Mass spectrometry measuring concentration rang

Indirect indicators of vitamin B12 deficiency include measurements of the metabolites homocysteine and methylmalonic acid (MMA) in serum and MMA in urine (see the Biochemical Perspectives section). Whereas the serum homocysteine concentration increases during folate or vitamin B12 deficiencies, the serum and urine MMA concentrations increase only in vitamin B12 deficiency. Therefore, MMA determinations can be used to differentiate vitamin B12 deficiency from folate deficiency. The normal concentration of MMA in serum ranges from 0.08 to 0.28 pmol/L. MMA is quantified using gas-liquid chromatography and mass spectrometry. Elevated concentrations of MMA and homocysteine in serum may precede the development of hematological abnormalities and reductions in serum vitamin B12 concentrations. One should be aware that other conditions, including renal in sufficiency and inborn errors of metabolism, can also result in elevated serum levels of MMA. 

The formation of Si containing reaction products has been investigated by mass spectrometry over a range of O2 concentrations from room temperature up to T= 890 Measured time profiles are displayed in Figure 4.5. 

In Laser Ionization Mass Spectrometry (LIMS, also LAMMA, LAMMS, and LIMA), a vacuum-compatible solid sample is irradiated with short pulses ("10 ns) of ultraviolet laser light. The laser pulse vaporizes a microvolume of material, and a fraction of the vaporized species are ionized and accelerated into a time-of-flight mass spectrometer which measures the signal intensity of the mass-separated ions. The instrument acquires a complete mass spectrum, typically covering the range 0— 250 atomic mass units (amu), with each laser pulse. A survey analysis of the material is performed in this way. The relative intensities of the signals can be converted to concentrations with the use of appropriate standards, and quantitative or semi-quantitative analyses are possible with the use of such standards. 

Only arc/spark, plasma emission, plasma mass spectrometry and X-ray emission spectrometry are suitable techniques for qualitative analysis as in each case the relevant spectral ranges can be scanned and studied simply and quickly. Quantitative methods based on the emission of electromagnetic radiation rely on the direct proportionality between emitted intensity and the concentration of the analyte. The exact nature of the relation is complex and varies with the technique it will be discussed more fully in the appropriate sections. Quantitative measurements by atomic absorption spectrometry depend upon a relation which closely resembles the Beer-Lambert law relating to molecular absorption in solution (p. 357 etal.). 

The detection of a test gas using mass spectrometers is far and away the most sensitive leak detection method and the one most widely used in industry. The MS leak detectors developed for this purpose make possible quantitative measurement of leak rates in a range extending aaoss many powers of ten (see Section 5.2) whereby the lower limit = 10 mbar l/s, thus making it possible to demonstrate the inherent gas permeability of solids where helium is used as the test gas. It is actually possible in principle to detect all gases using mass spectrometry. Of all the available options, the use of helium as a tracer gas has proved to be especially practical. The detection of helium using the mass spectrometer is absolutely ( ) unequivocal. Helium is chemically inert, non-explosive, non-toxic, is present in normal air in a concentration of only 5 ppm and is quite economical. Two types of mass spectrometer are used in commercially available MSLD s ... 

Table 11.4 summarizes measurements of various species in the stratosphere and troposphere by mass spectrometry through the early 1990s (Viggiano, 1993, and references therein). The altitude at which they were measured and the concentration ranges are shown, as well as whether they were detected using positive or negative ions (see later discussion). 

To establish a sensitive and specific liquid chromatography-mass spectrometry (time-of-flight) [LC-MS (TOF)] method for the determination of donepezil in human plasma after an oral administration of 5 mg donepezil hydrochloride tablet [29]. Alkalized plasma was extracted with isopropa-nol-n-hexane (3 97) and loratadine was used as internal standard (IS). Solutes were separated on a Cis column with a mobile phase of metha-nokacetate buffer (pH 4.0) (80 20). Detection was performed on a TOF mass spectrometry equipped with an electrospray ionization interface and operated in positive-ionization mode. Donepezil quantitation was realized by computing the peak area ratio (donepezil-loratadine) (donepezil m/z 380 [M + H]+ and loratadine m/z 383[M + H]+) and comparing them with calibration curve (r = 0.9998). The linear calibration curve was obtained in the concentration range of 0.1-15 jUg/1. The detection limit of donepezil was 0.1 /zg/1. The average recovery was more than 90%. The intra- and inter-run precision was measured to be below 15% of RSD... 

The availability of inductively coupled plasma mass spectrometry (ICPMS) has provided a method of detection of many impurities at very low concentrations directly in the organometallic compound itself. ICP mass spectrometry is a relatively recently developed chemical analysis technique that is useful in the detection of trace element concentrations in a liquid or solid matrix. ICPMS can measure the presence of almost all elements simultaneously, thus giving a detailed, semiquantitative picture of the impurity distribution in the sample. This technique has sensitivities for many elements in the parts-per-billion to parts-per-trillion range. It has the advantage that it is extremely sensitive and can analyze small samples (10 ml or less) of organometallics directly. The ICPMS technique employs a plasma to dissociate the material to be characterized into... 

---