Agilent 7694 Headspace Autosampler

Agilent 7694 Headspace Autosampler

  • Holds up to six 10- or 20 ml sample vials
  • Setpoint temperature range is between 40 and 200°C
  • The 44–sample vial tray
  • A robotic arm moves samples from the vial tray into the oven and back
  • You can program the system’s temperature up to 200°C

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The Agilent 7694 Headspace Autosampler for HP 5890 GC and Agilent 6890 GC

Headspace Autosampler

A headspace sampler is a GC autosampler accessory for introducing volatiles that are contained in liquid or solid samples into a gas chromatograph. The analytical technique is called “static headspace gas chromatography.” The term “headspace” refers to the space above the liquid or solid sample that you place in a sealed vial. The term “static” means that the volatiles in the headspace of the vial are at equilibrium with the same compounds in the liquid or solid sample.

The instrument extracts a reproducible volume of the headspace and injects it into the carrier gas flowing into the gas chromatograph. Food, packaging, pharmaceutical products, soil, and water are often tested to see if they meet quality criteria or regulatory standards. Fragrances and consumer products are analyzed using headspace in order to understand their composition. Forensics laboratories use headspace for measuring the percent of ethanol in human blood to see if a driver is legally intoxicated.

The ease with which a sample forms a gaseous headspace depends on the sample’s “partition coefficient.” See “Developing Methods” on page 68 for a more thorough explanation. After a programmed heating time, the headspace gas is extracted from the vial and injected into a GC for analysis.

The 7694 Headspace Sampler

GMI offers fully refurbished to specification HP Agilent 7694 headspace autosamplers and has multiple units in stock. The are re certified to specification, and ship with a full warranty. Installations are avaible upon request.

The 7694 Headspace Sampler provides an automated method to run up to 44 samples consecutively without operator attention. It is compatible with HP 5890 series GCs and Agilent 6890 series GCs. The sampler’s microprocessor optimizes the time spent for each run according to the values programmed in by the operator. Up to four different methods can be stored and used to analyze a series of samples.

The unit is made up of the, the oven and heated zones, the oven contains a circular aluminum sample carousel that can hold up to six 10- or 20 ml sample vials. There are three heated zones. They are the vial oven, the loop, and the transfer line.

The vial oven is where the vial is heated during thermal and chemical stabilization. Setpoint temperature range is between 40 and 200°C. At this point, the needle has not pierced the septum. The loop zone is controlling the temperature of the upper chamber, the valve, and the sample loop. The setpoint range of the loop is between 50 and 200°C. It is recommended that the loop temperature is kept 15°C higher than the vial temperature for most operations.

The 44–sample vial tray is located on top of the unit to the left of the oven. The tray is constructed of a flexible belt with dividers for each vial compartment. Tray rotation is controlled via the keypad to assist filling the tray with headspace vials. The tray can move forward and backward. A robotic arm moves samples from the vial tray into the oven and back.

Vials are lifted from the tray, carried across the unit until centered above a port in the oven, and then dropped into place. The rail supporting the robotic arm swings away to allow access to the oven.

Sampling System

The basic components include a 316–stainless–steel single–hole (side port) concentric vial–sampling needle or probe with an internal diameter of 0.5 mm, 316–SS six–port valve, nickel valve sample loop, set of two miniature solenoid valves, and nickel tubing. You can program the system’s temperature up to 200°C

Principles of Operation

General Operation

When the instrument is switched on, the sampler moves the first vial into position. (For models with a tray, the vial tray moves to the start position, placing the vial located in position one next to the robotic arm. For models without a tray (G1883), the carousel moves vial one to the start position.) The oven, sample loop, and transfer line begin heating to reach the setpoint values. Until the oven, sample loop, and transfer line setpoints are reached, the display reads 7694 Not Ready and the red “Not Ready” light is lit. If you press Start/ Stop before the machine is ready, the display reads Waiting for Ready and the “Not Ready” light flashes. When setpoints are reached, the display changes to 7694 Ready and the “Not Ready” light goes out.

During normal operation, when a run is in progress, the “Not Ready” light may light, depending on the values specified for the GC Cycle Time and the Vial Equil Time. When the “Not Ready” light goes on during a run, it simply means that the headspace sampler is not ready to insert the next vial into the oven because of timing restraints to maintain constant heating time.

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