The determination of chromium in biological materials by atomic absorption spectroscopy

Biological samples were mineralized with a mixture of nitric, sulfuric, and perchloric acids. The chromium was oxidized to chromium(VI) followed by extraction into methyl isobutyl ketone in the cold. The ketone extract was aspirated into a fuel-rich hydrogen-air flame, and the absorption recorded using the 357.9 nm line of chromium. The limit of detection for chromium was found to be 10 p.p.b. Tissue chromium levels of normal albino rats were determined. Increased chromium values were observed for animals maintained on a high chromium diet compared to those fed a deficient diet.     

Observations on the permanganate-arsenious oxide titration

The reduction of permanganate and the oxidation of manganous ion have been studied in a variety of acid solutions. The product appears to be an unstable complex of trivalent manganese. The manganic sulfate complex is pink in solution and the manganic arsenate complex is green. Complexes prepared in hydrochloric acid were found to be highly unstable and decomposed rapidly with the formation of free chlorine. The results of this work shed some light on the mechanism of the permanganate-arsenious oxide titration.     

The behaviour of an electrochemical detector used in liquid chromatography and continuous flow voltammetry: Part 1. Mass transport-limited current

A simple expression relating the current at a rectangular channel-type flow-through electrode to the volume flow rate of solution, cell dimensions and physical constants is derived. The expression for steady-state current is valid for laminar flow with neglect of longitudinal depolarizer diffusion. The equation is derived to extract information on the analytical utility of these cells, i.e. signal-to-noise ratio (SNR). For standard amperometric detection the optimum cell design is one in which the width of the cell is equal to the width of the electrode and the length and thickness of the cell are as small as possible, the limit of these dimensions either being physical or dictated by amplifier noise in the output. There is no optimum shape for an electrode of a given size. For standard amperometric detection with a constant cell volume, V, the optimum dimensions are given by b = ($\text{VD}\text{0.42}$U)^{$\text{1}\text{2}$}, (b = thickness, D = diffusion coefficient, -U= average volume flow rate). For flow rate-modulated operation, the optimum thickness is vanishingly small, and the electrode area (shape not critical) is given by A = 0.52 UbD^-1.     

The maximal sizes of faces and vertices in an arrangement

Let A be an arragement of n lines in the plane. Suppose that F₁,…,F_r are faces of A and that V,…,V_s are vertices of A. Suppose also that each F_i is a (V_j) of the lines of A intersect at V_j. Then we show that

$\text{∑}\text{i=1}\text{r}\text{t(F}{}_{\mathrm{i}}\text{+}\text{∑}\text{j=1}\text{s}\text{t(V}{}_{\mathrm{j}}\text{)?n+4}\text{r}\text{2}\text{+}\text{s}\text{2}\text{+ 2rs}$

.     

Integrating cavity quantum electrodynamics and ultracold-atom chips with on-chip dielectric mirrors and temperature stabilization

We have fabricated an atom chip device which combines the circuitry for magnetic trapping of cold atoms with high-finesse optical resonators suitable for cavity QED in the single-atom strong coupling regime. Fabry–Pérot optical resonators with finesse were formed between a micropatterned on-chip planar mirror with lateral dimension of ≤ 100 μm and a curved mirror suspended above the chip. The strong and rapid thermal coupling between on-chip electrical and optical elements was utilized to stabilize the cavity mirror separation with servo bandwidth exceeding 100 kHz during simulated operation of the atom chip. PACS 42.50.Pq; 03.75.Be; 42.82.Cr     

Structural determination of glycopeptidolipids of Mycobacterium smegmatis by high‐resolution multiple‐stage linear ion‐trap mass spectrometry with electrospray ionization

Glycopeptidolipids (GPLs) are abundant in the cell walls of different species of mycobacteria and consist of tripeptide‐amino‐alcohol core of D‐Phe‐D‐allo‐Thr‐D‐Ala‐L‐alaninol linked to 3‐hydroxy or 3‐methoxy C_26–34 fatty acyl chain at the N‐terminal of D‐Phe via amide linkage, and a 6‐deoxytalose (6‐dTal) and an O‐methyl rhamnose residues, respectively, attach to D‐allo‐Thr and the terminal L‐alaninol. They are important cell‐surface antigens that are implicated in the pathogenesis of opportunistic mycobacteria belonging to the Mycobacterium avium complex. In this contribution, we described multiple‐stage linear ion trap in conjunction with high‐resolution mass spectrometry towards structural characterization of complex GPLs as [M + Na]⁺ ions isolated from Mycobacterium smegmatis, a fast‐growing and non‐pathogenic mycobacterial species. Following resonance excitation in an ion trap, MSⁿ spectra of the [M + Na]⁺ ions of GPLs contained mainly b and y series ions that readily determine the peptide sequence. Fragment ions from MSⁿ also afford locating the 6‐dTal and O‐methyl rhamnose residues linked to the D‐allo‐Thr and terminal L‐alaninol of the peptide core, respectively, as well as recognizing the modifications of the glycosides, including their acetylation and methylation states and the presence of succinyl group. The GPL families consisting of 3‐hydroxy fatty acyl and of 3‐methoxy fatty acyl substituents are readily distinguishable. The MS profiles of the GPLs from cells are dependant on the conditions they were grown, and several isobaric isomers were identified for many of the molecular species. These multiple‐stage mass spectrometric approaches give detailed structures of GPL in complex mixtures of which the isomeric structures are difficult to define using other analytical methods. Copyright © 2012 John Wiley & Sons, Ltd.     

Control of material damping in high-Q membrane microresonators

We study the mechanical quality factors of bilayer aluminum-silicon-nitride membranes. By coating ultrahigh-Q Si(3)N(4) membranes with a more lossy metal, we can precisely measure the effect of material loss on Q's of tensioned resonator modes over a large range of frequencies. We develop a theoretical model that interprets our results and predicts the damping can be reduced significantly by patterning the metal film. Using such patterning, we fabricate Al-Si(3)N(4) membranes with ultrahigh Q at room temperature. Our work elucidates the role of material loss in the Q of membrane resonators and informs the design of hybrid mechanical oscillators for optical-electrical-mechanical quantum interfaces.     

The determination of zinc in blood plasma by atomic absorption spectrometry

Atomic absorption spectrometry has been used in the analysis of plasma zinc because of its sensitivity and simplicity. Dilution techniques reduce the viscosity of plasma and facilitate direct analysis, but viscosity differences can produce deviations in aspiration rates between sample and standard, and so cause errors. A direct (1 + 4) dilution of plasma with deionized water is suggested. Working zinc standards are prepared in 5% glycerol to approximate the viscosity characteristics and aspiration rates of the diluted plasma samples. The analytical curves for diluted plasma samples and 5% glycerol working standards proved identical. Plasma zinc concentrations are accurately calculated from a daily working curve. The accuracy of the method exceeds 99% and recovery of added inorganic zinc to a pooled plasma averages 99.8%. The precision is primarily limited by baseline drift. A confidence interval of ± 2 μg/100 ml was achieved by means of six contiguous 10s-integration readings. The method is free of nebulizer clogging and matrix interferences and is not subject to significant day-to-day variations. Because the method is accurate, sensitive, reliable and specific, it should be useful in the clinical laboratory.     

The apparent solubility product of cerous fluoride

The apparent solubility product of cerous fluoride has been determined to be 8.1 ± 1.1·10^-16 und 1.1 ± 0.5·10^-15 by radiometric and conductometric methods respectively. Hydrolysis of cerous fluoride is thought to be negligble. The effect of hydrogen-ion concentration on the solubility of cerous fluoride has been measured in solutions of perchloric acid of varying acidity. The solubility Was found to decrease slightly as the pH decreased from 5 to 2 and then to increase rapidly as the pH further decreased from 2 to 0.