17
Abnormal blank value
An increase in a blank value is mainly caused by the contamination of the gas line with
mercury. If contaminated components are the cause of the increase, it becomes difficult
to measure low concentrations of mercury. Identify the location where the problem
occurred, and clean or replace the component.
The location of the problem can be identified by installing the mercury removal filter at
an intermediate point in the line and performing a comparative measurement. Using a
Tygon tube or other means, install activated carbon for filter or a mercury collector tube
at an intermediate point in the line, and measure the amount.
* When you take a sample of the standard gas, mercury particles may adhere to the
syringe needle and contaminate the standard gas inlet. Wipe the tip of the needle
with Kimwipes or other material before feeding the gas.
Abnormal increase in sensitivity
An abnormal increase in peak sensitivity may be caused by the following two factors:
Problems with the standard gas
- the syringe is contaminated with mercury,
- the indicated temperature of the Mercury Vapor Calibration Box is low, or
- the septum of the Mercury Vapor Calibration Box is contaminated.
Decreased flow rate between H2 and the absorption cell
- leakage,
- clogging in the collector tube, or
- a failure in the pump