On-line Corrosion Product Monitor (OCPM)

On-line X-ray Fluorescence (XRF) Monitoring of Trace Metals in Flow Streams

Detora’s on-line trace metals monitoring systems incorporate technology developed for the electric power industry under the sponsorship of EPRI, the Electric Power Research Institute, Palo Alto, California.

Summary

Metals below the detection limit of direct XRF are collected on membrane filters for particulate metals, ion-exchange membranes for dissolved metals, or absorbent material for gaseous species.

Using proprietary technology the accumulated metals are measured on-line periodically while the collection medium continues in service.

The rate of metal accumulation is determined from the on-line data and combined with the sample volumes, also monitored on-line, to give concentrations in terms of micrograms or nanograms per liter (ppb or ppt).

»more information on the technology

Apparatus

XRF probe with electronic X-ray tube (no radioisotopes) and high resolution, solid-state detector.
Proprietary sample flow cell.
On-line flow sensor.
PC with all required software for instrument control and data acquisition, display and storage.

No reagents or liquid nitrogen required

Method

Metal particles accumulate on a filter, or dissolved metals accumulate on an ion-exchange membrane, in a specially designed flow cell. X-ray fluorescence measures the mass of the accumulated metals at pre-selected intervals. Sample volumes are continuously monitored.
With each new measurement, data files are updated in the following format:

Date/Time	Volume Increment(liters)	XRF Emission (counts/second)	Metal mass (micrograms)
3/21/01 16:44	10.684	25.5	132.94
3/21/01 17:16	10.532	28.1	148.29
3/21/01 17:48	10.554	29.6	157.14
3/21/01 18:20	10.510	33.7	181.34
etc...

Calculations

The controlling program automatically calculates the metal concentration from the raw mass and volume data as follows (using the example data above) :

Date/Time	Volume Increment(liters)	Metal mass (micrograms)	Concentration
3/21/01 16:44	10.684	132.94	no calculation on first measurement
3/21/01 17:16	10.532	148.29	(148.29 - 132.94)/10.532 = 1.46 ppb
3/21/01 17:48	10.554	157.14	(157.14 - 148.29)/10.554 = 0.84 ppb
3/21/01 18:20	10.510	181.34	(181.34 - 157.14)/10.510 = 2.30 ppb
etc...

Calibration

Thin–film standards are used for calibration. No reagents are required. Calibration is linear for most elements through 5000 total micrograms on a filter. (link to calibration standards page)

Multiple metals may simultaneously be monitored since single energy dispersant XRF measurement results in spectrum covering a range of emission energies. For example, the following spectrum was obtained from a cation exchange membrane sample containing 370 micrograms of each indicated metal: