SIBATA Class A Volumetric Flask with Glass Stopper - 2306A Series

Most lab errors in quantitative work trace back to the same root cause: a volumetric flask that was not calibrated to Class A tolerance, or one whose graduation line has shifted from thermal cycling and repeated cleaning. The SIBATA 2306A Series Volumetric Flask is certified to ASTM E-288 Class A specifications — the highest accuracy class for laboratory volumetric glassware — and meets USP standards for pharmaceutical-grade measurement. Each flask is machine-blown from premium borosilicate glass with a low coefficient of thermal expansion, fitted with a standard taper glass stopper that provides a leakproof, solvent-resistant seal, and calibrated "to contain" at exactly 20°C (68°F). The sharply defined, uniform-width graduation line leaves no ambiguity at the meniscus. If your analytical work demands traceability and accuracy at the volumetric flask stage, this is the series to standardize on across your 5mL through 2000mL size needs.

Features and Benefits

• ASTM E-288 Class A certified — the highest volumetric accuracy class: Class A certification means each flask is individually inspected to tolerance limits half as tight as Class B. For a 100mL flask, Class A tolerance is ±0.10mL. This level of accuracy is required for preparing primary standard solutions, HPLC mobile phases, and pharmaceutical assays where the concentration of the prepared solution directly affects downstream results.

• Meets USP standards for pharmaceutical glassware: The 2306A Series complies with United States Pharmacopeia glassware specifications, making it suitable for use in pharmaceutical QC laboratories, compounding environments, and any regulated setting where USP compliance is required or audited.

• Standard taper glass stopper included — leakproof and solvent-compatible: Every flask ships with a matching standard taper glass stopper. Glass-on-glass ground joints are chemically inert and provide a reliable seal against evaporation and solvent vapor loss — critical when working with volatile organic solvents or hygroscopic reagents that would degrade with a rubber or plastic closure.

• Machine-blown borosilicate body with heavy-beaded neck: The machine-blown construction produces consistent wall thickness and flask geometry across the entire production run — critical for Class A calibration reliability. The heavy-beaded, heavy-tubing neck is engineered specifically to accept standard taper stoppers with the mechanical strength to withstand repeated insertion and removal without neck deformation.

• Calibrated "to contain" (TC) at 20°C: The 2306A Series is calibrated TC — meaning the stated volume is the amount of liquid contained in the flask when filled to the graduation mark at 20°C. This is the standard calibration method for preparing solutions of known concentration. The calibration temperature is permanently marked on each flask alongside the volume designation.

• Sharply defined graduation line with large marking square: The single volumetric graduation mark is precisely fired at uniform width — there is no ambiguity about where the meniscus should sit. The large white marking square provides ample space for writing solution identity, concentration, preparation date, and analyst initials with a lab marker.

• Full size range from 5mL to 2000mL in one certified series: Ten sizes in a single product family with identical quality certification allow you to standardize your glassware purchasing and QC documentation across every volumetric preparation volume your lab requires — from micro-scale standard preparation at 5mL to large-batch solution making at 2000mL.

Specifications

Laboratory Applications

• Primary standard solution preparation: The most demanding use case for a volumetric flask — preparing a solution of precisely known concentration from a weighed primary standard. Class A certification ensures the volume delivered is within the tight tolerance required for the prepared standard to be used as a calibration reference without a correction factor.

• HPLC and UV-Vis mobile phase and standard preparation: Chromatographic methods require mobile phases and calibration standards prepared at precisely controlled concentrations. The 100mL, 250mL, and 500mL sizes are the most commonly used for HPLC standard preparation, while larger sizes serve mobile phase preparation where concentration accuracy directly affects peak area reproducibility.

• Pharmaceutical assay and compounding: USP compliance makes the 2306A Series suitable for use in licensed compounding pharmacies and pharmaceutical QC labs where glassware certification records may be required during regulatory inspections. The glass stopper eliminates any concern about plasticizer leaching from plastic closures into drug solutions.

• Environmental and water chemistry analysis: Preparing calibration standards for ICP, AAS, ion chromatography, and wet chemistry methods requires volumetric precision at every dilution step. The 50mL and 100mL sizes are the standard workhorses for serial dilution and standard preparation in environmental testing laboratories.

• Teaching and undergraduate analytical chemistry: The pack quantities (6, 4, or 2 per pack) make the 2306A Series practical for equipping student benches with Class A glassware without overspending. Students performing gravimetric and titrimetric analyses develop proper volumetric technique on the same class of flask used in professional analytical labs.

Frequently Asked Questions

What does Class A mean for a volumetric flask, and why does it matter?
Class A is the highest accuracy grade defined by ASTM E-288 for volumetric glassware. Class A flasks are individually calibrated to tolerance limits that are half as tight as Class B. For example, a 100mL Class A flask has a tolerance of ±0.10mL, while a Class B flask allows ±0.20mL. For preparing calibration standards, primary solutions, or any solution where concentration accuracy is directly audited, Class A is the required standard. Class B is acceptable for general-purpose dilutions where tight accuracy is less critical.

Which size should I choose — and what pack quantities are available?
Size selection depends on the volume of solution you prepare most frequently. The 100mL is the most common general-purpose size, covering the majority of standard preparation workflows. The 25mL and 50mL sizes are preferred for micro-scale standards and concentrated stock solutions. The 250mL and 500mL sizes serve HPLC mobile phase preparation and large-batch buffer work. The 1000mL and 2000mL sizes are used when preparing large volumes of standard solution that will be subdivided or diluted further. Pack quantities: 5mL, 10mL, 25mL come in packs of 6; 50mL, 100mL, 200mL, 250mL in packs of 4; 500mL, 1000mL, 2000mL in packs of 2. Each flask includes a matching glass stopper. If you need one each of the four most common sizes (10, 25, 50, 100mL) for bench setup or evaluation, the Variety Kit option (SKU 202GK-004) is available as a single dropdown selection on this page.

What is "to contain" (TC) calibration and how does it differ from "to deliver" (TD)?
A flask calibrated "to contain" (TC) holds exactly the stated volume when filled to the graduation mark at 20°C — meaning the volume is contained within the flask. A pipette calibrated "to deliver" (TD) releases the stated volume when drained. Volumetric flasks are always TC instruments: you fill to the mark, and the solution inside is the correct volume. Never drain a volumetric flask and expect the drained volume to be accurate — use a volumetric pipette for delivery.

Can the glass stopper be used with all solvents?
The standard taper glass stopper is compatible with virtually all laboratory solvents including concentrated acids (excluding HF), strong bases, ketones, alcohols, and chlorinated solvents. The only situation requiring caution is prolonged contact with highly concentrated sodium hydroxide or potassium hydroxide, which can etch glass surfaces and cause the stopper to seize in the neck over time. For strongly alkaline solutions stored long-term, substitute a PTFE or polyethylene stopper of the appropriate taper size.

Are these flasks compatible with SIBATA amber volumetric flasks (2307A Series) for light-sensitive work?
Yes. The 2307A Amber Volumetric Flask series uses the same Class A calibration standard, the same borosilicate glass construction, and compatible glass stoppers. If your analytical method requires protection from UV degradation — common with phenolphthalein indicators, photosensitive drug compounds, or certain metal chelates — the 2307A Series is the appropriate choice for the same volume sizes. Both series are available on LabSupplies.com.

Quality Assurance

SIBATA Scientific Technology has manufactured precision analytical glassware since 1932. The 2306A Series Volumetric Flasks are certified to ASTM E-288 Class A specifications and comply with USP glassware standards. Each flask undergoes individual calibration verification before shipment. SIBATA's ISO 9001-certified quality management system governs production and inspection across all volumetric glassware series. Every flask is backed by a 1-year manufacturer warranty.

Academic and Institutional Pricing

LabSupplies.com offers tiered quantity pricing for academic and research institutions. As an authorized dealer, we ship directly from USA inventory.