Mass reflectron

Mamyrin, B. A. Karataev, V. I. Shmikk, D. V. Zagulin, V. A. Mass reflectron New nonmagnetic time-of-flight high-resolution mass spectrometer. Zh. Eksp. Teor. Fiz. 1973, 64, 82-89. 

B. A. Mamyrin, V. I. Karataev, D. V. Shmikk, and V. A. Zagulin. The Mass-Reflectron, a New Non-Magnetic Time-of-Flight Mass Spectrometer with High Resolution. Sov. Phys. JETP, 37(1973) 45-48. 

The second way to improve the mass resolution significantly is to use an electrostatic mirror (mass reflectron) placed in the drift region of ions (Fig. 1.27). 

The experimentally established analytical and the physical characteristics of the laser mass-reflectron LASMA are presented in Table I. 

Mamyrin BA, Karataev VI, Shmikk DV, and Zagulin VA (1973) The mass-reflectron, a new nonmagnetic time-of-flight mass spectrometer with high resolution. Soviet Physics-JETP 37(1) 45 8. 

Mamyrin, B.A., Karataev, V.I., Shmikk, D.V., Zagulin, V.A. (1973) Mass-reflectron a New Nonmagnetic Time-of-flight High-resolution Mass-spectrometer. Zh. Eksp. Teor. Eiz. 64 82-89. 

As m increases, At becomes progressively smaller (compare the difference between the square roots of 1 and 2 (= 0.4) with the difference between 100 and 101 (= 0.05). Thus, the difference in arrival times of ions arriving at the detector become increasingly smaller and more difficult to differentiate as mass increases. This inherent problem is a severe restriction even without the second difficulty, which is that not all ions of any one given m/z value reach the same velocity after acceleration nor are they all formed at exactly the same point in the ion source. Therefore, even for any one m/z value, ions at each m/z reach the detector over an interval of time instead of all at one time. Clearly, where separation of flight times is very short, as with TOF instruments, the spread for individual ion m/z values means there will be overlap in arrival times between ions of closely similar m/z values. This effect (Figure 26.2) decreases available (theoretical) resolution, but it can be ameliorated by modifying the instrument to include a reflectron. 

Time-of-flight (TOF) instmments utilize the times taken by ions to pass (fly) along an evacuated tube as a means of measuring m/z values and therefore of obtaining a mass spectmm. Often a reflectron is used to direct the ions back along the TOF tube. 

The reflectron increases the spatial separation of the ions of different m/z values by making them travel up and down the flight tube, so the distance traveled is twice what it would be if the ions simply passed once along the tube from one end to the other. The reflectron also narrows the energy spread for individual m/z values, thus improving mass resolution. TOP analyzers are not necessarily equipped with a reflectron. 

For very high mass, when sensitivity is frequently critical, the reflectron is not used and lower resolution is accepted. 

Figure 3.7 Schematic of a time-of-flight mass analyser, involving the use of a reflectron .

In this instrnment, the final stage of the triple quadrnpole is replaced by an orthogonal time-of-fiight (ToF) mass analyser, as shown in Fignre 3.10. The con-fignration is typical of the latest generation of ToF instrnments in which a nnmber of reflectrons, in this case two, are used to increase the flight path of the ions and thns increase the resolution that may be achieved. 

Reflectron An ion lens nsed in the time-of-flight mass analyser to increase the distance travelled by an ion and thereby increase the resolntion of the instmment. 

We use laser photofragment spectroscopy to study the vibrational and electronic spectroscopy of ions. Our photofragment spectrometer is shown schematically in Eig. 2. Ions are formed by laser ablation of a metal rod, followed by ion molecule reactions, cool in a supersonic expansion and are accelerated into a dual TOE mass spectrometer. When they reach the reflectron, the mass-selected ions of interest are irradiated using one or more lasers operating in the infrared (IR), visible, or UV. Ions that absorb light can photodissociate, producing fragment ions that are mass analyzed and detected. Each of these steps will be discussed in more detail below, with particular emphasis on the ions of interest. 

The chemical compositions of the isolated Au SR clusters were investigated by mass spectrometry [15,16,18, 22,32-35]. TEM was used to confirm that the species detected by the mass spectrometer represents the clusters in the sample. Figure 3a is a schematic representation of the top view of the mass spectrometer, which consists of five stages of differentially pumped vacuum chambers. The apparatus accommodates two t5 pes of ion sources, electrospray ionization (ESI) and laser-desorption ionization (EDI), and a time-of-flight (TOE) mass spectrometer with a reflectron. Details of the apparatus and the measurement protocols are described below. 

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