Stuart J. Chalk

Accuracy in species analysis: speciated isotope dilution mass spectrometry (SIDMS) exemplified by the evaluation of chromium species☆

Abstract Speciated isotope dilution mass spectrometry (SIDMS) improves accuracy in the determination of chemical species in samples. It can be used to measure elements in their oxidation states as well as in organometallics or other molecular forms of species. SIDMS compensates for species transformations that occur in many of the steps of sample processing, including sampling process, storage, sample preparation and speciated measurement. It is also a diagnostic tool for identifying the most error prone steps. These combined capabilities provide a new method for establishing standard, legally defensible measurement tool in speciation analysis. Early speciation studies of Cr(VI) and Cr(III) demonstrate the unique advantages of SIDMS. Thus far, SIDMS has corrected up to 80% of the reduction of Cr(VI) to Cr(III). In theory, using SIDMS makes it possible to correct up to 90% species conversion with good precision. This paper describes how to apply the method to chromium and provides examples of the general steps.

The effects of salinity on acute toxicity of zinc to two euryhaline species of fish, Fundulus heteroclitus and Kryptolebias marmoratus.

It is well known that the toxicity of zinc (Zn) varies with water chemistry and that its bioavailability is controlled by ligand interactions and competing ions. Zn toxicity in freshwaters with varying water chemistry has been well characterized; however, far less attention has been paid to the toxicity of Zn in estuarine and marine systems. We performed experiments using two euryhaline species of killifish, Fundulus heteroclitus and Kryptolebias marmoratus, to investigate the effects of changing salinity on acute toxicity of Zn. Larvae (7- to 8-days old) of each species were exposed to various concentrations of Zn for 96 h at salinities ranging from 0 to 36 ppt and survival was monitored. As salinity increased, Zn toxicity decreased in both fish species, and at salinities above 10 ppt, K. marmoratus larvae were generally more sensitive to Zn than were those of F. heteroclitus. The protection of salinity against Zn toxicity in F. heteroclitus was further investigated to determine the role of Ca(2+). Increased Ca(2+) in freshwater protected against Zn toxicity to the same extent as did saline waters with an equal Ca(2+) concentration up to ∼200 mg/L Ca for F. heteroclitus and ∼400 mg/L Ca for K. marmoratus. These results suggest that these two species may have differing Ca(2+) requirements and/or rates of Ca(2+) uptake in water of intermediate to full-strength salinity (∼200-400 mg/L Ca(2+)) and thus differ in their sensitivity to Zn. The overall goal of this study was to better understand Zn toxicity in waters of different salinity and to generate data on acute Zn toxicity from multiple species over a range of salinities, ultimately for use in development of estuarine and marine biotic ligand models.

Determination of chloride by flow injection spectrophotometry with membrane reagent introduction

A single line manifold incorporating three Nafion® membrane reactors has been developed for the sequential introduction of components of the mercuric thiocyanate/iron(III)/acid reagent for the determination of chloride. Nitric acid was introduced at the first reactor to give sufficient ionic strength to allow cation exchange of FeSCN2+ at the second reactor, and Hg2+ at the third reactor. The composition of the reagent was adjusted by control of the flow rates of donor and acceptor streams, reagent concentration and reactor length. Calibration over the range 0.3–25 μg ml−1 was possible, though the calibration function was curved. The manifold was used to determine chloride in river water and in pond water at concentrations of 8 and 47 μg ml−1, respectively and gave results that were not significantly different from those obtained by an EPA method. The lower range sensitivity was 0.032 absorbance μg ml−1, which compares favorably with that of other flow injection methods, but the detection limit was 300 ng ml−1, considerably higher than that can be achieved by flow injection procedures. This was due to the presence of mixing noise caused by fluctuations in reagent concentration related to pulsations in the flow in both donor and acceptor streams. Valve switching and refractive index effects were absent.

Atmospheric Pressure Microwave Sample Preparation Procedure for the Combined Analysis of Total Phosphorus and Kjeldahl Nitrogen

An atmospheric pressure microwave digestion method has been developed for the combined analysis of total phosphorus and Kjeldahl nitrogen in complex matrices. In comparison to the digestion steps in EPA Methods 365.4 (total phosphorus) and 351.x (Kjeldahl nitrogen), this method requires less time, eliminates the need for a catalyst, and reduces the toxicity of the waste significantly. It employs a microwave-assisted digestion step, using refluxing borosilicate glass vessels at atmospheric pressure. Traditionally, this method has a time-consuming sample preparation step and generates toxic waste through the use of heavy metal catalysts. These advantages are gained by the combination of a high boiling point acid (sulfuric acid) and the application of focused microwave irradiation, which enhances the digestion process by direct energy coupling. NIST standard reference materials 1572 (citrus leaves), 1577a (bovine liver), and 1566 (oyster tissue) and tryptophan were analyzed to validate the method. Phosphorus concentrations were determined by the colorimetric ascorbic acid method outlined in EPA Method 365.3. Kjeldahl nitrogen concentrations were determined using EPA Method 351.1. The results of the analyses showed good precision and are in excellent agreement with the NIST published values for both elements.

Flow injection reagent introduction by supported liquid and nafion membranes: Determination of phosphate

The use of membrane tubing for the introduction of reagents for the determination of phosphate in waters by flow injection analysis was studied. The use of membranes eliminates the need for confluence points in the design of flow injection manifolds. This increases the sensitivity of the manifold by providing a sufficient reagent excess for the reaction without diluting the sample. Methods for the introduction of acid, molybdate and hydrazine were devised for the determination of phosphate by the Molybdenum Blue method. Several membranes were examined and Nafion and Accurel (microporous polypropylene) were found to be most useful. Molybdate introduction was achieved using a supported liquid membrane (SLM). Calibration was linear and a detection limit of 12 ppb phosphate (4 ppb phosphorus) was obtained.

Ozone degradation of residual carbon in biological samples using microwave irradiation.

In an attempt to produce complete oxidation of a biological matrix, bovine liver, ozone was investigated as an additional, potentially non-contaminating, oxidizing reagent after nitric acid digestion. Experiments were carried out to determine the decomposition efficiency of residual carbon species, primarily o-, m- and p-nitrobenzoic acids (NBAs), using ozone. The NBAs were degraded by purging sample digests with ozone, while heating the solutions with microwave energy at atmospheric pressure. The effects of the degradation temperature and solution pH on the ozonation of NBAs were determined. Solid phase extraction (C18) was used to extract NBAs from the acid digestate solutions prior to HPLC analysis. Reversed phase HPLC was used to determine NBA concentrations in digest solutions. After 2.5 h of purging ozone at 80 degrees C, 33.65 +/- 3.80% o-NBA degradation, 19.39 +/- 1.74% m-NBA degradation, and 26.47 +/- 3.36% p-NBA degradation were obtained.

The Open Spectral Database: an open platform for sharing and searching spectral data

BackgroundA number of websites make available spectral data for download (typically as JCAMP-DX text files) and one (ChemSpider) that also allows users to contribute spectral files. As a result, searching and retrieving such spectral data can be time consuming, and difficult to reuse if the data is compressed in the JCAMP-DX file. What is needed is a single resource that allows submission of JCAMP-DX files, export of the raw data in multiple formats, searching based on multiple chemical identifiers, and is open in terms of license and access. To address these issues a new online resource called the Open Spectral Database (OSDB) http://osdb.info/ has been developed and is now available. Built using open source tools, using open code (hosted on GitHub), providing open data, and open to community input about design and functionality, the OSDB is available for anyone to submit spectral data, making it searchable and available to the scientific community. This paper details the concept and coding, internal architecture, export formats, Representational State Transfer (REST) Application Programming Interface and options for submission of data.ResultsThe OSDB website went live in November 2015. Concurrently, the GitHub repository was made available at https://github.com/stuchalk/OSDB/, and is open for collaborators to join the project, submit issues, and contribute code.ConclusionThe combination of a scripting environment (PHPStorm), a PHP Framework (CakePHP), a relational database (MySQL) and a code repository (GitHub) provides all the capabilities to easily develop REST based websites for ingestion, curation and exposure of open chemical data to the community at all levels. It is hoped this software stack (or equivalent ones in other scripting languages) will be leveraged to make more chemical data available for both humans and computers.

The flow analysis database on the World Wide Web.

The field of flow injection analysis (FIA) is growing rapidly because much applied research is being conducted around the world. This creates a great need for information dissemination across the globe to keep researchers up to date on current research trends. With the internet becoming the tool for global communication, it seems appropriate that support of the growth in FIA should be via this medium. Thus, the flow analysis database (FAD) has been developed as a central resource for bibliographic information on the area of FIA and flow analysis in general.

Computational Chemistry Data Management Platform Based on the Semantic Web

This paper presents a formal data publishing platform for computational chemistry using semantic web technologies. This platform encapsulates computational chemistry data from a variety of packages in an Extensible Markup Language (XML) file called CSX (Common Standard for eXchange). On the basis of a Gainesville Core (GC) ontology for computational chemistry, a CSX XML file is converted into the JavaScript Object Notation for Linked Data (JSON-LD) format using an XML Stylesheet Language Transformation (XSLT) file. Ultimately the JSON-LD file is converted to subject-predicate-object triples in a Turtle (TTL) file and published on the web portal. By leveraging semantic web technologies, we are able to place computational chemistry data onto web portals as a component of a Giant Global Graph (GGG) such that computer agents, as well as individual chemists, can access the data.

Communication. Permeation tubes for calibration in flow injection analysis

The use of a permeation tube for the production of liquid stream calibration standards in the flow injection determination of ammonia was investigated. By varying the flow rate from 0.5 to 4.0 ml min–1, calibration standards over the range 1.5–0.18 ppm could be produced. The relationship between concentration of the resulting solution and the reciprocal of the flow rate was shown to be linear. The inherent high temperature dependence of the release rate necessitated the tubes being used under thermostated conditions. The release rate was found to vary between 136 and 158 ng min–1 cm–1 over a 7 d period. Taking all sources of uncertainty into account, the 95% confidence interval for the release rate varied between 12.0 and 16.2 ng min–1 cm–1 over the same 7 d period. The device was used in a manifold for the determination of ammonia in pond water in which the method of standard additions was employed.