Needle spargers

Figure 4.8. (a) Schematic diagram of a typical purge and trap-GC system. (Reprinted with permission from Nelson Thornes, Ref. 27.) (b) Needle sparger for purge and trap. 

Three types of purging vessels are commonly used frit spargers, fritless spargers, and needle spargers. The frit creates fine gas bubbles with large surface areas, which facilitate mass transfer of analytes into... 

Solid samples are analysed in special vessels (needle sparger, see Figure 2.21b,c) into which a needle with side openings is dipped. For foaming samples, the headspace sweep technique can be used. 

Figure 2.23 Glass apparatus for the purge and trap technique (Tekmar). (a) U-tube with/without frit (5 and 25 mL sizes), (b) Needle sparger left single use vessels, middle glass needle with frits, right vessels with foam retention, 5, 20 and 25 mL volumes.

Figure 33-2 shows a needle type sparger for slurries, soils, solid, foaming liquid samples, and viscous samples. This style comes in either 5 or 25 mL sizes. The sample is added to the tube, and a needle is inserted to the bottom of the sample to introduce the gas. The bulge near the top is to reduce any foaming. 

For what types of samples is a needle type sparger preferred ... 

The purge efficiency is defined as that quantity of the analytes, which is purged from a sample with a defined quantity of gas. It depends upon various factors. Among them are purge volume, sample temperature and nature of the sparger (needle or frit), the nature of the substances to be analysed and that of the matrix. 

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