A 7693A tower on a 7890B threw “ALS error 302: gripper failed to pick up vial” on position 47 of a 96-vial tray, twice in the same sequence, and then ran the rest of the tray clean. The analyst replaced the septum on that vial’s inlet, re-ran, and got the same error on a different position. The septum was never the problem. The tray had drifted about 0.8 mm in Z after a rail cleaning, and the gripper jaws were closing on the aluminium crimp skirt at an angle that let the vial slip about 1 in 40 picks. That ratio is exactly the kind of intermittent failure that gets blamed on the consumable.
Septa autosampler pickup error and misalignment almost never originate at the septum. They originate in the geometry between the tray, the gripper, the cap, and the needle guide. The septum is the last component in that stack, so it takes the blame when the stack is out of tolerance. This article is about the stack.
Every autosampler pickup is a four-body alignment: the vial body sits in a tray well, the cap sits on the vial, the gripper jaws close on the cap, and the needle later enters the septum through the cap’s centre hole. Any one of those four can drift. The septum only shows a symptom when the needle enters off-centre, and by then the misalignment has already happened upstream.
What you actually measure when you chase a pickup error is the position of the cap relative to the gripper, and the position of the septum relative to the needle guide. Those are two different dimensions. A gripper that picks the vial cleanly can still deliver it to the needle guide 0.5 mm off-centre, and that produces a coring pattern that looks like a bad septum lot. I have seen a lab replace three lots of septa before anyone put a dial indicator on the tray.
The four alignment dimensions that matter
- Tray Z-height (vertical): the distance from the tray floor to the gripper’s closed-jaw plane. Spec is usually ±0.3 mm on a 7693A or a TriPlus RSH; drift past 0.5 mm produces intermittent pickup failures.
- Tray X/Y registration: the lateral position of the well centre relative to the gripper home position. Spec is ±0.2 mm. Drift here produces consistent failures on one edge of the tray and clean picks on the opposite edge.
- Gripper jaw tolerance: the gap between the closed jaws. On a crimp cap with an 11 mm skirt, closed-jaw gap should be 10.6 to 10.9 mm; on a screw cap with a 9 mm thread, 8.6 to 8.9 mm. Worn jaws open up by 0.3 to 0.5 mm over about 200,000 picks.
- Cap seating depth: how far the cap skirt sits down over the vial neck. A crimp that is 0.4 mm high seats the septum 0.4 mm high, and the needle guide clearance disappears.
If you can only check one dimension, check tray Z-height. It is the one that drifts first, it is the one that produces the intermittent pattern, and it is the one most labs never measure because the instrument does not report it.
What each error code is actually telling you about alignment
Autosampler error codes are not interchangeable. Each one points at a specific dimension. I keep this mapping taped inside the service panel on every tower in the lab, because the codes are not consistent across vendors and the manual does not spell out the alignment implication.
| Instrument | Error code / message | Most likely alignment cause | First measurement |
|---|---|---|---|
| Agilent 7693A / 7693 | ALS error 302: gripper failed to pick up vial | Tray Z-height drift, or gripper jaw gap > 11.0 mm | Tray Z-height with a depth gauge at the well |
| Agilent 7693A | ALS error 303: vial not detected in gripper | Cap seated high (crimp not fully formed), or jaw worn | Cap skirt height on 10 random vials |
| Agilent 7693A | ALS error 304: gripper failed to release vial | Jaw gap < 10.4 mm (over-tight), or cap skirt out of round | Jaw gap at closed position |
| Thermo TriPlus RSH | “Vial not found in tray” | Tray X/Y registration drift, or well insert missing | Well centre position vs. gripper home |
| Thermo TriPlus RSH | “Vial transport error” | Gripper jaw gap, or cap not seated | Jaw gap, then cap seating depth |
| Shimadzu AOC-20i / 20s | “Vial pick-up error” | Tray Z-height, or needle guide misalignment | Tray Z-height, then needle guide concentricity |
| Waters 2707 / 2777 | “Vial transfer failed” | Gripper jaw gap, or tray well wear | Jaw gap, then well diameter |
The pattern to watch for: if the same code fires on the same tray position, the problem is local (a worn well or a bent cap). If the code fires on random positions, the problem is global (tray Z-height, gripper jaw gap, or needle guide concentricity). Random-position failures are the ones that get misattributed to the septum, because the analyst sees a different vial each time and assumes the consumable is inconsistent.
Cap seating is where most “septa failures” actually start
A crimp cap that is not fully formed sits high on the vial neck. The septum sits high with it. The needle guide then has less clearance than the design allows, and the needle enters the septum at an angle. That angle produces an off-centre puncture, and an off-centre puncture produces coring on the next injection. The analyst sees coring and blames the septum. The cap was the cause.
Two numbers matter here. First, crimp skirt height: on an 11 mm aluminium crimp cap, the formed skirt should sit 6.3 to 6.6 mm below the top of the cap after crimping. A skirt at 6.9 mm is high and will cause pickup and needle-entry problems. Second, crimp force: most bench crimpers are set to 2.5 to 3.5 bar of applied force depending on the cap style; a crimper that has drifted to 2.0 bar produces high skirts on about 5 to 8 percent of vials, which is exactly the intermittent pattern that gets blamed on the consumable.
For screw caps, the equivalent number is torque. A screw cap on a 9 mm thread should be tightened to 0.9 to 1.2 N·m. Below 0.8 N·m the cap sits high and the septum is not compressed. Above 1.5 N·m the cap can distort the vial neck and the septum can extrude. I have watched a lab torque a whole tray to 2.0 N·m “to be safe” and then wonder why every fifth vial produced a pickup error. The caps were fine. The torque was not.
How to measure cap seating in under a minute
Take ten vials from the tray at random. Set a depth gauge on the vial base and measure to the top of the cap. The reading should be consistent to ±0.15 mm across all ten. If the spread is wider than that, the crimper or the torque driver is the problem, not the vial septa. This is the single fastest diagnostic in the whole alignment workflow and almost nobody runs it.
Gripper tolerance: the dimension that wears silently
Gripper jaws are a wear item. They close on an aluminium crimp skirt about 200,000 times over a typical two-year service life, and the jaw faces polish and open up. The instrument does not report jaw wear. It reports pickup failures, and only after the jaw gap has drifted past the point where the vial slips.
The measurement is simple. Open the gripper to its service position, close it on a gauge block or a calibrated pin, and measure the gap with a feeler gauge. On an 11 mm crimp cap, the closed-jaw gap should be 10.6 to 10.9 mm. If it reads 11.0 mm or more, the jaw is worn and the vial will slip under load. If it reads 10.4 mm or less, the jaw is over-closing and will distort the cap skirt, which produces a different failure: the vial is picked but not released.
Replacement jaws are inexpensive and take about 20 minutes to fit. I have seen labs spend more than the cost of a jaw set on replacement septa in a single quarter because nobody measured the jaw gap.
Two field cases where the septum was innocent
Case 1: the tray that drifted 0.8 mm in Z
Symptom: a 7693A on a 7890B threw ALS error 302 on random positions, about 1 in 40 picks, always after a sequence of more than 60 vials. The error never repeated on the same position. The analyst had replaced two lots of septa and one lot of caps before calling me.
Measurement: I put a depth gauge on the tray floor at four corners and the centre. The front-left corner read 0.8 mm lower than the rear-right. The tray rail had been cleaned two weeks earlier and not re-seated to the detent. The tray was sitting on the rail at a slight angle, so the Z-height at the far end of the tray was out of spec by the time the sequence reached position 47.
Fix: re-seat the tray to the detent, re-check Z-height at four corners, confirm ±0.3 mm across the tray. The error stopped. Total time: 15 minutes. Total cost of the misdiagnosis: two lots of septa and about four hours of analyst time.
Case 2: the crimper that drifted to 2.0 bar
Symptom: a TriPlus RSH threw “vial transport error” on about 6 percent of vials, always on vials from a specific crimped batch. The lab had switched to a new box of autosampler vial caps and assumed the caps were out of spec.
Measurement: I measured cap skirt height on 20 vials from the batch. The mean was 6.8 mm, with a range of 6.6 to 7.0 mm. Spec is 6.3 to 6.6 mm. The crimper had drifted to 2.0 bar applied force. Every cap in the batch was high by about 0.3 mm.
Fix: re-set the crimper to 3.0 bar, re-crimp the batch, re-measure. Skirt height came back to 6.4 to 6.6 mm. The transport errors stopped. The caps were fine. The crimper was not.
Needle guide concentricity: the dimension that hides behind the septum
The needle guide is a small metal or polymer insert above the septum that centres the needle as it descends. If the guide is off-centre relative to the vial, the needle enters the septum at an angle. That produces an off-centre puncture, and off-centre punctures produce coring on the next injection. The analyst sees coring and replaces the septum, and the coring comes back on the next vial.
The measurement is a concentricity check. Drop a 0.5 mm gauge pin through the guide with a vial in place and confirm it enters the septum within 0.3 mm of the septum centre. If it enters further off-centre than that, the guide is misaligned or the vial is not seated squarely in the well. Both are alignment problems, not consumable problems.
This is the one dimension where the septum genuinely can contribute, but only if the septum is the wrong thickness for the cap. A 3.0 mm septum in a cap designed for a 1.5 mm septum sits proud and shifts the effective needle entry point. Check the septum thickness against the cap’s design spec before you blame the guide. The HPLC vial cap geometry is not universal across vendors, and a mixed box of caps and septa is a common cause of exactly this failure.
What the instrument manufacturers actually specify
The alignment tolerances are documented, but they are scattered across service manuals and installation guides rather than the user manual. The Agilent chromatography consumables and columns documentation gives tray Z-height and gripper tolerances in the service section. The Thermo Fisher chromatography and sample handling guides give the TriPlus RSH alignment procedure. The Restek technical resources are useful for the cap and septum dimension side of the stack, particularly the crimp and torque specs. None of these sources put the four dimensions in one place, which is why the misdiagnosis is so common.
For regulated work, the alignment check belongs in your preventive maintenance schedule, not in your troubleshooting workflow. A tray Z-height check every 500 hours of instrument time and a gripper jaw gap check every 1,000 hours will catch the drift before it produces a pickup error. That is a 15-minute check twice a year on a typical instrument, and it eliminates most of the intermittent failures that get blamed on the consumable.
A troubleshooting checklist for pickup errors and misalignment
Work through this in order. Do not skip to the septum.
- Read the error code. Match it to the table above. Note whether it fires on the same position (local) or random positions (global).
- Check tray Z-height at four corners and the centre. Spec is ±0.3 mm. Drift past 0.5 mm produces intermittent pickup failures.
- Check tray X/Y registration. Spec is ±0.2 mm. Drift produces failures on one edge of the tray.
- Measure gripper jaw gap at closed position. Crimp cap: 10.6 to 10.9 mm. Screw cap: 8.6 to 8.9 mm.
- Measure cap skirt height on 10 random vials. Crimp: 6.3 to 6.6 mm. Spread should be ±0.15 mm.
- Check crimper force or torque driver. Crimp: 2.5 to 3.5 bar. Screw cap: 0.9 to 1.2 N·m.
- Check needle guide concentricity. Gauge pin should enter septum within 0.3 mm of centre.
- Check septum thickness against cap spec. A 3.0 mm septum in a 1.5 mm cap is a misalignment cause, not a consumable cause.
- Only now check the septum lot. If all eight measurements above are in spec and the pickup error persists, the septum is a candidate. It is rarely the answer.
For reference on the regulatory side, U.S. EPA SW-846 test methods for waste and materials does not specify autosampler alignment, but it does require that sample integrity be maintained through the analytical sequence. A pickup error that causes a re-run is a data integrity event, and the alignment check is the evidence that you controlled it. Write the check into the method validation and into the PM schedule.
Decision rule
When a pickup error or misalignment symptom appears, measure the tray Z-height and the gripper jaw gap before you touch the septum. If both are in spec, measure the cap skirt height and the crimper force. If those are also in spec, measure the needle guide concentricity. Replace the septum only after all four measurements have ruled out the alignment stack. The septum is the last component in a four-body alignment, and it is almost never the one that drifted.
References & further reading
Related resources from our lab consumables network:
- Septa at septacaps.com
- Vial Septa at vialsepta.com
- Hplc Vial at hplcgc.com
- Autosampler Vial at autosamplerhplc.com
External references and standards:
