The AULA 254 is used for fully automatic determination of mercury traces in liquid samples and sample digests. The instrument carries out routine analysis: sample after sample following exactly the preselected procedure thus increasing efficiency and productivity of your lab. Applications include:
Schematic flow diagram:
AULA-254 Gold with Automatic Sample Digester ASD
The working principle of the system is based on the continuous flow method. First the mercury contained in the sample is transformed into the elemental state by addition of a reducing agent to the sample flow. In a cross-flow reactor the mercury is stripped with a gas stream and carried into the optical cell which is made entirely of fused silica. There the quantitative determination of mercury is obtained by measuring UV absorption at a wavelength of 253,7 nm at room temperature. This analytical technique is commonly known as cold vapor atomic absorption spectrometry (CVAAS), a method that has proved itself as extremely sensitive and selective over many years.
In contrast to a typical multi-element AAS the AULA is specially designed for mercury determination. This allows top performance in analytical applications. The use of a highly stable low-pressure electrodeless mercury discharge lamp (EDL) in connection with the latest UV detector techniques result in excellent baseline stability and low detection limits.
Surprisingly easy to use the AULA-WIN offers all features of a modern analytical software. It has been developed with extensive input from our users. Samples, calibration standards and quality control standards (QCS) are entered into the carrousel screen.
AULAWIN Measurement table and signal graph (1 ppb-Peak)
A sample table is created automatically and can be viewed in the table screen. Sample dilution factors as well as sample weight and final fill up volume for digestion of solid samples can be entered in the table. The result of the measurement is calculated automatically from the chosen calibration function and displayed in µg/l or µg/kg. The QCS function assures a high level of reliability of the analytical results.
The results of the analyses together with the data necessary for quality assurance (date, time, user ID, sample number, calibration data, instrument parameters) are stored in a file. They are available at any time for display and printout. Worksheet templates can be created and stored to minimize setup time for routine work.
No long purging or rinsing procedures even when samples with high concentrations are analyzed. The typical duration of a full measurement cycle is 60 ... 180 seconds.
The quick screening mode allows performing analyses in even a shorter time.
Measurements of up to 20 calibration standards and up to 53 samples and check standards are carried out fully automatically. Standards and samples are filled into 10 ml glass vials and positioned on the auto-sampler turntable. Reagent solution (for example tin-(II)-chloride) and rinse solution (reagent water) are filled in the corresponding glass tanks. Then the stripping gas flow is adjusted and measurement is started by a keystroke.
AULA-254 Gold: reaction part
The measurement cycle can be interrupted at any time by the operator for selecting any sample to be measured next. Readings and instrument status are displayed in real-time on the screen.
The stability of the baseline is checked prior to each measurement and the zero point is adjusted automatically. The typical zero drift during a measurement is below 0.0001 absorbance units.
The instrument automatically interrupts the measurement if samples with mercury concentrations exceeding the measuring range are detected.
In this case the system will clean itself immediately by purging. After being diluted, the rest of the sample can be analyzed.
Blanks measured after a sample with high mercury concentration demonstrate that there is virtually no carry over
Mercury vapor has a general tendency to absorb on surfaces causing a memory effect (carry over).
This undesirable property has been minimized by using selected materials (fluoropolymer, borosilicate glass, Tygon LFL) for sample and reagent conducting components and by heating the optical bench. In addition, the auto-sampler probe and the sample tubing are rinsed after each sample. This also allows a high sample throughput.
Even samples with concentrations in the upper measuring range do not produce a carry over to the following sample.
Unlike traditional mercury analyzers, which use drying tubes for removing water vapor from the sample gas, the AULA 254 uses a maintenance-free thermoelectric dehumidifier. The dew point of the gas is decreased below ambient temperature thus the water condenses on the wall of a small glass tube and flows back into the reactor.
The stability of the carrier gas flow has a direct effect to the reproducibility of measurements. For this reason the AULA-254 Gold system uses a highly precise (1.5 % accuracy) electronic mass flow controller (MFC).
The mercury cannot escape into the working environment, as any free mercury is collected in a sulfurized activated carbon absorber. If the cartridge needs replacement a message appears on the control panel.
The analyzed sample no longer contains any mercury.
Comparison of microwave digested samples (light blue) and samples directly measured with AULA-ASD (red):
Sample A: seepage water from chlor-alkali plant
Sample B: tank rinsing water from chlor-alkali plant
Sample C: effluents from PTFE production plant
Sample D: sewer plant effluent
The AULA-254 can be equipped with an optional sample preparation system for aqueous samples. The digestion procedure derives from standard methods commonly used in the laboratory.
The sample is automatically drawn from the auto-sampler vial and is continuously mixed with a strong oxidizing reagent (e.g. potassium permanganate, bromide-bromate). Subsequently the sample/oxidant mixture is heated to approx. 98 °C in a heated coil. After the oxidation step hydroxylamine hydrochloride and tin-(II)-chloride are added for reduction of mercury into the elemental state which is then extracted by a stream of carrier gas (Argon or nitrogen).
Comparison of measurements with microwave digested samples (8 ml sample + 2 ml nitric acid + 2 ml hydrogen peroxide) show a good accordance.
Normally it takes less than 4 minutes to perform an automatic analysis.
Average reagent consumption for 100 analyses is:
Typical applications of the AULA-ASD system include analysis of aqueous samples that have to be digested oxidatively before reduction: surface water, groundwater, effluent, process water.
The integrated GoldTrap preconcentration module drastically enhances the detection limit to values lower than 1 ng/l.
Using ultrapure reagents and following the guidelines for mercury analysis at ultratrace levels (e.g. given in EPA method 245.7 or method 1631) a measuring range from 1 ppt to 5000 ppt can be achieved. This complies with the performance data given in EPA method 245.7 or 1631.
An outstanding property of the newly developed GoldTrap is its minimum thermal inertia. This has become possible by use of a wafer thin ceramic substrate. As a consequence heating and cooling rates become very fast. Analysis durations are comparable to the direct method.
The AULA-254 Gold allows the user to select if analyses shall be carried out with or without a preconcentration step. This makes the instrument versatile for any application.
UV absorption (CVAAS),
Wavelength = 253,7 nm
Principle of preconcentration:
Amalgamation on gold surface,thermal desorption by rapid heating (MI GoldTrap)
Electrodeless low-pressure mercury lamp (EDL)
Reference beam method
Fused silica (Suprasil),
Length approx. 230 mm,
heated, approx. 45°
argon (optional nitrogen), 4-6 l/h;
stabilized with electronic mass flow controller
53 place random access, turntable-type
10 ml, glass; aluminium foil disc covers
approx. 1 ml
Heating coil temperature:
approx. 98 °C (AULA-ASD only)
none, Auto zero before each measurement
typ. 60 - 180 seconds
AULA-WIN, Windows ™ compatible
Electrical power supply:
115 VAC / 60 Hz; 230 VAC / 50 Hz
El. power consumption:
approx. 100 VA
(AULA 254-ASD: 120 VA)
approx. 37 x 38x 44 cm (W x H x D)
Bench space requirements:
approx. 50 x 70 cm (W x D) (PC not included)
approx. 14 kg (PC not included)
As a leading supplier of high precision analytical equipment, we strive at all times to offer top quality solutions. Our products are manufactured according to the ISO 9001 quality regulations.