- What it is. This pH 4 buffer solution is a color-coded red pH standard used to calibrate pH meters and electrodes in the acidic range. It is offered in 1-pint and 1-gallon sizes.
- Why calibrate at pH 4. Two-point calibration sets both the electrode's zero point and its slope. pH 7 sets the zero point, and pH 4 sets the slope for acidic measurements. Bracketing acidic samples between pH 4 and pH 7 lets the meter interpolate readings rather than extrapolate them, improving accuracy across the acidic range.
- How a buffer holds its pH. A buffer contains a weak acid and its conjugate base, or a weak base and its conjugate acid, in balanced amounts. When small amounts of acid or base enter the solution, one partner neutralizes them, so the pH barely moves. That resistance to change is what makes a buffer a reliable reference point for calibration, unlike plain water.
- Why color-coded red. Red is the widely used color for pH 4 buffers, alongside yellow for pH 7 and blue for pH 10. Color coding lets technicians grab the right buffer at a glance and reduces mix-ups during multi-point calibration.
- The most stable calibration point. Acidic buffers are less affected by carbon dioxide from the air than alkaline buffers, so an opened pH 4 buffer typically stays within specification longer than pH 10. Good practice still applies: keep the container closed, pour only what you need, and discard used buffer.
- Temperature matters. Buffer pH shifts slightly with temperature. Calibrate at the same temperature as your samples, use a meter with automatic temperature compensation, and apply any temperature-correction values supplied with the buffer for the most accurate readings.
- Two sizes for different workloads. The 1 pint size (ZB1628-16.1) suits benches that calibrate a few times a week. The 1 gallon size (ZB1628-128) suits QC and production labs that calibrate several meters daily and want a lower cost per calibration.
- Calibration best practice. Rinse the electrode with deionized water, blot it gently between buffers, immerse it in a fresh buffer in a clean beaker, stir gently, and wait for a stable reading before accepting each point. Calibrate before each day's measurements, or more often as the method requires, and record the meter-reported slope to track electrode health.
- Where it is used. Use pH 4 buffer to calibrate benchtop, portable, and in-line pH meters in food and beverage, pharmaceutical, environmental, plating, and teaching labs, wherever samples are acidic. It pairs with Lab Pro's Buffer Solution pH 7, Yellow, and Buffer Solution pH 10, Blue for full three-point calibration, and with Buffer Solution pH 2 for strongly acidic samples.
Technical Specifications
| Product | pH 4 buffer solution, color-coded red |
| Nominal pH | 4 at 25 °C |
| Color Code | Red |
| Use | pH meter and electrode calibration, slope setting for acidic samples |
| Package Sizes | 1 pint; 1 gallon |
Available Variants
- ZB1628-16.1: 1 pint for occasional calibration.
- ZB1628-128: 1 gallon for labs that calibrate several meters daily.
Applications / Common Uses
- pH meter calibration: Sets the electrode slope for acidic measurements alongside pH 7.
- Slope verification: Checks electrode response after cleaning or reconditioning.
- Daily QC checks: Confirms meter accuracy before acidic sample runs.
- Food and beverage testing: Brackets acidic products such as juices and fermented foods.
- Teaching labs: Demonstrates buffer behavior and meter calibration.
Storage, Handling & Shipping
Store pH 4 buffer tightly closed at room temperature, protected from light and freezing. Keep it free of contamination by pouring portions into a clean beaker for each calibration and never dipping an electrode into the stock.
- Storage temperature: Store at room temperature and protect from light and freezing.
- Contamination control: Pour the amount needed into a clean beaker; never return used buffer to stock or dip an electrode into the stock container.
- Shelf life: Use before the expiration date on the label; once opened, use within the period stated on the certificate or label.
- Rinsing: Rinse electrodes with deionized water between buffers to prevent carryover.
Related Categories & Services
- Shop Buffers by Lab Pro for related products in this category.
- Explore PH Buffers & Test Kits and Buffers, Standards & Solutions.
- Vendor Managed Inventory (VMI) Program: Lab Pro can stock, track, and replenish this item on site so it never runs out. Contact info@labproinc.com or 888-452-2776 to set up a VMI assessment.
