capillary columns

Capillary Columns

Nicholas H. SnowDepartment of Chemistry, Seton Hall University,

400 South Orange Avenue, South Orange, NJ 07079

snownich@shu.edu

Capillary/Open Tubular Column

WCOT - Wall Coated Open Tubular

Capillary Column Dimensions

Other Types of Capillary Columns

Tubing Material

• Stainless Steel– reactive

• Glass– can be made inert– difficult to handle

• Fused Silica– flexible– most inert– most popular

Fused Silica Surface

• Contains 0.1% -OH groups

• Very inert• Uniform chemical

surface

Fused Silica

• High tensile strength• Flexible• Sheath of polyimide• Very inert

Capillary vs. Packed

Packed Column - ECD

Capillary Column - ECD

Important Column Parameters

Column Diameter

Column Length

Column Length Recommendations

Stationary Phase Film Thickness

• Starting point: 0.25m• Compromise: resolution and

capacity• Practical operating

temperatures• Speed or resolution

Thick Film Stationary Phase

• Advantages– increased retention for

volatiles– increased capacity

• Disadvantages– less efficient– higher temperatures– higher bleed

Natural Gas

Thin Film Stationary Phase

• Advantages– high efficiency– lower elution

temperatures– fast analysis

• Disadvantages– low capacity– limited trace analysis

Thin Film SeparationAir Freshener

Stationary Phase Requirements

• Selectivity• Low Bleed Rate• Reproducibility

Common Stationary Phasespolysiloxane gum phases

Stationary Phasespolyglycol

Crosslinked Stationary Phases

• More stable• Clean by rinsing• Longer lifetimes

Carrier Gas Flow Rate

Review - Capillary Columns

Review - Capillary Columns

Column Selection