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PubMed1995

Comparison of transcervical and transabdominal chorionic villus sampling loss rates in nine thousand cases from a single center.

OBJECTIVES: Our purposes were (1) to compare the safety of transabdominal and transcervical chorionic villus sampling with the use of a consistent technique at one center and (2) to determine whether the training of fellows can be accomplished without an increase in the loss rate. STUDY DESIGN: We performed a retrospective comparison of transabdominal and transcervical chorionic villus sampling loss rates from procedures performed by three principal operators between 1984 and 1992. The type of procedure was chosen by the operator at the time of the procedure on the basis of placental location. RESULTS: Procedures 1 through 2573 were performed solely by transcervical chorionic villus sampling and had an overall fetal loss rate of 5.12%. With the addition of transabdominal chorionic villus sampling the overall fetal loss rate dropped to 3.07% (p < 0.0001). Three and one half years after the start of transabdominal chorionic villus sampling (about 1300 transabdominal chorionic villus sampling procedures), the transabdominal chorionic villus sampling loss rate was significantly better than the transcervical loss rate (p = 0.035), and the difference widened steadily after that. During the same time period seven fellows performed 716 procedures for a fetal loss rate among fellows of 2.72%. CONCLUSIONS: (1) Under optimal circumstances (one center, large numbers, few operators, consistent technique, operator choice of best approach), transabdominal chorionic villus sampling may be inherently safer than transcervical chorionic villus sampling. (2) The addition of transabdominal chorionic villus sampling decreases overall chorionic villus sampling loss rates. (3) Although the number of procedures performed by fellows is small, it appears that with close supervision by experienced operators successful training of fellows can be accomplished without adverse effects on loss rates.

Chi-Square Distribution↗

PubMed2005

Built environment and behavior: spatial sampling using parcel data.

PURPOSE: The quality and economy of inferential research rely heavily on the sampling method. This paper addresses a methodological challenge in environment-behavior research: sampling respondents in relation to their built environmental characteristics. METHODS: A discussion of issues related to traditional neighborhood-based sampling serves to introduce a new spatial sampling strategy. Spatial sampling consists of defining conceptual population of interest, constructing spatial sample frame using parcel-level environmental data in GIS, examining the sample frame, determining the sampling design and size, and drawing the samples. An application of this method is illustrated using a recent study examining environmental correlates of walking and biking. RESULTS: Spatial sampling with parcel-level data ensures sufficient variations in and proper distributions of the environmental variables of interest, while controlling for the conditions of no interest. The use of the individual as unit of analysis offers an economic, generalizable, and easily interpretable approach to environment-behavior research, and discourages the potentially erroneous a priori definition of neighborhoods and aggregation problems. CONCLUSIONS: With its capacity to consider a broad range of detailed environmental variables, spatial sampling contributes to finding new or stronger environment-behavior associations and to the growing number of studies using the social ecologic model.

Bicycling↗

PubMed2003

Usefulness of multiple-site venous sampling in the treatment of adrenocorticotropic hormone-producing pituitary adenomas.

BACKGROUND: While venous sampling for adrenocorticotropic hormone (ACTH) may be the most accurate way to establish a diagnosis of Cushing's disease, its usefulness for lateralization of adenomas is limited even in combination with simultaneous bilateral sampling methods. Therefore, to increase accuracy in predicting the lateralization of adenomas, we performed a trial in which we carried out simultaneous venous sampling from multiple sites of the cavernous sinus (CS) and inferior petrosal sinus (IPS). Here we report on the usefulness of our method in the correct tumor lateralization in patients with Cushing's disease. METHODS: Eighteen patients with Cushing's disease underwent simultaneous bilateral ACTH sampling. The samples were obtained from the anterior, middle, and posterior CS and the IPS. CS sampling after stimulation with corticotropin-releasing hormone (CRH) was also performed. The central-to-peripheral ACTH ratio (c/p ratio) was calculated using sampling data from each site; the lateralizing gradients (right versus left) were calculated using the c/p ratio. Instead of the conventional method where the lateralization gradient is based on sampling data from a single site, we used the distribution of the c/p ratio determined from multiple-site data. RESULTS: There was no significant difference in the mean lateralization gradient obtained from each set of sampling data (p > 0.05). With the conventional method, correct tumor lateralization was obtained in 50% of tumors in the IPS; 72.2 to 77.8% of tumors in the CS; and 77.8% of tumors in the middle CS after CRH. Our method using ACTH contour analysis based on multiple sites produced correct results in all 18 of the patients examined. The difference in correct calls between the conventional method and our method was significant (p < 0.05). CONCLUSIONS: Multiple-site sampling of ACTH is valuable for lateralizing the adenoma in patients with Cushing's disease; it produces more correct results than does single venous sampling.

Adenoma↗

PubMedDate not supplied

Evaluation of sampling methods in research reported in selected clinical nursing journals: implications for nursing practice.

This article summarizes standards relating to sampling methodology, identifies deviations from these standards in research studies reported in selected clinical nursing journals, and provides suggestions for improving sampling methods to enhance the applicability of research for nursing practice. A random sample of 30 research reports published in 1986 in five clinical nursing journals was examined. Nearly 97 per cent of the published studies contained at least one major deficiency in sampling methodology. More than two thirds failed to describe the sampling frame, sample size, or number of refusals, withdrawals, and/or cases lost. Thirteen per cent did not report sampling methods. More than half made generalizations that were inappropriate for the sampling method used; 43 per cent did not acknowledge any limitations of their sample. Sample sizes were small, and statistical power to detect significant differences was low. These deficiencies in sampling procedures could detract from the value of the research that nurses are encouraged to use as a basis for practice. This article provides specific recommendations for remedying these deficiencies to help ensure the scientific merit of the research published for nursing practice.

Clinical Nursing Research↗

PubMed2002

Evaluation of concurrent personal measurements of acrylonitrile using different sampling techniques.

In a retrospective assessment of employee exposure to acrylonitrile (AN) for an epidemiological study, investigators from the National Cancer Institute (NCI) and the National Institute for Occupational Safety and Health (NIOSH) evaluated the feasibility of using historic acrylonitrile air samples without modification. The evaluation discussed here was to determine whether the air sampling results across plants were comparable. During site visits to each plant conducted between 1984 and 1986, study investigators collected personal air samples for four days on approximately ten jobs per day. During these visits, IHs at seven of the eight plants also collected personal samples to compare their sample values to the study-collected sample values. Each plant's IH collected these concurrent measurements for their own use and independent of the IHs at the other plants. The plant IHs had no common sampling protocol but, rather, used professional judgment in deciding sampling logistics for their concurrent measurement. In addition, each plant IH used a different laboratory to analyze samples (the study industrial hygienists used one laboratory). Three sampling methods were used by plant industrial hygienists to collect concurrent measurements: charcoal tubes, passive monitors, and porous polymer tubes. The study investigators only used charcoal tubes. Two hundred and sixty four (264) pairs of concurrent measurements were collected. To assess the +/- comparability of the data sets, paired-observation tests were used. The two sets of charcoal tubes were found to compare favorably with each other. The study's charcoal tubes were 1.2 times higher than results from plant passive monitors. No correlation was found between the study's charcoal tube results and plant porous polymer tube results, although the means for 34 pairs of samples were equivalent. As a result of this evaluation, the investigators decided that no adjustments would be made to the plant measurements. This type of evaluation should be considered when using measurement data in multisite epidemiological studies.

Acrylonitrile↗

PubMedDate not supplied

Determination of carbon disulfide at the workplace by sampling on charcoal tubes--problems and solutions.

The aim of the study was to check the reliability and comparability of different analytical methods for ambient monitoring of carbon disulfide (CS2). A stationary sampling system, consisting of a charcoal sampling tube and pump, and two personal sampling systems, consisting of a charcoal sampling tube and a portable pump and of a diffusive charcoal sampler have been compared. The limits of quantification, within-series precision, between-series precision, recovery, and comparability of the methods were investigated. For passive sampling the recovery was determined by three different techniques. For a sampling time of 6 hours the limit of quantification was 0.2 ppm for the personal sampling and 0.01 ppm for the stationary sampling system. The within-series precision was between 5 and 8%. For personal sampling the between-series precision was between 9 and 12% using a passive sampler. The recovery ranged between 45 and 85% depending on the quotient of eluent volume and charcoal mass. The comparison of the two personal sampling methods in a field study using linear regression demonstrated with statistical certainty an excellent concordance of the methods. The study shows that particularly the method for determining air levels of carbon disulfide by passive sampling is associated with high systematic errors. If these errors are unknown or ignored they will result in highly underestimated exposure data for carbon disulfide.

Carbon Disulfide↗

PubMed2006

Sampling for collection of central line-day denominators in surveillance of healthcare-associated bloodstream infections.

OBJECTIVE: To determine the feasibility of estimating the number of central line-days at a hospital from a sample of months or individual days in a year, for surveillance of healthcare-associated bloodstream infections. DESIGN: We used data reported to the National Nosocomial Infections Surveillance system in the adult and pediatric intensive care unit component for 1995-2003 and data from a sample of hospitals' daily counts of device use for 12 consecutive months. We calculated the percentile error as the central line-associated bloodstream infection percentile based on rates per line-days minus the percentile based on rates per estimated line-days. SETTING AND PARTICIPANTS: A total of 247 hospitals were used for sampling whole months and 12 hospitals were used for sampling individual days. RESULTS: For a 1-month sample of central line-days data, the median percentile error was 3.3 (75th percentile, 7.9; 90th percentile, 15.4). The percentile error decreased with an increase in the number of months sampled. For a 3-month sample, the median percentile error was 1.4 (75th percentile, 4.3; 95th percentile, 8.3). Sampling individual days throughout the year yielded lower percentile errors than sampling an equivalent fraction of whole months. With 1 weekday sampled per week, the median percentile error ranged from 0.65 to 1.40, and the 90th percentile ranged from 2.8 to 5.0. Thus, for 90% of units, collecting data on line-days once a week provides an estimate within +/-5 percentile points of the true line-day rate. CONCLUSION: Sample-based estimates of central line-days can yield results that are acceptable for surveillance of healthcare-associated bloodstream infections.

Adult↗

PubMed2005

A modelling approach to estimate the sensitivity of pooled faecal samples for isolation of Salmonella in pigs.

The objective of this study was to develop and parametrize a mathematical model of the sensitivity of pooled sampling of faeces to detect Salmonella infection in pigs. A mathematical model was developed to represent the effect of pooling on the probability of Salmonella isolation. Parameters for the model were estimated using data obtained by collecting 50 faecal samples from each of two pig farms. Each sample was tested for Salmonella at individual sample weights of 0.1, 0.5, 1, 10 and 25 g and pools of 5, 10 and 20 samples were created from the individual samples. The highest test sensitivity for individual samples was found at 10 g (90% sensitivity), with the 25 g test sensitivity equal to 83%. For samples of less than 10 g, sensitivity was found to reduce with sample weight. Incubation for 48 h was found to produce a more sensitive test than incubation for 24 h. Model results found increasing sensitivity with more samples in the pool, with the pools of 5, 10 and 20 being more sensitive than individual sampling, and the pools of 20 being the most sensitive of those considered.

Animals↗

PubMed1994

Pituitary tumour localization in patients with Cushing's disease by magnetic resonance imaging. Is there a place for petrosal sinus sampling?

OBJECTIVE: We wished to analyse the relative value and diagnostic accuracy of bilateral simultaneous inferior petrosal sinus blood sampling for plasma ACTH measurements when compared with pituitary magnetic resonance imaging (MRI) for the preoperative localization of microadenoma (tumour diameter < 10 mm) within the pituitary fossa in patients with Cushing's disease. DESIGN: Pituitary MRIs were assessed blind and independently. The sinus blood sampling was performed before and after administration of corticotrophin releasing hormone (CRH). The ratios of the ACTH concentrations in plasma samples from the inferior petrosal sinuses to the concentrations in peripheral blood plasma samples (the IPS:P ratio) and the ratios of the ACTH concentrations in samples from both inferior petrosal sinuses (the intersinus gradient) were calculated. PATIENTS: Twenty consecutive patients with Cushing's disease were prospectively studied. All but two patients subsequently underwent transsphenoidal exploration of the pituitary fossa. RESULTS: In three of 20 patients (15%), positioning of catheter tips in both inferior petrosal sinuses was unsuccessful. The diagnosis of Cushing's disease was confirmed by the greater basal IPS:P ratio amounting to > or = 2.0 in 13 of 17 patients (76%), and amounting to > or = 3.0 in CRH-stimulated peak samples in 15 of 17 patients (88%). Anatomical variations of the inferior petrosal sinus, precluding reliable conclusions about lateralization of pituitary venous ACTH drainage, were observed in five of 20 patients (25%). Adding the three patients with technical failure and one patient who presented with a macroadenoma (tumour diameter 11 mm), this left interpretable data with regard to lateralization of the microadenomas in only 11 of 20 patients (55%). In 15 of 20 patients (75%) a pituitary microadenoma was found at MRI. In 14 of these 15 patients (93%) a tumour was indeed found at that position at subsequent transsphenoidal operation. Concordance between the lateralization by the intersinus gradient and microadenoma localization by MRI was observed in six of 11 cases (55%) when using basal samples and in seven of 11 cases (64%) when using peak samples obtained after stimulation with CRH. Concordance between the lateralization by the intersinus gradient and subsequent microadenoma localization at surgery was observed in seven of 11 patients (64%) before and in eight of 11 cases (73%) after CRH stimulation. Reversal of the intersinus gradient after CRH stimulation, suggesting a shift in the lateralization to the contralateral side of the gland, was found in three of 12 cases (25%). CONCLUSIONS: Bilateral simultaneous inferior petrosal sinus blood sampling for plasma ACTH measurements before and after CRH stimulation successfully confirmed the diagnosis of pituitary dependent Cushing's disease in 15 of 17 patients (88%) in whom this diagnosis was suspected on the basis of conventional biochemical testing. Magnetic resonance imaging, however, is superior to bilateral simultaneous inferior petrosal sinus blood sampling for the localization/lateralization of pituitary microadenomas in patients with Cushing's disease. Therefore, bilateral simultaneous inferior petrosal sinus blood sampling should be reserved for the assessment of those patients with Cushing's syndrome in whom either the results of biochemical tests are equivocal and/or subsequent pituitary magnetic resonance imaging gives unconvincing results.

Adenoma↗

PubMed2006

Using probability vs. nonprobability sampling to identify hard-to-access participants for health-related research: costs and contrasts.

This article compares the recruitment costs and participant characteristics associated with the use of probability and nonprobability sampling strategies in a longitudinal study of older hemodialysis patients and their spouses. Contrasts were made of people who accrued to the study based on probability and nonprobability sampling strategies. Probability-based sampling was more time-efficient and cost-effective than nonprobability sampling. There were no significant differences between the respondents identified through probability and nonprobability sampling on age, gender, years married, education, work status, and professional job status. Respondents from the probability sample were more likely to be Protestant and less likely to be Catholic than those from the nonprobability sample. Respondents from the probability sample were more likely to be Black, whereas those from the nonprobability sample were more likely to be White. There are strengths and shortcomings associated with both nonprobability and probability sampling. Researchers need to consider representativeness and external validity issues when designing sampling and related recruitment plans for health-related research.

Aged↗

PubMed2006

Short communication: effectiveness of sample duplication to control error in ruminant digestion studies.

Eight ruminally cannulated lactating dairy cows from a study on the effect of dietary rumen-degraded protein on production and digestion of nutrients were used to assess using sample duplication to control day-to-day variation within animals and errors associated with sampling and laboratory analyses. Two consecutive pooled omasal samples, each representing a feeding cycle, were obtained from each cow in each period. The effectiveness of sample duplication in error control was tested by comparing the variance of the difference in treatment means when taking 2 samples from each cow in each period to the variance when taking only one sample. Compared with no duplication, sample duplication improved precision by reducing variance by 50, 40, 31, 23, 23, and 9% for, respectively, rumen-undegraded protein flows, ruminal neutral detergent fiber digestibility, microbial nonammonia N flow, microbial efficiency, organic matter flow, and organic matter truly digested in the rumen. For these same variables, reductions in the standard errors of the difference between treatment means due to sample duplication represented 100, 87, 73, 59, 58, and 27% of the predicted reductions resulting from doubling the number of experimental units without sample duplication. Sample duplication can substantially reduce experimental error originating from day-to-day variation within cows, sample collection, and laboratory analyses, thus improving statistical power in ruminant digestion studies.

Animals↗

PubMed2000

Epidemiology 1, 2, 3: study and sample design.

Bad sample designs and selection bias have plagued studies on schistosomiasis, and as a result some believe that schistosomiasis is too focal, making it difficult to draw reliable samples. The Epidemiology 1, 2, 3 (EPI 1, 2, 3) sample design, although complex, demonstrates that sampling theory is readily applicable to epidemiologic studies of schistosomiasis. The EPI 1, 2, 3 sampling scheme was designed to achieve the smallest feasible standard errors given EPI 1, 2, 3 objectives and certain logistical constraints. The sample design is a multi-stage selection of villages (ezbas, which were stratified by size) and households within each of 9 purposely selected Egyptian governorates. Villages and households were systemically selected from census frames. The sampling of ezbas was especially difficult because of the lack of complete sampling frames and their wide variation in population size. Ultimately, ezbas were stratified by size and then randomly selected from each stratum. Sample sizes for villages and ezbas and individuals within ezbas were calculated based on EPI 1 and 2 objectives, respectively. No re-selection was made for non-respondents. A 20% subsample of the full sample was drawn for clinical and ultrasonographic examinations. The sample selected from individual governorates closely parallel the age structure of the 1986 census of the respective rural populations. Details of the study design and related methods are given below.

Egypt↗

PubMed2003

Impact of random and fixed (optimal) sampling approach on the Bayesian estimation of clearance.

BACKGROUND AND OBJECTIVE: The population pharmacokinetic approach is based on sparse sampling. In sparse sampling approaches, the selection of the time point(s) is very critical for the prediction of pharmacokinetic parameters. Several investigators have shown that the predictive performance of the Bayesian approach is influenced by the initial estimates of pharmacokinetic parameters as well as the time of blood sampling. The objective of this study is to evaluate the impact of random and fixed sparse sampling approach on the Bayesian estimation of clearance. METHODS: Three drugs were selected for this study. Two sparse sampling methods (random or fixed) using Bayesian approach were used to assess clearance in healthy subjects following a single oral dose. The initial estimates of the model parameters and inter- and intra-subject variabilities were obtained from the previous pharmacokinetic studies conducted in healthy volunteers. The predicted clearance values using sparse sampling (1, 2 or 3 blood samples per subject) were compared with the clearance values obtained by extensive sampling. RESULTS AND CONCLUSION: The results indicated that both random and fixed sampling approaches, irrespective of number of blood samples, can be used to estimate mean population as well as post hoc predicted individual clearance (Bayesian) with accuracy. However, the precision of the prediction of clearance was found to be better with fixed rather random blood sampling approach.

Bayes Theorem↗

PubMed2004

[The algorithm of eliminating the similar samples in the process of calibration and prediction].

During the manufacture and debugging of the NIR instruments it is compulsory to make final calibration analysis to verify whether the instruments operate correctly. However, the conventional method of NIR calibration needs to make calibration analysis for the instruments with all the samples at hand. In fact in order to cover the samples that will be encountered in the future the amount of the samples set and the labor that the personnel need to offer are enormous. In this paper a new algorithm is presented which can be used to effectively eliminate the similar samples in the original sample set. By using this algorithm we have chosen 94 optimal samples in the original 178 sample set successfully. After performing calibration experiment we found that the sample set chosen by this algorithm are equally representative to the original sample set and obtained almost the same precision compared to the original sample set when the two sample sets were individually calibrated. This algorithm brings great relief to the labor of the workers, presents the possibility of performing more experiments and greatly improves the efficiency of performing calibration experiment. As a result, the amount of calibration sets and the labor of the personnel are reduced remarkably.

Algorithms↗

PubMed1993

Sampling a hidden population: noninstitutionalized drug users.

As the spread of AIDS continues, there is an urgent need to understand patterns of drug use among drug users. While it is recognized that probability samples are scientifically preferable, there is a need to balance the realities of field research targeting an elusive population with the need for a sound sampling plan. A purposive or targeted sampling plan can increase the possibility of obtaining a representative sample of drug users. Targeted sampling involves using several sampling methods. First, neighborhoods with high concentrations of drug users are identified within the community in order to identify clusters of individuals in the target population. Once the geographic areas from which to sample have been identified, stratification can be used as an effective way to get a representative sample from neighborhoods with differing drug use patterns. The sampling plan can be further strengthened by the use of quota sampling to ensure that subgroups of drug users are adequately represented in the sample.

Epidemiologic Methods↗

PubMed1998

Random vs. systematic sampling from administrative databases involving human subjects.

OBJECTIVE: Two sampling techniques, simple random sampling (SRS) and systematic sampling (SS), were compared to determine whether they yield similar and accurate distributions for the following four factors: age, gender, geographic location and years in practice. METHOD: Any point estimate within 7 yr or 7 percentage points of its reference standard (SRS or the entire data set, i.e., the target population) was considered "acceptably similar" to the reference standard. The sampling frame was from the entire membership database of the Canadian Chiropractic Association. The two sampling methods were tested using eight different sample sizes of n (50, 100, 150, 200, 250, 300, 500, 800). From the profile/characteristics, summaries of four known factors [gender, average age, number (%) of chiropractors in each province and years in practice], between- and within-methods chi 2 tests and unpaired t tests were performed to determine whether any of the differences [descriptively greater than 7% or 7 yr] were also statistically significant. The strengths of the agreements between the provincial distributions were quantified by calculating the percent agreements for each (provincial pairwise-comparison methods). Any percent agreement less than 70% was judged to be unacceptable. RESULTS: Our assessments of the two sampling methods (SRS and SS) for the different sample sizes tested suggest that SRS and SS yielded acceptably similar results. Both methods started to yield "correct" sample profiles at approximately the same sample size (n > 200). CONCLUSION: SS is not only convenient, it can be recommended for sampling from large databases in which the data are listed without any inherent order biases other than alphabetical listing by surname.

Age Factors↗

PubMed2002

A functional neuropeptide Y Leu7Pro polymorphism associated with alcohol dependence in a large population sample from the United States.

BACKGROUND: Quantitative trait locus studies, and observations in animals manipulated for the neuropeptide Y (NPY) gene suggest that variation within this gene may contribute to alcoholism. A recent population study suggested that the Pro7 allele of a functional NPY polymorphism (Leu7Pro) may be associated with increased alcohol consumption. We tested whether the Pro7 allele is associated with alcohol dependence in European Americans (EA). METHODS: The design was a population study comparing the Leu7Pro allele frequencies in alcohol-dependent subjects and controls. Population stratification potential and diagnostic specificity was studied by genotyping individuals from additional populations and psychiatric diagnostic classes. We studied 2 independently collected samples of EA alcohol-dependent subjects (sample 1, n = 307; sample 2, n = 160) and a sample of psychiatrically screened EA controls (n = 202); 8 population samples, including African Americans and European Americans (total n = 551); and 4 samples of individuals with Alzheimer disease, schizophrenia, posttraumatic stress disorder, and major depression (total n = 502). The main outcome measure was the difference in Leu7Pro allele frequencies between alcohol-dependent subjects and controls. RESULTS: The frequency of the Pro7 allele was higher in the alcohol-dependent subjects (sample 1, 5.5%; sample 2, 5.0%) compared with the screened EA controls (2.0%) (sample 1 vs controls, P=.006; sample 2 vs controls, P=.03). The attributable fraction (excess morbidity) in similarly affected populations, owing to the Pro7 allele, was estimated to be 7.3%. The frequency of the Pro7 allele was equal or lower in the population samples, as compared with the screened EA controls (0%-2.2%), with 1 exception (Bedouins). We found no significant evidence that the association of the Pro7 allele with alcohol dependence was due to an association with a comorbid psychiatric disorder. CONCLUSIONS: These results suggest that the NPY Pro7 allele is a risk factor for alcohol dependence. This is only the second specific genetic mechanism ever identified that modulates risk for alcohol dependence.

Alcohol Drinking↗

PubMed1999

Homogeneous sample preparation for automated high throughput analysis with matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry.

This work presents a simple method for obtaining homogeneous sample surfaces in matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) for the automated analysis of peptides and proteins. The sample preparation method is based on applying the sample/matrix mixture onto a pre-deposited highly diluted matrix spot. The pre-deposited crystals act as seeds for the new sample containing crystals which become much smaller in size and more evenly distributed than with conventional methods. This 'seed-layer' method was developed, optimised and compared with the dried-droplet method using peptides and proteins in the 1000-20,000 Da range. The seed-layer method increases the surface homogeneity, spot to spot reproducibility and sample washability as compared with the commonly used dried-droplet method. This methodology is applicable to alpha-cyanohydroxycinnamic acid, sinapinic acid and ferulic acid, which all form homogeneous crystal surfaces. Within-spot variation and between-spot variation was investigated using statistics at a 95% confidence level (n = 36). The statistical values were generated from more than 5000 data points collected from 500 spectra. More than 90% of the sample locations results in high intensity spectra with relatively low standard deviations (RSDs). Typically obtained data showed an RSD of 19-35% within a sample spot as well as in-between spots for proteins, and an RSD of < or = 50% for peptides. Linear calibration curves were obtained within one order of magnitude using internal calibration with a point-RSD of 3% (n = 10). The sample homogeneity allows mass spectra (average of 16 laser shots) to be obtained on each individual sample within 15 sec, whereby a 100 spot target plate can be run in 25 min. High density target plates using the seed-layer method were prepared by spotting approximately 100 picoliter droplets onto the target, resulting in sample spots < or = 500 microns in diameter using a flow-through piezo-electric micro-dispenser. By using this automated sample preparation step lower standard deviations are obtained in comparison to manually prepared samples.

Coumaric Acids↗