Proffessional point of view
How to select the best mercury analyzer?
Mercury measurement is used in various fields, such as environment assessment and quality control, and there are many regulations which require mercury measurement.
In case of the purpose of research or investigation -- the sampling method, demand sensitivity, and portability (on site measurement) etc. -- it is necessary to take into consideration and to select the analyzer.
- Sample form (Solid, Liquid or Gas)
- Plastic, Food, Living body samples, etc.
- Factory effluent, Environmental water, Drink water, Sewer, etc.
- Environmental air, Working environment, LPG, etc.
- USEPA 7473, ASTM D 6722-01, etc.
- JIS K0102, Notification of 59 of MOE, etc.
- JLPGA-S-07, Mannual of Measuring Methods of Toxic Air Pollutants, etc.
What does “samples” mean?
It means the substance (application) with which analysis and measurement are presented.
What does “official measurement methods” mean?
When carrying out the qualitative analysis and quantitative analysis of an element in chemical analysis, “official measurement methods” mean the specified methods by an official testing body such as an international organization, a state or research institute.
When some measuring methods are accepted in the official measurement methods, please select the best mercury analyzer for the following to reference.
- Mercury concentration of the samples.
- (When there are several kinds of measuring objects) The concentration range of the samples.
- An organic substance, an inorganic substance, or a composite material.
- The physical characteristics, such as an inflammability, resolvability, pH, the boiling point, the melting point, and the flash point.
With the product of Nippon Instruments Corporation (NIC), when a measuring object is clear, please look for the measuring device of “Search mercury analyzer from application” or the purpose of “Search mercury analyzer from analysis method” of this site.
Two kinds of measurement methods
-- Thermal Decomposition and Reducing Vaporization
Roughly there are two kinds of mercury analyzers, “Thermal Decomposition” and “Reducing Vaporization”.
Since Reducing Vaporization analyzer can generally measure many amounts of samples at once, it is more suitable for low concentration measurement. However, in case of the measurement of solid samples, it is necessary to elect the best pretreatment (sample decomposition) for the application in order to get the hominized solution by the pretreatment (sample dcomposition).
On the other hand, when the concentration range of a measuring object is wide (ppb to ppm order etc.), since it is easy to generate a memory effect, Thermal Decomposition is suitable.
When an organic matter, an inorganic substance, or a composite material is measured, Thermal Decomposition is sometimes prefered because a pretreatment (sample decomposition) is complicated.
Considering other physical characteristics it is necessary to select the best mercury analyzer.
Two kinds of measurement principles
(Atomic Absorption Spectrometry and Atomic Fluorescence Spectrometry)
It is possible to select the suitable mercury analyzer from the viewpoint of the measurement principles.
There are some mercury analyzers which offers two kinds of measurement methods, Atomic Absorption Spectrometry and Atomic Fluorescence Spectrometry for the same application.And the mercury analyzers by Atomic Fluorescence Spectrometry is observed in many regulating methods overseas.
It is possible to quantify a low concentration sample very much, and Atomic Fluorescence Spectrometry is effective to quantify it in a little amount of samples from the ability to obtain the sensitivity of about 10 times or more rather than Atomic Absorption Spectrometry.
Moreover, since Atomic Fluorescence Spectrometry can't be easily subject to the influence of an interference element compared with Atomic Absorption Spectrometry, it is applied also to the oil dedicated analyzers which measure hydrocarbon.
Atomic Absorption Spectrometry: AAS
Ultraviolet light that is emitted from a mercury lamp is irradiated into a flow cell with a quartz glass window. When elemental vapor phase mercury passes through this flow cell, mercury atoms at the ground state absorb the light and make transitions into the excited state. Mercury concentration can be measured through this absorption of light (absorbance), and this measuring method is called atomic absorption spectrometry. For mercury measurement, mercury lamps with a wavelength of 253.7 nm is used.
Atomic Fluorescence Spectrometry: AFS
Ultraviolet light that is emitted from a mercury lamp is irradiated into a flow cell with a quartz glass window. When elemental vapor phase mercury passes through this flow cell, mercury atoms at the ground state absorb the light and make transitions into the excited state. Mercury atoms at the excited state emit fluorescence while they are immediately changing back into the ground state. This fluorescence intensity is measured from the direction perpendicular to the optical axis. The intensity is proportional to the mercury concentration. Inert argon gas is used as the carrier gas.
This method ensures a sensitivity ten times of or higher than that of atomic absorption spectrometry, and is approved by many institutions outside Japan, such as EPA (Environmental Protection Agency) in the U.S, as an official mercury analytical method.
Relation between “Measurement method” and “Measurement principle”
The relation between “Measurement method” and “Measurement principle” of the mercury analyzer is shown in the following figure.
Firstly the measurement method is classified into “Thermal Decomposition” and “Reducing Vaporization”, then each of them is classified again into two measurement principles, “Atomic Absorption Spectrometry” and “Atomic Fluorescence Spectrometry”.
On-site mercury measurement
In case of the investigation purpose measurement, the mercury concentration may fall after sampling till measurement.
Among mercury analyzers, there is some analyzers suitable for on-site measurement at site.
In order to make change over time minimum on-site measurement is the most effective way, but there are sometimes various problems such as the analyzer is too big and heavy to carry to the site, the way of pretreatment (sample decomposition) is restricted and the power supply situation is not good, etc. The selection of mercury analyzer by its measuring samples and measurement environment is important.
EMP-2 series by Nippon Instruments Corporatin are the most suitabel models for on-site mercury measurement with rechargable battery included in its light and ultra compact body.
Form analysis which quantifies the form of mercury
Mercury exists in three forms such as Metal mercury, Organic mercury and Inorganic mercury.
Although mercury speciation analysis which quantifies each form is conducted, metal mercury (Hg0) occupies approx. 95% of total mercury in the air and generally mercury concentration measurement was conducted representative by Hg0.
Recently the demand for the mercury speciation analysis is increasing.
Speciation analysis is possible also by the mercury analyzers presented by Nippon Instruments Corporation.
Since a measurement method changes with kind of samples or mercury forms, please contact us about details.