Injection Nebulizers DIN

Direct injection nebulization is based on the principle of injecting a liquid sample under high pressure directly into the base of the plasma torch. The benefit of this approach is that no spray chamber is required, which means that an extremely small volume of sample can be introduced directly into the ICP-MS with virtually no carryover or memory effects from the previous sample. Because they are capable of injecting 5 pL of liquid, they have found a use in applications where sample volume is limited or where the material is highly toxic or expensive. 

They were initially developed more than 15 years ago and found some success in certain niche applications that could not be adequately addressed by other nebuliza-tion systems, such as introducing samples from a chromatography separation device into an ICP-MS or the determination of mercury by ICP-MS, which is prone to severe memory effects. Unfortunately, they were not considered particularly user-friendly, and as a result became less popular when other sample introduction devices were developed to handle microliter sample volumes. More recently, a refinement of the DIN has been developed, called the direct inject high-efficiency nebulizer (DIHEN), which appears to have overcome many of the limitations of the original design. The advantage of the DIHEN is its ability to introduce microliter volumes into the plasma at extremely low sample flow rates (1-100 pL/min) with an aerosol droplet size similar to a concentric nebulizer fitted with a spray chamber. The added benefit is that it is almost 100% efficient and has extremely low memory characteristics. A schematic of a commercially available DIHEN system is shown in Eigure 17.14. 

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A novel interface to connect a ce system with an inductively coupled plasma mass spectrometric (icpms) detector has been developed (88). The interface was built using a direct injection nebulizer (din) system. The ce/din/icpms system was evaluated using samples containing selected alkah, alkaline earths, and heavy-metal ions, as well as selenium (Se(IV) and Se(VI)), and various inorganic and organic arsenic species. The preliminary results show that the system can be used to determine metal species at ppt to ppb level. 

In addition to concentric pneumatic nebulizers that are used most frequently for the majority of atomic spectrometric systems, a range of other nebulizers also exist. Some nebulizers that are used for plasma instrumentation, e.g. direct injection nebulizers (DIN) or ultrasonic nebulizers (USN), increase... 

Two different kinds of direct injection nebulizers are available commercially. The total consumption nebulizer was developed by Greenfield et al. [36] for ICP optical emission spectrometry. The concept for the Cetac direct injection nebulizer (DIN) was developed by Fassel, Houk, and coworkers [35,37]. It has a narrow sample-carrying capillary [30-50 xm inner diameter (i.d.), 0.5 to 1 m long] that extends slightly past the nebulizer gas tube. A second, auxiliary or makeup, nebulizer gas is introduced through another concentric tube outside the nebulizer gas tube. A gas displacement pump (up to 1500 psi) or HPLC pump is used to deliver the sample to the nebulizer through the long, narrow capillary. 

The key to a successful HPLC-ICP-MS coupling is the interface. In the simplest case the outlet of an HPLC column (4.6 D10 mm) is connected to a conventional pneumatic or crossBow nebulizer. The use of capillary or megabore (0.32D1.0mm) HPLC systems that are becoming popular, especially for RPC, requires the use of micronebulizers, either direct injection nebulizers (DIN) or micronebulizers (e.g., Micromist, DS-5) bttcd with a small-volume nebulization chamber. 

Although there has been limited use with CE interfaces, the direct injection nebulizer (DIN) was first described by Shum et al. - and later used by Liu et al. for CE (Fig. 2E). In this design, the nebulizer introduces the sample very near the plasma inside the ICP torch and eliminates the spray chamber assembly. Close to 100% analyte transport efficiency can theoretically be obtained with the DIN, but the nebulizer is restricted to very low liquid flow rate and thus is well matched to CE interfacing. This design does induce local plasma cooling due the lack of desolvation and detection limits are only slightly improved over other nebulizer designs. 

OCN), which is a variation of the pneumatic concentric nebulizer built from flexible capillary mbes, was used in an interface. The OCN has had little application in CE interfaces, owing to its generally lower sensitivity performance when compared to other pneumatic nebulizers used with ICP-MS detection.The direct injection nebulizer (DIN), previously described in The Nebulizer, was used by Liu et al. in a CE interface. The electrophoretic capillary was directly inserted through the central sample introduction capillary of the DIN. A platinum grounding electrode was positioned into a three-port connector. This connector contained the DIN sample introduction capillary as well as a make-up buffer flow. These alternative nebulizers have been successfully used in CE interfaces, but the pneumatic designs dominate the interface systems reported in the literature. 

The most definitive assessment of the metal composition of metalloproteins comes from the application of element-specific detection methods. CE-ICP-MS provides information not only about the type and quantity of individual metals bound to the proteins but also about the isotopes of each element as well [11,12]. Elemental speciation has become increasingly important to the areas of toxicology and environmental chemistry. Such analytical capability also opens up important possibilities for trace element metabolism studies. Figure 1 depicts the separation of rabbit liver metallothionein containing zinc, copper, and cadmium (the predominant metal) using CE-ICP-MS with a high-sensitivity, direct injection nebulizer (DIN) interface. UV detection (200 nm) was used to monitor the efficiency of the CE separation of the protein isoforms (MT-1 and MT-2), whereas ICP-MS detection made it possible to detect and quantify specific zinc, copper (not shown), and cadmium isotopes associated with the individual isoform peaks. 

ICP-AES is often used to determine the concentrations of various elements in a sample. However, an element may be present in a variety of chemical forms or species. By coupling an ICP-AES detector to an ion-chromatographic column, a more complete description of the sample species can be obtained. Such a coupling generally requires a nebulizer to introduce the column effluent into the ICP. Conventional pneumatic nebulizers operate at about 1 mL/min sample flow and may introduce as little as 1 % of the sample into the plasma. A newer direct-injection nebulizer (DIN) operates at sample flow rates only 5 to 10 % that of a conventional nebulizer [2. >). 

Sn BuSn ", Bu2Sn ", and BusSn Marine sediment and harbor sediment Ion pair Hypersil CDS 15 cm X 1 mm, 5 pm ICP-MS Sodium 1-pentanesulfonate and tropolone used as counterions direct injection nebulizer (DIN) used 1998 437... 

Organolead speciation analysis has also been achieved by the use of modified silica capillaries following nebulization with a direct injection nebulizer (DIN), which is very suitable for the introduction of liquid samples into ICP-MS. 

Fig. 2 A, The concentric nebulizer B, The cross-flow nebulizer, C, The ultrasonic nebulizer (USN) D, The microconcentric nebulizer (MCN) by CETAC. The body of this nebulizer is made of plastic and E, The direct injection nebulizer (DIN).

Descriptions of other sample introduction systems, including ultrasonic nebulization (USN), direct injection nebulization (DIN), and electrothermal vaporization (ETV), can be found in the literature [64—66]. 

The sample introduction from an LC column to ICP-MS is performed by a nebulizer. The usual nebulizers are pneumatic nebulizers, such as Meinhard, crossflow, or microconcentric nebulizers (MCNs). Additionally, there is the ultrasonic nebulizer (USN), the direct-injection nebulizer (DIN), and the hydraulic high-pressure nebulizer (HHPN). The nebuli-zation efficiency depends on nebulizer type and is typically low for Meinhard and crossflow nebulizers (only around 1—5 %, [23]), whereas it is high for the DIN and USN. 

Chilled spray chambers and desolvation systems Direct injection nebulizers (DIN)... 

The direct injection nebulizer (DIN) is a total consumption device. The entire aerosol generated by the nebulization process is injected directly into the plasma. No spray chamber is used to classify the size of the droplets formed by nebulization, so this technique is 100% efficient. Precision and washout times were significantly improved using this approach. Use of this device also leads to reduced memory effects. 

Shum, S. C.-K. (1993). Measurement of elemental speciation by liquid chromatography inductively coupled plasma mass spectrometry (LC-ICP-MS) with the direct injection nebulizer (DIN). Unpublished Ph.D.Thesis, Iowa State University,Ames. 

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