OnGuard cartridges

In principle, care must be taken in the analysis of waste water samples so that the ion exchanger being used does not be contaminated by organic material such as fats, oils, surfactants, etc. They can be removed from the sample via solid phase extraction on suitable materials (e.g. OnGuard cartridges). Further details regarding the subject of sample preparation may be found in Section 8.9... 

In US EPA Method 314.0, the determination of the matrix conductivity threshold (MCT) is required to assess the maximum concentration of common inorganic anions that the column should tolerate before observing significant loss of sensitivity for perchlorate. For samples that exceed the MCT, a dilution or sample pretreatment using OnGuard cartridges is required. EPA Method 314.1 eliminates these procedures by using a Cryptand concentrator column that... 

Extract was prepared from the leaves and roots of two years old olive plants with water at room temperature. Internal standard as D-3-0-methylglucopyranose(MeGlu) was used and added In appropriate volume. Extraction was accomplished by shaking for 15 min and finally the suspension was centrifuged at 3000 rpm for 10 min. Before the injection the aqueous phase was filtered and passed on a cartridge OnGuard A (Dionex)to remove anion contaminants. 

Fig. 1. Trace bromate determination using matrix elimination and preconcentration. See text for details. Peaks 1, fluoride 1.0 mg/1 2, unknown 3, chlorite, 0.01 mg/1 4, bromate 0.005 mg/1 5, chloride, 200 mg/1 6, nitrite 0.1 mg/1 7, bromide, 0.01 mg/1 8, chlorate, 0.01 mg/l 9, nitrate, 10.0 mg/l 10, o-phosphate, 0.1 mg/l 11, sulfate, 200 mg/l. Sample B was pretreated with OnGuard II Ag, H cartridges. Samples also contained 200 mg/l bicarbonate.

Fig. 3. Schematic of the three-layer OnGuard II Ba/Ag/H sample pretreatment cartridge.

The determination of iodide in milk (2% milkfat) by ion chromatography coupled with pulsed amperometric detection on a silver electrode is an application that benefits from matrix elimination of fats. The pulsed amperometric waveform improves reproducibility by electrochemically cleaning the working electrode on each pulse. In addition, the fats are removed from the sample using a disposable cartridge containing a polymeric reversed phase resin (OnGuard II RP, Dionex Corp.). When 50 jal of 0.1 mg/1 iodide was added to 200 jal of prepared milk, the recovery was 100%. The iodide peak area and retention time RSDs were 1.4% and 0.4% respectively [28]. 

Fig. 4. IC-MS of chloroacetic acid and bromoacetic acid in a matrix containing 1000 mg/1 chloride, without (A) and with (B) sample pretreatment. Peaks 1, chloroacetic acid, 8 mg/l 2, bromoacetic acid, 7 mg/l TIC, total ion chromatogram, m/z 92.5-93.5, extracted ion for chloroacetic acid, m/z 137-139.2, extracted ion for bromoacetic acid. B After sample is passed through OnGuard II Ag/H cartridge.

Sample preparation is different for investigating meat seasonings. Because of their high organic compound content, the aqueous solutions cannot be injected directly but must be treated with OnGuard-RP extraction cartridges. The cartridges contain an non-... 

Figure 10.411 Hardware design of Dionex OnGuard II SPE cartridges.

---