**4.3. Trace and ultra-trace analysis**

There has been considerable interest in the determination of ions at trace levels as, for example, in applications need high-purity water as in semiconductor processing and the determination of trace anions in amine treated waters. For this investigation, we will define "trace" as determinations at or below 1 µg/l (ppb) levels. The Semiconductor Equipment and Materials International (SEMI) recommended the use of IC for tracking trace ionic contaminants from 0.025 to 0.5 µg/l [18]. In addition, the Electric Power Research Institute (EPRI) has established IC as the analytical technique for determining of trace level concentrations of sodium, chloride and sulfate down to 0.25 µg/1 in power plant water [19].

To determine ions at mid µg/l to mg/l (ppb to ppm) levels with IC, a sample size of 10 to 50/µl is sufficient. To determine ions at lower levels, then a preconcentration or trace enrich‐ ment technique has typically to be utilized [20]. With this method, the analytes of interest are preconcentrated on another column in order to "strip" ions from a measured sample volume. This process concentrates the desired species resulting in lower detection limits. However, preconcentration has several disadvantages, compared with a direct method, additional hardware is required. A concentrator column is used to preconcentrate the ions of interest, a sample pump is needed for loading sample, an additional valve is often required for switching the concentrator column in and out-of line with the analytical column and extra time is required for the preconcentration step. It was of interest to explore the development of a high-volume direct-injection IC method that would facilitate trace ion determinations without a separate preconcentration step. This would represent a significantly simpler and more reliable means of trace analysis.

mended for such samples. The chromatogram of heavy metals separation is represented in

Ion Exchange Chromatography - An Overview

http://dx.doi.org/10.5772/55652

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**Figure 9.** Chromatograms of blank sample (a), standard mixture (b), sample of thyroid from the control group (c), and

sample of thyroid of a patient with diagnosed nodular goitre (d) [22].

**Figure 8.** IC system configuration for direct-injection sample loading [21].

\* LOD—limit of detection; LOQ—limit of quantitation; LOQ= 10/3 LOD.

**Table 1.** Comparison of metal ions concentrations measured by IC and certified values [22].

Figure 9.

Kaiser et al. [21] described the evaluation of on-column preconcentration for enhancing sensitivity and enabling trace ion determination in high-purity water. They developed a highvolume direct-injection method for trace level determinations (low to sub µg/l) of anions and cations by ion chromatography as shown in Figure 8. The chromatographic signal was enhanced by increasing the sample volume up to 1300/µl with no significant loss in peak efficiency. Total analysis times were less than 30 min and the method detection limits for most ions ranged from 10 to 400 ng/l (ppt). The methods described exhibit increased sensitivity and greater reliability than methods using conventional preconcentration. Lower detection limits were achieved by increasing sample size with no significant loss neither in peak efficiency nor in peak resolution. Trace levels (low to sub µg/l) were determined without the added com‐ plexity of a concentrator column or loading pump and valve.
