A customer sent me a datasheet last month where the residual volume was listed as “< 0.5 mL.” That is not a specification. That is a wish. The sheet had no method line, no sample size, and no statement of whether the figure came from a gravimetric check on 30 vials or a single caliper pass on one. When I asked, the answer was “typical.” That vial cost $0.31 less than ours per unit, and the customer had already failed a USP <621> system suitability check twice on a 1.5 mL fill because the actual residual was 0.61 mL on the worst vial in the tray.
Reading a voa vial datasheet is a skill, and most buyers do not have it. The specifications and what each value means on a volatile organic analysis vial sheet are not uniform across suppliers. Some lines are measured on every lot. Some are measured once at qualification. Some are copied forward from a mold drawing and never checked again. This guide is about telling those apart before you sign a purchase order.
I have written and audited more of these sheets than I care to count. Here is how I read one now, line by line.
Every number on a datasheet falls into one of three categories, and the sheet almost never labels them for you.
- Guaranteed (specification): a limit the supplier commits to, with a stated test method, sample size, and acceptance criterion. If a lot fails, you have recourse. Example: “Residual volume ≤ 0.40 mL, gravimetric, n=30 per lot, 20 ± 2 °C.”
- Typical (nominal): a central value from qualification or historical data with no lot-by-lot guarantee. Example: “Residual volume 0.30 mL typical.” You cannot reject a lot against this.
- Nominal (drawing value): the dimension on the mold print. Example: “Body OD 22.5 mm.” This is what the tool was cut to, not what came out of the press last Tuesday. Glass shrinks and warps; the drawing is the intent, not the result.
If a sheet says “22.5 mm” with no tolerance band and no inspection note, treat it as nominal. If it says “22.5 ± 0.2 mm, verified per lot by go/no-go gauge,” that is a specification. The gap between those two statements is where most purchase disputes live.
A well-built voa vial sheet will tell you which category each line sits in. A weak one will blur them so that every number looks equally firm. When in doubt, ask the supplier to mark each line G, T, or N. A good one will do it without complaint. A bad one will send a revised PDF that still does not say.
The dimensional lines: which are gauged and which are drawn
Dimensions are the easiest place to hide a nominal value behind a decimal point. Here is what to look for on each line.
Crimp finish (GPI 13-425, 15-425, 18-400, 20-400, 24-400)
The GPI finish number is a standard, not a measurement. 13-425 means 13 mm thread diameter, 425 thread finish. The supplier either conforms to the Glass Packaging Institute drawing or they do not. Ask for the conformance statement, not the number. A sheet that lists “13-425” with no reference to the GPI drawing is telling you the mold was cut to that spec, which is not the same as saying the finished vials pass a thread gauge. I have seen lots where the thread pitch was off by enough to cause septa to skew under the crimper, and the sheet still said “13-425.”
For a 20 mL headspace or VOA vial, the finish is almost always 18 mm or 20 mm crimp, and the corresponding septa and caps come from the same supply chain. If you are matching caps, the septa supplier should be able to quote the same GPI drawing number. Mismatched finishes are the number one cause of crimp leaks I see in the field.
Body OD and height
These are the lines most often nominal. A “22.5 mm OD” on a 20 mL vial is the mold dimension. Real production runs ±0.15 to ±0.30 mm depending on the glass supplier and the gob weight. If your autosampler tray has a 22.7 mm pocket, you need the upper tolerance, not the nominal. Ask for the actual measured range on the last three lots. If the supplier cannot produce it, they are not measuring.
Height matters for the same reason. A 20 mL vial at 75.5 mm nominal will vary ±0.4 mm easily. If the autosampler gripper references the bottom of the vial, that variance can translate to a 0.4 mm offset at the needle, which is enough to bend a 23-gauge needle on a hard stop.
Neck OD and crimp ring diameter
These are the dimensions that determine whether your crimper seats properly. The crimp ring diameter on an 18 mm finish should be 17.5 to 18.1 mm depending on the cap style. If the sheet lists only the nominal, you cannot predict whether the crimper will over- or under-crimp. Under-crimp leaks under pressure; over-crimp cracks the glass at the neck. Both show up as failed blanks on the GC, not as visible defects.
The volume lines: residual, fill, and headspace are not interchangeable
Volume is where datasheets lie most often, and where the consequences are most expensive.
Residual volume
Residual volume is the volume left in the vial after the sample is poured out under a defined protocol. The protocol matters: drain time, drain angle, temperature, and whether the vial was shaken all change the answer. A sheet that says “< 0.5 mL” without stating the protocol is not a specification. A useful line reads: “Residual volume ≤ 0.30 mL, gravimetric, drained 30 s at 45° from vertical, 20 ± 2 °C, n=30.”
If you are doing SW-846 work with 40 mL VOA vials, residual volume directly affects the dilution you can claim. A 0.5 mL residual on a 40 mL vial is a 1.25% carryover. On a 5 mL sample that is significant.
Fill volume and headspace
Fill volume on a VOA vial sheet is usually nominal. The useful number is the headspace, because that is what the GC sees. A 20 mL vial filled to 15 mL leaves 5 mL headspace plus the septa dome. If the sheet says “20 mL capacity” and nothing else, you have no idea what headspace you will get at your working fill. Ask for the headspace at your target fill volume, measured, not calculated.
Graduation accuracy
If the vial is graduated (some 10 mL and 20 mL VOA vials are), the graduation tolerance is a specification you should demand. A typical line reads “± 0.20 mL at 10 mL.” Anything looser than that and the graduation is decorative.
Septa and closure lines: the part of the sheet that gets skipped
The closure specifications are often on a separate sheet or a footnote, and that is exactly where the failures hide.
Septa thickness and durometer
A standard 20 mm silicone/PTFE septa is 3.0 mm thick with a 45 ± 5 Shore A durometer. If the sheet lists thickness but not durometer, you cannot predict crimp behavior. Soft septa (35 Shore A) seat easily but extrude under pressure. Hard septa (55 Shore A) hold pressure but need more crimp force and tend to coring under a needle. The vial septa you choose should be matched to your crimper setting and your autosampler needle gauge.
Puncture count
Puncture count is a specification that most sheets do not list, and it should. A silicone septa rated for 10 punctures with a 22-gauge needle at 2 mm/s will start leaking at puncture 8 in my experience. A PTFE-faced silicone septa rated for 5 punctures on the same needle will hold to 5 reliably. If the sheet says “multi-puncture” with no number, it is a marketing claim, not a spec. Ask for the test method: needle gauge, puncture speed, and leak criterion (usually < 0.5 psi drop over 30 s at 15 psi).
Closure torque and crimp force
For screw-thread VOA vials (some 10 mL and 20 mL formats), the sheet should state a torque range. 0.8 to 1.2 N·m is typical for a 13-425 screw cap with a PTFE-lined septa. Below 0.8 N·m you get leaks under autosampler pressure; above 1.2 N·m you crack the neck. For crimp vials, the sheet should state a crimp force range in newtons or a crimper setting. If it does not, you are guessing.
Chemical and thermal lines: the ones that are almost always nominal
Temperature ratings and chemical resistance claims are the least-tested lines on most sheets. Here is how to read them.
Temperature rating
A “usable to 200 °C” line on a VOA vial sheet is usually a material claim, not a test result. Borosilicate 3.3 glass softens around 820 °C, so 200 °C is trivially within range for the glass. The real question is the septa and the cap. A silicone septa rated to 200 °C will outgas heavily above 150 °C, which contaminates your headspace. If the sheet lists a single temperature for the whole assembly, it is wrong. Ask for separate ratings for glass, septa, and cap, and ask what test (thermogravimetric, or a headspace blank at temperature) supports each.
Chemical resistance
“Resistant to most solvents” is not a specification. A useful line names the test: “24 h immersion in methanol at 40 °C, no weight change > 0.5%, no extractables > 10 µg/mL by GC-MS.” If the sheet has no test, treat the claim as nominal.
Spotting a sheet that hides its test method
Here is my checklist. If a sheet fails three or more of these, I do not buy from that supplier without a lot-by-lot COA and a first-article inspection.
- No method column. Every guaranteed value should name the test (gravimetric, go/no-go, optical, GC-MS) and the sample size.
- No sample size. “n=1” and “n=30” are different products. A sheet without n is a sheet without statistics.
- No acceptance criterion. “≤ 0.40 mL” is a criterion. “Approximately 0.35 mL” is not.
- No temperature or humidity for the test. Glass dimensions move with temperature; residual volume moves with drain temperature. A method without conditions is not reproducible.
- “Typical” used as a guarantee. If the only number is typical, you have no recourse on a bad lot.
- No lot traceability statement. The sheet should say how a lot number maps to a test record. If it does not, the COA is decorative.
- Revision date missing or older than two years. A sheet that has not been revised since the mold was cut is a drawing, not a specification.
I also check the supplier’s own instrument documentation. If you are running an Agilent autosampler, the Agilent GC accessories documentation lists the tray pocket dimensions and gripper tolerances. If the vial sheet’s nominal OD plus its stated tolerance exceeds the tray pocket, you have found a mismatch the supplier should have flagged. The same check works against Thermo Fisher sample handling specs for their autosamplers. A supplier who knows their product will have already done this cross-check and will put the compatible instrument list on the sheet.
Two field cases where the sheet was the problem
Case 1: the residual volume that was not measured
A contract lab running EPA 8260 on 40 mL VOA vials started seeing elevated blank responses for toluene on about one lot in five. The vial sheet said “residual volume < 0.5 mL.” We pulled 30 vials from the suspect lot, drained them per a defined protocol (30 s at 45°, 20 °C), and weighed the residual water gravimetrically. Mean was 0.42 mL, but the 95th percentile was 0.71 mL. The sheet’s “< 0.5 mL” was a typical value, not a limit. The fix was to require a guaranteed ≤ 0.30 mL with n=30 per lot and a stated drain protocol. Blank failures dropped to zero over the next six lots.
The lesson: the number was not wrong. The category was. A typical value presented as a limit is a trap.
Case 2: the crimp finish that was nominal
A pharma customer was getting septa skew on about 2% of vials on a 20 mm crimp line. The sheet said “20 mm finish.” We measured the crimp ring diameter on 50 vials with a pin gauge and found a range of 19.4 to 20.3 mm against a nominal 20.0. The upper end was out of spec for the crimper’s seating pocket. The supplier had been running the mold at nominal with no gauge check. The fix was a go/no-go gauge per lot and a requirement that the sheet state the ring diameter tolerance (± 0.15 mm). Skew dropped to under 0.1%.
If you are matching crimp vials to caps, the HPLC vial and GC vial suppliers in your network should be able to confirm the same GPI drawing. A finish that is nominal on one sheet and gauged on another is a supply chain problem waiting to happen.
A decision checklist for the next datasheet you read
Print this and keep it next to the PDF.
| Line on sheet | Ask for | Reject if |
|---|---|---|
| Residual volume | Guaranteed limit, drain protocol, n ≥ 30, temperature | “Typical” or “<” with no method |
| Body OD / height | Measured range on last 3 lots, gauge method | Nominal only, no tolerance |
| Crimp finish | GPI drawing number, go/no-go gauge per lot | Number only, no conformance statement |
| Septa durometer | Shore A value ± tolerance, thickness | Thickness only |
| Puncture count | Number, needle gauge, speed, leak criterion | “Multi-puncture” |
| Torque (screw cap) | Range in N·m, test method | Single value or absent |
| Temperature rating | Separate for glass, septa, cap; test method | Single number for assembly |
| Chemical resistance | Named solvent, time, temperature, extractables limit | “Resistant to most solvents” |
| Lot traceability | Lot-to-record mapping, COA sample | No statement |
If you want a second opinion on a sheet, send it to a supplier who publishes their own methods. A good one will tell you which lines are weak even if they are not selling you the vial. Restek’s technical resources are a useful cross-reference for what a properly documented consumable spec looks like.
What to do when the supplier will not give you the method
Walk. I mean it. A supplier who cannot tell you how a number was measured cannot tell you whether the next lot will meet it. The cost of a failed run, a re-extraction, and a client call is far more than the per-unit savings. In my experience the price gap between a well-documented vial and an undocumented one is 8 to 15 cents per unit. The cost of one failed 8260 batch is hundreds of dollars in labor and solvents, before you count the client relationship.
If you are stuck with a supplier who will not document, require a first-article inspection on every lot: 30 vials, gravimetric residual, pin-gauge finish, and a headspace blank at your working temperature. That is a 20-minute test and it will catch the lots that would have failed you.
The decision rule
Read every line on a voa vial datasheet as either a guarantee or a wish. A guarantee has a method, a sample size, an acceptance criterion, and a test condition. A wish has a number and an adjective. Buy only against guarantees, and require the method in writing before the PO is issued. If the sheet does not distinguish the two, the sheet is the problem, not the vial.
References & further reading
Related resources from our lab consumables network:
External references and standards: