ABSTRACTS
Pittcon 2011
Speciation of Inorganic Arsenic in Food by Hydride Generation Anion Exchange Liquid Chromatography Atomic Fluorescence Spectrometry with Online Ultraviolet (UV) Digestion (HG-LC-UV-AFS)
The occurrence of inorganic arsenic in food has received worldwide concern during recent years due to its toxicity and adverse health effects. It is known to be human carcinogen and can cause skin and bladder cancer. Inorganic arsenic (arsenite and arsenate) are not only commonly found in the groundwater, they are also found to be the predominant species in some food such as rice. Reliably monitoring inorganic arsenic levels in food samples are one of the most urgent task in order to assess its impact on human health.
Several extraction methods have been developed for the extraction of arsenic species from food samples, especially in rice. A nitric acid based extraction method was found to be most suitable in that DMA, MMA and arsenobetaine remain untouched in the media. Inorganic arsenic is then quantified as As(V). The proposed procedure quantitatively recovers the most common arsenic species such as inorganic arsenic, DMA, MMA and arsenobetaine. The speciation analysis of the above mentioned species was based on an anion-exchange liquid chromatography coupled with hydride generation atomic fluorescence spectrometry with online UV digestion of the methylated and organic As species. A reference material (NIST SRM 1568a rice flour) was used for the quantification and speciation. Recoveries of inorganic arsenic and DMA were found to be nearly 100%.
Antimony Speciation in Sweeteners Using Liquid Chromatography Hydride Generation Atomic Fluorescence Spectrometry (HPLC -HGAFS)
Antimony and its compounds have no known biological role, are nearly as toxic as lead and have been listed as priority pollutants by the US EPA, Council of the European Union (EU) and German Research Community (DFG). Elevated level of Sb was found in various brands of sweeteners in the market which again raise the concern of its impact on human health. Total antimony and its speciation in sweeteners have been carried out using atomic fluorescence spectrometry. Antimony (III) and (V) was separated and quantified by an anion exchange column with a mobile phase containing 200mM ammonium tartrate at pH 5. The majority of Sb in sweeteners was found to be the more toxic Sb(III).
Online Measurements of Arsenic and Mercury Using Atomic Fluorescence Spectrometry
Given the challenging legislative framework, many of our customers operate in, it is essential that any in-process As or Hg analyser gives the security of complete compliance yet and also has the flexibility to meet future regulatory requirements. The online analyser described in this work provides just that security through a unique combination of continuous As or Hg measurement, custom chemistry and the inherent sensitivity of atomic fluorescence detection, all with the additional benefit of low operator intervention saving time and money. The authors believe that the recently developed As online liquid instrument is the first instrument of its kind worldwide.
Designed and manufactured for long-term stability in hostile environments, the online analyser introduces a number of novel features which combine the convenience of laboratory based systems with the ease of use demanded by process analysis. In addition, a comprehensive user friendly software package for data acquisition, statistical analysis, reporting and display is described. The software performs real time calculation and presentation of the analyte content for each process concerned. The software can be readily customised to suit individual needs for monitoring and reporting.
Online determination of mercury in sour natural gas streams
Accurate determination of mercury in petrochemical streams is important for environmental and operational/safety reasons. Mercury damage to petrochemical plant can lead to long downtime and high costs, both in replacement parts and due to lost production. Mercury has caused corrosion and in some cases failure of aluminium components including heat exchangers, rotors and condensers. Mercury has also been shown to be responsible deactivation of palladium hydrogenation catalysts which are commonly used for selective hydrogenation of alkynes in the C2 to C4 fraction.
Online determination of mercury in natural gas streams is used to confirm correct operation of activated carbon or precious metal-based mercury removal units (MRUs) or to confirm mercury levels of product streams are within specification. Whilst these measurements are themselves non-trivial, they can be far more difficult when the petrochemical source is contaminated as in some areas by high levels of hydrogen sulfide. These sour gas streams may contain levels of H2S from 4 ppm to >20 % hydrogen sulfide. Determination of mercury in the sour gas streams is therefore necessary to ensure the continuance of the production process.
This poster presents an amalgamation-atomic fluorescence spectrometry-based online analyser for the determination of mercury in sour gas. The instrument is based on PSA’s long established range of online and offline mercury in natural gas instrumentation. Data will be presented confirming the efficacy of the technique in sour gas containing up to 18 % hydrogen sulfide.
Mercury Speciation and Total Mercury in Fish and Seafood Products
Mercury has long been the focus of attention since the early tuna fish scares in Japanese diets. The form of the mercury is of considerable importance and the ability of the analysts to measure these reliably requires sensitive and accurate methodology and measurements. Atomic Fluorescence Spectrometry provides the measurement tool and examples of its coupling to a range of chromatographic techniques will be described.
Pittcon 2010
Speciation of Mercury in Hair using GC-AFS and HPLC-UV-CV-AFS
The use of atomic fluorescence spectrometry (AFS) coupled to gas and liquid chromatography has been used for mercury speciation measurements for a number of years. The major routes of human exposure to mercury is via inhalation of mercury vapour as Hg0 from sources such as dental amalgams and occupational exposure, consumption of fish products as CH3Hg+ and also from vaccines which contain the Thiomersal preservative CH3CH2Hg+ (known in the US as Thimerosal).
Different mercury species have varying toxicological effects and also different routes of detoxification. Total mercury in hair for a non exposed person is typically in the range of 0.4 to 6.0mg/g which is several 100 times higher than the level typically found in blood. It has been reported[1] that the mercury in first cut baby hair from children with Autism is significantly lower suggesting that they have an inability to excrete mercury from their system. The excretion mechanism is not fully understood at this time and therefore there is a need for reliable methods to determine Hg speciation in hair samples.
This paper will compare different analytical extraction methods and their suitability for liquid and gas chromatography coupled to AFS. Data will be presented for a wide range of hair samples and comparisons made for different exposure groups.
[1] Holmes A S, Blaxill, M F & Haley B E, Int. J. Toxicol. 2003, 22 (4) 277
Online Process Analysis of Mercury in Petrochemical Streams
Knowledge of the mercury content in petrochemicals is extremely important. Firstly, mercury is highly toxic and is of environmental concern and secondly, the damage caused to petrochemical plants can be financially crippling especially when unscheduled shutdowns are forced. Mercury has been found to be responsible for many cases of selective hydrogenation catalyst deactivation. Palladium based catalysts are commonly used for the selective hydrogenation of alkynes in the steam cracking of C2 to C4 cuts. Mercury is known to be the cause of corrosion problems with alumina-based heat exchangers, rotors and condensers at natural gas refinery plants. Heat exchanger replacement is a costly operation due to the capital investment of the exchanger itself and the plant down time incurred for its replacement. This paper describes how atomic fluorescence spectrometry (AFS) can be applied to the measurement of mercury in petrochemical samples such as natural gas, LPG, LNG, naphtha and condensates. Typically these measurements are performed using offline laboratory techniques which are highly dependent on the sampling protocols utilized and the sample storage method. This is especially problematic for volatile forms of Hg which are easily lost from the sample. We have recently developed online process analyzers for both liquid and gaseous petrochemical streams. These are typically used in conjunction with mercury removal technologies so that the efficiency can be monitored in real time thus protecting expensive downstream apparatus. The performance characteristics of the analyzers will be discussed with reference to sampling, calibration, accuracy, precision and long term reliability.
The origins of the ‘Dumarey equation’ describing the saturated mass concentration of mercury vapour in air
Mercury has been recognised as an environmental air pollutant for many years. Usually analyses are carried out by cold vapour amalgamation coupled to atomic spectrometry techniques with a calibration based on injection of air saturated with mercury vapour. All these measurements are ultimately traceable to the saturated mass concentration of mercury in air at a given temperature, as this relationship underpins the calibration procedure.
The saturated mass concentration of mercury vapour in air is given indirectly via the ideal gas law by a variety of empirical equations describing the vapour pressure of mercury. Recent work to develop a standardized European method for the measurement of mercury vapour in air has brought into sharp focus the requirement to define the most suitable relationship for the saturated mass concentration of mercury in air.
The ‘Dumarey equation’ has been the dominant relationship used to calculate the saturated mass concentration of mercury vapour in air for over 25 years. However, the origin of the equation and the validation data supporting its accuracy has never been published. We now address that deficiency and compare the Dumarey equation with other data sets to which it has been wrongly attributed in the past, and describe why it remains superior to the use of mercury vapour pressure data in combination with the ideal gas law.
[1] Huber, M L, Laesecke A, Friend D G, Ing. Eng. Chem. Res. 2006, 45, 7351
Rapid Arsenic Speciation Analysis in Water Samples
Inorganic arsenic (arsenite and arsenate) are the most common arsenic species found in water samples. They are proven to be carcinogenic due to their much higher toxicity than organic arsenic forms. Fast and accurate screening of inorganic arsenic species in water samples has increasingly received great attention. Arsenic generally presents in water samples at low ng/ml levels, and the transformation between arsenite and arsenate can also be troublesome during the sample collection and transportation processes. In this presentation, a fast, easy yet accurate sampling method and sensitive analysis protocol is proposed for arsenic speciation in water samples.
Two cartridges (A and B) were used to collect water samples for arsenic speciation. An aliquot of the water sample (100 ml) was passed through cartridge A or B. Cartridge A is packed with a modified C8 absorbent which only retains arsenite, and cartridge B is packed with anion exchange material which only retains arsenate. Samples were collected on these cartridges on site and subsequently shipped to the lab. Cartridges not only pre-concentrate arsenic in the water samples, but also avoid the inter-specie transformation. Upon receipt of the sample in the lab, 10 ml of 25 % (v/v) HCl was passed through the cartridge and the arsenite or arsenate was eluted. The eluent was then pre-reduced by the addition of 2% KI (m/v) prior to the analysis by hydride generation – atomic fluorescence spectrometry. This procedure greatly reduces the risk of specie transformation, as well as increasing the precision and sensitivity of the analysis.
Developing international standards for sub ppb determination of the hydride forming elements in water samples using AAS and AFS
This paper will focus on the methodology for the hydride generation of As, Sb and Se prior to measurement using AAS and AFS. Data from a series of International ISO Interlaboratory trials undertaken by seventeen laboratories will be presented.
Analytical performance data from the participating laboratories will be critically evaluated and discussed.
The benefits of atomic fluorescence and atomic absorption will be compared.
Air Quality VII
SI Traceability of Mercury Calibrations
Dr Warren Corns, Prof Peter Stockwell and Dr Matthew Dexter, PS Analytical Ltd, Arthur House, Unit 3 Crayfields Industrial Estate, Orpington, Kent, BR5 3HP, UK.
Dr Andrew Brown and Dr Richard Brown, Analytical Science Team, National Physical Laboratory, Teddington, Middlesex, TW11 0LW, UK.
Dr Ronny Dumarey, ArcelorMittal Gent, John Kennedylaan 51 | B-9042 Gent, Belgium
The calibration of gas phase mercury monitors depends upon having a reliable calibration standard. Traditionally, the most robust means of calibrating online equipment was the manual injection of mercury-saturated air. The Dumarey equation, a well characterised relationship between temperature and saturated concentration, together with knowledge of the gas temperature and volume injected is used to determine the mass of mercury introduced. The accuracy of this procedure will be critically discussed, including thermodynamic and kinetic considerations and experimental data demonstrating systematic biases. In addition to this, the uncertainty and SI traceability relating to the validity of the Dumarey equation will be presented. This work was conducted due to the recently proposed saturated vapour pressure equation by NIST, which is approximately 7% higher than the Dumarey equation.
The authors have developed a mercury calibration gas generator based on the dilution of Hg saturated vapour at known temperature using certified mass flow controllers. The expanded uncertainty of this device was calculated to be 1.7% when operated in the range of 1 to 10µg/m3. The accuracy of the generator was independently verified using Isotope Dilution CV-ICP-MS and also by gravimetric techniques. The data from these tests strongly support the use of the Dumarey equation as the most appropriate relationship between temperature and Hg saturated vapour concentration. Amongst other applications, this device has been used for the online calibration of workroom air monitoring equipment and natural gas and stack gas analysers, thus minimising operator time required compared to the manual injection technique.
A simple device, based on the dilution of the calibration gas under controlled conditions, has been developed to enable the automatic calibration of air monitoring equipment at the ng/m3 concentration level to be carried out routinely. The accuracy and stability of this approach will be demonstrated for the application of online ambient air measurements.
Expanded Uncertainty Model for the Determination of Total Gaseous Mercury in Ambient Air using Amalgamation coupled to Atomic Fluorescence Spectrometry
Dr Warren Corns and Prof Peter Stockwell, PS Analytical Ltd, Arthur House, Unit 3 Crayfields Industrial Estate, Orpington, Kent, BR5 3HP, UK.
Dr Andrew Brown and Dr Richard Brown, Analytical Science Team, National Physical Laboratory, Teddington, Middlesex, TW11 0LW, UK.
Measurements of mercury in ambient air are assuming greater importance, because of increasing health concerns and legislative requirements. The general public and the environment can be exposed to mercury originating from natural, domestic or industrial processes. Coal-burning power plants are the largest anthropogenic source of mercury emissions to the air. Burning hazardous wastes, the chlor-alkali industry, crematoria, breaking mercury products, and spilling mercury, as well as the improper treatment and disposal of products or wastes containing mercury, can also release it into the environment.
In order to have confidence in measured values and to assess compliance with target values, measurements must be made with validated methodologies which have traceable uncertainty statements associated with them. This paper presents a practical uncertainty budget for the measurement of vapour-phase mercury in ambient air, sampling onto a gold-coated silica adsorption tube and measuring with atomic fluorescence spectrometry. Moreover, this budget may be generalized for other related measurement methods for mercury vapour and other ambient air pollutants. All significant sources of uncertainty will be discussed and estimated. Expanded relative uncertainties at the 95% confidence interval will be estimated for exemplar measurements made by the National Physical Laboratory (NPL) as part of the UK Heavy Metals Monitoring Network. Long term TGM data will be presented representing numerous sites around the UK and Europe in rural, urban and industrial locations. The model has been incorporated into the ISO/CEN draft method 15852 entitled “Standard method for the determination of Total Gaseous Mercury
Arsenic Speciation in Atmospheric PM 2.5 and PM 10 using Hydride Generation - Atomic Fluorescence Spectrometry
Dr Warren Corns, Prof Peter Stockwell, PS Analytical Ltd, Arthur House, Unit 3 Crayfields Industrial Estate, Orpington, Kent, BR5 3HP, UK.
Dr V Oliveira, Dr JL Gomez-Ariza and Dr D Sanchez-Rodas, University of Huelva, Campus Univ, El Carmen, 21071, Huelva, Spain
Air quality is of great concern to human health. Atmospheric pollution caused by metals in particulate matter has a major impact especially for arsenic because of its high toxicity and carcinogenic properties. Arsenic is released to the atmosphere by the smelting of metals, the combustion of fuels, and the use of pesticides; volcanic activity is the main natural source. Airborne particles are classified according to their size distribution. Physical speciation studies commonly distinguish between total metal concentration in total suspended particles (TSP), or particulate matter with a diameter of specified size, for example 10 or 2.5 μm (PM10 or PM2.5).
Arsenic speciation is of interest because the toxicity varies depending on oxidation state and molecular structure. Inorganic species of arsenic such as arsenite, As(III), and arsenate, As(V) are more toxic that methylated species such a monomethylarsonate (MMA) and dimethlylarsinate (DMA). Inorganic as (III) is more toxic than As(V) not only by ingestion but also by inhalation.
This study summarizes the work to develop quantitative liquid extraction procedures for chemical speciation of arsenic in atmospheric TSP. Different extracting solutions (water, H3PO4, and NH2OH.HCl) were investigated with the aid of microwave or ultrasonic radiation. The optimised extraction procedures were applied to TSP samples collected at the city of Huelva, an industrialized urban site in south-western Spain. |
