Thomson unit

Mass spectrometry is a sensitive analytical technique which is able to quantify known analytes and to identify unknown molecules at the picomoles or femto-moles level. A fundamental requirement is that atoms or molecules are ionized and analyzed as gas phase ions which are characterized by their mass (m) and charge (z). A mass spectrometer is an instrument which measures precisely the abundance of molecules which have been converted to ions. In a mass spectrum m/z is used as the dimensionless quantity that is an independent variable. There is still some ambiguity how the x-axis of the mass spectrum should be defined. Mass to charge ratio should not lo longer be used because the quantity measured is not the quotient of the ion s mass to its electric charge. Also, the use of the Thomson unit (Th) is considered obsolete [15, 16]. Typically, a mass spectrometer is formed by the following components (i) a sample introduction device (direct probe inlet, liquid interface), (ii) a source to produce ions, (iii) one or several mass analyzers, (iv) a detector to measure the abundance of ions, (v) a computerized system for data treatment (Fig. 1.1). 

The ions produced in the source are separated in the analyzer according to their mass-to-charge (m/z) ratios. The Thomson unit (Th, named for a famous mass spec-trometrist) corresponds to an m/z ratio of 1 it is widely used in mass spectrometry. In a GC-MS context, we often speak too generally about mass measurement because z = 1 in electron ionization and positive chemical ionization and z = -1 in negative chemical ionization. 

In summary, starting with 105°F gas at atmospheric pressure, the theoretical work necessary to liquify one pound of methane is 510.8 Btu or 352 hp/MMcfd. The simplified liquefaction process, as illustrated, uses a turboexpander/compressor and a small propane refrigeration unit. The 41.25% efficiency breaks down as follows one-fourth contributed by the turboexpander/compressor at 35.8% efficiency one-sixteenth contributed by the mechanical propane refrigeration unit at 43% efficiency, at a moderate temperature where its efficiency is high and a large fraction—eleven-sixteenths—contributed at 58.2% efficiency by compression and Joule-Thomson condensation energy. 

The turboexpander lowers the temperature of the product to -100°F, causing it to liquify. Now at 350 psig pressure, the liquid from this process enters the demethanizer tower where it mingles with the previously introduced stream of liquid. The turboexpanders provide a 92% recovery rate while the former system, a backup Joule-Thomson valve, was able to provide only a 60% recovery rate. The volume of gas entering the turboexpanders can vary up to 10% yet, the different flowrates do not significantly affect the efficiency of these units, which are rated at 2,400 hp at 16,000 rpm. 

In the course of his research on electromagnetic waves Hertz discovered the photoelectric effect. He showed that for the metals he used as targets, incident radiation in the ultraviolet was required to release negative charges from the metal. Research by Philipp Lenard, Wilhelm Hallwachs, J. J. Thomson, and other physicists finally led Albert Einstein to his famous 1905 equation for the photoelectric effect, which includes the idea that electromagnetic energy is quantized in units of hv, where h is Planck s con-... 

University of Kent, Canterbury, United Kingdom Thomson, William (Lord Kelvin) (1824-1907)... 

Campion, R.P. and Thomson, B., Proc. 1st Conf. Polymers in Automotive Fuel Containment, Birmingham, UK, Rapra, Shawbury, United Kingdom, 2000. 

Derham, C.J. and Thomson, B. Proc. 4th Conf. Oilfield Engineering with Polymers, London, MERL, Hitchin, United Kingdom, 2003, paper 1. 

Peffer, N.J., Hanvey, J.C., Bisi, J.E., Thomson, S.A., Hassman, C.F., Noble, S.A. and Babiss, L.E. (1993) Strand-invasion of duplex DNA by peptidic nucleic acid oligomers. Proceedings of the National Academy of Sciences of the United States of America, 90, 10648-10652. 

Fig. 6.16. Cross-cut of Uhlig s cryostat with pulse tube refrigerator, dilution unit and Joule-Thomson... 

Note Some mass spectrometrists use the unit thomson [Th] (to honor J. J. Thomson) instead of the dimensionless quantity m/z. Although the thomson is accepted by some journals, it is not a SI unit. 

Symbol used to denote the dimensionless quantity formed by dividing the mass of an ion in unified atomic mass units by its charge number (regardless of sign), m/z should be written in italic and lower case. The Thomson (Th) is sometimes used as unit but it is not recommended. 

B. J. Thomson and A. M. Wild, "Factors Affecting the Rate of Burning of a Titantium - Strontium Nitrate Based Composition," Proceeding of Pyrochem International 1975, Pyrotechnics Branch, Royal Armament Research and Development Establishment, United Kingdom, July, 1975. 

In the paper which has just been read to the Society, Dr. Thomson has remarked, that oxalic acid unites to strontian as well as to potash in two different proportions, and that the quantity of acid combined with each of these bases in their super-oxalates, is just double of that which is saturated by the same quantity of base in their neutral compounds. 

But since the publication of Mr. Daltons theory of chemical combination, as explained and illustrated by Dr. Thomson, the inquiry which I had designed appears to be superfluous, as all the facts that I had observed are but particular instances of the more general observation of Mr. Dalton, that in all cases the simple elements of bodies are disposed to unite atom to atom singly, or, if either is in excess, it exceeds by a ratio to be expressed by some simple multiple of the number of its atoms. 

Several sources of information were vital in the preparation of individual monographs of biologies that are approved and marketed in the United States. They include online databases provided by the Food and Drug Administration, drug manufacturers literature, and drug information available online from Thomson Micromedex. 

In mass spectrometry, the mass-to-charge ratio (m/z) is mostly measured as a dimensionless number. Sometimes the unit known as the Thomson [Th], in honour of J. J. Thomson, is applied. 

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