For accurate concentration readings across a wide range of conditions, the Thermo Scientific™ Mercury Freedom System should be checked for linearity. Also, according to US EPA regulation, the integrity of the system must be checked weekly to ensure the transport and conversion of oxidized mercury. Here are five tips and tricks to keep in mind when performing these checks:
In order to pass a system integrity check, the oxidizer is required to produce greater than 50% oxidized mercury. The total converter efficiency is required to be equal to or greater than 90% of the span concentration with an alternate specification of 0.8ug/m3 absolute difference between the reference value and the analyzer response. For a complete description of the converter efficiency calculation including the chlorine dilution factor, see the Mercuric Chloride Generator manual.
In order to perform the System Integrity Check (SIC), the system needs to be at the operating temperature for at least 12 hours. Additionally, there should be no active alarms for temperatures or pressures. Probe covers must be on to ensure there are no cold spots. Sufficient chlorine flow must be present, therefore physically measure the chlorine coming out of the chlorine cylinder downstream of the orifice. This value will also be needed to calculate the converter efficiency. For more information see the Preparation Worksheet for Systems Integrity Check Technical Bulletin.
My SIC failed, now what? A failed integrity check usually does not necessarily mean the converter core or the oxidizer needs replacement. The most common causes of failed integrity checks are cold spots in the probe or the tubing inside the probe needs replacement. This usually occurs between the dilution module and the orifice assembly and from the orifice assembly to the converter. Other common causes of a failed SIC are melted tubing, leaks at the hydrator or leaks at the inlet of the oxidizer. Poorly coated filters, filters that have been over-sonicated, or filters that have been washed with a caustic cleaner may cause problems and need to be replaced. Filters typically need to be replaced semi-annually or as required by process conditions.
If your system linearity fails, first perform a complete advanced system calibration. After the system calibration, run and verify linearity on the Thermo Scientific Model 80i Mercury Analyzer and Thermo Scientific Model 81i Mercury Calibrator by doing a three-level instrument span. This will help rule out potential sources of non-linearity. If your instrument span proves to be non-linear, make sure your Model 81i Mercury Calibrator has been NIST-certified and has been passing required QA checks. To obtain and maintain NIST certification, learn more about our Mercury Calibrator Certification Services.
If your system was mothballed, now is the time to update firmware and hardware such as the lamps, converter core, and hydrator. The Model 81i Mercury Calibrator must be certified and if you need support with NIST-certification, we can help with our calibrator certification services. For a more comprehensive evaluation of your mothballed system, request a Mercury Recommissioning Services consultation.