Page 6 Advanced User Guide Agilent Technologies Use this manual as a resource when developing a method.
Most information relates to the parameters available from the instrument keypad, shown in Figure 1 below. Figure Connect to the HS instrument, open the method editor, and click the help icon or press F1. Advanced Operation Page Headspace Analysis Introduction Headspace Analysis Headspace analysis is a technique for analyzing volatile organic compounds using gas chromatography.
Headspace analysis samples the ambient volume above a sample matrix, where the volatile compounds exist in gaseous form at predictable levels.
Page Static Headspace Sampling Techniques Introduction Static headspace sampling: This technique uses a closed sample container and a sampling system. After placing the sample matrix into the sealed sampling vial, the sample matrix is heated for a specified time, during which the vial can also be agitated shaken to help drive volatile compounds from the matrix and into the headspace volume.
Page 13 Pressure transfer system Valve and loop systems The valve and loop system, as used in the A, also heats and agitates the vial for a specified time.
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However, the Agilent system uses a sample loop of known size to collect the sample. Lower vial into carousel. Figure 4 Basic A HS vial process flow, 12 vial model Figure 5 shows the workflow for a vial processed by the vial model HS with tray.
Page 17 Lift vial onto sample carousel. In addition, the oven can shake the vials at 9 different acceleration levels. In addition to simply heating the vial, which may generate enough internal pressure on its own, the HS can provide additional gas to help with extraction. Page Fill With Constant Volume How the A Headspace Sampler Works Fill with constant volume In this mode, the HS pressurizes the sample vial with a specified volume of carrier gas, then maintains the resultant pressure for the specified hold time.
This mode is useful if you need to calculate the exact molar amounts of sample and carrier gas in the vial or sample loop. The six port valve switches, allowing the pressurized sample to vent through the sample loop. The HS provides a selection for extraction type as an advanced function.
See Figure 8 Figure 9. At the same time, the HS vents residual pressure from the vial optional. After the inject time elapses, the six port valve returns to its original position. Page Overview This chapter describes techniques to create and refine a method, using the available method parameters and method features of the A HS.
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It describes all the method parameters available, and discusses how various parameters impact an analysis. This chapter assumes basic familiarity Theory of headspace analysis The equations describing headspace theory derive from three physical laws associated with vapor pressure, partial pressures, and the relationship between vapor pressure of an analyte above a solution and the concentration of that analyte in the solution.
This means that the sample amount and vial size need to be kept the same. Page 31 Where K is small, reducing the phase ratio will produce a higher concentration of analyte in the headspace volume. The A can use a variety of sample vials.
Select a sample vial and sample amount to create a higher concentration of analyte. Page 32 Where K is small, reducing the phase ratio will produce a higher concentration of analyte in the headspace volume.
Page Consider The Gc Inlet Method Development Consider the GC Inlet Normally, the choice of inlet is determined by the available However, note that for inlet types where the analytical column runs directly into the headspace sampler six port valve, the analytical column is not in the GC oven for its entire length.
Page Load A Similar Method When starting a new method, begin with a method for a similar sample type. The HS includes the methods listed in Table 1. Refer to the Operation guide for general information and procedures. Temperatures Press [Temp] and enter the desired values for the vial oven, sample loop, and transfer line temperatures.
The HS must determine the appropriate parameters.
If in Default mode, the final pressure is displayed. Loop equilibration If in Custom mode, default value: 0. Set the value in the column temperature program. See Table 8 parameters. Edit column temp program? Select and press [Enter] to edit. Final temperature 1 The GC column oven temperature at the end of the ramp period.
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See Figure Select Purge time and enter the purge time. If experiencing carryover, try increasing the purge flow or purge time to sweep any residual sample vapors from the system.
It provides useful tips and background information that will help you develop methods using the HS. It is not a general discussion of headspace chromatography, but rather a collection of information to help you use the Agilent A to best advantage.
As the HS increments the method parameter for each new vial, the new value is displayed. Pressurizing the vial As described in Valve and loop systems, the HS pressurizes the vial, then vents the vial to atmosphere through the sampling loop. The HS can control the rate of gas transfer through the loop, as well as the initial head pressure within the vial and the residual pressure left in the vial when sampling ends. The HS sampler then inserts a fixed volume of gas into the vial.
In this case, the actual final vial pressure is not known, since it depends on the initial pressure and the compressibility of the added volume of gas. Then then vent valve will open completely. The HS does not control the sampling system at this point. When the pressure reaches 0 relative to atmospheric, the vent valve closes. Page 51 Method Development Multiple extractions Two typical uses for multiple extraction mode are kinetic studies and calibration.
Note that the vial is punctured only once during the extractions. Concentrated extractions This mode can be useful for trace analysis, where the sample can accumulate in the GC inlet or other trap before being swept onto the GC column. This control is provides through the Sequence action parameters.
These parameters provide the flexibility to handle relatively minor issues with the level of attention appropriate for your workflow. Dyn leak test action: Available only when leak detection is enabled. Enter which action to take if a vial fails the dynamic leak test. In addition, if using a barcode reader additional sequence actions are available.
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The HS stops all vial processing, for the current sample vial and all other sample vials. For HS models with a vial tray, the HS returns all sample vials to the tray, beginning with the sample vial which had the problem. Page Optimizing Throughput Method Development Optimizing Throughput The vial model HS automatically manages its timings to maximize the throughput of samples submitted to it for processing. Upon starting a sequence, it compares the methods used for each vial, then determines how and when to place each vial in the oven to minimize any downtime between GC runs.
Use the blanks to check for carryover.
If carryover is found, resolve it. See the Troubleshooting manual. Page About The Barcode Reader The Barcode Reader About the Barcode Reader When used with an Agilent data system and the optional headspace control software, the barcode reader provides the data on the vial label to the data system for inclusion in reports.
Also, mismatches between the expected barcode value, as entered into the data system sequence, and the barcode actually read will be logged and can trigger specific actions.
Barcode reader settings are method parameters.
They can change from sample to sample in a sequence by changing the method. If a checksum fails, the HS logs and error and the sequence will follow the barcode sequence action specified in the method.
Module Accessory When not installed, only GC carrier gas control is available. Page Configuration Parameters Select the gas type used for the carrier gas.
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Page 68 Configuration Standby flow: Enter the flow rate of purge gas that flows through the sample loop, sample probe, and vent between sequences. Page 71 Configuration then the system is ready for next analysis.
Receiver is any sequence controller. Receiver is any module performing runtime- controlled activities.
Start Relay Contact Closure : A millisecond contact closure. Used as an isolated output to start another device that is not compatible or connected with APG Remote pin 3. Page 73 The sample is injected by switching the sample loop into the carrier gas stream.