Thermo Scientific IonPac CG16, Руководство по эксплуатации продукта

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Product Manual for IonPac CS16 Page 54 of 65
A. Weak Cation Exchangers
Carboxylated resins (used in the IonPac CS12, CS12A, CS14, CS15, CS16, CS17 and CS18) are weak acid cation
exchangers. These resins have high selectivity for hydronium ion and are used with weak acid eluents. When the
sample pH is high (pH 5), the weak cation exchange sites on the contaminated tubing are ionized and divalent
cations are preferentially retained. When the sample pH is low (< pH 4), these sites are protonated by the sample and
rendered inactive, so that the divalent quantification is not affected.
B. Testing for Loop Contamination when Using Carboxylated Cation Exchange Columns
A simple test can be performed (when using a column such as the IonPac CS16 which contains a carboxylated resin)
with methanesulfonic acid or sulfuric acid to see if the sample loop has been contaminated:
1. Prepare a standard containing 0.5 ppm of calcium and add a small amount of 0.2 mM sodium hydroxide so that
the final pH of the standard is between 6.5 and 7.5.
2. With the sample loop in the load position, flush the loop with just enough standard to rinse and fill the loop (e.g.
if the loop is 25 mL, flush it with no more than 100 mL).
3. Run the standard and record the peak area.
4. Repeat steps 2 and 3, but this time flush the loop with about 5 mL of standard.
5. If after repeating steps 2 through 4, the peak area for calcium recorded in 4 is significantly larger than that in 3,
then the sample loop is contaminated and acting as a concentrator.
6. Replace the sample loop with new tubing and repeat this test.
7. If there is still a quantification problem, check other components of the system (tubing, injection valve, detector
cell) or call your Dionex representative.
If you have a divalent quantification problem in your system but you neither have the time nor replacement parts, you can
still get accurate results for divalent cations if any one of the following applies:
1. Your application involves high levels of divalent cations e.g. > 5 ppm calcium; the “concentration error” is
small percentage-wise.
2. The pH of your samples and standards is < 4.
3. A constant volume of sample (and standard), only slightly larger than the sample loop, is flushed through the
loop at a constant sampling flow rate.
6.4. High Background or Noise
In a properly working system, the background conductivity using the operating conditions described in Section 4,
“Operation,” should be < 1 µS with a CSRS 300 (4-mm). If the background is low but the system is noisy, an air bubble may
be trapped in the system. With the system running, disconnect the
ELUENT IN line from the suppressor and apply pressure
to the open port with your gloved finger to dislodge a suspected bubble. Reconnect the line. Do not take too long to do this,
as the current is still being applied to the CSRS 300 and the eluent flow is needed to produce regenerant.
Check the conductivity flow cell for bubbles. See the conductivity detector manual for details.
A system with a high background (> 3 µS) will probably also have high noise, resulting in increased detection limits.
Document No. 031747-05 © 2010 Dionex Corporation December 2010