Photo Ionization Detector PID

The photo ionization detector (PID) operates on the principle of energy absorption of photons emitted by a UV lamp in the detector housing. The absorbed energy leads to ionization of the molecule by release of an electron from the excited molecule M according to Eq. (2.26). 

The number of ions produced is proportional to the absorption coefficient of the molecule and the intensity of the lamp. 

The PID is mainly used for the analysis of aromatic pollutants, for example, BTEX or PAH, or halogenated compounds in environmental applications. Many EPA methods, for example, 602, 502 or 503.1, cover priority pollutants in surface or drinking water. Typical for the PID is the detection of impurities air, also with mobile detectors. This is due to the fact that the energy of the UV lamp is sufficient to ionize the majority of organic air contaminants, but insufficient to ionize the air components oxygen, nitrogen, water, argon and carbon dioxide. 

Use Field analysis of volatile halogenated hydrocarbons, BTEX, polyaromatic hydrocarbons (PAHs), and so on. 

Limitations Only for substances with low IPs ( 10eV) consult manufacturers data. 

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The contractor at Site H had established area and personnel sampling consistent with HAZWOPER requirements. A photo ionization detector (PID) and a real-time aerosol monitor (RAM) were used on a daily basis to screen for potentially hazardous levels of contaminants. On a weekly basis, personal air samples were collected and submitted for laboratory analysis. PPE requirements, however, were often not based on this data because the oversight agency had established inflexible minimum PPE requirements. The audit team found many of the PPE requirements on Site H to be excessive in light of site monitoring data and hazard determinations. 

As a minimum, the flame ionization detector (FID) or the photo-ionization detector (PID) must be available at industrial sites handling hazardous substances. 

A photo-ionization detector (PID) measures VOCs in concentrations from ppbv up to lOOOOppmv. A PID is a very sensitive broad-spectrum monitor, like a low-level lower flammable limit (LEL) monitor. 

The photo ionization detector (PID) contains an ultraviolet lamp that emits photons that are absorbed by compounds (aromatic rings, alkynes, and alkenes) in the ionization chamber. The ions created are then collected at electrodes, thus giving a signal. The most common use for this detector is for the analysis of BTEX. 

Other than phosgene and the cyanide agents, most chemical warfare agents are thought to have ionization potentials of less than 10.6 eV. Therefore screening with photo ionization detectors (PIDs) and flame ionization detectors (FIDs) is possible. However, because these systems will not differentiate... 

Figure 2.16 Electron capture detector(ECD) (a) and photo-ionization detector (PID) (b). The BCD must be installed in an well ventilated position owing to it containing a radioactive source. The PID contains a UV source from which the photons are emitted, having a pre-selected energy, using a filter which prevents undesired carrier gas ionization M + hv M+ - - e ). Examples of filters LiF at ll.SeV, MgFj at 9.6-10 eV, sapphire at 8.4 eV. On contact with the electrodes the molecules return to uncharged state, ionization being therefore reversible. The use of the make-up gas provides an optimal flow.

The primary method of analyzing carbon disulfide in air is by adsorption on an activated charcoal tube followed by solvent elution for subsequent quantification. GC equipped with either an electron capture detector (ECD), photo-ionization detector (PID), or FPD has been used for measuring carbon disulfide after elution from the solid phase. Detection limits of low ppm levels of carbon disulfide in the air sample were achieved with these techniques (McCammon et al. 1975 Peltonen 1989 Smith and Krause 1978 UK/HSE 1983). NIOSH has recommended GC/FPD (method 1600) for determining carbon disulfide in air. The range of quantification is 3-64 ppm for a 5-L air sample (NIOSH 1984b). 

The detectors used in gas chromatography for the detection of individual VOCs can also provide information about a mixture without a separation step. These VOC detectors include, for example, the flame-ionization detector (FID) and the photo-ionization detector (PID). Other direct-reading instruments have also been used for determining VOCs, such as photoacoustic spectroscopy (PAS) (see Chapter 1.6). Other types of sensors (e.g. electronic noses ) may become important in the future. 

It was found that these sensors can detect many gases, such as air. He, Ar, and gas mixtures, without gas separation (Modi et al. 2003). We need to note that ionization gas sensors such as photo-ionization detectors (PID), flame-ionization detectors (FID), or electron-capture detectors (ECD) are not suitable for direct application to gas mixtures. These detectors work in conjunction with a gas chromatography setup that separates the mixture into distinct bands that can then be qnalitatively and quantitatively analyzed (Modi et al. 2003). In addition, FID has poor selectivity and requires bulky and hazardous... 

Several detectors are used for VOCs analysis by GC flame ionization detector (FID), photo ionization detector (PID), electron capture detector (BCD), electrolytic conductivity detector (ELCD), mass spectrometer detector (MSD or MS), and Fourier-transform infrared detector (FTIRD). For the in-depth reviews of the detectors, readers are directed to Refs. [52-54]. Examples of ICP-MS or microwave-induced plasma atomic emission spectrometry (atomic emission detector, AED) have been reported as detection technique after chromatographic separation [55,56]. Current trends and developments in GC analysis of VOCs have been recently reviewed by the group of Dewulf [16,57]. Mass spectrometer detectors allow low detection limits in single/selected ion monitoring (SIM) and a qualitative confirmation by full scan mode or by means of other ion selected as qualifier. 

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