INTERNATIONAL CONFERENCE ON MERCURY AS A GLOBAL POLLUTANT (ICMGP) ABSTRACTS
ICMGP - The 14th International Conference on Mercury as a Global Pollutant (2017)
PP106 - Determination of Methylmercury in Scottish birds of prey using LC-PVG-AFS
Authors: Shaun T. Lancaster, Gabriela Peniche, Mark Taggart, Warren T Corns and Jorg Feldmanm and Eva Krupp (Aberdeen Uni, Edinburgh Uni, North Highland College and PSA)
A new, simpler sample preparation and analysis technique for methylmercury has been recently developed for seafood and hair matrixes. The method combines a simplified methylmercury extraction and photochemical vapour generation (PVG) of Hg0 with liquid chromatography and atomic fluorescence spectrometry (LC-AFS). This reduces the number of reagents required to methanol and APDC for offline extraction and online separation of Hg species, and acetic acid combined with UV photolysis, which generates volatile Hg0 in one single step.
Since then, the method has been applied to a study of methylmercury in the livers of Scottish birds of prey (raptors). The extraction was optimised for liver matrix using dolphin liver CRM DOLT-4 as proxy, giving good recoveries within 90–110%. A preliminary study has been carried out to assess the methylmercury concentrations in Scottish raptor livers using 33 samples from a broad range of raptor species. All samples were dried by lyophilisation, powdered, and homogenised. The samples were tested for reproducibility, which was found to be below 5% RSD in all cases, and to establish a methylmercury concentration range in the livers of Scottish birds of prey, which was found to vary over two orders of magnitude from 0.216–20.8 mg kg-1 across the 33 samples analysed.
PP107 - Solubility and oxidation of Hg0 in KCl trapping solutions used for the determination of oxidized Hg in flue gas
Authors: Gianmarco De Feo, Matthew A Dexter and Warren T Corns (PSA)
Mercury fractionation data in flue gas from thermal combustion sources is of great value to the mercury research community. Results are used not only for the development and optimization of mercury control technologies, but also to provide emissions data which are ultimately used for modelling the fate and transportation of Hg species in the environment. The most commonly used and approved method for the fractionation of Hg in Flue Gas is the ASTM D6784-16 “Standard Test Method for Elemental, Oxidized, Particulate Bound and Total Mercury in Flue Gas Generated from Coal Fired Stationary Sources” (Ontario Hydro). The method applies the use of 1 mol/l KCl trapping solutions to selectively preconcentrate oxidized Hg from the flue gas matrix. The main concern with this approach is related to the selectively of the trapping solution. Trace levels of impurities present in the trapping solution and dissolved acid gases introduced from the flue gas matrix may cause oxidisation of elemental Hg thereby producing a positive bias in the measurement of the oxidised Hg fraction.
An analytical method was developed to determine the degree of oxidation of elemental Hg and the solubility of elemental Hg in the KCl solution. The dimensionless Henry’s Law constant was used to determine the solubility of elemental Hg in the KCl trapping solution at the experimental conditions typically used during flue gas sampling. Experiments were conducted by injecting a known mass of mercury vapour into a gas stream purging a temperature-controlled extraction vessel containing a known volume of trapping solution. The rate of oxidation and solubility profile was studied using different gases at concentrations typically found in flue gas. The rate of release of Hg was then measured using amalgamation-AFS by installing gold traps at the gas exit of the extraction vessel and this data was used to establish the dimensional Henry’s law constant. The constant is directly related to the solubility of Hg in solution. In the absence of the oxidization the amount of elemental Hg injected should be recovered by transfer in the gas phase of the extraction vessel. The degree of oxidation can therefore be established by the residual mercury left in trapping solution after purging and analytically by using propylation GC-AFS. A summary of a bottom up expanded uncertainty model will be presented along with the impacts on the accuracy of the results for the ASTM D6784-16 method for the elemental and oxidized mercury fractions.
PP108 - Traceability of mercury chloride permeation tubes for the calibration of gas phase oxidized Hg measurement systems
Authors: Warren T. Corns, Jasmina Allen, Tony Rogers and Gianmarco De Feo (PSA)
The use permeation tube devices are a commonly used technique for producing gas standards for instrument calibration. Certification by the vendor or supplier is normally performed by establishing the gravimetric loss from the permeation tube over a period of time, at a specified temperature which is accurately and precisely controlled. Suppliers claim that the permeation devices are capable of generating a SI traceable calibration gas that is stable for a long period of time provided that the compound within the permeation tube is still present and the conditions of use are carefully controlled. This however is not the case for mercury chloride. Although this compound is thermally stable and exhibits sublimation is it difficult to transport and the permeation rate is highly dependent on the conditions of use such as temperature and flow. Required permeation rates are in the picogram or low nanogram per minute range which means that certification using gravimetric loss takes a considerable amount of time and the uncertainty can be high. One further complication is that the commercially available apparatus for permeation tube operation are not compatible because the transportation of mercury chloride gas requires a close coupled heated sample line.
The determination of oxidized mercury in ambient air and from thermal combustion sources is a critical and important measurement. Despite the recognized importance, measurements are mostly performed without calibration simply because of the lack of SI traceable calibration devices available. As part of the EMPIR 16ENV01 MercOx Metrology project we have been conducting research on the use of HgCl2 permeation tubes. We will summarize their optimal conditions in relation to temperature and flow and how these influence permeation rates. A newly developed permeation tube apparatus and two channel direct mercury analyser based on AFS will be described. This system offers a real time Hg fractionation measurement of total and elemental Hg. These results will be compared using KCl /brominated carbon sorbent traps which are commonly used for Hg fractionation in stack gas. A bottom up expanded uncertainty budget on the use of permeation tubes will be also be presented.
PP109 - Measurement of oxidised mercury in gas phase emissions and the atmosphere: uncertainty budgets for calibration gas sources
Authors: Matthew A Dexter and Warren T Corns (PSA)
Traceable determination of total gaseous mercury, elemental Hg and oxidised mercury in gas emissions and in the atmosphere depends upon the use of traceable calibration methods. European Metrology Programme for Innovation and Research’s (EMPIR) Project 16ENV01 MercOx is focussed on the development of SI traceable measurement for the different mercury species in emission sources and in the atmosphere. In order to perform a SI traceable measurement there is a requirement for an SI traceable calibration method. Calibration gases for oxidised mercury are notoriously difficult to generate and to transport due to the adsorption and desorption phenomena, requiring them to be generated at the point of use. The practicality of introducing these gases to sampling and measurement systems is problematic especially when considering the vast array of analytical approaches that are utilized for this application.
The MercOx project is considering and developing a range of mercury(II) chloride calibration gas generators, based on methods including:
oxidation of elemental mercury calibration sources,
permeation devices,
evaporation of liquid standards
and dilution of mercury(II) chloride saturated vapour.
The uncertainty associated with the concentration of generated calibration standards used can have a substantial impact on the overall uncertainty of a measurements made using the associated technique. This in turn can affect the fitness for purpose of those measurements.
This poster presents expanded uncertainty budgets for a variety of HgCl2 generators, particularly those developed for the MercOx project and, for comparison, uncertainty budgets for commercially available Hg0 calibration gas generators.
The estimated uncertainty varies by technique and required concentration. Typical expanded uncertainties for calibration gases in the 20 µg/m³ range are less than 20 %.
The 13th International Conference on Mercury as a Global Pollutant (ICMGP) 2017
PP097 - Attaining a laboratory reference material for the routine measurement of methylmercury in rice
Authors: Shaun T. Lancaster, As'adatu Abatemi-Usman, Robert L. Martin, Parinda Manorut, Jorg Feldmanm and Eva Krupp (Aberdeen Uni)
Rice is a staple food for many countries around the globe, but it is also known to accumulate MeHg – the most toxic mercury species to humans. Therefore, accurate determination of this species in rice is mandatory. However, while a certified Reference material (CRM) exists for total Hg in rice, there is no CRM for MeHg in a rice matrix. In earlier work, we could show that the % of MeHg in rice can vary substantially. Therefore, we aimed to create a laboratory reference material (LRM) for our purposes, in order to assess the performance of routine measurements. One kg of long grain white rice was purchased from a local supermarket and ground into a fine powder and mixed well. It was then analysed repeatedly, using a TMAH/HCl digestion followed by pre-concentration CV-AFS. MeHg and Hg2+ were separated by RP-LC and on-line chemical oxidation and reduction with acidified Br-/BrO3- and SnCl2 was used prior to AFS detection. This method has been proven to be accurate and precise by cross-calibration using species specific isotope dilution mass spectrometry.
For the determination of precision and accuracy, the rice powder was split into several sub-sets and analysed repeatedly to assess variation between the sub-sets. The measurement of the samples gave a concentration range between 3.05mg kg-1 and 3.68mg kg-1, averaging at 3.36mg kg-1. Further analysis will include the testing of the materials shelf-life.
PP098 - A new simplified extraction method for the determination of MeHg in seafood by LC-UV-CV-AFS
Authors: Shaun T. Lancaster and Eva Krupp (Aberdeen Uni), Cornelius Brombach (Bremen Uni) and Dr Warren T Corns (PSA)
Rice is a staple food for many countries around the globe, but it is also known to accumulate MeHg – the most toxic mercury species to humans. Therefore, accurate determination of this species in rice is mandatory. However, while a certified Reference material (CRM) exists for total Hg in rice, there is no CRM for MeHg in a rice matrix. In earlier work, we could show that the % of MeHg in rice can vary substantially. Therefore, we aimed to create a laboratory reference material (LRM) for our purposes, in order to assess the performance of routine measurements. One kg of long grain white rice was purchased from a local supermarket and ground into a fine powder and mixed well. It was then analysed repeatedly, using a TMAH/HCl digestion followed by pre-concentration CV-AFS. MeHg and Hg2+ were separated by RP-LC and on-line chemical oxidation and reduction with acidified Br-/BrO3- and SnCl2 was used prior to AFS detection. This method has been proven to be accurate and precise by cross-calibration using species specific isotope dilution mass spectrometry.
For the determination of precision and accuracy, the rice powder was split into several sub-sets and analysed repeatedly to assess variation between the sub-sets. The measurement of the samples gave a concentration range between 3.05mg kg-1 and 3.68mg kg-1, averaging at 3.36mg kg-1. Further analysis will include the testing of the materials shelf-life.
ORAL - Analytical Challenges - Determination of Mercury in Raw Wet Natural Gas
Authors: Warren T. Corns (PSA) and Shamakh Mohamed (Khalda Petroleum Company, Salam Gas Plant)
The determination of Hg in natural gas is a well-established procedure which is routinely used by many laboratories at gas processing plants worldwide. ISO 6978 and ASTM 6350 are the two methods that are most commonly used and these methods are based on gold amalgamation with atomic absorption/fluorescence spectrometry. These methods however were developed and originally validated for dry export gas. In this case, the sample matrix is relatively simple as the sample has undergone numerous gas processing purification steps including dehydration, acid gas treatment, removal of contaminants such as hydrogen sulphide and mercury and also separation of heavier hydrocarbons. When the methods are applied to sample point locations upstream of gas treatment numerous issues may be encountered and as such special sampling precautions have to be made to ensure that the accuracy of the method is not compromised. Data will be presented from an inter-laboratory field study highlighting the complications of determining Hg in raw untreated natural gas.
Laboratory studies were subsequently conducted using a simulated raw natural gas stream containing saturated water and BTEX components. The gas stream was spiked with a known concentration of elemental Hg using a dynamic Hg generator system. The effect of these components on the accuracy of gold amalgamation with atomic fluorescence was studied. Several types of gold adsorbents including silica coated with gold nanoparticles and gold-platinum wire were studied at different collection temperatures. This work led to the development of a new sampling arrangement which was tested in the field on wet untreated natural gas. Field data will be presented from gas plant in Egypt where upstream measurements of Hg are conducted as process monitoring on site. This accuracy of the measurement is crucially important to the oil gas and petrochemical industry because of the requirements of these sites to fully understand the fate and transport of Hg across the processing plant.
ORAL - Determination of Hg species by photochemical reduction - AFS
Authors: Shaun T. Lancaster and Eva Krupp (Aberdeen Uni) and Dr Warren T Corns (PSA)
The most commonly employed technique for the determination of mercury using Atomic Fluorescence Spectrometry in a variety of matrices involves cold vapour generation. Usually, this is achieved chemically by oxidising all organic mercury species to Hg2+, followed by a reduction to Hg0 with SnCl2 or NaBH4. However, this method uses a plethora of chemicals which is costly and prone to error and instrumental issues due to the complex wet chemistry necessary. Another pathway is petrochemical vapour generation (photo-CVG), which has been used in the past in conjunction with CV-AFS as an alternative method of cold vapour generation. Previously, photo CVG has been applied to total mercury measurements using formic acid. It has been shown that formic acid rapidly decomposes when subjected to UV radiation, giving rise to species which easily reduce all mercury species to Hg0 using short irradiation intervals. This method promises a much simpler approach, which uses fewer and more environmentally friendly chemicals to give results which are comparable or even more sensitive than cold vapour approach. However, the future of this technique lies in the ability to successfully apply this to mercury speciation. Thus, new LC-UV-CV techniques based on the method are being sought. One successful route used a method whereby a 70/30 MeOH/H20 solution containing mercapto-ethanol as a mobile phase for reverse phase C18 separation, with on-line addition of formic acid: water samples spiked with Hg2+, MeHg+ and EtHg+ produced good quality chromatograms using this approach. In this work, we apply this method to a wide range of matrices such as wastewater, food, fish and clinical samples.
The 12th International Conference on Mercury as a Global Pollutant (ICMGP) 2015
PP086 - Mercury Speciation in Commercially Important Seaweeds using Liquid Chromatography Cold Vapor Atomic Fluorescence Spectrometry (HPLC-CV-AFS)
Authors: Dr Bin Chen, Dr Warren T Corns (PSA), Liam Morrison (National Uni of Ireland), Christoph-Cornelius Brombach and Eva Krupp (Aberdeen Uni)
Mercury and its presence in the marine environment can be of natural (geogenic) or anthropogenic origin. Seaweeds accumulate metals to levels several orders of magnitude higher than those present in the surrounding seawater and have been widely used as bio-monitors of water quality, avoiding the logistical difficulties associated with representative and comparative sampling of seawater and sediments. Furthermore, they integrate short-term fluctuation in metal concentrations and reflect bioavailable concentrations in the water. Mercury exists in both inorganic and organic forms (methylmercury) and toxicity depends on the chemical form. A recent European study has highlighted that algae, fish and shellfish remain a major source of mercury exposure for humans. Consequently, the speciation analysis of mercury in marine biota is important in terms of public health and ecotoxicology.
The content of total and methylmercury in three marine macroalgae species from a pristine location of the North Eastern Atlantic Ocean (Galway Bay, Ireland) was determined using cold vapor atomic fluorescence spectrometry (CV-AFS). Total mercury concentrations ranged from 2.6 to 46.5 ng g-1 (dry weight). Mean methylmercury concentrations ranged from 0.05 – 1.83 ng g-1 (dry weight). Laminaria digitata had the highest total mercury content whereas Ascophyllum nodosum had the highest methylmercury content. The data from this study represent baseline levels of Hg in commercially important seaweeds and highlight the variability in concentrations of both total and methyl mercury among brown seaweeds.
ORAL - Determination of Methylmercury in Rice using Liquid Chromatography Cold Vapor Atomic Fluorescence Spectrometry (HPLC-CV-AFS) with Automatic Online Solid Phase Extraction (SPE) Preconcentration
Authors: Dr Bin Chen, Dr Warren T Corns (PSA), Christoph-Cornelius Brombach, Eva Krupp, Jörg Feldmann (Aberdeen Uni) and Jen-How Huang 3 (Basel Uni)
Rice is the staple food for more than half of the world’s population and its consumption may represent a major route of methylmercury intake. The anoxic condition for rice growing benefits particularly methylmercury (MeHg) accumulation in rice grains by increasing the bioavailability of Hg and the methylation rate due to elevated activities of Hg methylating microorganisms in the rhizosphere.
The concentrations of MeHg in rice samples are generally very low (ng g-1) which is particularly challenging for routine monitoring. Sophisticated method such as Isotope Dilution ICP-MS is very costly and not widely available. HPLC-CV-AFS offers excellent sensitivity at much lower cost. Speciation of MeHg at low ng level is nearly impossible with most instrumentation without using preconcentration techniques. In this work, an automated online SPE preconcentration procedure based on the strong interaction of mercury with an in-house developed sulfur containing sorbent and the subsequent separation and analysis by HPLC-CV-AFS was established.
The method was applied to the analysis of more than 80 rice samples collected around the world for rice MeHg. The study includes grained rice, baby-food rice and rice products like rice noodles. A comparison was carried out between this method and species-specific isotope dilution gas chromatography inductively coupled plasma mass spectrometry (SSID-GC-ICPMS) for 19 samples, showing a slope of 1.0134 and a correlation coefficient of 0.972. The method was further evaluated with standard addition and the results were not significantly different. Additionally, species inter-conversion during digestion was investigated and could be excluded. MeHg concentrations were found to range from 0.45 to 4.55 µg kg-1 and MeHg is in average 80.4 % of T-Hg. The developed method requires a minimal amount of sample preparation with a LOD of 0.120 ng g-1 for MeHg in rice. The method is fully automated and can be widely used in the labs for routine analysis to produce reliable results.
ORAL - Mercury Mass Balance Distribution during Ethylene Production
Author: Dr Warren T Corns (PSA)
Knowledge of the mercury content in petrochemical feed-stocks and refinery products is extremely important. 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 even at low concentrations. These are typical based on palladium or platinum which form a strong amalgam with Hg. Mercury is also known to be the cause of corrosion problems with aluminum-based heat exchangers which operate at cryogenic temperatures, 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. Because of these facts many plants install mercury removal systems to ensure that important parts of the plant are protected, this means that periodic measurements of the outlets of these removal systems need to be made to ensure that they are working correctly. Also other parts of the plant require accurate measurements to help provide a better understanding of the fate of mercury.
This presentation will focus on the analytical challenges and techniques to perform a mass balance of Hg on an ethylene plant. Atomic Fluorescence Spectrometry was utilized to determine Hg in various streams including gas, liquid and solid phase samples and the results were applied to the mass flow rates across the plant. A butane feedstock containing 18ppbw of Mercury was responsible for the rapid degradation of an acetylene reactor catalyst which was replaced and later protected by Hg removal beds. Mercury was partly removed during acid gas treatment and gasoline stripping. The majority of mercury was found in the C2 cracked gas as this represented the bulk mass flow. Mass balance data will be presented in addition to emission rates to the environment. The development of a model to predict Hg condensation rates in relation to process conditions will also be presented and discussed.
ORAL - Accuracy and Uncertainties of Mercury Fractionation in Crude Oil, Natural Gas Condensates and Naphtha using Cold Vapour Atomic Fluorescence Spectrometry
Authors: Dr Warren T Corns & Dr Bin Chen (PSA)
Crude oil and condensates are primary feedstocks for the petrochemical industry. Understanding the mercury speciation in these samples is critical for refining operations since the presence of mercury even at low concentrations can have a detrimental effect on numerous refining operations. These include the poisoning of expensive hydrogenation catalysts, corrosion of aluminium alloys in steam cracker cold boxes and reducing product quality. Products contaminated with mercury tend to offer a lower premium and therefore understanding the amount of mercury in the feedstock is essential.
There are also environmental aspects that have to be considered, since the combustion of hydrocarbons essentially contributes to the anthropogenic emissions of mercury to the atmosphere. Removal of mercury from crude oil and other petrochemical products is extremely challenging and the optimization of such processes cannot be achieved without knowledge of the mercury species present in the sample and how they might be transformed during refining operations.
The chemistry of mercury in crude oil and gas condensates is complex. Numerous chemical forms of mercury with different chemical and physical properties may be present in samples. The speciation of mercury is highly dependent upon the source, production stage, sampling and the age and storage of the sample. The stability of elemental mercury in hydrocarbon samples is questionable given the high volatility and readiness to adsorb on metallic surfaces and suspended material in the sample.
In this presentation we will review a Hg fractionation procedure to quantify mercury in in crude oil, condensates and naphtha. Hg Fractions include total Hg, dissolved Hg, particulate Hg, ionic Hg, organic Hg and elemental Hg. A GC-AFS method was also used to determine volatile species such as Dimethylmercury. Summation of the mercury in different fractions is a good indication of the accuracy of the procedure and in most cases very acceptable summations are obtained. In some instances however there are high uncertainties associated with ionic and organic Hg fractions and little is known of what species these fractions include. Data will be presented showing the diversity of Hg fractions found in various sample types.
The 11th International Conference on Mercury as a Global Pollutant (ICMGP) 2013
PP069 - Are Certified Reference Materials an Effective Tool for Method Validation?
Authors: Dr Bin Chen, Dr Warren T Corns and Dr Peter B Stockwell (PSA)
Quality Assurance (QA) program is vital for any laboratories who wish to be successful in an increasingly competitive market. The object of QA is to ensure that the right result is provided on the right specimen at the right time, and interpreted according to the right reference data. As one of the many participating members of United Kingdom National External Quality Assessment Service (UK NEQAS), urine specimens are distributed to us at a regular frequency, and aim to cover the range likely to be encountered in clinical practice.
Urinary mercury is an excellent bio marker because it is non-invasive and it reflects the recent high Hg exposure. A method based on cold vapour generation atomic fluorescence spectrometry was developed for the accurate and reliable analysis of total mercury concentrations in human urine. A
Seronorm urine reference material was initially used for external QC (EQC) for the method validation. Urine samples were oxidised using the following approaches: a) bromide/bromate and hydrochloric acid; b) nitric acid and c) nitric acid and hydrogen peroxide.
Our results showed that total mercury can only be analysed accurately and reliably when c) method was used for the sample preparation. The Seronorm CRM however yielded correct results when any above-mentioned method was used therefore it could not act as an effective QC material for this type of application. An EQC program alone is not effective enough even though the reference material is a well-known and well-established material. Therefore an internal QC program (IQC) such as matrix spike recovery test should be used at all times alongside with an EQC program in order to achieve correct results for any individual sample.
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ORAL - An Introduction to Mercury in the Oil and Gas Processing Industry
Author: Warren Corns (PSA)
Mercury is a naturally occurring trace contaminant in hydrocarbon reservoirs which is distributed in all phases (oil, gas and water). The concentration of mercury at the well head is highly variable ranging from non-detectable quantities to saturated levels. Even low concentrations of Hg can be significant because of the large quantities of oil and gas processed. The presence of mercury may affect the oil and gas industry in a number of areas including damage to the processing plant, contamination of Hg in hydrocarbon products, environmental emissions and waste disposal. There is also a health and safety issue that needs to be considered. The inventory of mercury releases from this industry is rarely considered in global budgets and little is known about the fate and transportation of mercury from the raw to final products and to the environment.
Knowledge of the mercury content in petrochemical feed-stocks and refinery products is extremely important. 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 even at low concentrations. These are typical based on palladium or platinum which form a strong amalgam with Hg. Mercury is also known to be the cause of corrosion problems with aluminum-based heat exchangers which operate at cryogenic temperatures, 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. Because of these facts many plants install mercury removal systems to ensure that important parts of the plant are protected, this means that periodic measurements of the outlets of these removal systems need to be made to ensure that they are working correctly. Also other parts of the plant require accurate measurements to help provide a better understanding of the fate of mercury.
This presentation will provide a general introduction and summarize what we understand and believe to be fate of Hg and the potential impact of mercury from the oil and gas industry as a global pollutant.
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ORAL - Industrial challenges for calibration of gas-phase mercury analysers
Authors: Matthew A Dexter, Warren T Corns & Peter B Stockwell (PSA)
Traceability of gas-phase mercury analyser calibration is of particular concern with all mercury analysis. It is important to ensure that the calibration used is appropriate for the sample being analysed, particularly in terms of the species present and, in some cases, the sample matrix. Elemental mercury calibration based using either the ‘bell-jar’ approach or a calibration gas generator is widely available. In some cases, such as ambient air and coal-fired utility stack monitoring, oxidised sources of mercury namely mercury chloride are needed for calibration and system integrity tests. Unknown species and pg m-3 concentrations are a particular challenge for RGM measurement. Even if a traceable source of these gases is available, storage, transport and delivery of the gases to the analyser can be extremely challenging.
Calibration of mercury analysers using the ‘bell-jar’ technique, injecting volumes of mercury saturated air using a gas tight syringe is typical for gas phase mercury analysers. This technique is frequently used to provide calibration points in the 0.1-10 ng mass range. This range can be orders of magnitude above the masses collected for automated air monitoring with 10-60 min sample collection periods, with the results measured close to the zero-points on the calibration, with resulting errors. Alternative calibration techniques and analyser operations can be adopted to ensure the results are interpolated on the calibration curve. Continuous flow calibration sources are needed at low ng m-3 concentrations to allow validation of amalgamation trapping efficiency and to test sampling apparatus integrity as spiking tests using small quantities of mercury-saturated air may exhibit different behaviour. These techniques are however generally more complicated or require undesirable compromises to be made.
Suitable calibration strategies can be particularly difficult where transient sources of mercury emissions are monitored, for example waste disposal systems or crematoria. Here a very wide dynamic range is required, with ‘baseline’ emissions at sub-µg m-3 levels and transients at mg m-3 to saturated levels. To ensure that the overall emissions are measured accurately, good calibration is required in both of these ranges. (Inaccurate ‘baseline’ emission results over hours or days can affect the average emissions levels as much, or more, than poorly monitored mg m-3 spikes.) Particularly where transient emissions can occur, the duration and timing of calibrations needs to be carefully arranged to minimise the loss of transient data.
When used in industrial settings, it is important that analyser calibrations are straight forward and readily understood by the equipment operators. Analytical considerations can easily be misunderstood or be neglected in favour of user convenience, particularly as users are unlikely to have an analytical or scientific background.
This presentation will provide an overview of analytical challenges for the calibration of gas-phase mercury analysers, presenting some examples and solutions.
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The 10th International Conference on Mercury as a Global Pollutant (ICMGP 2011)
PP057 - Mercury Emissions from Crematoria using Online Hg CEM
Authors: Dr Warren T Corns, Matthew Dexter and Dr Peter B Stockwell (PSA)
Anthropogenic emission of mercury into the environment continues to cause concern. Increasing control of atmospheric mercury emissions is resulting in the gradual overall fall in mercury emissions. UK annual mercury emissions are estimated to have fallen dramatically over the last 3 decades. In contrast to the overall fall, mercury emissions from crematoria have increased significantly. The increase in emissions is readily attributable to the use of amalgam fillings and, due to better dental health, a large decrease in the number of people edentate at the time of death. Estimates of the mass of mercury present in an average cremation vary significantly, with estimates generally between 0.9 g and 3.0 g.. The mass present depends on dental health practices, thus varying with time period and with country.
Mercury emissions during the cremation process are almost entirely due to the presence of amalgam fillings in the cadaver. This leads to very significant variation in the concentration of mercury emitted, in each cremation. Concentrations vary between low ug/m3 to several mg/m3.
The P S Analytical Sir Galahad amalgamation-atomic fluorescence spectrometer is a proven technique for the determination of mercury in a wide range of gaseous media. This paper presents summary results of an initial study of mercury emissions on a single crematory stack at a UK crematorium and introduces a Hg CEM, specifically designed to continuously monitor mercury concentrations in cremation gases for regulatory purposes or online process control of mercury abatement equipment.
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PP058 - Speciation of Mercury in Urine by Cold Vapour Atomic Fluorescence Spectrometry
Authors: Dr Bin Chen, Dr Warren T. Corns and Dr Peter B. Stockwell (PSA)
Urine is one of the most widely used ‘non-invasive’ biomarkers for risk assessment of mercury exposure. The sample pre-treatment procedure for urine analysis usually involves simple dilution with deionised water or diluted acid, its validity is generally supported by the analytical results of freeze-dried urine reference material. In real samples, however, the spike recoveries were found to be largely dependent of the individual urine matrix, despite the excellent recovery obtained for the reference material. The interference caused by the organic matter in the urine samples is far from negligible. In this work, several sample pre-treatment procedures have been investigated for total mercury and mercury speciation in urine samples, followed by the detection of atomic fluorescence spectrometry. The challenge of mercury speciation using HPLC lies in the poor separation of Hg(II) and methylmercury peaks when 2-mercaptanethanol was (most commonly) used as modifier. In this work, a newly developed mobile phase based on APDC modifier provides clear baseline separation for mercury species within 15 minutes, followed by the online UV digestion and HPLC-CV-AFS. The accuracy and precisions of the procedures were not only validated by the reference materials, also by the spike recoveries of inorganic and methylmercury in almost every urine samples analysed.
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PP059 - Development of low level calibration apparatus for TGM measurements
Authors – Dr Warren T Corns, Tony Rogers (PSA) | Richard Brown and Andrew Brown (NPL)
The determination of TGM in ambient air and natural gas is analytically challenging because of the low concentrations encountered. In both cases sub ng/m3 detection limits are required to monitor accurate trends. The most commonly used technique is amalgamation – AFS with the calibration being performed by injection of air saturated with Hg vapour at ambient temperature. Whilst this a well proven convenient calibration approach small microliter injection volumes are required to allow mercury mass equivalent absolute calibrations in the range of the samples even when relatively large sample volumes are used. The uncertainty of measurement increases dramatically when the lowest portion of the calibration relationship is used which is often the case for measurements of TGM. In addition to this the analytical performance of gold traps at low ng/m3 concentrations may not be the same as injecting a small quantity of air saturated with Hg vapour at mg/m3 concentrations. This is more evident when gold traps become passivated over time and when two traps give widely different results. The extent of passivation is often unknown and accepting the highest result is analytically flawed because there is a strong possibility that several traps are giving low recoveries to different extents.
A more valid approach to calibration can be achieved using continuous flow dynamic Hg vapour generators operated in the ng/m3 range. Two approaches will be presented and compared. The first approach was based on the two fold dilution of saturated source of mercury at a controlled temperature. Mass flow controllers are used to generate the initial flows and the concentration generated is in the ug/m3. The second dilution was achieved using a critical orifice and eductor pump arrangement. The main advantage of this setup was the rapid stabilization time. The second approach was based a specially fabricated temperature controlled Hg permeation tube with mass flow controllers. The accuracy and precision data generated from both devices when coupled to a PSA amalgamation AFS will be presented. Both calibration devices were found to offer an excellent solution to calibrating fully automated TGM instrumentation.
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PP060 - Process Analysis of Mercury in Petrochemical Streams
Authors: Dr Warren T Corns and Dr Peter B Stockwell (PSA)
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.
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The 9th International Conference on Mercury as a Global Pollutant (ICMGP 2009)
PP045 - SI Traceaility of Mercury Calibrations
Authors: Dr Warren T Corns, Dr Matthew A Dexter, Dr Peter B Stockwell (PSA), Richard Brown, Andrew Brown (NPL) Ronny Dumarey
Mercury is a highly toxic and persistent pollutant found in ambient, indoor and workplace air. Coal-burning power plants are the largest anthropogenic source of mercury emissions to the air, whilst the chlor-alkali industry, crematoria, breaking mercury products, and the burning and improper disposal of products or wastes containing mercury, can also release mercury into the environment. Human exposure to mercury can also be via dental amalgam and the ingestion of crops, animal products or water contaminated by mercury following deposition processes.
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PP044 - SI Traceability of Calibration Techniques for Online Gas-phase Mercury Monitors
Authors: Dr Warren T Corns, Dr Matthew A Dexter, Dr Peter B Stockwell (PSA), Richard Brown, Andrew Brown (NPL) Ronny Dumarey
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 newly 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 10 µg/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.
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PP043 - Flow Injection Gas Chromatography and Atomic Fluorescence Spectrometry (FI-GC-AFS) for the Ultra-Trace Level Mercury Speciation in Various Environmental and Biological Samples
Authors: Dr Warren T Corns, Dr Bin Chen, Jasmina Allen and Dr Peter B Stockwell (PSA)
The performance of atomic fluorescence spectrometry (AFS) has been improved tremendously over the last four decades since its first application in 1960s. Detection limits of AFS for mercury species being reported are among the best of any other analytical methods. AFS particularly offers great sensitivity, selectivity and stability for elemental and speciation analysis for Mercury. In this presentation, several recent studies using vapour generation AFS are discussed, including: a) the sample preparation for the speciation of mercury in hair, blood and water samples; b) the online derivatization of inorganic and organic mercury using flow injection with cold vapour AFS systems; c) the online pre-concentration of various mercury species, and followed by d) online separation and detection using GC-AFS system. Detection limits of are in the range of sub pg for mercury species including elemental Hg, methylmercury, dimethylmercury and ethylmercury. The excellent stability and convenience of the newly developed instruments will also be demonstrated.
7th International Conference on Mercury as a Global Pollutant (ICMGP 2004)
PP009 - Mercury Speciation: A Fully Automatic Gas Chromatography/Atomic Fluorescence Instrument
Authors: Dr Peter B Stockwell and Dr Warren T Corns (PSA)
Mercury is a widely distributed pollutant in the environment. There have been many incidents where its presence has caused damage both to humans and to production plants. Legislation is normally based on the total mercury content and the acceptable levels are always being reduced. However, its organic compounds, particularly methylmercury, are far more toxic than elemental mercury or its inorganic salts. Such widespread hazard and toxicological concern have stimulated great demand for reliable, precise and sensitive methods for the determination of organomercurials in water, sediments, fish and other biological samples. The general method for the determination of methyl and ethylmercury halides (MM and EM) involves gas chromatography with electron capture detection. However, tedious sample work-up protocols and poor chromatographic response (on packed columns) have shown the need for the development of new methods in this field. Atomic fluorescence detection offers significant advantages for the analyst and the potential of this technique is further exploited by coupling to chromatographic separation techniques.
A fully automated instrument will be described using a commercial available gas chromatograph with this highly sensitive and specific atomic fluorescence detector. This provides a sensitive method for the determination of methyl- and ethylmercury, free from deficiencies associated with earlier methods. MM and EM are first released from the sample matrix by the combined action of acidic potassium bromide and cupric ions and extracted into dichloromethane. The initial extracts are subjected to thiosulfate clean-up and the organomercury species are isolated as their chloride derivatives by cupric sulphate addition and subsequent extraction into a small volume or organic solvent. Capillary gas chromatography coupled with an atomic fluorescence detector system proved to be a very selective and sensitive technique with excellent separation efficiencies for methyl- and ethylmercury. The absolute detection limit for both MM and EM was found to be 0.2 pg. Data provided by the system has been used to determine the mercury speciation in plant soils, sediments and waste samples, interesting examples of the speciation found in these types of samples will be presented.
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PP008 - Online Mercury Speciation in Flue Gas from Coal Fired Stationery Sources
Author: Dr Warren T Corns (PSA)
Accurate measurement of mercury speciation in flue gas from coal fired power utilities and waste incinerators is necessary to model the fate and transportation of mercury in the atmosphere and to evaluate the effectiveness of mercury control technologies. Wet chemical impinger based methods are available for total mercury and mercury speciation. These methods are expensive to perform, cumbersome, time consuming and labour intensive. There is clearly a need to continuously monitor mercury emissions and therefore a reliable approach using amalgamation atomic fluorescence spectrometry was developed.
There a numerous measurement and sampling issues that have to be addressed to ensure accurate results are obtained. Sampling in the presence of reactive flyash is problematic using conventional filtering techniques since captured flyash may collect mercury or change the speciation. To overcome this problem we have developed an inertial filter that uses a sintered porous tube. The process was evaluated using dynamic spiking of elemental and oxidized forms of mercury into flue gas with high flyash content. To perform these experiments continuous calibration systems based on dilution of saturated mercury vapors were developed. The relative accuracy was found to be less than 10% of the theoretical value based on saturated vapour calculations.
Speciation was achieved using both wet and dry speciation modules. The purpose of these units was to generate two streams specific to elemental and total mercury. Oxidized mercury was determined by difference. The influence of flue gas components on the accuracy of the measurement will be discussed. Flue gas species such as Chlorine and combinations of NOx and HCl were found to reduce the amalgamation efficiency and therefore various chemical pretreatment were employed to overcome this problem. The developed instrumentation has been successfully used in the field at various locations on power stations in Europe and the USA and typical data.
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PP007 - Online Determination and Removal of Mercury from Natural Gas Streams
Authors: Dr Warren T Corns, Dr Peter B Stockwell and Dr Derek Bryce (PSA)
Natural gas and its liquid condensates are primary feedstocks for a variety of industrial processes. Mercury in natural gas is known to cause corrosion problems with aluminum heat exchangers, rotors and condensers. The replacement of heat exchangers is a costly operation with high capital investment and huge financial losses due to unscheduled plant shutdown. Mercury has also been found to be responsible for the de-activation of expensive hydrogenation catalysts. It is therefore important to remove and accurately determine mercury from natural gas streams to ensure the protection of downstream refinery equipment. In this paper we will describe the development and application of an online process mercury analyser to monitor the efficiency of mercury removal beds. Instrumentation based on dual amalgamation coupled to atomic fluorescence spectrometry was developed and subsequently installed at a production facility in the USA. Sampling strategies to ensure a representative sample was obtained without mercury losses were developed. Inlet concentrations of Hg were found to be quite variable and up to 8ug/Nm3 whilst the concentration after Hg removal was typically less than 15 ng/Nm3. The results for online measurements were periodically validated using offline measurements and these typically gave good agreement to within +/- 10%. The detection limit was found to be 1 picogram Hg absolute, this equates to 1 ng/m3 for a 1-litre sample volume collection. The measurement cycle was 5 minutes.
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