Analytical Notes
Agilent Vapor Generation Accessory VGA 77 and VGA 77P User’s Guide 61
Standards
Prepare your calibration standards from stock solutions.
For some samples it will be necessary to compare the calibration
slopes using the normal calibration method with those obtained
using the standard additions method. If the slope is not the same, you
should use the standard additions technique for the analysis.
Reductant—Sodium Borohydride
The recommended sodium borohydride (NaBH
4
) concentration is
0.6% w/v. However better results will be obtained for difficult
samples containing high concentrations of metals if the sodium
borohydride concentration is reduced to 0.3% w/v.
NOTE
Stannous chloride reductant is recommended for mercury determinations. See
Page 64.
Always stabilize the solution by first adding sodium hydroxide
(NaOH 0.5% w/v). Since sodium borohydride will decompose
significantly in one or two days, you should not prepare more than
500 mL at a time. At a flow rate of about 1 mL per minute, this
should be enough for continuous operation over a typical working
day. Stability may be improved by passing the solution through a
5 micron filter. You can also extend the working life of the solution
by storing at 5 °C. (The solution should remain stable for
approximately one week if stored at 5 °C.) Allow the solution to
reach room temperature prior to analysis.
Pump Tubing
The pump tubing should be checked regularly by checking the flow-
rate (see Page 44 ‘Pump adjustment’).
NOTE
When concentrated acid is first pumped through the acid tube, the inside of the
tubing may turn white, but this does not impair the efficiency of the tube.
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