Analytical Notes
Agilent Vapor Generation Accessory VGA 77 and VGA 77P User’s Guide 59
Contamination
When first establishing your analytical method you must always
check for contamination before carrying out your program.
NOTE
Traces of potassium iodide (KI) will interfere severely with determinations for
bismuth, mercury, selenium and tellurium. You must always ensure that the
VGA 77 system is completely free of residual iodide ions (e.g., KI) before
attempting to determine these elements.
The most practical way of minimizing contamination problems is to
provide a separate module (including the reagent containers and
pump tubes) for these elements. Page 79 lists spares and part
numbers.
Another form of contamination can occur when changing from a high
level standard to a low level standard. You must make sure that all
tubing in the module is thoroughly rinsed.
Memory Effects
Because the VGA 77 uses a chemical reaction to produce the
elemental hydrides, some memory effects can be encountered in the
reaction products when changing between low and high level
standards. Always allow several minutes when moving from a high to
a low level standard.
You should also ensure that the standards are prepared at the same
concentration as the samples.
Certain types of plastic can cause memory effects for mercury. Keep
mercury top standard concentration as low as practicable.
Background Absorption (AA only)
In general, background correction is not necessary for vapor
generation work. Occasional exceptions may be encountered. For
example, when determining low level arsenic in the presence of
another hydride forming element.
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