The OnGuard^® II Cartridges are designed to remove matrix interferences such as phenolics, metals, cations, anions, or hydrophobic substances encountered in many ion chromatography applications. Available in 1-cc and 2.5-cc high-capacity formats, these cartridges incorporate new OnGuard cartridge hardware.

OnGuard II A

The OnGuard II A is used in the removal of anionic contaminants from sample matrices and for the neutralization of highly acidic samples. These cartridges contain styrene-based, anion-exchange resin in the bicarbonate form. Capacity: 0.7 meq/1-cc cartridge, 1.75 meq/2.5-cc cartridge.

OnGuard II Ag

The OnGuard II Ag packing is a silver-form, high-capacity, sulfonated, cation-exchange resin. This resin is similar to the OnGuard II H packing except the ionic form is silver. These cartridges remove chloride, bromide, and iodide from sample matrices. An OnGuard II H cartridge should be used after the OnGuard II Ag cartridge to remove dissolved Ag. Capacity: 2.0–2.2 meq/1 cc cartridge, 5.0–5.5 meq/2.5 cc cartridge.

OnGuard II Ba

The OnGuard II Ba resin is a styrene-based, sulfonic acid resin in the barium form, designed for the removal of high concentrations of sulfate from sample matrices. For reproducible, quantitative determinations in low-ionic-strength samples, these cartridges should be activated with a chloride-based activating solution. Samples treated with the activated OnGuard II Ba cartridge should then be passed through an OnGuard II Ag cartridge to remove the added chloride, and then passed through an OnGuard II H cartridge or a MetPac^TM  CC1 chelating column to remove the residual silver counter ions. Capacity: 2.0–2.2 meq/1 cc cartridge, 5.0–5.5 meq/2.5 cc cartridge.

OnGuard II H

The OnGuard II H is used in the removal of high levels of alkaline earths and transition metals from sample matrices and in the neutralization of highly alkaline samples such as sodium hydroxide or sodium carbonate. Carbonate can then be removed by sparging the sample. These cartridges contain 16% cross-linked, styrene-based, sulfonic acid resin in the hydrogen form. This resin is designed to have very high selectivity for multivalent cations such as calcium and transition metals. Capacity: 2.0–2.2 meq/1 cc cartridge, 5.0–5.5 meq/2.5 cc cartridge.

OnGuard II M

The OnGuard II M is used for the removal of transition metals and matrix elimination of alkali and alkaline earth metals. These cartridges contain an iminodiacetate resin in the ammonium form, ready to use with no lengthy preparation required. Capacity: 0.4 meq/1 cc cartridge, 1.0 meq/2.5 cc cartridge.

OnGuard II Na

The OnGuard II Na is used in the removal of high levels of alkaline earths and transition metals from sample matrices without acidifying the sample. This ensures good recovery of acid labile analytes such as nitrite. These cartridges contain 16% cross-linked, styrene-based, sulfonic acid resin in the sodium form. This resin is designed to have very high selectivity for multivalent cations such as calcium, magnesium and transition metals. Capacity: 2.0- 2.2 meq/1-cc cartridge, 5.0-5.5 meq/2.5-cc cartridge.

OnGuard II P

The OnGuard II P is recommended for removing the phenolic fraction of humic acids, tannic acids, lignins, anthocyanins, and azodyes from samples prior to analysis by anion or cation exchange. These cartridges contain polyvinylpyrrolidone (PVP) polymer which has very high selectivity for phenolics, azo-containing compounds, aromatic carboxylic acids, and aromatic aldehydes. PVP has very high selectivity for iodine as the triiodide complex. Capacity: 6.0 meq/1 cc cartridge, 15 meq/2.5 cc cartridge.

OnGuard II RP

The OnGuard II RP is recommended for removing substances such as aromatic dyes, some aromatic carboxylic acids, hydrocarbons, and surfactants from sample matrices. These cartridges contain a macroporous divinylbenzene resin that has a very high selectivity for hydrophobic substances, especially unsaturated or aromatic organic substances. Contains 0.3 g resin/1 cc cartridge, 0.75 g resin 2.5 cc cartridge.

OnGuard II Ag/H

The OnGuard II Ag/H is a layered cartridge that contains OnGuard II Ag resin and OnGuard II H resin.  The OnGuard II Ag/H Cartridge contains a styrene-based sulfonic acid resin in the silver form(OnGuard II Ag).  The OnGuard Ag easily removes chloride, bromide, and iodide from concentrated sample matrices such as brines. 

The OnGuard II Ag/H also contains a 16% crosslinked, styrene-based, sulfonic acid resin in the hydrogen form (OnGuard II H).  The resin has a very high selectivity for polyvalent cations such as calcium and transition metals.  The cartridge is ideal for the removal of high levels of alkaline earths and transition metals from sample matrices, for the neutralization of caustic samples, and for the removal of carbonate. 

The OnGuard H resin is placed at the outlet of the two-layer cartridge in order to trap soluble silver and other cations in the sample.  This two-layer cartridge can be used in place of two single cartridges used in series and has the added advantage of the higher silver-capacity.

OnGuard II Ba/Ag/H

The OnGuard II Ba/Ag/H is a layered cartridge that contains OnGuard II Ba resin, OnGuard II Agresin and OnGuard II H resin. The OnGuard II Ba/Ag/H Cartridge contains a styrene-based sulfonic acidresin in the barium form (OnGuard II Ba) for the removal of high concentrations of sulfate from sample matrices. The OnGuard II Ba/Ag/H Cartridge also contains a styrene-based sulfonic acid resin in the silver form (OnGuard II Ag). The OnGuard Ag easily removes chloride, bromide, and iodide from concentrated sample matrices such as brines. The OnGuard II Ba/Ag/H also contains a 16% cross-linked, styrene-based, sulfonic acid resin in the hydrogen form (OnGuard II H). The resin has a very high selectivity for polyvalent cations such as calcium and transition metals. The cartridge is ideal for the removal of high levels of alkaline earths and transition metals from sample matrices, for the neutralization of caustic samples, and for the removal of carbonate. The OnGuard H resin is placed at the outlet of the threelayer cartridge to trap soluble silver andother cations in the sample. This threelayer cartridge can be used in place of three single cartridges used in series and has the added advantage of the higher silver capacity.

Accessories

The OnGuard Sample Prep Station is an accessory for simultaneous pretreatment of multiple samples with the OnGuard sample pretreatment cartridges. When used with Dionex 0.5-mL PolyVials and a vacuum source, the OnGuard Sample Prep Station permits semiautomatic pretreatment of up to 12 samples. Samples may also be treated manually using standard Luer tip syringes. The OnGuard Sample Prep Station has individual stopcock valves on each sample tube to allow control of individual flow rates. The station will also hold six 10-mL volumetric flasks.