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SIS AP2000 AutoProbe™ - Description of System

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New Automated Direct Insertion Probe for the PolarisQ™ and TRACE DSQ™ Mass Spectrometers from Thermo Electron Corp.

SIS AP2000 attached to the PolarisQ or TRACE DSQ.

The AutoProbe™ System is an Automated Direct Exposure Probe (DEP) for the Finnigan PolarisQ™ and TRACE DSQ™ Mass Spectrometer Systems. The AutoProbe™ System injects samples directly into the MS source for mass spec sample analysis with no chromatographic separation. This permits samples to be analyzed in 3 minutes or less. The AutoProbe™ operates in the Thermo Finnigan Xcalibur™ MS Software environment and is fully integrated with the Xcalibur™ software, including system setup, methods setup, system operation and data storage.

The direct probe was one of the earliest techniques used to introduce samples into a mass spectrometer. The technique is still popular today because it provides a means to perform rapid sample analysis with minimal or no sample preparation. The electron impact (EI) mass spectrometer mode of operation can be used when the sample to be analyzed is relatively pure or when chromatographic separation of a mixture is not required. Direct probe analysis has also been widely used with Chemical Ionization (CI) mass spectrometry. The simplicity of the CI spectrum permits the analysis of mixtures, whose spectra are difficult to interpret using the EI mode of operation.

Applications of the direct probe technique include the screening of drug and pharmaceutical samples, quality control sample analysis, spot analysis of chemical reaction mixtures to monitor rates of synthesis, and the analysis of compounds which cannot be chromatographed. The AutoProbe System is used where high volumes of samples need to be analyzed quickly or it can be used in an "Open Access" environment where it can be used by multiple users with minimal MS expertise.

Figure 2 - AutoProbe System Components

  1. Linear Thrust Column
  2. Probe Rod
  3. DEP Probe Tip
  4. MS Probe Interface
  5. Isolation Valve Assembly
  6. Electronic Vacuum Gauge Pressure Sensor
  7. Isolation Valve Relay Switches
  8. Filament Current Controller
  9. Relay
  10. CTC Power Supply
  11. AutoProbe Microprocessor Controller
  12. Servo Controller for Linear Thrust Column
  13. Electronic Manifold
  14. Autosampler Syringe
  15. CTC PAL column

Figure 3 - AP2000 AutoProbe DEP Probe Tip (Plug in Replaceable Tips)

The Direct Exposure Probe (DEP) uses a platinum wire on the end of a probe for the analysis of samples. Samples for analysis are dissolved in a suitable solvent and 0.125 to 1.0 ul of the prepared sample solution is injected onto a small platinum wire loop on the tip of the probe. After the probe has been inserted into the mass spec source, the platinum wire is heated with a small current to desorb the sample into the mass spec source for analysis. This DEP probe filament can be set to a constant current or can be programmed in up to three ramp steps. This versatility of analysis enables the user to optimize the analysis depending on the sample being analyzed.

The DEP or DCI technique is used for the analysis of samples that are not volatile enough to be introduced into the mass spectrometer via a GC and therefore must be directly introduced into the mass spectrometer source. This technique is known as a 'soft' ionization technique in which thermally labile samples can be ionized with less fragmentation compared to conventional EI (Electron Impact) mass spec analysis. A typical DEP analysis can be completed in 1 to 3 minutes. However, the technique is normally used for single component samples since minimal separation of samples is possible with this technique and samples with 2 or more components may be difficult to interpret.

Frequently DEP sample analysis is performed utilizing CI (Chemical Ionization) mass spectrometer techniques, which produces less fragmentation in the mass spectrometer. Due to the increased abundance of a molecular ion and reduced fragmentation in the CI techniques, it is possible to analyze and interpret mixtures of two or more compounds in a sample with this technique.

Figure 4 - Injection of Sample onto the DEP Probe via the CTC Autosampler syringe

A CTC PAL Autosampler is interfaced to the AutoProbe. A wide range of sample trays can be fitted to the CTC PAL Autosampler from which the samples can be loaded onto the DEP probe wire via a syringe. The system permits the cleaning of the syringe between samples. The system also permits the accurate and reproducible delivery of 0.125 to 1.0 ul samples onto the DEP Probe wire.

The AutoProbe adds the dimension of automatic sample loading and unattended analysis to the DEP probe technique. Samples can be analyzed at the rate of 2.0 to 5.0 minutes per sample. Sample analysis time can vary, but a typical sample analysis time is composed of the steps listed below:

1. Position Probe for Sample Loading 15 seconds
2. Load Sample onto Probe Tip 30 seconds
3. Solvent Removal 10 seconds
4. Take probe through isolation valve and into MS source 35 seconds
5. DEP analysis of sample 45 seconds
6. Clean Probe tip with high temperature bakeout 15 seconds
7. Return Probe to position for next sample analysis 30 seconds

TOTAL ANALYSIS TIME   180 seconds (3.0 minutes)

The above typical analysis above requires 3 minutes per sample. However several of the steps can be increased or decreased, depending on the samples being analyzed.

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Figure 5 - Thermo Finnigan Xcalibur Instrument Configuration Window

The AutoProbe is software controlled and fully integrated within the Thermo Finnigan Xcalibur MS software. The AutoProbe is set up in Xcalibur as an accessory instrument in the Instrumentation Configuration Window. The method parameters for the operation of the AutoProbe, including ramp rates and times of other system parameters, are entered into data screens controlled within the Xcalibur system software.

Figure 5 - AutoProbe Method Setup Window for entering probe operational parameters

AutoProbe samples for analysis are placed into sample vial blocks on the CTC PAL Autosampler (Figure 4). A syringe picks up the sample and delivers it to the injection area on the Autoprobe console top. The syringe then injects the sample onto the wire loop at the end of the DEP probe tip.

Figure 6 - Injection of sample onto the DEP wire coil

The standard sequence of operation of the AutoProbe system is as follows.

1. Samples are prepared in solution in a concentration range between 1 ng/ul and 1000 ng/ul.
2. The operator sets up a sequence of samples, methods, and processing actions in Xcalibur and starts a run.
3. The Xcalibur software signals the AutoProbe, CTC PAL Autosampler, and MS to prepare for an analysis.
4. The DEP probe moves to the load position.
5. Xcalibur signals the CTC PAL Autosampler to begin a sample run by loading a selected sample.
6. Between 0.125 ul and 1.0 ul of sample are injected onto the DEP filament wire.
7. After the sample is injected onto the DEP filament, the solvent is evaporated from the sample in air. (Alternately, the solvent may be evaporated later inside the vacuum or not at all.)
8. The probe moves to the first vacuum seal, and the electric solenoid valve opens to evacuate the probe inlet.
9. After the vacuum reaches 200 millitorr (adjustable), the probe moves to the second vacuum seal, and the pneumatically controlled ball valve opens. (If a leak occurs, the sequence is paused, the AutoProbe resets itself, and an error is recorded on the log window.)
10. The probe moves to its final position against the MS source. The MS is signaled to begin scanning just before this position is reached.
11. The Xcalibur software downloads the DEP filament current values to the AutoProbe controller and the filament begins its temperature ramp. (The AutoProbe can do up to three filament ramps.)
12. The MS stops scanning and collecting data once the filament ramps are complete.
13. The probe moves away from the MS source about 1" and does an optional filament bakeout to clean the DEP wire and prepare for the next sample.
14. After bakeout, the probe moves to the second seal in the isolation valve, the pneumatic ball valve closes, and the electric solenoid closes.
15. The probe returns to its home position and waits for the signal for the next sample.
Sample Analysis

Figure 7 - AutoProbe Analysis of Caffeine Sample (AP1000 on the TRACE MS)