Replication Precision Research Articles

Wet deposition of phosphorus in Florida

Wet deposition of phosphorus was measured at 10 sites across Florida originally established as part of the Florida Atmospheric Mercury Study conducted between 1992 and 1996. Monthly integrated samples were collected and analyzed using a total analytical protocol that incorporated “clean lab” conditions for sample equipment preparation and Aerochem Metrics collectors modified for suitability to use for ultra-trace elements. Samples also were collected aboard 15 m towers to minimize any influence on measured deposition by insects, etc., and locally originating particles that do not contribute to true net deposition. Extensive replication of samples in the field was conducted (ca. 83%). The average absolute difference between replicates was 16.2%, with a median absolute difference of 9.5%. Replicate precision was poorest for concentrations above 0.080 mg P l −1, suggesting that concentrations above this level are contaminated. The wet deposition concentrations and fluxes of phosphorus measured in this study are appreciably lower than those reported by previous investigators for wet deposition in Florida, and lie at the lower end of measurements reported in the recent literature. For example, the volume weighted mean concentration and flux for wet deposition across all our study sites averaged 0.005 mg P l −1 and 7.5 mg P m −2 yr −1, respectively, which is approximately 50% and 32% lower than that reported by Hendry et al. (1981 in Atmospheric Pollutants in Natural Waters. Ann Arbor Science, Ann Arbor. MI, pp. 199–215). Our lower measurements likely reflect three factors: (1) the ultra-trace element sampling and analytical protocols; (2) improved collector design to eliminate sampling artifacts (e.g., splash-off contamination and transfer of contaminants from the dry bucket); and (3) placement of collectors off the ground surface. Lower VWM concentrations were observed near the Florida coast; otherwise, strong spatial patterns across the state were absent. Seasonal variations in VWM also were not pronounced, although deposition fluxes were highest during the summer wet season in response to the strong seasonal distribution of rainfall.

A Critical Evaluation of Tangential-Flow Ultrafiltration for Trace Metal Studies in Freshwater Systems. 2. Total Mercury and Methylmercury

Laboratory and field investigations of 10 kDa polyethersulfone (PES) and regenerated cellulose (RCL) membranes were conducted to evaluate the utility of ultrafiltration (UF) for low-level mercury determinations in freshwaters. Laboratory investigations focused on blank levels, sorption loss, and charge rejection; while field investigations addressed mass balance closure, replicate precision, and permeate trends in concentration. A thorough mass balance approach was used throughout the investigation, and experiments were conducted across typical gradients in freshwater pH, specific conductance, and dissolved organic carbon (DOC). The minimum source-water HgT concentration that could be confidently processed from a 5 L volume was 0.5 ng L-1 for PES and 1.4 ng L-1 for RCL as determined by three times the standard deviation of our method blank. The minimum source-water MeHg concentration was 0.5 ng L-1 for PES and 0.2 ng L-1 for RCL based on river-water mass balance results. Mass balance closures were generally better for RCL than PES, especially for MeHg where 95% of the residuals (n = 21) were within ±30% of closure. Duplicate UF separations on RCL membranes, and between RCL and PES membranes, agreed within 16% in the colloidal and dissolved fractions for both total mercury (HgT) and MeHg. Mercury sorption loss and charge rejection were greater for PES membranes than RCL membranes, especially for low ionic strength waters (<100 μS cm-1). Increases in permeate concentration were observed as the UF separation progressed, and preconditioning the membrane with a subsample of the feed solution did not substantially improve the performance. Overall, RCL outperformed PES membranes in low ionic strength waters and therefore is preferred for investigations of mercury partitioning under ambient freshwater conditions.

A Critical Evaluation of Tangential-Flow Ultrafiltration for Trace Metal Studies in Freshwater Systems. 1. Organic Carbon

The utility of tangential flow ultrafiltration (TFUF) for size fractionation of natural organic matter (NOM) in freshwater streams was investigated, focusing on characterization or elimination of potential artifacts. Spiral-wound polyethersulfone (PES) and regenerated cellulose (RCL) membranes with nominal molecular weight limits of 10 kilodalton (kDa) and 100 kDa were compared as part of a large project assessing the utility of large volume (>5 L) ultrafiltration for determining trace metal speciation in freshwaters. With careful cleaning, reliable fractionations of carbon and trace metals in freshwater can be obtained, and a detailed protocol necessary to avoid potentially significant biases is presented. Both PES and RCL membranes can be cleaned efficiently to provide low carbon blanks (<0.03 mg C L-1) and recleaned at least 10 times without compromising membrane integrity. For RCL, residual acid from the cleaning procedure can lower the permeate pH to below 4 in low-alkalinity river samples, but this acid can be removed prior to sample filtration with a simple treatment. Mass balance experiments with stream NOM show good recovery (99.7% ± 9.5%, n = 67). Sorption losses are very low (on average, <2%) to RCL membranes but are higher for PES. Replicate precision is typically better than ±5% for carbon. There are significant differences between PES and RCL membranes: permeate carbon levels are similar, but RCL predicts a larger >10 kDa fraction and carbon sorption is more significant on PES. These findings could be explained by greater hydrophobic interactions of dissolved organic carbon with PES and charge interactions with RCL. A strong negative correlation is observed between the percent of colloidal carbon (10 kDa − 0.4 μm) and the log specific conductance of streamwaters (R 2 = 0.71).

A new method for the determination of trichloroacetic acid in spruce foliage and other environmental media.

Trichloroacetic acid (TCAA) is a phytotoxic chemical, present throughout the environment. The majority of methods for analysis of TCAA require chemical derivatisation and multiple extraction steps prior to analysis by gas-chromatography. Here, a new analytical method for TCAA determination in environmental matrices is reported. The method is based on a modified Nielsen-Kryger steam distillation that combines into one 1 h reflux the thermal decarboxylation of TCAA to CHCl3 and the partitioning and concentration of the CHCl3 into 5 ml of hexane, which is analysed by GC. Sample preparation is minimal and no matrix standard additions are required. The background CHCl3 in the sample is removed prior to extraction by degassing the solution for 1 h with nitrogen. Optimisation of the method gave recoveries from three separate solutions of 0.31 ppb aqueous TCAA standards of 93 +/- 15% (n = 9), 110 +/- 9% (n = 9) and 105 +/- 11% (n = 6). The extraction method has been compared with a decarboxylation and headspace GC method for determination of TCAA in Sitka spruce needles. No significant difference in TCAA concentration or replicate precision between the two methods was observed.

Construction and evaluation of automated gas chromatography for the measurement of anthropogenic halocarbons in the atmosphere

An automated gas chromatography system for analyzing atmospheric halocarbons was constructed and evaluated. A cryogenic trap was developed to facilitate automation and, at the same time, conserve liquid nitrogen. Concentration calibration was accomplished by the use of multi-component gas mixtures with ambient concentration levels. Reproducibility was evaluated with replicate precision of about 1–2% for most of the measured halocarbons, substantially better than that of our previous manual system of 4–6%. The linearity of this automated system was confirmed by two independent methods, with one varying injection volume and the other varying injection concentration, and both were in excellent agreement. The system was successfully employed in canister and in-situ measurements. Concentrations of CCl 4 was found to be extremely uniform with average concentration of 102 pp (v/v), very close to its global background value. The standard deviation of 106 samples was 1.5% for CCl 4 which is almost equivalent to its analytical precision. This uniform property associated with CCl 4 atmospheric distribution can be a useful tool for testing system’s reproducibility and stability.

Estimating the abundance of benthic invertebrates:a comparison of procedures and variability between observers

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 138:93-101 (1996) - doi:10.3354/meps138093 Estimating the abundance of benthic invertebrates: a comparison of procedures and variability between observers Benedetti-Cecchi L, Airoldi L, Abbiati M, Cinelli F Different procedures for underwater sampling of epifaunal organisms were compared for their robustness to bias due to observers and precision using multifactorial sampling designs. Variability among 3 observers was tested in relation to: (1) the method employed to estimate the percent cover of organisms (visual vs point-intercept technique); (2) the size of quadrats (50 x 50 vs 20 x 20 cm); (3) stress (sampling at the beginning vs the end of the dive), and (4) random factors that were likely to change from dive to dive. Precision was expressed in terms of standard errors (over 3 replicates) obtained with each method and size. Two cnidarians (Astroides calycularis and Leptosammia pruvoti) and 2 sponges (Petrosia ficiformis and Geodia cydonium) were considered in this study because of their abundance at the study site (a submarine cave). Much of the variability was related to significant differences between observers that changed from dive to dive for estimates of the cover of A. calycularis, and from dive to dive and with method for L. pruvoti. The small quadrats were more precise than the large ones when used to estimate the percent cover of A. calycularis and L. pruvoti, irrespective of method. In contrast, for P. ficiformis the small quadrats were more precise if sampled with the visual method, while the reverse occurred for the large quadrats. A trend toward a greater precision of the large quadrats sampled with the visual method was evident for G. cydonium, although no significant effects were found. Pilot studies and cost-benefit analyses were also used to determine the optimal allocation of resources (time) for sampling epifaunal organisms at different spatial scales in the cave, for each method and size of quadrats. The small units in conjunction with the visual method were most efficient. This procedure offered the best compromise between repeatability among observers, precision and maximization of replication for a fixed amount of resources. The large quadrats in conjunction with the visual method were probably more adequate for G. cydonium, given the apparent greater precision provided by this procedure for the large sponge. Caution is recommended in employing different researchers working on the same sampling project in extreme environments, at least before divergence among observers to changing environmental conditions is accounted for. Design of sampling . Robustness . Precision . Efficiency . Submarine caves . Invertebrates . Cost-benefit analyses Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 138. Publication date: July 25, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Development and validation of a gradient reversed-phase high-performance liquid chromatographic assay for S(−-2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin (N-0923) from a transdermal delivery system

A gradient reversed-phase HPLC method for potency determination of N-0923 (10 mg0 from a transdermal delivery system (TDS), was developed and validated with single point calibration yusing internal standard quantitation. N-0923 and the internal standard, N-0434, are eluted from a reversed-phase C 18 column using a gradient which contains 0.1 M triethylamine-0.04 M citrate buffer, pH 5.9, water, and acetonitrile with UV detection at 272 nm. N-0923 is isolated from the transdermal delivery system by extraction with n-heptane followed by extraction of the resulting organic phase with 0.1 M citric acid containing the internal standard. The method weas free from matrix interferences in both untreated and forced degraded placebo delivery systems. Acceptable linearity and quantitative recovery form spiked placebo delivery systems over the range 50–150% of nominal label claim were demonstrated. Within-day assay precision from individual samples of active transdermal dlivery systems ( n = 10) was 5.6% R.S.D. The detection limit was at least 0.1 μg/ml which is equivalent to 0.05% of the working standard concentration. Replicate injection precision at this level was 0.08% R.S.D. ( n =4). Analysis of thermally stressed active and placebo delivery systems with this HPLC method and photodiode-array detection showed that the chromatography was stability-indicating as demonstrated by the absence of measurable interferences from principal degradation products of either the N-0923 or the delivery system excipients.

Supercritical Fluid Extraction of Organochlorine Pesticides from Soil

Abstract A supercritical fluid extraction (SFE) method was developed for the extraction of 21 organochlorine (OC) pesticides from soil using dichloromethane as cosolvent and magnesium sulfate as drying agent. Average recoveries of spiked OCs from six different soils generally ranged from 70 to 95%, with an average replicate precision of ± 13%. For the extraction of two soils containing “native” OCs, the SFE method gave generally similar or higher concentrations compared to Soxhlet extraction. The precision of replicate analyses of native OCs using SFE and Soxhlet extraction was ± 0.009 and ± 0.007 ug/g, with 24 and 13 degrees of freedom respectively.

Proficiency Testing of Factor VIII:C Activitiy Assays at the Canadian Red Cross Society National Reference Laboratory

A national proficiency testing program has been established to monitor the accuracy and precision of factor VIII:C (FVIII:C) assays performed at the various Blood Services Centres of the Canadian Red Cross Society involved in the collection and processing of either donor blood designated for component production or plasma destined for fractionation. This paper describes the preparation, design, and results of the first four exercises involving 19 laboratories. The exercices were designed to allow the investigation of intralaboratory variability between replicate samples and precision of assays as well as the causes of interlaboratory variability. The implementation of this program has led to improved precision and interlaboratory agreement on FVIII;C assays. These improvements were achieved mainly as a result of a modification in the method for sample dilution, an increase in both replicate testing of the same sample and the number of sample dilutions, and a reduction in the number of reagent systems used by various centres.

New method for isolating and quantifying intermediate and beta-very-low-density lipoprotein cholesterol

We describe a new method, useful to clinical laboratories, for assessing intermediate density (IDL) or beta-very-low-density (beta-VLDL) lipoprotein cholesterol. The technique involves selective precipitation properties of the qualitative Wieland and Seidel post-electrophoretic method that immobilizes IDL and beta-VLDL in the beta-zone of an agarose slide (Clin Chem 1973;19:1139-41). In our method, we separate low-density lipoprotein (LDL) in a second electrophoretic step, in which LDL moves toward the anode, and then quantify the cholesterol of the above lipoproteins remaining in the precipitate band at the beta-zone. Replicate within-run precision (CV) of 15 aliquots of a sera pool was 10.1%. The correlation with sequential ultracentrifugation of 30 samples was r = 0.96 (P less than 0.001). Serum reference values for 30 normal individuals are 57 +/- 7.0 mg/L. Seven phenotype III hyperlipoproteinemic patients had the highest concentrations of IDL or beta-VLDL cholesterol in serum, 1620 +/- 346 mg/L.

An automated procedure for measuring biotinidase activity in serum.

In this automated procedure for quantifying biotinidase activity in human serum, a manual colorimetric method that measures conversion of the enzyme's artificial substrate N-biotinyl p-aminobenzoate was modified for use with a Technicon AutoAnalyzer II. The intra-run replicate precision (CV) was 2.1% and the day-to-day CV was 4.6% for quality-control sera. Results were linearly related to biotinidase activity in serum over the complete range of clinically relevant values, 0.2 to 11.0 U/L. Moreover, results of the automated assay were not significantly different from those of the manual assay. Because the automated procedure is faster and more precise, we recommend it for population-based studies and some screening studies.

Differences between monkey visual cortex cells in triplet and ghost doublet informational symbols relationships.

On the basis of the recent discovery that precisely replicating triplets of impulses present in All-Interval histograms of spike trains generated by visual cortex cells of Rhesus monkeys are surrounded by multiple copies of "ghost doublets" of such triplets, we have examined and compared in detail, the spike trains generated by four complex cells in the striate cortex of curarized monkeys with respect to: (1) The number of precisely replicating triplet patterns embedded in trains of discharges generated in response to specific Hubel-Wiesel stimulation; (2) The effect of time separating the occurrence of such replicating triplets on the number and time distribution of their ghost doublets; (3) The effect of decreasing the precision criterion for the detection of replicating (parent) triplets (from the standard 0.14 ms criterion to 0.5 ms) on the relationships between triplets and their ghosts and (4) The comparison of the distributions in time of ghost doublets around the first and second copies of triplets when the time intervals separating them were greater than or less than 0.5 s. We found that the precision of replication of triplets varies somewhat from one cell to another, and that ghosts doublets are more copiously associated with replicating triplets emitted near in time to each other than with triplets emitted after larger time intervals, except in the case of one cell. In order to assess the statistical significance of our findings, we systematically shuffled the order of occurrence of intervals in every burst of all the records of one of the studied cells and repeated the analysis. Both the number of replicating triplets and of associated ghost doublets is significantly depressed (but not totally obliterated) by the above shuffling procedure. Finally, further implications based on a model of neural information transmission in the form of temporal correlations between spikes are discussed.

Evidence on precise time-coded symbols and memory of patterns in monkey cortical neuronal spike trains.

High-resolution examination of pulse sequences generated by single visual cortex cells of the rhesus monkey in response to precisely controlled visual stimuli has disclosed (i) that the outputs of such neurons contain highly improbable (P less than 10(-7) numbers of identical triplets of precisely repeating pulse patterns; (ii) that the precision of such matches is better than 1/6000th of a second; (iii) that there is a similarly improbable high number of precisely matching pairs of triplets and anti-triplets, about half of which are present in symmetrical quadruplets of the form A-B-A, and that precisely replicating quadruplets and quintuplets are similarly generated in improbably large numbers; (iv) that identical triplets occur highly preferentially during immediately succeeding presentation of the same stimulus to the eye; and (v) that identical triplet (and doublet) patterns occur much more frequently in the responses of the same nerve when the eye receives identical or similar stimuli in different experiments than when dissimilar stimuli are applied. From these findings it is concluded (i) that the high precision of pattern replication required for triplets of pulses in time to serve to encode specific inputs and to permit their decoding through spatial summation is met (observations i-iii); (ii) that stimulus-specific triplets symbolize components of responses to specific stimuli (observation iv); (iii) that a temporary memory store of previous responses exists (observations iv and v); and (iv) that the mammalian brain uses precise patterns of discharges in time to represent and store specific data, rather than statistical qualities associated with pulse trains to symbolize qualitative stimulus components.

Determination of trace and minor elements in coal: A comparison between instrumental photon and thermal neutron activation analysis

Instrumental photon and neutron activation techniques have been compared through the determination of sixteen major, minor and trace constituents in two British Columbian coals and a standard coal. Between the two techniques, the results generally agreed to within one standard deviation with replicate precision being maintained, for both techniques, below twenty percent at worst and down to five percent or better for several elements. Almost all of the elements having environmental, industrial or economic significance in fossil fuels can be determined with good sensitivity by either of these two methods, both of which share the advantages of being non-destructive and multi-element in nature and sufficiently accurate as demonstrated in this paper.

Anisotropy of magnetic susceptibility: Empirical evaluation of instrumental precision

Measurement of the anisotropy of magnetic susceptibility (AMS) in rock specimens is complicated when magnitude differences between two of the three principal susceptibilities which are conventionally used in defining the susceptibility ellipsoid approach the precision limits of the instrument used. To evaluate this problem, the precision is reported for 5 replicate measurements of low field AMS in 34 samples (including diamagnetic samples) with susceptibilities ranging between 5.73 × 10−3 and 2.94 × 10−5 in mass SI units using a torsion fiber magnetometer. (These samples are available upon request for interlaboratory calibration.) Precision appears to be controlled by the within‐sample axial susceptibility ratios and not by the susceptibility magnitudes. It is observed for the instruments used in this study that when the axial ratios (χa/χc or χb /χc are equal to or less than 1.002, then the replicate precision for those axes is poor. When the axial ratios are greater than 1.005, then the precision is excellent. Such replicate AMS measurements for any given instrument provide an empirical means to determine a practical method for rejecting AMS data that are not sufficiently anisotropic for reliable measurement.

Experiments on X-ray lithography using synchrotron radiation from the VEPP-2M storage ring

During the last few years the electron-positron storage ring VEPP-2M of the Institute of Nuclear Physics in Novosibirsk has been used as an efficient source for X-ray lithography in the intermediate wavelength range (λ ∼ 10 A ̊ ) . Selection of the required part of the SR spectrum is done by means of a mask substrate fabricated from silicon of 2 μm thickness; Al windows can be installed before the X-ray mask. Exposures can be made in vacuum or in helium. The lithographic system can be used to fabricate one-layer devices on 100 mm diameter wafers with a production rate of 10–12 wafers per hour. The influence of the geometric conditions and of various temperature modes of exposure on the precision of replication from the mask onto the resist film have been investigated. Parameters of several X-ray and electron resists are studied. A lithographic system for fabricating multilayer devices is being developed. At present near to the storage ring a special room with clean-room environment is being built. Two SR beam lines come into it. The first beam line brings SR from the bending magnet. In the future the second beam line will bring SR from the special “lithographic wiggler”. In this room all operations on wafer preparation, subsequent processing steps of resist and masked surfaces after X-ray lithography and control of the patterns obtained will be carried out.

Comparison of three wet‐alkaline methods of digestion of biogenic silica in water

SUMMARY. Methods for determination of low levels of biogenic silica (0.2–0.4 mg SiO2) in aqueous samples after digestion with three wetalkaline extraction procedures compared favourably in both precision of replicates and recovery of silica utilized by diatoms in budgeted cultures. Leaching samples with 0.2 M NaOH for 10–15 min at 100°C was the least time consuming procedure. Also interference from silicate minerals was lower for this method than leaching with either 0.5 or 5% Na2CO3 for 2 h at 85°C. The use of filters to concentrate samples enables detection of low levels of biogenic silica with colorimetric procedures. Polycarbonate filters are recommended in preference to cellulose acetate or polyvinyl chloride filters for sample collection. Time‐course experiments are recommended for establishing digestion times and determining the presence of mineral silicate interference. Wet‐alkaline digestion methods are recommended for routine analysis of biogenic silica in suspended matter in preference to infra‐red analysis, alkaline fusion and hydrofluoric acid/nitric acid methods.

Determination of Nitrilotriacetic Acid in Waters and Waste Waters by Gas-Liquid Chromatography, Differential Pulse Polarography and a Colorimetric Method

Abstract A comparison of gas-liquid chromatography, differential-pulse polarography and a colorimetric method for the determination of nitrilotriacetic acid in settled sewage, sewage effluent, potable water, soil extracted water and deionised water has been undertaken. Differential-pulse polarography has also been applied to the determination of nitrilotriacetic acid in saline samples. By statistical analysis of replicate determinations, accuracy and precision have been evaluated, and calibration linearity assessed. Interferences were observed for sewage samples when analysed by all three methods. Precision was generally higher for differential-pulse polarography down to 100 μgl−1, although only gas-liquid chromatography is applicable to concentrations below 25μgl−1 in non-saline samples. The colorimetric method was not applicable to concentrations below 500 μgl−1 of nitrilotriacetic acid.

Automated Immunochemical Method for Determination of Urinary Protein of Plasma Origin

An automated continuous-flow procedure has been developed for the rapid determination of urinary proteins of plasma origin. Antiserum to whole human plasma was used as the reagent, and the antigen-antibody reactions were quantitated by nephelometry. By adding polyethylene glycol (mol wt 6000-7500) to the reaction medium, reaction time was decreased to less than 3 min; no sample blanks were required; and samples were analyzed at a rate of 70 per hour. Recovery studies yielded an average of 98.5% of the added protein. In-run replicate precision (CV) of the method was 1.45%; day-to-day precision was 2.58%.

A simplified procedure for the measurement of total hydroxyproline in urine

A simple method for the estimation of hydroxyproline is described. Removal of acid, salts and pigments from hydrolysed urine is achieved by passing the urine hydrolysate through a column of ion retardation resin. Oxidation and chromophore development follow directly on an aliquot of the column elutate. All the parameters of the reaction have been studied and conditions described which give the most sensitive and stable colour development. Recoveries of 97% or better are obtained with precision of replicates of ± 3%. The method is inexpensive, rapid and not subject to interference from other compounds commonly present in urine.