Multianion analysis, applications of ion chromatography - Determination of Anions in Natural and Treated Waters - page 669

During trace analyses, the sample flask always contains water of extremely low ionic
content. Attempts to clean the flask often resulted in contamination. All glassware used
should be thoroughly rinsed and then soaked for a minimum of 24h with triple distilled
water.
Remote loading of concentrator columns
All concentrators were flushed with eluent for 4min before loading. A 10ml glass syringe
with a stainless steel Luer adaptor was used for remote loading of concentrator columns.
A female Luer adaptor was attached to the column and the sample was forced through the
column by manual pressure. Excessive force resulted in leakage along the plunger and
through the Luer fitting. Remote loading by pump is also possible. Loaded concentrators
were then placed in line before the separator column using the flared Teflon tubing
connectors provided with each column.
Suppressor column use for trace determinations
Ion chromatography suppressor columns are used to remove highly conductive eluent
ions from the separator column effluent before entering the conductivity cell. During
anion determinations, the suppressor exchanges H + for Na + thus converting the highly
conductive sodium bicarbonate, sodium carbonate eluent to a weakly conductive, dilute
carbonic acid solution. One consequence of suppressor column use is that solutions with
lower conductance than the carbonic acid exiting the suppressor column cause a negative
inflection in the detector output or base line. Because sample water is less conductive
than the carbonic acid solution, it causes such a negative deflection or water dip
approximately 2min after injection during anion determinations.
In order to obtain reproducible results, trace sample ions of interest must be separated
from the water dip. Using the sodium bicarbonate sodium carbonate eluent listed above a
chloride peak will not separate from the dip when using a concentrator column in
conjunction with a fully regenerated (100% H + form) 6×250mm suppressor column.
Acceptable precision is obtained, though, by converting approximately 50% of the H +
form suppressor resin to the sodium form. This causes the water dip to become narrower
and to elute earlier, thus separating the dip from the chloride peak.
Another method which permits chloride trace determination is to decrease the volume
of the suppressor column. As with the partially exhausted larger suppressor, the water dip
is separated from the chloride peak. Smaller columns naturally have less capacity than
larger columns; in order to avoid delays due to frequent regeneration of these smaller
columns, a dual suppressor system was used. One suppressor may be regenerated while
the other is used for analysis. Fig. 12.32 shows the flow system used for the dual
suppressor column flow system.
Adjust the conductivity cell and meter to a reading of 147µmho cm −1 at 25°C using a
0.001mol L −1 potassium chloride solution.
Procedure
Load various sample volumes onto concentrator columns by glass syringe or by pump.
Concentrators loaded by syringe were placed before