UNISIL Technical Data

Unisil is a specifically prepared silica acid that has been processed to an exceptional degree of uniformity in order to provide maximum resolution of closely related organic materials. Quality control of three factors has been maintained in preparing this silicic acid. The product has been thoroughly acid- washed to remove trace mineral impurities that might provide sites for irreversible absorption of some substances. In addition, "tailing" phenomena are minimized by the use of acid-washed silicic acid. Finally, the particle size of Unisil has been controlled, by sieving, to a narrow range. The grades we offer -100-200 mesh, 200-325 mesh - are completely free of dust. Consequently, flow rates of common eluting agents such as hexane, chloroform, benzene, ethyl acetate and methanol are such that the use of diatomaceous earth as a diluent is not necessary. With small scale columns, using 10-20 grams of absorbent, flow rates of 2-6 m./min are easily obtained, while colums containing a pound of silicic acid have given flow rates up to 20 ml/min.

Unisil offers complete fractionation in one column with a relatively small quantity of silicic acid. Duplication of separations is very good. It is an excellent material for separation of lipids such as neutral non-glyceride lipids, glyceride lipids, glycolipids, phospholipids, cholesterol, and the like.

The moisture content of silicis acid is often an important factor controlling separations-especially with the use of non-polar solvents as eluting agents. Unisil is supplied in a heat-activated form by drying at 100 degrees centigrade for 12-15 hours just prior to shipping. This treatment provides a medium moisture content that is optimum for many separations.

A standard procedure for refining silicic acide is: A preliminary screening is carried out by dry sieving, and all material passing a 325-mesh screen is discarded. Approximately 100 grams of silicic acid is treated with 250 ml of 3 N hydrochloric acid in a glass vessel and stirred for 30 minutes with a nonmetallic pa ddle. This silicic acid is allowd to settle, the aqueous acid decanted, and the residue washed repeatedkt with deionized water for two days until the supernatant liquid reaches a pH of 4.5 ti 5.5. Usually 20 to 40 water changes are required. The silicic acid is then washed with acetone, filtered, resuspended several times in fresh acetone, then dried in glass trays under an infrared lamp for 16-20 hours. A final screening provides material of 100-to 200 mesh size, which is dried in an oven with 20 to 25 inches vacuum for two hours at 50 degrees centigrade. It may be kept in closed containers for several months without apparent change. Used silicic acid is washed with methanol, followed by deionized water an acetone, and dried as in the original preparation.

At Clarkson we've modified this standard procedure to produce the highest grade silicic acid available.

Laboratory Analysis

Unisil Activated Silicic Acid 100-200 Mesh and 200-325 Mesh

Maximum Limits
Loss on Ignition	8.000%
Loss on Drying	Min. 5.000%
Chlorine (Cl)	.010%
Heavy Metals (Pb, for example)	.002%
Iron (Fe)	.001%
Nonvolatile with HF	.200%
Organic Impurities	.001%

Chromatography Grade Silicic Acid 100-200 Mesh and 200-325 Mesh, and Powder

Maximum Limits
Loss on Ignition	10.000%
Loss on Drying	Min. 5.000%
Chlorine (Cl)	.010%
Heavy Metals (Pb, for example)	.002%
Iron (Fe)	.001%
Nonvolatile with HF	.200%

Availability

Clarkson UNISIL is available in 100-200 Mesh, 200-325 Mesh in 100 gram bottles or by the case (six 100 gram bottles to a case).

Chromatography grade Silicic Acid is available in 100 Mesh, and through 325 Mesh and is packaged in 500 gram bottles and 100 lb. drums. (Price reduction for multiple drum orders.)

Material Handling

Silicic acid can range in PH from 4.5 to 7.0. It is water loving and midly corrosive. Silica dust mask and gloves must be worn when handling the powder on a regular basis.

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