4800 Mass Spectrometer MI Optics Tuning Manual
Applied Biosystems/MDS Sciex internal training notes (company confidential, for internal use only). 54 pages, version A07 with narration notes. Authors: Frank J Mello (MALDI TOF/TOF North America Territory Specialist), Bill Loyd (MDS Sciex R&D), Serguei Raspopov (GSSC Service Product Manager). ~2008-era engineer tuning guide for MI Optics hardware upgrade.
What is MI Optics
“Manufacturing Improved Optics” — factory ion optics improvements shipped starting January 2008, first covering serial numbers 205/207/247 onward. Delivers Reflector resolution and MSMS fragment resolution improvement, and resolved Source 1 charging during polarity switching.
Three hardware change families:
- 2-Stage Mirror: second-generation uni-directional grid material (fine uni-directional wires, not traditional 90-degree crossing grid). Not retrofitted to old systems, but when a mirror is replaced on an old system, the MI part ships (P/N 1026871 “FRU, Reflectron Mirror”). Installing it changes tuning characteristics.
- Source 2 / CID region: Source 2 resistor network changed from pogo pin to micro-jacks (resistor legs inserted directly into Source 2 Grid plates); internal dimensioning of Source 2 and CID region modified.
- Source 1 Lens redesign: lens now epoxied into a single insulator encircling it (moved away from ion beam, eliminating charging off insulator); Ground Lens flush-mounted, no thickness gauge needed. Upgrade kit P/N 1030966 “FRU, 3 Stage Source 1 Upgrade, 2008”.
Reflector Mode Tuning (5 parameters, in order)
Order: Manual DE1 -> Lens 1 -> M2/S1 ratio -> Mirror 1 voltage -> G/S1 ratio. With MI optics, Decel and Mirror Deflectors are usually no longer needed.
| Parameter | MI default/start | Range | Notes |
|---|---|---|---|
| DE1 time | 600 ns (assuming G/S1=80%) | 500-750 ns | Must be “Manual Enable”; set before other params |
| Lens 1 | 3.0 kV | 1.5-5.0 kV | Lower values improve resolution, higher values improve signal |
| M2/S1 ratio | 1.090 (old optics 1.020) giving M2=21.8 kV | step 0.005 | Controls peak symmetry: 1.050 high-mass tail, 1.130 low-mass tail, 1.100 roughly symmetrical |
| Mirror 1 voltage | manual centering | fine 3V (0.003 kV) steps | Lowering M1 shifts resolution center UP the mass axis (inverse-linear, opposite of intuition) |
| G/S1 ratio | 80% (Grid 16.0 kV @ Source1 20 kV) | 77-83% typical | Higher ratio “narrows” resolution curve; lower ratio “broadens” it. At 77% all masses pass FSU with margin |
Universal iron rules: X1 Deflector ALWAYS set to 0.000 kV — do not tune it, align laser beam to center of extraction aperture instead, then adjust X2 for max signal (all modes). Note the 4800 X-deflectors move beam front-to-back (not side-to-side), opposite of 4700/Voyager.
Installation acceptance specs: Reflector m/z 1296>12500, 1570>14000, 2093>17000, 2465>17000, 3657>12500. MSMS m/z 175>2000, 684>3000, 1056>3500, 1441>5000.
MSMS 1 kV Tuning
Tune fragment resolution first, then TIS. Parameter order: Lens 3 -> Lens 1 -> S1 Voltage Divider -> S1 Offset -> M2/S2 -> Mirror 1 -> S1 Lens -> Collision Cell Offset.
| Parameter | MI default | Range | Notes |
|---|---|---|---|
| Lens 3 | 2.0 kV (old optics 1.0) | 1.0-3.5, typical 2.0-3.0 | Strong effect on fragment resolution AND fragment ratios; re-optimize after other params |
| Lens 1 | 2.7 kV (old 2.4) | 2.4-3.6 | Affects fragment resolution/intensity/TIS resolution; may need +/-0.1 kV re-tune after TIS |
| S1 Voltage Divider | 1.008 (old 1.006) | 1.007-1.009 | Primary modifier of DE2 (Source 2 pulse); wrong value makes MSMS impossible to tune. S2 Voltage Divider NEVER adjust, always 1.000 |
| S1 Offset | 0.000 mm | -0.2 to +0.2 mm | Primary modifier of DE1 (Source 1 pulse); also sets ion focus in TIS gate. 0.100 mm increase -> TIS Offset must decrease 0.250 mm. Properly optimized for fragment resolution is usually close to the proper TIS value automatically |
| M2/S2 ratio | 1.1833 (same as old optics) | — | Primary control of fragment resolution curve broadness/narrowness |
| S1 Lens | 3.2 kV | raised with Lens 1 | Lens1<=2.7 -> 3.2; 2.7-3.0 -> 3.3-3.5; >3.0 -> 3.4-3.6 |
| CC Offset | -0.040 | -0.030 to -0.050, step 0.005 | Mis-tune shows as 175 m/z peak splitting (-0.020 splits into two peaks but full-spectrum looks like “better” resolution — highly deceptive); 175/1056 ratio drops from 44% to 23% |
TIS (Timed Ion Selection) tuning — acceptance criteria
- High/Low Mass TIS Distance geometry once set for 1 kV must NOT be changed for 2 kV or Negative mode. Typical properly-tuned gap between High and Low TIS Distance: 3.5-5.5 mm
- Healthy TIS Mixture signature: at Relative Resolution 50, 1296 shows low-mass tailing and 1302 shows high-mass tailing; at Relative Resolution 400 the tailing reverses, 1296 is clearly lower than 1297, and 1302 is clearly higher than remaining 1303 -> indicates good ion packet segregation and precursor selectivity
- Metastable Suppressor: adjust Propagation Delay for tracking (increase Delay must accompany increase Distance, e.g. 75 ns->135 ns pairs with Distance 996->998.5 mm). Acceptance check: Angiotensin 1183/1296 and ACTH 1326/2465 ratios equal in both spectra
MSMS 2 kV Tuning
Prerequisite: all 1 kV tuning passed acceptance before 2 kV (beam path to TIS gate is identical).
- Copy directly from optimized 1 kV mode: Source 1 Focus through Decel deflectors, Lens 1, S1 Offset, TIS Offset (TIS Offset may need slight tweak if S1 Voltage Divider changed)
- Must re-optimize: Lens 3 (MI default 4.0 kV, range 3.5-5.0), S1 Voltage Divider (tunes about 0.001-0.002 higher than 1 kV), M2/S2 (MI puts 2 kV closer to 1.210 vs old optics 1.250; typical range 1.190-1.230), M1, CC Offset, Metastable Offset/Voltage. S1 Divider / LM3 / M2-S2 / M1 require multi-round iteration
- 2 kV-specific phenomenon — neutral loss species (water or ammonia losses, e.g. Angiotensin 1279, Glu-Fib 1552): MSMS process products, NOT on-plate degradation. Loss species can dominate over precursor, interfering with Metastable Suppressor setting. Correction: lower Metastable Suppressor voltage from default 1000 V to 350-550 V AND compensate Metastable Offset negatively (extreme case: 450 V + Offset -1.6 mm almost removes loss species but precursor isotopic resolution degrades — take a balanced value in practice)
Implications for instrument software / automated tuning (relates to 4800-MALDI-TOF电气系统总览-ServiceGuide第7章)
- Tuning is a strongly order-dependent parameter graph with feedback loops (S1VD / Lens3 / M2S2 / M1 iterate with each other) — software wizards should NOT be linear one-shot forms; must express iteration and linked compensation (the S1 Offset : TIS Offset 0.100mm : -0.250mm fixed mapping is directly automatable)
- Multiple “NEVER TOUCH” red-line params (X1=0.000 kV, S2 Voltage Divider=1.000) — software should hard-lock these
- “looks better but is a trap” cases (CC Offset -0.020 fake high 175 resolution) show that monitoring only peak resolution misleads — auto-tuning must simultaneously watch fragment ratios and zoomed peak shape
- Default values differ by hardware generation (M2/S1 1.020->1.090 etc.) — software needs hardware-generation-aware config archive; old systems retrofitted with MI mirror MUST re-run full tuning