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Mercury Process Analyzer

PA-2 / PA-2 Gold


Continuous Detection of Mercury in Water and Aqueous Solutions



  • Fully automatic system
  • Easy menu-driven operation
  • Proven and reliable detection method: AAS
  • Measuring ranges from 10 ppt to 100 ppm
  • High flexibility of sample pretreatment
  • Suited for complex sample compositions
  • Low reagent consumption
  • Corrosion-protected construction
  • Automatic self diagnosis system for reliable operation


On-line Process Control of Mercury with the PA-2

Mercury Instruments

The mercury process analyzer PA-2 is used for continuous monitoring of mercury concentrations in industrial processes. Applications include effluent and quality control in chlorine-alkali plants, monitoring of scrubber water of waste incinerators and power plants, control of industrial sewage and purification plants, quality control of sulphuric acid, drinking water. Special version also for concentrated caustic solutions (NaOH, KOH).

On-line Measurement of mercury in concentrated (50%) caustic soda with the PA-2 (left), the sample passes a specially designed dilution system (right). Installation in a chlorine-alkali plant.

PA-2 or PA-2 Gold?

The PA-2 Systems come with either the VM-3000 or the UT-3000 photometer
to meet different requirements regarding accuracy and sensitivity of measurements:

  • PA-2: arrowVM-3000
  • PA-2 Gold: arrowUT-3000
    Thanks to its GoldTrap, the UT-3000 is able to measure Hg in ultra trace concentrations ( ppt range).

Flexibility in Sample Digestion

In practice mercury analysis sample matrices very often show different and variable compositions. Depending on the chemical process the forms of mercury differ: elementary, ionic, dissolved as a salt, as an organic compound or as insoluble sulfide.

The PA-2 offers a variety of sample pretreatment procedures to allow highly precise determination of total mercury in all these samples, with the results from the PA-2 showing very good correlations with standard laboratory analyses.

High flexibility is achieved by the modular structure of the sample pretreatment module. This allows the user to choose from the different digestion methods, for example:

  • Sample preoxidation with hydrochloric acid + potassium permanganate
  • Sample preoxidation with sulphuric acid + potassium permanganate
  • Sample preoxidation with hydrochloric acid + sodiumchlorate
  • Sample preoxidation with Fenton´s reagent

The integrated heated reaction module boosts sample digestion. The duration of reactions can be adapted to the need of your application by employing reaction coils of different lengths.

Proven Measurement Principle

The detection of mercury contained in the sample occurs in an optical cell made of fused silica (Suprasil). In a first step mercury is reduced to the elementary state by means of tin(II)chloride or NaBH4. Subsequently mercury is stripped from the aqueous phase with an air stream and carried into the optical cell. Here the UV absorption measurement is conducted at a wavelength of 253,7 nm.

This analytical technique called "cold vapor atomic absorption spectroscopy (CVAAS)" shows extreme sensitivity and selectivity. It has been reliable and proven for many years. In contrast to the occasionally recommended atomic fluorescence method the analytical technique utilized by the PA-2 is extremely low in interference and does not require an amalgamation step nor expensive noble gas as a carrier.

Industrial Grade Design

To provide optimum protection against corrosive environments all parts of the PA-2 Mercury Analyzer are enclosed in an industrial-grade cabinet made of fibreglass-reinforced polyester (protection class IP 66; NEMA 4X; etc.). The electronic circuitry is shielded from the wet chemical section by a chemically resistant wall.

Continuous and Interval Operation

Mercury Instruments

Left: PA-2 for continuous monitoring of Hg in scrubber water (coal fired power station, Germany).
Right: PA-2 monitoring mercury concentration of waste water in a chemical industrial plant.

The PA-2 analyzer is controlled by a built-in computer and operates fully automatic. The continuous measuring mode can be switched over to a periodic measuring mode (for example 10 minutes of measurement every hour).

Auto-Cal. Check: periodically the instrument switches from the sample stream to a calibration solution to check any deviation from the reference value. A status signal is generated if the value measured is out of range.

Auto-Zero: the zero line of the analyzer is adjusted automatically after a preset period of time.

Self-Cleaning: Precipitations like manganese dioxide are dissolved by an automatic rinse step which makes manual cleaning superfluous.

Easy to Operate

The PA-2 is operated via a waterproof membrane keypad. All inputs required are selected in a readily understandable menu shown on the graphical display. It is also possible to initiate some functions like Auto Zero from an external computer via the RS 232 interface.

Display and Output of Measurements

Mercury Instruments

The analytical results are continuously displayed on an LCD in micrograms per litre and as absorption units. A linear electrical signal (4 ... 20 mA) is also output and can be connected to a recorder or to the analog input of a data aquisition system.


Data displayed during continuous measurement mode

Automatic Self Diagnosis System

The PA-2 is equipped with sensors to detect malfunctions of the system and triggers an alarm for the operator. The following functions/malfunctions are checked and indicated:

  • Reagent flow
  • Sample flow
  • Stripping air flow
  • Leakage of fluids
  • Photometer lamp
  • Calibration

These features permit reliable unattended operation.
Malfunctions are reported to the user both optically and via a status signal.

Minimum Maintenance Work and Maximum Service Life

The PA-2 is not a laboratory analyzer simply converted for process applications but has especially been designed for operation under harsh industrial conditions. The number of parts subject to wear has been minimized and particularly durable components have been chosen for use in critical locations. This results in extended maintenance intervals. The stripping unit is based on an aerosol-free principle and the need for cleaning the optical cell is particularly low.

Communication with External Computers

The following data is available at the serial RS 232 interface: Actual mercury concentration Status (Ready - Maintenance - Malfunction)

Thanks to the bidirectional interface, operational functions like "Zero Adjustment", "Calibration Check" and "Start Measurement" can be triggered externally

PA-2 Mercury Process Analyzer: Technical Specifications

Measuring principle: UV-Absorption
Wavelength: 253.7 nm
UV source: Electrodeless low-pressure mercury lamp
Stabilization method: Double beam (reference beam) method
Optical cell: Fused silica (Suprasil)
Optical cell heating: approx. 55°C
Measuring range: PA-2:
0.1 ... 1 µg/l to 0...10 mg/l
PA-2 Gold:
0,01 ... 1 μg/l to 0,1 ... 10 μg/ll
Response time (99% signal): approx. 1 minute
Carrier gas: Air, approx. 30 L/h, 1 bar
Pump for liquids: Multichannel peristaltic pump
Reduction reagent: Tin-II-chloride or alternatively sodiumhydroborate
Reagent consumption: approx. 3 l / week for each reagent
Sample digestion: HCl or H2SO4, KMnO4 or H2O2 or Fenton´s Reagent or Na-chlorate (depending on sample composition)
Liquid-gas separation: Aerosol-free principle
Input device: Waterproof membrane keypad
Display of readings: Graphical LC display with background illumination
Output for concentration: 4...20 mA; RS 232 bidirectional
Output for status: Operational - Service - Malfunction, according to NAMUR 64 recommendations
Housing: Fibreglass-reinforced polyester, for use in highly corrosive environment - Reagent storage cabinet made of chemically resistent plastic material
Protection class: IP 66 (EN 60529/ NEMA 3; 3R; 4; 4X; 12; 13)
Power Supply: 230 V / 50 Hz (115 V / 60 Hz option)
Power consumption: 250 W max.
Air consumption: Instrument air, approx. 30 l / h,
1 - 6 bar (14 - 85 psi)
Dimensions: 775 x 612 x 329 mm (WxHxD)
Weight: approx. 50 kg
Mercury Instruments 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.


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