Learn More About “Purge and Trap”

Learn More About “Purge and Trap”

About?purge and trap, do you purge clearly? And do you really trap accurately?

1. Fundamentals of Purge and Trap

Dynamic headspace is relative to static headspace. Different from the static headspace, the dynamic headspace does not analyze the headspace sample in an equilibrium state, but uses flowing gas to “sweep” the volatile components in the sample, and then uses a trap to sweep out the substances After adsorption, the sample was sent to GC for analysis by thermal desorption. Therefore, it is usually called the?purge-and-trap?(Pung&Trap) sampling technique, which we also use below.

40ml TOC Vials

In most purge-and-trap applications, ammonia is used as the sweep gas, which is bubbled through the sample solution. Under continuous airflow, the volatile components in the sample escape with the ammonia gas and are concentrated by a trapping device equipped with an adsorbent. After a certain purging time, the components to be measured enter the trap completely or quantitatively. At this time, the purge gas is turned off, and the trap is connected to the carrier gas path of the GC through the switching valve. At the same time, the trap tube is rapidly heated to desorb the trapped sample components and then enter the GC for separation and analysis with the carrier gas. Therefore, the purge-trap principle is dynamic headspace extraction-adsorption trap-thermal desorption-GC analysis.

Purge-and-trap?sampling is widely used in environmental analysis, such as the analysis of organic pollutants in drinking water or wastewater. It is also used for the analysis of volatile substances (such as odor components) in food. Obviously, many samples analyzed by purge-trap technology can also be analyzed by static headspace technology, but the former has higher sensitivity and can analyze the analysis with a relatively high boiling point (low vapor pressure), and purge-trap is generally better than static headspace technology. Headspace equilibration time is short.

2. Selection of?System?Operating?Conditions

(1) Temperature

There are three temperatures to be controlled in purge-trap analysis, the first being the?sample purge?temperature. The aqueous solution is mostly purged at room temperature, as long as the purging time is long enough, it can meet the analysis requirements. Sometimes in order to shorten the purging time, the sample can also be heated, but the side effect of increasing the temperature is to increase the volatilization of water. For non-aqueous solutions, such as some meat products, a higher purge temperature is used.

The second is the?trap?temperature. There is a difference between adsorption temperature and desorption temperature. The adsorption temperature is usually room temperature, but low-temperature freezing capture technology can also be used for gases that are not easily adsorbed. That is, use cold air, liquid carbon dioxide or liquid nitrogen to control the temperature of the trapping tube. As for the desorption temperature, it is an important parameter of the?purge-trap?technology, which should be optimized and determined according to the properties of the components to be measured and the properties of the adsorbent.

TOC Vials

The desorption temperature of the commercial automatic purge-trap injector can reach up to 450°C, but most of the standard methods for environmental analysis (such as American method A) use a purge temperature of about 200T.

The third is the temperature of the?connecting tubing, which should be high enough to prevent condensation of the sample. The commonly used connecting pipe temperature for environmental analysis is 80-150°C.

Amber TOC vial

(2) Purge gas flow rate and purge time

The?purge gas flow rate?depends on the concentration of the analyte in the sample, its volatility, its interaction with the sample matrix (such as solubility), and its adsorption in the trapping tube. When using ammonia, the flow rate range is 20-60ml/min. It can be slightly higher when using gas, but the purging effect of nitrogen is not as good as that of regas. The reason is that nitrogen is more soluble in water than ammonia. Note that when the purge flow rate is too high, it will affect the trapping of the sample, resulting in the loss of sample components.

No alt text provided for this image

The?carrier gas flow rate?during desorption depends primarily on the column used. When using a packed column, it is 30-40ml/min; when using a large diameter column, it is 5-10ml/min; when using a conventional capillary column, the carrier gas flow rate should be set according to the split or splitless mode.

Purge time?is one of the important parameters of purge-trap technology, which must be optimized and determined according to specific samples. In principle, the longer the purge time, the higher the analytical reproducibility and sensitivity. However, considering the analysis time and work efficiency, the shortest possible purge time should be selected on the premise of satisfying the analysis requirements. In actual work, the purge time can be determined by measuring the recovery rate of the standard sample.

For example, to determine pollutants such as benzene and ethylbenzene in wastewater, uncontaminated clean water can be used as a blank sample, and the analyte is added quantitatively, and then the recovery curve of different purge times is drawn through experiments.

40ml storage vial

3. Factors of?affecting?results

There are basically two factors that affect the results of?purge and trap?determination, one is the?purge-trap injector?itself, and the other is the?GC conditions. The former includes desorption temperature, purge gas flow velocity, purge time and analysis conditions, etc., so these conditions should be strictly controlled for their reproducibility. And the latter is the same as normal GC. It is recommended to use the internal standard method or standard addition method for quantification to reduce the influence of fluctuations in operating conditions on the results.

Others, such as the appropriate use of salinization effects (incorporation of NaCl), increase extraction efficiency, but must be properly handled between sample analyses.

要查看或添加评论,请登录

Bonnie Sun的更多文章

  • V817 Stands For...?

    V817 Stands For...?

    Different products have different part number. However, they are not random, each and every of them means something.

  • INTRO:9mm Short Thread Vials ND9

    INTRO:9mm Short Thread Vials ND9

    Welcome to Lear’s newsletter~ Chromatography vials are contains used to transport your sample matrix to the instrument…

  • How are HPLC vials used for drug analysis?

    How are HPLC vials used for drug analysis?

    HPLC (High-Performance Liquid Chromatography) vials are used for drug analysis in a variety of ways. HPLC is a widely…

  • Factors To Consider When Buying HPLC Vials

    Factors To Consider When Buying HPLC Vials

    When buying HPLC vials, there are several factors to consider to ensure that you choose the right product for your…

  • Why HPLC vials can be damaged?

    Why HPLC vials can be damaged?

    HPLC (High-Performance Liquid Chromatography) vials can be damaged due to several reasons, including: 1. Physical…

  • 2mL HPLC Vials: The Future of Chromatography Sample Preparation

    2mL HPLC Vials: The Future of Chromatography Sample Preparation

    High-Performance Liquid Chromatography (HPLC) is a technique widely used in the pharmaceutical, biotechnology, and…

    1 条评论
  • PTFE HPLC Syringe Filter

    PTFE HPLC Syringe Filter

    Polytetrafluoroethylene (PTFE) membranes are resistant to almost all solvents, acids and alkalis, with high mechanical…

  • Six Materials of Syringe Filter Membrane

    Six Materials of Syringe Filter Membrane

    There are various materials for syringe filter membranes. Today I will show you the characteristics of various…

  • Four Factors Affecting Chromatographic Peaks

    Four Factors Affecting Chromatographic Peaks

    Do you know what is causing the chromatographic peaks to move forward or backward? And how to solve them? Let me tell…

    2 条评论
  • Do you Know These HPLC Terms?

    Do you Know These HPLC Terms?

    On a liquid chromatograph, after the sample is separated from the mobile phase through the chromatographic column, it…

    6 条评论

社区洞察

其他会员也浏览了