Bracketing Approach Research Articles

Vestigial skeletal structures in dinosaurs

The existence of vestigial structures is one of the main lines of evidence for macroevolution. Here I introduce a phylogenetic bracketing approach to the identification of vestigial structures and apply it to Dinosauria. According to this approach, a structure is considered vestigial if, in comparison with its homolog in at least three successive outgroups, it is reduced to one-third or less its size relative to adjacent structures and if at least distally it has lost the specialized morphology present in the three outgroups. This approach identifies fingers IV and V as vestigial in dinosaurs in general, II–V in sauropods, III in Tyrannosauridae and Caudipteryx, II and III in Shuvuuia and I and III in modern birds. The entire forelimb distal to the elbow is vestigial in Abelisauridae. Vestigial parts of the pelvic girdle and hindlimb include the pubic shaft in Iguanodontia and Ceratopsia, the entire pubis in Ankylosauria, the first metatarsal in derived Iguanodontia, the first metatarsal shaft in Theropoda and the fifth toe in dinosaurs in general. Derived Centrosaurinae and some Chasmosaurus exhibit vestigial supraorbital horns. Some centrosaurines have a vestigial nasal horn. The antorbital cavity is vestigial in Thyreophora, Iguanodontia and Ceratopsidae. I recommend that this information be exploited to increase public awareness of the evidence for macroevolution.

High precision determination of silver isotope ratios in commercial products by MC-ICP-MS

Silver isotope ratios in several fortified commercial products were determined by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). Mass discrimination and instrument drift were corrected for by a combination of internal normalization with Pd and standard-sample-standard bracketing, without assuming identical mass bias for Pd and Ag. The certified value of 1.07638 for 107Ag/109Ag in NIST SRM 978a was used for mass bias correction of 106Pd/108Pd in two adjacent solutions of SRM 978a. Their average was then used for mass bias correction to calculate the mass bias corrected Ag isotope ratio in the sample. An approximately 2.5-fold improvement in precision of determination of δ107/109Ag was obtained with the use of the proposed technique compared to data obtained solely with a standard-sample-standard bracketing approach. Internal and external precisions (2SD) of ±0.05‰ (n = 10) and ±0.04‰ (n = 19) for δ107/109Ag were obtained, suitable for the detection of varying Ag isotope abundances in commercial products fortified with Ag. Amongst the commercial products examined, no significant differences were detected in Ag isotopic compositions among NIST 978a standard, Ag high purity metal (Johnson Matthey Plc), Ag Nanopowder (Sigma-Aldrich) and Silversoft socks. Significant differences in Ag isotope ratios were found among NIST SRM 978a standard, a colloidal Ag dietary supplement, decanethiol functionalized Ag nanoparticles and X-static socks. The X-static socks and decanethiol functionalized Ag nanoparticles have negative δ107/109Ag values of −0.08 ± 0.05‰ and −0.15 ± 0.02‰ (2SD, n = 4), respectively, and the colloidal Ag dietary supplement has +0.83 ± 0.06‰ (2SD, n = 4). These observations suggest that such data may provide a useful tool for fingerprinting sources of Ag in the environment.

Exploring Deprotonation Reactions on Peptides and Proteins at Atmospheric Pressure by Electro-Sonic Spray Ionization-Mass Spectrometry (ESSI-MS)

Electrospray ionization mass spectrometry (ESI-MS) rapidly became established as the method of choice for the production of large biomolecular ions in the gas phase. For peptides and proteins, ESI leads to the formation of multiply charged ions, in both the positive and negative ion mode. The charge-state distribution is directly related to the conformation of the macromolecular ions and to proton transfer reactions in the gas phase. Deprotonation reactions of multiply charged peptide and protein ions were studied by introducing volatile reference bases at atmospheric pressure between an electro-sonic spray ionization (ESSI) source and the inlet of a mass spectrometer. This new set-up offers the unique possibility to measure the apparent gas-phase basicity GBapp of multiply charged ions by a bracketing approach. The proof of principle was made using bradykinin derivatives, substance P and insulin chain B. We obtained values in excellent agreement with known GBapp values obtained at low pressure. These experiments were extended to seven model proteins showing that the thermodynamical properties of protein ions are directly correlated to the amino-acid sequence and the conformation in the gas phase. We also demonstrated that salt bridges between ionized basic and acidic sites still exist in the gas phase, confirming that electro-sonic spray is a very soft ionization technique.

Investigation of Deprotonation Reactions on Globular and Denatured Proteins at Atmospheric Pressure by ESSI-MS

Deprotonation reactions of multiply charged protein ions have been studied by introducing volatile reference bases at atmospheric pressure between an electrosonic spray ionization (ESSI) source and the inlet of a mass spectrometer. Apparent gas-phase basicities (GB(app)) of different charge states of protein ions were determined by a bracketing approach. The results obtained depend on the conformation of the protein ions in the gas phase, which is linked to the type of buffer used (denaturing or nondenaturing). In nondenaturing buffer, the GB(app) values are consistent with values predicted by the group of Kebarle using an electrostatic model (J. Mass Spectrom.2002, 38, 618) based on the crystal structures, but taking into account salt bridges between ionized basic and acidic sites on the protein surface. A new basicity order for the most basic sites was therefore obtained. An excellent agreement with the charge residue model (CRM) is obtained when comparing the observed and calculated maximum charge state. Decharging of the proteins in the electrosonic spray process could be also useful in the study on noncovalent complexes, by decreasing repulsive electrostatic interactions. A unified mechanism of the ESSI process is proposed.

A simplified procedure for the determination of stable chlorine isotope ratios (δ37Cl) using LA-MC-ICP-MS

Stable chlorine isotopes (37Cl, 35Cl) are considered as important tracers of geochemical processes, especially in subduction zone systems. However, high-quality chlorine isotope data are scarcely available. Here we present a comparatively simple procedure for the precise and accurate determination of stable chlorine isotope ratios (δ37Cl) using LA-MC-ICP-MS. Chlorine was extracted from solid samples by pyrohydrolysis. After quantitative precipitation as AgCl the dried precipitates where analysed in a sample-standard bracketing approach using a weak laser ablation (0.3 J/cm2) for sample evaporation. Atlantic Ocean sea salt and the sea water standard IAPSO were used as SMOC (standard mean ocean chloride) for normalisation (δ37Cl = 0 ‰). The precision and accuracy of the presented method was validated analysing the reference materials JB-1a and JB-2. The chlorine isotope ratios of these standards were determined as δ37ClJB-1a = (−0.99 ± 0.06) ‰ and δ37ClJB-2 = (−0.60 ± 0.03) ‰ (errors 2SE), respectively, in accordance with published data. Applying the presented method a total amount of less than 1 μg of chlorine was consumed during a typical measurement including 10 ablation periods on the sample.

Rapid and Precise Measurements of Gas-Phase Basicity of Peptides and Proteins at Atmospheric Pressure by Electrosonic Spray Ionization-Mass Spectrometry

Deprotonation reactions of peptide and protein ions have been studied by introducing volatile reference bases at atmospheric pressure between an electrosonic spray ionization (ESSI) source and the inlet of a hybrid quadrupole time-of-flight mass spectrometer. This new setup offers the unique possibility to measure the apparent gas-phase basicity GBapp of multiply charged ions by a bracketing approach. A very good agreement has been obtained with reference values obtained by Fourier transform-ion cyclotronic resonance (FT-ICR), validating our approach. The measurements were then extended to larger biomolecules such as insulin and myoglobin in native and denaturing buffers. The main advantages of this methodology are measurements at atmospheric pressure with good sensitivity (for concentrations less than 10 microM in denaturing or nondenaturing buffer), very good precision (less than 2%), and in a short time (less than 30 min to screen up to 23 volatile reference bases).

High-precision measurement of mercury isotope ratios in sediments using cold-vapor generation multi-collector inductively coupled plasma mass spectrometry

An on-line Hg reduction technique using stannous chloride as the reductant was applied for accurate and precise mercury isotope ratio determinations by multi-collector (MC)-ICP/MS. Special attention has been paid to ensure optimal conditions (such as acquisition time and mercury concentration) allowing precision measurements good enough to be able to significantly detect the anticipated small differences in Hg isotope ratios in nature. Typically, internal precision was better than 0.002% (1 RSE) on all Hg ratios investigated as long as approximately 20 ng of Hg was measured with a 10-min acquisition time. Introducing higher amounts of mercury (50 ng Hg) improved the internal precision to <0.001%. Instrumental mass bias was corrected using (205)Tl/(203)Tl correction coupled to a standard-sample bracketing approach. The large number of data acquired allowed us to validate the consistency of our measurements over a one-year period. On average, the short-term uncertainty determined by repeated runs of NIST SRM 1641d Hg standard during a single day was <0.006% (1 RSD) for all isotope pairs investigated ((202)Hg/(198)Hg, (202)Hg/(199)Hg, (202)Hg/(200)Hg, and (202)Hg/(201)Hg). The precision fell to <0.01% if the long-term reproducibility, taken over 11 months (over 100 measurements), was considered. The extent of fractionation has been investigated in a series of sediments subject to various Hg sources from different locations worldwide. The ratio (202)Hg/(198)Hg expressed as delta values (per mil deviations relative to NIST SRM 1641d Hg standard solution) displayed differences from +0.74 to -4.00 per thousand. The magnitude of the Hg fractionation per amu was constant within one type of sample and did not exceed 1.00 per thousand. Considering all results (the reproducibility of Hg standard solutions, reference sediment samples, and the examination of natural samples), the analytical error of our delta values for the overall method was within +/-0.28 per thousand (1 SD), which was an order of magnitude lower than the extent of fractionation (4.74 per thousand) observed in sediments. This study confirmed that analytical techniques have reached a level of long-term precision and accuracy that is sufficiently sensitive to detect even small differences in Hg isotope ratios that occur within one type of samples (e.g., between different sediments) and so far have unequivocally shown that Hg isotope ratios in sediments vary within approximately 5 per thousand.

Determination of mass-dependent molybdenum isotopic variations by MC-ICP-MS: An evaluation of matrix effects

Several analytical techniques are currently used to determine mass-dependent molybdenum isotopic variations in natural materials using multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), including different methods for the separation of Mo from the sample and the correction for instrumental mass-dependent isotopic fractionation (instrumental mass bias). Both internal (“double-spiking” using two enriched Mo isotopes) and external (“zirconium doping” with standard-sample bracketing) techniques have been used in previous studies to deal with the effects of instrumental mass bias. The results of these studies have indicated that the precision for Mo isotopic analyses of natural (matrix-bearing) samples is a factor of ∼4–7× better using a double spike. Here we present a detailed study of the ability of MC-ICP-MS to determine, both precisely and accurately, the isotopic composition of Mo extracted from molybdenite using a low blank, high yield two-column procedure for Mo separation and a simple standard-sample bracketing approach to correct for instrumental mass bias. Based on analyses of molybdenites, the precision of this technique is shown to be similar to published double-spike data (within a factor of ∼2). All three of the known types of potential matrix effects in the MC-ICP-MS are also evaluated: automatrix effects, matrix effects due to Zr doping and matrix effects due to elements in the sample other than Mo and Zr. Each of these matrix effects is found to be either insignificant or controllable. Analyses of five molybdenites of hydrothermal origin reveal a range in their Mo isotopic composition that is a factor of ∼4 greater than the previous range reported for such samples. More detailed work is required to elucidate the origin of these mass-dependent Mo isotopic variations in molybdenites.

Investigations for determination of Gd and Sm isotopic compositions in spent nuclear fuels samples by MC ICPMS

Precise isotopic determination of gadolinium and samarium in spent nuclear fuels is necessary to validate neutronic calculation codes. This study presents an analytical strategy to correct mass bias phenomenon inherent to MC ICPMS for precise and accurate samarium and gadolinium isotope measurements. An external standard bracketing approach to correct for mass discrimination and an exponential law fractionation correction have been applied in this work. Due to the lack of isotopic reference materials for Gd and Sm, the reproducibility of all of the isotopic ratios has been evaluated on the basis of natural spex solution commonly used for ICPMS. These solutions have been analysed for comparison and discussion about their representative isotopic values by thermal ionization mass spectrometry. On the basis of TIMS and MC ICPMS investigations, it was observed that: (1) the choice in representative isotopic values of the elements are essential to obtain accurate isotopic results and (2) the dependence of the mass bias of gadolinium and samarium masses must be taken into account for precise and accurate isotopic results. A reproducibility better than 0.1% was obtained with extensive measurements of Gd and Sm solutions by MC ICPMS. When measured isotope intensities were high enough, standard deviation of Gd and Sm isotopic ratios for purified fractions of Gd and Sm fuel samples were better than 0.2%. From the results obtained in this study, the potential of MC ICPMS techniques for determination of precise and accurate Gd and Sm isotopic compositions was clearly demonstrated for nuclear applications.

Isotope ratio determination of antimony from the transient signal of trimethylstibine by GC-MC-ICP-MS and GC-ICP-TOF-MS

Isotope ratio measurements of organometal(loid) species are of interest in order to determine isotope fractionation of the heavy metal(loid)s which can elucidate their pathways in the environment. We describe isotope ratio measurements of organoantimony using gas chromatography coupled to ICP-MS. We studied the influence of various parameters on the isotope ratio determination of the transient signal from trimethylstibine, using capillary gas chromatography coupled to both multicollector and time of flight ICP-MS with a simultaneous aspiration of aqueous samples creating wet plasma conditions. The influence of different mathematical models on the precision of the isotope ratio determination of transient signals was studied. The trapezium integration of full or half peak gave precisions of 0.08% and 0.02% using the MC-ICP-MS, whereas the ICP-TOF-MS gave values of around 0.2%. The multicollector ICP-MS used as a detector showed a chromatographic isotope fractionation of trimethylstibine. (CH3)3123Sb eluted earlier than (CH3)3121Sb, with a shift of the 123/121 ratio of about 2%. Two different approaches were attempted to correct instrumental mass bias effects in order to descriminate natural isotope fractionation. First, we introduced Cd and Sb in aqueous solution simultaneously with the GC carrier and ICP Ar gas flow. Secondly, we used a standard-sample bracketing approach using a gas standard introduced via the GC. Real samples from a laboratory sewage sludge fermentor were measured and isotope fractionation of the biologically produced trimethylstibine was observed (δ 123Sb +10 and +19‰). The gas samples were analysed for timethylstibine co-eluting with volatile organic compounds using GC-MS. Chloroform was found to co-elute, but had no significant influence on the isotope ratio of antimony in timethylstibine analysed by GC-ICP-MS. Hence, there would be a strong indication that isotope fractionation takes place when antimony is methylated by anaerobic bacteria.

Comparison between tendency-oriented perimetry (TOP) and octopus threshold perimetry

ObjectiveTo compare the results obtained by a new ultra-short automated perimetry test known as Tendency-Oriented Perimetry (TOP), which is an algorithm based on estimation of thresholds from information gathered from adjacent points with those obtained by a standard bracketing approach. TOP is designed to save up to 1/5 of the time taken by standard strategy by presenting each stimulus once on each location (instead of 4 to 6 times per location with the standard technique) and reaching a final threshold estimate by gathering information from responses to adjacent locations. DesignProspective, multicenter, observational comparative case series. Participants/methodsFour academic institutions provided data from testing 57 subjects, 15 with a normal ocular exam and 42 with a variety of visual field abnormalities. A total of 228 visual fields were analyzed. Two examinations of standard thresholding testing (Octopus program 32) and two examinations of the TOP program were obtained in each subject the same day. Main outcome measuresComparison of global indices such as mean deviation (MD), square root of loss of variance (sLV), topographical defects, point by point differences, reproducibility, sensitivity/specificity, and time required to complete the test. ResultsCorrelation coefficient of global indices between both tests was high, with mean deviation of r = 0.97 (SE[YX] ± 1.65 decibels) and square root of loss variance of r = 0.93 (SE[YX] ± 1.10 dB). Mean sensitivity tended to be 1 dB higher while MD tended to be 1 dB lower with TOP strategy. Reproducibility was equally good between both tests for threshold determination as well as for all global indices (MS, MD per quadrant, and LV). Cluster criteria for abnormality demonstrated TOP versus 32: sensitivity of 89/87; specificity of 90/77; positive predictive value of 96/91; negative predictive value of 75/68; and accuracy of 89/84. Mean time taken by this beta version of TOP was 4.05 minutes standard deviation ± 0.55 versus the standard 32 version taking 14.65 minutes standard deviation ± 3.75. ConclusionsTOP was four times faster than the traditional full-threshold technique and was successful in detecting visual field abnormalities. Defects with TOP tended to be smaller, shallower, and with softer edges than with standard approach. TOP could prove an alternative to traditional perimetric techniques.

Experimental and theoretical investigation of gas phase complexes between chloride ion and some chloroethenes

Analysis of the negative ions produced from trichloroethene (TCE) and Z-1,2-dichloroethene ( Z-1,2-DCE) in air at atmospheric pressure in an APCI source revealed the occurrence of the corresponding complexes with chloride ion. In contrast, under the same experimental conditions no such complexes were detected for E-1,2-dichloroethene ( E-1,2-DCE) and tetrachloroethene (PCE). A bracketing approach and competition experiments produced the following Cl −-affinity scale: Z-1,2-DCE > TCE > PCE, E-1,2-DCE, benzene (39.3 kJ mol −1). The results of collision induced dissociation experiments on these (Cl −) (M) complexes suggest rather weak bonding interactions. Quantum chemical calculations at the DFT Becke3-LYP level (B3LYP/6-311+G(d,p)//6-31+G(d)) support this conclusion [the calculated binding energy (kJ mol −1) are: 58.6, 56.1, 43.5, and 15.1 for Z-1,2-DCE, TCE, E-1,2-DCE and PCE, respectively]. The calculations also show that such complexes are planar, with an almost linear C–H ⋯ Cl − arrangement in the case of TCE and E-1,2-DCE. In contrast, Z-1,2-DCE binds Cl − via both hydrogens to give a symmetric complex. A similar geometry is also predicted for the very weakly bound (Cl −)(PCE) complex.

The quasi-likelihood approach to statistical inference on multiple time-series with long-range dependence

The paper gives a unified approach to dealing with multiple long-memory time-series possessing a variety of singularities in their spectrum, based on the quasi-likelihood function. It proposes quasi-maximum-likelihood estimation and the quasi-likelihood ratio test for statistical inference purposes. A large-sample theory is given by means of a bracketing function approach under very general conditions, without the usual assumptions of Gaussianity or exact martingale differences for innovation processes. The paper also discusses the particular characteristic of modelling long-memory time-series which influences the type of the quasi-likelihood function and produces distinct differences in the asymptotic properties of related statistics.

A Bracketing Approach for Estimating Regional Economic Impact Multipliers and a Procedure for Assessing Their Accuracy

There has been a resurgence in the use of impact multipliers of the economic base type in the United States, particularly in response to recent legislation and judicial decisions which require socioeconomic as well as environmental impact analyses. This paper presents a bracketing approach whereby upper and lower bounds of the multiplier are estimated. It also presents and applies a procedure that can be used to test the accuracy of alternative methods for estimating economic base multipliers.