High-performance Ammonia ISE: Thermo Scientific’s New Orion Ammonia ISE is Designed to EPA-approved Methods for Wastewater

Thermo Scientific has developed a new, high performance Orion Ammonia Ion Selective Electrode (ISE) that can measure down to 0.01 ppm
quickly and accurately. This electrode is ideal for measuring dissolved ammonia in wastewater or other samples. This new electrode was built with years of Orion expertise in the industry with EPA approved methods for wastewater, specifically Standard Methods 4500 – NH3 D and E, ASTM D1426 -98,03 (B) and former EPA method 350.3.
The ammonia electrode can also be used to measure the ammonium ion (NH4+) after converting to ammonia (NH3) or organic nitrogen after
Kjeldahl digestion of the sample. Nitrate samples can be measured using an ammonia electrode. The use of the Thermo Scientific Orion Nitrate Test Kit makes this possible. After samples and standards are made basic, nitrate is converted to ammonia by addition of a special reagent. Ions, such as chloride, that could cause interference with the nitrate electrode at high levels have no effect on when performing this test with the ammonia electrode. This technique can be performed on samples containing 0.1 to 20 ppm of nitrate-nitrogen.
Ammonia measurement by ion selective electrode offers many benefits for the user. A key benefit is cost savings. Measurement of ammonia by ISE is inexpensive per test as compared to other techniques which require more costly equipment. In addition, only a small sample size is required and minimal sample preparation is needed. For example, when testing according to StandardMethods 4500 – NH3 D, sample distillation is unnecessary. Unlike the Nesslerization technique for ammonia, toxic metals are not used in the ISE method. The ammonia electrode can be used over a wide concentration range, from 0.01 to 17,000 ppm as NH3
or 0.01 to 14,000 ppm ammonia reported as Nitrogen (N). Ammonia ISE analysis provides a quick measurement, five minutes (at the lowest levels) or less, while providing accuracy comparable to other accepted methods. The electrode can be used in samples in the temperature range of 0 to 50o C. The measurement is not affected by sample colour or turbidity.
Performing measurements with reproducible, accurate results when
measuring low level ammonia samples can be difficult at times. There are a number of factors that contribute to the rapid, reproducible results when measuring low levels of ammonia. Previously, proper
installation of membranes could be challenging as the user needs to stretch the membrane just right over the electrode body. This is not the case with the new high performance ammonia electrode.
No stretching of the membrane is needed. It is just gently placed across the electrode body. In addition to this, pre-assembled
bodies with membranes are available. These provide much more accurate
results than previously designed bonded membrane caps that many manufacturers use. Both of these factors eliminate one of the major disadvantages of existing ammonia electrodes where membranes
can be hard to install or bonded membranes do not provide optimum results.
Ammonia samples must be aqueous and can not contain organic solvents. Ionic strength adjustor (ISA) must be added to all samples and standards just prior to measurement. This will adjust the pH above 11.
Solutions will be blue when using the Orion 951211 ISA. In this basic solution, all ammonium ions will be converted to ammonia.
There are different techniques available to the analyst when measuring ammonia with an ISE. Direct measurement is a popular procedure used when measuring a large number of samples. The system is calibrated using a series of standards.
The concentration of the samples is determined by a single reading that is compared to the standards. As an additional aid to easier low level
measurements, the Orion Star series ISE meters all feature a special calibration mode to improve the measurement accuracy at low levels. Known addition is an incremental technique that is used to measure
ammonia concentration without calibration. Known addition measures dilute samples by placing the electrode in a sample and adding an aliquot of a standard solution to determine the concentration.
The measurement of ammonia in waste water is an important measurement.
Labs strive to meet the EPA and local regulatory requirements and perform a measurement that is quick, accurate and cost efficient. Care must be taken in the process to ensure samples are prepared properly and analysed quickly. With the proper equipment and good laboratory
technique, the analyst can be confident of the results they achieve with their ammonia measurement every time.