Acrylonitrile (CAS 107-13-1, UN 1093) is a volatile, flammable unsaturated nitrile transported under Class 3/6.1, Packing Group I. The liquid has a closed-cup flash point of -5 °C, a vapor pressure of 11.0 kPa at 20 °C, and a density of approximately 0.81 g/cm³ at 20 °C. The density gap with water is sufficient to produce rapid water stratification in storage tanks. In polymer supply chains, acrylonitrile enters ABS, SAN, polyacrylonitrile, nitrile rubber, and adiponitrile process routes. The phrase “Acrylonitrile Sample Request: What a Legitimate Pre-Shipment Process Looks Like” therefore refers not to a marketing sample but to a controlled aliquot drawn from the commercial cargo, preserved under inhibitor and temperature conditions, and tied to the purchase order by documentation. If that tie is absent, the sample cannot support a quality dispute after shipment.

The sample request is a technical document as much as a commercial instruction. A legitimate pre-shipment sample exists only when the sample label, the chain-of-custody record, the retained counter sample, and the certificate of analysis identify the same shore tank, vessel tank, or ISO tank container without contradiction. The sample also has to reflect the actual cargo condition at the time of loading. A retained laboratory batch, a pilot-plant aliquot, or a sample drawn from a different lot cannot serve as a pre-shipment sample for a titled cargo.

What Must a Pre-Shipment Sample Request Include Before Loading?

The request should carry the commercial specification revision, the lot or tank number, the requested test panel, and the jurisdiction or end-use constraint that dictates the analytical threshold. For acrylonitrile, the requesting party must state whether the sample is intended for independent re-analysis under ISO/IEC 17025, for process compatibility testing in a polymer line, or for regulatory submission under a specific inventory registration. Without that stated purpose, the supplier may submit a generic retained sample from a previous batch and still claim compliance with the sample request.

A legitimate pre-shipment request should also define the sample volume, storage temperature, and preservation. For a full test panel including gas chromatography, Karl Fischer water, acidity, color, density, and inhibitor content, a minimum of 500 mL is defensible because it permits duplicate analyses and a retained sub-sample. The sample container should be amber borosilicate glass with a PTFE-faced cap, filled to not more than 80% by volume for thermal expansion, and cooled to 2–8 °C after drawing. The request should require that the sample label state the product name, grade, lot number, date and time of sampling, sampling location, seal number, and the name of the person who drew the sample.

The sampling point must be specified. A sample drawn from a laboratory pilot batch, a retained sample cabinet, or a different shore tank is not a pre-shipment sample. For bulk liquid acrylonitrile, the relevant point is normally the shore tank after recirculation or the loaded vessel tank after loading. For ISO tank containers, the relevant point is the container discharge valve after homogenization or, where homogenization is not possible, both top and bottom samples to detect water or inhibitor stratification.

A representative pre-shipment sample is drawn only after the tank content has been recirculated long enough to reduce stratification. Acrylonitrile water ingress in shore tanks tends to form a lower aqueous phase because water has a density of 1.00 g/cm³ while the monomer remains near 0.81 g/cm³ at 20 °C. Drawing from a static bottom valve can therefore produce a water result of 0.5–2.0% in a lot whose average water content is below 0.25%. The sampling procedure should record the recirculation pump flow rate, the duration of circulation before sampling, and the liquid temperature at the time of draw. For ISO tank containers without a recirculation loop, a top-and-bottom sampling kit should be used. The COA must state both values when the top and bottom water or inhibitor results differ by more than the analytical repeatability limit.

The sample receipt laboratory should inspect the container before opening. A seal number that does not match the chain-of-custody form, a bottle with a cracked cap, or a warm sample above 10 °C at receipt invalidates the sample for formal quality arbitration. If the sample arrives warm but with an intact seal, it may still be analyzed for informational purposes, but the receiving laboratory should not use it as the sole basis for rejection of the cargo.

Certificate of Analysis Verification and Retained Counter-Sample Requirements

The COA must be sample-specific and must report actual measured values, not typical specification values. A COA that lists only “passes” or “conforms” without numerical results should be treated as insufficient for a pre-shipment sample. For acrylonitrile, the COA should include purity, water, acidity, color, density, and inhibitor concentration at minimum. The method reference and instrument identification should be stated for each result. If a consensus method is used, the standard designation should appear, such as ASTM E203-16 for water by Karl Fischer titration, ASTM D1209-05(2019) for Pt-Co color, ASTM D1613-17 for acidity as acetic acid, and ASTM D4052-18a for density. For MEHQ inhibitor, no single consensus method is uniformly applied; the COA should therefore state the in-house method number, HPLC detection conditions, and validation status.

A retained counter sample is not optional in a legitimate pre-shipment process. The supplier should retain a sealed aliquot from the same drum, tank, or container under the same inhibitor and storage conditions as the shipped sample. Typical retention is 90 days after the cargo arrives at the discharge port, or longer if the purchase order requires. The retained sample should be stored in a dark refrigerator at 2–8 °C and should carry a tamper-evident seal. Its value is evidentiary: if the buyer’s sample is damaged in transit, the supplier can draw from the retained counter sample for re-analysis.

For inhibited acrylonitrile, the following table lists a representative pre-shipment test panel. The acceptance ranges are common commercial specification values and must be subordinate to the purchase order.

Beyond analytical results, the documentation set is part of the sample itself. The following table identifies the minimum documents that should accompany a legitimate pre-shipment acrylonitrile sample.

When the Sample Is Drawn from a Shore Tank Rather Than the Loaded Container

A shore-tank sample is the most common pre-shipment sample because it is available before loading starts and allows the buyer to approve the cargo for loading. Its limitation is that it cannot detect contamination introduced after the sampling valve: loading line residue, manifold dead legs, ship-tank heel, or a poorly cleaned ISO tank interior. A legitimate pre-shipment process therefore separates quality approval from contamination control. The shore-tank sample may be used to approve the specification profile, while a post-loading sample from the vessel tank or ISO container is retained as the contamination reference.

When only a shore-tank sample is available, the sampling record should include the tank cleaning certificate, the wall-wash result, the previous cargo, the nitrogen pad pressure, and the loading start time. If the previous cargo is not compatible with acrylonitrile, the buyer should require a loaded container sample and not rely on the shore-tank aliquot. The cleaning certificate should state the cleaning medium, contact time, and the analytical method used to verify residue removal.

In bulk vessels, the IMO IBC Code requires an inhibitor certificate for acrylonitrile as a cargo requiring inhibition. The certificate must state the inhibitor type, concentration, date added, and shelf life. The inhibitor certificate is separate from the COA and should be checked before the sample is released for shipment. If the inhibitor is below the specified minimum at the time of sampling, the lot is not a stable liquid for normal transport.

Inhibitor Loss, Water Strata, and Closed-Cup Flash Point Verification

MEHQ inhibitor concentrations in commercial acrylonitrile typically fall between 35 mg/kg and 50 mg/kg. The lower boundary is operationally sensitive. If a pre-shipment sample arrives with an inhibitor result below 30 mg/kg, the receiving laboratory should request the supplier’s inhibitor addition log and check the storage temperature history, because partial polymerization can consume inhibitor and produce a visible haze or increased non-volatile residue. A clear sample is not proof of adequate inhibition; only the quantified inhibitor value confirms stability for the intended transit time.

Water stratification is a recurring false rejection issue in acrylonitrile sampling. Because the density difference is large, a poorly drawn static bottom sample can show water levels above 0.5% while the average tank content is below 0.25%. The COA should therefore record the sampling point and the recirculation status. If the water result is high, a re-sample from the recirculated tank is required before rejecting the lot for high water, unless the purchase order explicitly limits bottom-sediment and water by a bottom-sample method.

Closed-cup flash point testing is not part of every acrylonitrile COA, but it becomes relevant when contamination with lower-boiling solvents is suspected. Acrylonitrile has a closed-cup flash point near -5 °C; a contaminated sample may show a lower flash point or a wider flammability range. If a low flash point is reported, the sample should be re-tested and compared against the cargo tank history before the material is accepted.

If the receiving laboratory finds a damaged seal, a missing chain-of-custody form, or a sample that has warmed above 10 °C during transit, the formal status of the aliquot changes. It may be analyzed for screening only, but it cannot be used as the sole basis for rejecting the cargo. The receiving inspector should photograph the package before opening, record the seal number, and request a replacement from the retained counter sample. A legitimate pre-shipment sample request succeeds only when the sample, the COA, the inhibitor certificate, and the chain-of-custody records identify the same cargo lot without contradiction.