Time data acquisition rates

If the LC part is optimized to deliver peaks in a shorter time or more peaks in the same time when compared to a conventional method, we must consider the system s ability to handle data. Because the speed optimization described above will produce much narrower peaks, widths below 1 sec can be achieved easily. However, the data acquisition rate and data filtering steps must be considered. 

Careful setting of the scan range is recommended. The narrower the scan range, the higher the number of data points per peak. This is not necessarily a linear relation it can depend on the MS. If a large mass range and fast data acquisition rate are required, a time-of-flight (ToF) MS would be... 

MS operated at 20 to 40 Hz data acquisition rates in centroid or profile mode and at a mass range of 900 amu. The resulting cycle times varied from 49 to 62.22 The longest system overhead time was 21 sec and the shortest was 8 sec—a difference of 260 percent Translated into throughput, the difference equals almost 400 samples per day ... 

It is important to ensure that the data collection rate is fast enough for peaks with low retention times in order to ensure good reproducibility of all peak parameters. For modern instrumentation, this is generally not a problem for example, FID detectors are typically able to achieve a data acquisition rate of 50-250 Hz using the standard instrument configuration. 

We next develop a method to estimate the data acquisition rate necessary to measure a first-order rate coefficient to a specified accuracy. The probability distribution of the signal pulses in time (with no background) is given by... 

Hardware. To employ the IDA, the user must supply a clock signal, a begin scan signal, and data acquisition hardware. The hardware to accomplish this has been based on a PDP 11/20 minicomputer or a KIM microcomputer plus additional external hardware (13-15). The clock signal determines the rate at which the diodes are interrogated during readout and was 33 kHz with the minicomputer and 125 kHz with the microcomputer. This means the time to read out all 512 diodes and hence the minimum integration time varies from 15 ms to 3.7 ms, respectively. For the microcomputer, direct memory access (DMA) circuitry was used to increase the data acquisition rate. 

The NMRI technique uses an induction coil surrounding the sample to image nuclear spin density that results from the nuclear spin system rearrangement. An initial magnetic pulsed field orients the nuclear spin system and then it relaxes back toward a random state. Because of the relaxation time and that tomographic reconstruction is needed to extract the 3-D details, there are time limitations (Altobelli et al., 1992) (currently of the order of 10-ms, at best). Consequently, the technique has been used mostly for steady or quasi-steady laminar flows because of the rather low data acquisition rate. However, modifications to allow turbulent and unsteady flows to be investigated have been reported and new... 

The advantages of on-line computer operation, then, include elimination of the middle man by substituting an electronic interface, possible direct computer control of the experiment, and possible real-time interaction between the computer and the experiment. Because the computer can make computations and decisions at speeds exceeding most ordinary data-acquisition rates, it can modify the experimental conditions during the experiment. An additional advantage, of course, is that the logistic barriers of the remote computer system are eliminated. 

A similar mass spectrometric detection system is available commercially and is realized by a multiplexing electrospray inlet in combination with a time-of-flight (TOF) mass spectrometer that has a sufficiently high data acquisition rate. Like the above-described optical switch, the effluent of the HPLC channels is nebulized in individual probe tips and sprayed toward a rotating cylinder with a slit. By stepping this slit very rapidly from one probe tip to another, again a data acquisition rate of approximately one spectrum per channel can be reached in 1 second. Unlike the multiplex PDA detector, this multiplex mass spectrometric detector is normally connected to a HPLC system by a flow splitter. ... 

Figure 3 (A) Single-column GC analysis result. (B) Selected incompletely resolved heartcuts from A are directed to a second column where improved separation is achieved. Here two heart-cuts are performed. (C) Illustration of multidimensional analysis GC/MS, where the second dimension is a mass spectrum recorded at the mass spectral data acquisition rate. The success of this approach depends on the uniqueness of the mass spectrum at each point in the chromatogram. (D) The comprehensive two-dimensional GC method ideally spreads out the components in a two-dimensional space, according to the characteristics of each of the columns. Each component has a characteristic D and D retention time in the plane.

---