Auto-samplers

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By adding auto-samplers to your lab, gas chromatograph throughput efficiencey can be increased. Wasson-ECE offers two types of auto-samplers: the Gas AutoSampler (AS201) for heating and injecting pressurized gas phase samples, and the Pressurized Liquid AutoSampler (LS100) for injecting pressurized liquid samples at ambient temperatures.

Gas Autosampler

Gas AutoSampler

The Gas AutoSampler automates delivery of pressurized gas samples to a GC at atmospheric pressure. The Gas AutoSampler includes an oven and heated transfer system that can send samples to the GC at temperatures of up to 150°C. Samples to be analyzed are placed in the auto-sampler oven. The auto-sampler can hold twelve 500-cc sample cylinders or nine 1-liter cylinders.
Technicians then enter sample information into the chromatography system computer, which also allows them to select the time interval between sample injection, set the temperature of the oven, log the sample injection times, and create data reports. The Gas AutoSampler is a stand-alone instrument that sends samples to the GC through a heated bridge, ensuring that samples are injected at oven temperature. This heated pathway is purged with carrier gas between each sample, and a vacuum pump ensures an extremely low level of cross-contamination (typically less than 50 ppm) between each sample purge.

Liquid Autosampler

Pressurized Liquid AutoSampler

Laboratory automation for pressurized liquid samples is also available for liquid samples such as liquefied petroleum gas (LPG) and natural gas liquids (NGL). Liquid samples at pressures up to 1200 psi are stored in steel sample systems. The pressurized Liquid AutoSampler uses inert gases to maintain pressure so that samples remain in liquid phase in this ambient-temperature system as they are passed to the gas chromatograph and analyzed.
When samples enter the laboratory, they are connected to the Liquid AutoSampler, which will convey pressurized samples to the gas chromatograph. Sample cylinders with 1/4 inch tube fittings, VCO, or "Quick Connect" fittings can be inserted directly into the top plate of the sampler. These fittings will hold the sample cyclinders vertically, ensuring that samples are drawn from the bottom of the cylinder. Sample cylinders with smaller tube fittings can be held vertically with an optional cylinder rack.

Accuracy and Precision

Automating the sample injection process increases efficiency and prevents technicians from having to perform time-consuming, repetitive tasks. The Gas AutoSampler ensures that sample analysis is not only faster, but also more precise, accurate, and consistent. Compare the GC analysis results for the following 2 mL samples of n-pentane and n-hexane at 100 psi in propane. In the first run, the sample is sent to the GC from the auto-sampler at ambient temperature; in the second run the auto-sampler heats the samples to 130°C before injection.

Table 1: Increase in Detector Accuracy and Precision with Heated Gas AutoSampler
  Unheated Sample Sample at 130° C    
  Avg. Peak Area % Rel. Standard
Deviation
Avg. Peak Area % Rel. Standard
Deviation
Percent Change in Area Percent Change in Rel. Standard
Deviation
Component  
Propane 867938 0.22% 849415 0.23% -2.1% +0.01%
n-Pentane 24025 10.2% 41282 1.35% +72% -8.85%
n-Hexane 16475 16.7% 56087 0.80% +240% -15.9%

The auto-sampler showed a 240% increase in sensitivity to n-hexane and a 72% increase in sensitivity to n-pentane in the gas sample when heated. Make sure you're getting the range and sensitivity you need by adding the Gas or Liquid AutoSampler system to your gas chromatograph.