Performance Verification Statement for the Real Tech Real Nitrate Analyzer GL Series

Ref. No. [UMCES] CBL 2017-050

ACT VS17-05

BACKGROUND AND OBJECTIVES

The Alliance for Coastal Technologies (ACT) is a NOAA- and EPA-funded partnership of

research institutions, state and regional resource managers, and private sector companies that are

interested in developing, improving, and applying sensor technologies for studying and monitoring

coastal environments. ACT was established on the premise that instrument validation of existing

and emerging technologies is essential to support both coastal science and resource management.

The overall goals of ACT’s verification program are to provide industry with an opportunity to

have a third-party test their instruments in both controlled laboratory settings and in diverse field

applications within a range of coastal environments, and to provide users of this technology with

an independent and credible assessment of instrument performance.

ACT partnered with the multi-agency Challenging Nutrients Coalition on the Nutrient

Sensor Challenge to help address the environmental and ecological problems associated with

nutrient pollution. A critical step in this process is facilitating the development and adoption of the

next-generation of

in-situ

nutrient sensors and analyzers. To that end, the ACT Technology

Verification model was applied to the Nutrient Sensor Challenge to test instrument performance in

laboratory and field tests against reference water samples analyzed using EPA-approved standard

methods.

The report within contains the test results for Real Tech’s Real Nitrate Sensor during the

ACT Performance Verification. A synthesis of the testing protocols and reference sample analysis

are provided below. A complete copy of the verification protocols is available on the ACT website

at the following link:

challenge/Download/Nutrient_Challenge_Test%20Protocols_PV16_01.pdf

INSTRUMENT TECHNOLOGY TESTED

Spectrophotometry is a well-known analytical technique that uses light in the ultraviolet

(UV) and visible (VIS) wavelength range to measure substances that absorb or reflect light across a

range of wavelengths. Nitrate ions have a natural absorbance peak in the 200-210 nm wavelength

range in the UV spectrum and strongly absorb light between 200 and 240 nm. As the concentration

of nitrates in water increases, the absorbance of light in this distinct wavelength range will also

increase.

Real Tech’s Real Nitrate Sensor (denoted as Real-NO3 throughout the report) operates by

shining UV-VIS light from a xenon flash lamp through a quartz measurement cell and the

absorbance between 200-240 nm is measured for nitrate concentration. In addition, reference

wavelengths in the UV-VIS spectrum are also measured and used to compensate for common

interferences with nitrate measurement, such as organic compounds, iron, and turbidity or

suspended solids. The absorbance data are then converted to a milligram per liter (mg/L)

concentration value using chemometrics, and custom software algorithms programmed in the

sensor controller. The sensor comes factory calibrated with a standard nitrate algorithm. The

calibration can be further improved upon by incorporating site-specific data into the existing data

set. This way, the sensor can learn the characteristics of the on-site water and improve its accuracy

over time. No reagents are used for nitrate detection purposes.

To compensate for drift and instability associated with volatile light sources, the sensor

continuously rotates from a test position to a reference position. This proprietary measurement

technique allows for a high degree of accuracy and repeatability.