparation, and analysis.

The variability associated with the aflatoxin test procedure used to estimate aflatoxin levels in bulk shipments of hazelnuts was investigated. Sixteen 10 kg samples of shelled hazelnuts were taken from each of 20 lots that were suspected of aflatoxin contamination. The total variance associated with testing shelled hazelnuts was estimated and partitioned into sampling, sample preparation, and analytical variance components. Each variance component increased as aflatoxin concentration (either B1 or total) increased. With the use of regression analysis, mathematical expressions were developed to model the relationship between aflatoxin concentration and the total, sampling, sample preparation, and analytical variances. The expressions for these relationships were used to estimate the variance for any sample size, subsample size, and number of analyses for a specific aflatoxin concentration. The sampling, sample preparation, and analytical variances associated with estimating aflatoxin in a hazelnut lot at a total aflatoxin level of 10 ng/g and using a 10 kg sample, a 50 g subsample, dry comminution with a Robot Coupe mill, and a high-performance liquid chromatographic analytical method are 174.40, 0.74, and 0.27, respectively. The sampling, sample preparation, and analytical steps of the aflatoxin test procedure accounted for 99.4, 0.4, and 0.2% of the total variability, respectively.

Aflatoxins↗
PubMed1991

Reverse sample genome probing, a new technique for identification of bacteria in environmental samples by DNA hybridization, and its application to the identification of sulfate-reducing bacteria in oil field samples.

A novel method for the identification of bacteria in environmental samples by DNA hybridization is presented. It is based on the fact that, even within a genus, the genomes of different bacteria may have little overall sequence homology. This allows the use of the labeled genomic DNA of a given bacterium (referred to as a "standard") to probe for its presence and that of bacteria with highly homologous genomes in total DNA obtained from an environmental sample. Alternatively, total DNA extracted from the sample can be labeled and used to probe filters on which denatured chromosomal DNA from relevant bacterial standards has been spotted. The latter technique is referred to as reverse sample genome probing, since it is the reverse of the usual practice of deriving probes from reference bacteria for analyzing a DNA sample. Reverse sample genome probing allows identification of bacteria in a sample in a single step once a master filter with suitable standards has been developed. Application of reverse sample genome probing to the identification of sulfate-reducing bacteria in 31 samples obtained primarily from oil fields in the province of Alberta has indicated that there are at least 20 genotypically different sulfate-reducing bacteria in these samples.

Journal Article↗
PubMed2000

An automated method of sample preparation of biofluids using pierceable caps to eliminate the uncapping of the sample tubes during sample transfer.

Biological samples are normally collected and stored frozen in capped tubes until analysis. To obtain aliquots of biological samples for analysis, the sample tubes have to be thawed, uncapped, samples removed and then recapped for further storage. In this paper, we report an automated method of sample transfer devised to eliminate the uncapping and recapping process. This sampling method was incorporated into an automated liquid-liquid extraction procedure of plasma samples. Using a robotic system, the plasma samples were transferred directly from pierceable capped tubes into microtubes contained in a 96-position block. The aliquoted samples were extracted with methyl-tert-butyl ether in the same microtubes. The supernatant organic layers were transferred to a 96-well collection plate and evaporated to dryness. The dried extracts were reconstituted and injected from the same plate for analysis by liquid chromatography with tandem mass spectrometry.

Blood Chemical Analysis↗
PubMed1994

[A simple method for measurement of cerebral blood flow using 123I-IMP SPECT with calibrated standard input function by one point blood sampling; validation of calibration by one point venous blood sampling as a substitute for arterial blood sampling].

In a simplified method for measurement of cerebral blood flow using one 123I-IMP SPECT scan and one point arterial blood sampling (Autoradiography method), input function is obtained by calibrating a standard input function by one point arterial blood sampling. A purpose of this study is validation of calibration by one point venous blood sampling as a substitute for one point arterial blood sampling. After intravenous infusion of 123I-IMP, frequent arterial and venous blood sampling were simultaneously performed on 12 patients of CNS disease without any heart and lung disease and 5 normal volunteers. The radioactivity ratio of venous whole blood which obtained from cutaneous cubital vein to arterial whole blood were 0.76 +/- 0.08, 0.80 +/- 0.05, 0.81 +/- 0.06, 0.83 +/- 0.11 at 10, 20, 30, 50 min after 123I-IMP infusion, respectively. The venous blood radioactivities were always 20% lower than those of arterial blood radioactivity during 50 min. However, the ratio which obtained from cutaneous dorsal hand vein to artery were 0.93 +/- 0.02, 0.94 +/- 0.05, 0.98 +/- 0.04, 0.98 +/- 0.03, at 10, 20, 30, 50 min after 123I-IMP infusion, respectively. The venous blood radioactivity was consistent with artery. These indicate that arterio-venous difference of radioactivity in a peripheral cutaneous vein like a dorsal hand vein is minimal due to arteriovenous shunt in palm. Therefore, a substitution by blood sampling from cutaneous dorsal hand vein for artery will be possible. Optimized time for venous blood sampling evaluated by error analysis was 20 min after 123I-IMP infusion, which is 10 min later than that of arterial blood sampling.

Amphetamines↗
PubMed1995

Sample self-stacking and sample stacking in zone electrophoresis with major sample components of like charge: general model and scheme of possible modes.

A theoretical study is presented of zone electrophoretic behavior of samples that contain one or more minor analytes and at least one major ionogenic component of like charge. Based on a simple model comprising weak univalent anionic electrolytes, conditions are derived under which analytes are temporarily focused isotachophoretically into very narrow zones by a sample self-stacking effect provided by the major sample components. Requirements for minimal/maximal mobility and a background coion concentration dependent minimal concentration of a major sample component (stacker) are presented. For systems in which sample self-stacking does not apply, an expression for the concentrating factor is derived that involves the effects of both nonselective (classical) and selective sample stacking, the latter being a consequence of electrophoretic separation of the minor analyte from the major component. The theory derived is discussed with selected model examples by using both numerical calculation and computer simulation.

Electric Conductivity↗
PubMed1996

Stability of free prostate-specific antigen in serum samples under a variety of sample collection and sample storage conditions.

OBJECTIVES: Four studies were conducted to characterize the stability of free and total prostate specific antigen (PSA) under various sample collection and storage conditions. METHODS: In the first study, fresh blood from 11 patients was drawn and allowed to clot at room temperature (RT). Serum was prepared by centrifugation 1, 3, 5, or 8 hours after the blood draw and tested to determine the free and total PSA levels. In the second study, serum specimens from 12 individuals were stored at RT or 4 degrees C and were tested on days 0, 1, 2, and 7. In the third study, four fresh serum samples were subjected to five freeze-thaw cycles and tested after each cycle. In the fourth study, 29 fresh samples were aliquoted, frozen at -20 degrees C or -70 degrees C, and monitored for long-term stability. RESULTS: Approximately 1% of the free PSA was lost per hour of clotting time. Between 2% and 3% of the free PSA was lost per day of storage at 4 degrees C or 23 degrees C. About 0.9% of the free PSA was lost per month of storage at -20 degrees C compared with about 0.4% per month at -70 degrees C. Total PSA appeared to be stable throughout these studies. CONCLUSIONS: Our results suggest that routine serum preparation and refrigerated storage of samples for up to 24 hours is acceptable for the measurement of both free and total PSA. Samples that are to be retained for longer than 24 hours should be frozen. Samples stored for extended periods should be kept at -70 degrees C.

Aged↗
PubMed1995

Delayed matching-to-sample performance of hens: Effects of sample duration and response requirements during the sample.

Six domestic hens were trained under a delayed matching-to-sample procedure with red and green keylights as sample and comparison stimuli and a 1.5-s delay interval. The hens were trained to stop pecking the sample stimuli when a tone sounded. Duration of the sample stimuli (2 to 10 s) and the number of pecks required on the key on which these stimuli were presented (0 to 10) were altered across conditions. Both the response requirement on the sample key and the duration of sample presentations affected accuracy. These findings are in agreement with those of earlier studies using other species and somewhat different procedures.

Journal Article↗
PubMed1998

Elastic modulus of equine hoof horn, tested in wall samples, sole samples and frog samples at varying levels of moisture.

The elastic (E-) modulus of hoof horn samples as a function of moisture content was determined from different segments of the equine hoof. 110 hoof horn specimens with different pigmentation taken from six adult warm-blooded horses with no obvious pathological changes within t he foot were used for the 177 tension and bending tests which were performed in accordance with ASTM D 5026, ASTM D 5023 and DIN 53.457. E-moduli were determined under physiological conditions with mean 761.8, SD +/- 295.4 N/mm for dorsal wall samples, 708 +/- 280.4 N/mm2 for lateral wall samples, 230 +/- 92.4 N/mm2 for sole horn and 9.9 +/- 0.6 N/mm2 for frog horn. Dorsal wall and lateral wall did not differ significantly. E-moduli of the various hoof horn segments differ significantly when tested under physiological moisture. The physiological moisture content also varies significantly between the segments: wall samples mean 22.7 +/- SD 3.4%, sole samples 31.5 +/- 3.1%, frog samples 34.6 +/- 3.3%. In contrast, the E-moduli and the moisture contents of the various segments were approximately identical, when tested after drying at 65% humidity over 6 days.

Animals↗
PubMed1998

On-column sample preconcentration using sample matrix switching and field amplification for increased sensitivity of capillary electrophoretic analysis of physiological samples.

An on-line sample concentration method using sample matrix switching and field amplification peak stacking has been developed. A microbore LC guard column is used to slightly retain the analytes in order to switch from a high ionic strength sample matrix (the physiological fluid) to a low ionic strength matrix (the LC mobile phase). The eluted LC peak is then trapped in a CE system and preconcentrated by field amplification peak stacking. The concentrated sample peak is then analyzed by CE. Compared to normal hydrodynamic injection, the sensitivity was increased by more than 500-fold without loss in resolution. A limit of detection of less than 10 nM for a physiological sample was achieved using UV adsorption detection. This method can be used for negatively or positively charged analytes.

Bupivacaine↗
PubMed1991

Sampling success and risk by transabdominal chorionic villus sampling, transcervical chorionic villus sampling and amniocentesis: a randomized study.

A total of 3347 women were randomized to either transabdominal chorionic villus sampling, transcervical chorionic villus sampling or amniocentesis. Unless induced or spontaneous abortion had occurred, they had all completed up to 28 weeks of pregnancy at the time of analysis. No significant difference was seen between total fetal loss in the transabdominal chorionic villus sampling group and the amniocentesis group (6.2% and 6.6%, respectively, SE difference 0.92%, p = 0.01). The total fetal loss in the transcervical group was 10.1%. When the number of failed procedures and those cases which were evaluated as infeasible for the assigned method, are compared, the overall sampling efficacy is less good transcervically than transabdominally. After pooling our data with data from the Canadian randomized study and the American non-randomized study, the difference in risk between transcervical chorionic villus sampling and amniocentesis was 2.1%, SE difference = 0.64%, p = 0.8.

Clinical Trial↗
PubMed2005

Evaluation of sample recovery of malodorous livestock gases from air sampling bags, solid-phase microextraction fibers, Tenax TA sorbent tubes, and sampling canisters.

Odorous gases associated with livestock operations are complex mixtures of hundreds if not thousands of compounds. Research is needed to know how best to sample and analyze these compounds. The main objective of this research was to compare recoveries of a standard gas mixture of 11 odorous compounds from the Carboxen/PDMS 75-microm solid-phase microextraction fibers, polyvinyl fluoride (PVF; Tedlar), fluorinated ethylene propylene copolymer (FEP; Teflon), foil, and polyethylene terephthalate (PET; Melinex) air sampling bags, sorbent 2,b-diphenylene-oxide polymer resin (Tenax TA) tubes, and standard 6-L Stabilizer sampling canisters after sample storage for 0.5, 24, and 120 (for sorbent tubes only) hrs at room temperature. The standard gas mixture consisted of 7 volatile fatty acids (VFAs) from acetic to hexanoic, and 4 semivolatile organic compounds including p-cresol, indole, 4-ethylphenol, and 2'-aminoacetophenone with concentrations ranging from 5.1 ppb for indole to 1270 ppb for acetic acid. On average, SPME had the highest mean recovery for all 11 gases of 106.2%, and 98.3% for 0.5- and 24-hr sample storage time, respectively. This was followed by the Tenax TA sorbent tubes (94.8% and 88.3%) for 24 and 120 hr, respectively; PET bags (71.7% and 47.2%), FEP bags (75.4% and 39.4%), commercial Tedlar bags (67.6% and 22.7%), in-house-made Tedlar bags (47.3% and 37.4%), foil bags (16.4% and 4.3%), and canisters (4.2% and 0.5%), for 0.5 and 24 hr, respectively. VFAs had higher recoveries than semivolatile organic compounds for all of the bags and canisters. New FEP bags and new foil bags had the lowest and the highest amounts of chemical impurities, respectively. New commercial Tedlar bags had measurable concentrations of N,N-dimethyl acetamide and phenol. Foil bags had measurable concentrations of acetic, propionic, butyric, valeric, and hexanoic acids.

Acetophenones↗
PubMed1990

A new comprehensive technique of catheterisation, blood sampling, sample preparation and sample analysis by means of high-pressure liquid chromatography for pharmacokinetic studies with estradiol-linked nitrosoureas and their metabolites.

Estradiol-linked nitrosoureas are offering new perspectives in the antineoplastic chemotherapy of estradiol-receptor positive mammary carcinomas. In such a molecule estradiol has the function of a carrier which brings about a specific accumulation of the anticancer drug in estradiol-receptor containing tumor cells. However, there is only little knowledge about the pharmacokinetic behavior of this new group of anticancer agents. For that reason a new comprehensive technique of catheterisation, blood sampling, sample preparation and sample analysis with high-pressure liquid chromatography (HPLC) for preclinical pharmacokinetic studies with estradiol-linked nitrosoureas and their metabolites has been developed. N-(2-Chloroethyl)-N-nitroso-carbamoyl-L-alanine-estradiol-17-ester (CNC-alanine-estradiol-17-ester) and N-(2-chloroethyl)-N-nitroso-carbamoyl-L-alanine (CNC-alanine) were used as test compounds. The drugs were tested in female Sprague-Dawley rats with chemically induced mammary carcinomas. The laboratory animals were supplied with two catheters prior to the pharmacokinetic experiments. The blood samples were drawn from the vena cava catheter after the drug had been applied through a vena jugularis catheter. The compounds were extracted from plasma with C18 silicagel reversed phase cartridges. The clean-up technique delivered clear samples only slightly contaminated with the biological matrix. The recovery from plasma was 75 +/- 5% for the hormone-linked CNC-alanine-estradiol-17-ester and 70 +/- 5% for the unlinked CNC-alanine. The analysis was carried out by means of HPLC.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine↗
PubMed1993

[Planning of sampling for linkage analysis. Sample size and sampling method].

There is a proposed method for evaluation of the minimal sample size needed for the predefined quality of the linkage decision. It is applied to samples of arbitrary structured pedigrees ascertained via proband in accordance with different ascertainment schemes. The quality of the linkage decision is determined by the I and II type errors of the likelihood ratio constructed with a simple alternative hypothesis about the recombination fraction value. Comparison of these minimal sample sizes for different ascertainment schemes leads to a possibility to choose the best of them when the model of genetic control of two traits is given. A possibility to evaluate each of these ascertainments by a cost of the sample collection and to point out the cheapest is considered.

Genes, Dominant↗
PubMed2001

Large-volume sample stacking for on-capillary sample enrichment in the determination of naphthalene- and benzenesulfonates in real water samples by capillary zone electrophoresis.

We investigated the on-line preconcentration of a test mixture of 15 substituted and unsubstituted naphthalene(NSs) and benzenesulfonates (BZSs) by large-volume sample stacking (LVSS). Analyses were carried out by capillary zone electrophoresis (CZE) with on-column UV detection. In particular, we focused on how experimental variables such as the inside diameter of the capillary, the volume of sample introduced and polarity switching influenced the enrichment procedure. The best results were obtained when 300 nl were injected and stacked using a bubble cell capillary. Under these conditions, LVSS increased the detector response of conventional hydrodynamic injection by a factor of 40. The limits of detection of the method were between 5 and 10 microg l(-1). Determinations were reproducible, in terms of peak area and migration time, under such conditions. The performance of the method was examined by determining NS and BZS in real samples, such as tap, river and surface waters and inflow/outflow waters from a water treatment plant. Real samples were injected directly into the CZE column with little or no preparation.

Benzenesulfonates↗