Here we report results from the analyses by enzymatic digestion and reversed-phase ion-pairing liquid chromatography mass spectrometry (RPIP-LC-MS) of active pharmaceutical ingredient (API) unfractionated heparins (UFHs) from six different manufacturers and one USP standard sample. We employed a reverse phase ion-pairing chromatography method using a C(18) column and hexylamine as the ion-pairing reagent with acetonitrile gradient elution to separate disaccharides generated from the digestion of the heparins by lyase I and III (E.C. 4.2.2.7 and 4.2.2.8) before introduction into an ion-trap mass spectrometer by an electrospray ionization (ESI) interface. Extracted ion chromatograms (EICs) were used to determine the relative abundance of the disaccharides by mass spectrometry. Eight disaccharides were observed and a similar composition profile was observed from digests of 20 UFH samples. The compositional profile determined from these experiments provides a measure of the norm and range of variation in "good" heparin to which future preparations can be compared. Furthermore, the profile obtained in the RPIP-LC-MS assay is sensitive to the presence of the contaminant, oversulfated chondroitin sulfate A (OSCS), in heparin.

We present the design, guided by theory to eighth order, and the first evaluation of a Fourier transform ion cyclotron resonance (FT-ICR) compensated trap. The purpose of the new trap is to reduce effects of the non-linear components of the trapping electric field; those non-liner components introduce variations in the cyclotron frequency of an ion based on its spatial position (its cyclotron and trapping mode amplitudes). This frequency spread leads to decreased mass resolving power and signal-to-noise. The reduction of the spread of cyclotron frequencies, as explicitly modeled in theory, serves as the basis for our design. The compensated trap shows improved signal-to-noise and at least a three-fold increase in mass resolving power compared to the uncompensated trap at the same trapping voltage. Resolving powers (FWHH) as high as 1.7 × 107 for the [M + H]+ of vasopressin at m/z 1084.5 in a 7.0-Tesla induction can be obtained when using trap compensation.

We describe a method for tuning electrically compensated ion cyclotron resonance (ICR) traps by tracking the observed cyclotron frequency of an ion cloud at different oscillation mode amplitudes. Although we have used this method to tune the compensation voltages of a custom-built electrically compensated trap, the approach is applicable to other designs that incorporate electrical compensation. To evaluate the effectiveness of tuning, we examined the frequency shift as a function of cyclotron orbit size at different z-mode oscillation amplitudes. The cyclotron frequencies varied initially by ϳ12 ppm for ions with low z-mode oscillation amplitudes compared with those with high z-mode amplitudes. This frequency difference decreased to ϳ1 ppm by one iteration of trap tuning. (J Am Soc Mass Spectrom 2010, 21, 451-454) © 2010 Published by Elsevier Inc. on behalf of American Society for Mass Spectrometry F ourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) offers ultra high mass resolving powers and accurate mass measurements that surpass those of other methods. The trap serves as the heart of the instrument, allowing ions to be stored, fragmented, and analyzed. Ion motion in traps is confined in the radial direction by a strong homogeneous magnetic field, and in the axial direction by a three-dimensional quadrupolar electrostatic trapping well. As a consequence of the finite dimensions of the trapping-plate electrodes, the electrostatic trapping potential within the trap is only approximately quadrupolar. The resulting outwardly directed radial electric field (E r ) opposes the effect of the magnetic field and causes a shift in the observed cyclotron frequency of the ions and a procession of the ion clouds' guiding center (magnetron motion).A problem arises because the effect of the E r field is not constant, causing the observed cyclotron frequency to depend on ion-mode amplitudes within the trap. Among the efforts to design a trap in which the ion cyclotron frequency is independent of its mode amplitudes are those that attempt to eliminate the radial electric field by creating an electrostatic well shape that approximates a particle-in-a-box [1-9] (E r ϭ 0). Other strategies seek a design that more closely approximates the desired three-dimensional quadrupolar trapping potential [10 -15] (E r /r ϭ constant). The outcomes are traps with complex electrode shapes that follow the equipotential lines of a perfect, three-dimensional quadrupolar potential (i.e., a hyperbolic trap) and others with electrodes segmented into many parts to which individual compensation voltages are applied to shape the trapping potential.Our solution to this problem is an electrically compensated trap [10] whose implementation requires that correct voltages be applied to the electrodes to reduce the sensitivity of cyclotron frequency as a function of mode amplitudes (i.e., d /dA z,r ¡ 0). Despite our best efforts, the compensation voltages calculated by theory do not afford optimum performance, although we did find an imp...

We recently described a new electrically compensated trap in FT ion cyclotron resonance mass spectrometry and developed a means of tuning traps of this general design. Here, we describe a continuation of that research by comparing the ion transient lifetimes and the resulting mass resolving powers and signal-to-noise (S/N) ratios that are achievable in the compensated vs. uncompensated modes of this trap. Transient lifetimes are ten times longer under the same conditions of pressure, providing improved mass resolving power and S/N ratios. The mass resolving power as a function of m/z is linear (log-log plot) and nearly equal to the theoretical maximum. Importantly, the ion cyclotron frequency as a function of ion number decreases linearly in accord with theory, unlike its behavior in the uncompensated mode. This linearity should lead to better control in mass calibration and increased mass accuracy than achievable in the uncompensated mode.

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