Agilent GC Pressure Flow Calculator

Poiseuille's Law for GC Flow:

\[ Flow\ Rate = \frac{\pi (ID/2)^2 \times Pressure\ Drop}{8 \eta L} \]

Inner Diameter (ID):

Pressure Drop:

psi

Viscosity (η):

Pa·s

Length (L):

Flow Rate:

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1. What is Poiseuille's Law for GC Flow?

Poiseuille's Law describes the flow of fluids through cylindrical tubes. In gas chromatography (GC), it's used to calculate the flow rate of carrier gas through the column based on column dimensions, pressure, and gas viscosity.

2. How Does the Calculator Work?

The calculator uses Poiseuille's Law:

\[ Flow\ Rate = \frac{\pi (ID/2)^2 \times Pressure\ Drop}{8 \eta L} \]

Where:

\( ID \) — Inner diameter of the column (mm)
\( Pressure\ Drop \) — Pressure difference across the column (psi)
\( \eta \) — Viscosity of the carrier gas (Pa·s)
\( L \) — Length of the column (cm)

Explanation: The equation calculates volumetric flow rate through a cylindrical tube, considering the tube's geometry and the fluid's physical properties.

3. Importance of Flow Rate Calculation

Details: Accurate flow rate calculation is essential for optimizing GC separation efficiency, retention times, and peak shapes. Proper flow rates ensure reproducible results and method transferability.

4. Using the Calculator

Tips: Enter inner diameter in mm, pressure drop in psi, viscosity in Pa·s, and column length in cm. All values must be positive and greater than zero for accurate calculation.

5. Frequently Asked Questions (FAQ)

Q1: What are typical viscosity values for common carrier gases?
A: Helium: ~20 μPa·s, Hydrogen: ~9 μPa·s, Nitrogen: ~18 μPa·s at room temperature.

Q2: Why is flow rate important in GC?
A: Flow rate affects retention times, peak separation, and detection sensitivity. Optimal flow rates provide the best compromise between analysis time and resolution.

Q3: How does column diameter affect flow rate?
A: Larger diameter columns require higher flow rates to maintain optimal linear velocity, while narrower columns work better with lower flow rates.

Q4: Can this calculator be used for liquid chromatography?
A: While the principle is similar, liquid chromatography involves different considerations due to liquid compressibility and higher viscosities.

Q5: What are typical GC flow rates?
A: Typical flow rates range from 0.5-5 mL/min depending on column dimensions, carrier gas, and application requirements.