The UNICO 1200 Series Spectrophotometer is a single-beam, general-purpose instrument designed for laboratory use, particularly in the visible wavelength region of the electromagnetic spectrum (325 nm to 1000 nm). It is suitable for various applications including clinical chemistry, biochemistry, petrochemistry, environmental protection, food and beverage analysis, water and wastewater testing, and other quality control fields. The instrument features a digital display for photometric results and is designed for ease of operation.
Function Description
The spectrophotometer operates on a principle involving five main components: a light source, a monochromator, a sample compartment, a detector, and a digital display.
- Light Source: A halogen lamp provides the necessary light for analysis.
- Monochromator: This component isolates the specific wavelength of interest from the light source and eliminates unwanted second-order radiation. Light from the halogen lamp is focused onto the entrance slit of the monochromator. A collimating mirror directs the beam onto a grating, which disperses the light to produce a spectrum. A portion of this spectrum is then focused onto the exit slit by another collimating mirror.
- Sample Compartment: Designed to hold the sample solution, this compartment allows the light beam to pass through the sample. Filters within the compartment help to eliminate unwanted second-order radiation from the diffraction grating. The compartment can accommodate 10 mm test tubes or 10 mm square cuvettes with different cuvette holders, and it can accept pathlengths up to 50 mm with optional holders.
- Detector: After passing through the sample, the light beam reaches a silicon photodiode detector. The detector converts the transmitted light into an electrical signal.
- Digital Display: This display shows the absorbance or transmittance values derived from the electrical signal produced by the detector.
The instrument offers four measurement modes:
- T (Transmittance) mode: Displays the percentage of light transmitted through the sample.
- A (Absorbance) mode: Displays the absorbance of the sample.
- C (Concentration) mode: Used to measure the concentration of unknown samples by comparing them to a standard solution. This mode is recommended when the relationship between absorbance and concentration is linear, and the standard solution's concentration should be higher than the most concentrated sample.
- F (Factor) mode: A specialized mode for measuring unknown sample concentrations using a previously determined factor to convert absorbance readings to concentration.
Usage Features
The UNICO 1200/1201 is designed for straightforward operation with several user-friendly controls:
- MODE Button: Cycles through the four measurement modes (T, A, C, F). An LED light indicates the currently selected mode.
- 0A/100%T (∧) Button: Used to adjust the digital display reading to 100%T or 0.000A when a blank reference solution is in the sample compartment.
- 0%T (∨) Button: In T mode, this button is used to adjust the digital display reading to 00.0%T by blocking the optical light beam with a black block (S-1200-111) placed in the cuvette holder.
- ENT (PRINT) Button:
- In A and T modes, it sends the displayed results to a printer.
- In C mode, it sets the concentration value of the standard solution.
- In F mode, it sets the factor number and then switches the instrument to C mode. To print results in C mode, the MODE button should be pressed until the LED light is off, then the ENT button.
- WAVELENGTH Knob: Allows the user to select the desired wavelength in nanometers (nm). The selected wavelength is shown in the Wavelength Readout Window.
Basic Operation Steps:
- Warm-up and 0%T Check: Turn on the instrument and allow 15 minutes for warm-up. Check the 0%T by inserting the black block into the cuvette holder, closing the lid, and selecting T mode. The display should read 00.0%T; if not, press the 0%T button.
- Mode Selection: Select either T or A mode using the MODE button.
- Wavelength Selection: Turn the WAVELENGTH control knob to set the desired wavelength.
- Blanking: Insert a blank cuvette into the sample compartment, close the cover, and set 0.000A or 100%T using the 0A/100%T button. Remove the blank cuvette and set it aside.
- Sample Measurement: Rinse a second cuvette with the sample solution, fill it, wipe it, and place it in the sample compartment. Close the cover and read the T or A value from the digital display.
Concentration Mode Usage:
- Select the desired wavelength and A mode.
- Insert the blank solution cuvette and set 0.000A.
- Switch to C mode.
- Insert a standard solution of known concentration and adjust the digital display to match the standard's value using the ∧ and ∨ buttons.
- Press the ENT button. If the required factor is too high (>1999), divide the concentration by 10 and re-enter C mode, then adjust the standard value.
- Insert sample cuvettes to read unknown concentrations directly.
- To find the multiplier used to convert Abs to Concentration, switch to F mode after measuring all samples.
Factor Mode Usage:
- After setting wavelength and zero Abs with a blank solution, select F mode.
- Insert a sample cuvette.
- Use the ∧ and ∨ buttons to set the digital display to the desired multiplier value.
- Press the ENT button. The spectrophotometer will switch to C mode.
- Read the concentration value of the sample directly. If the sample concentration is too high, dilute the sample and multiply the reading by the dilution factor. Alternatively, divide the factor value by "10" or "100" and re-enter the "new" factor value, then multiply the readout by the corresponding multiple.
Maintenance Features
Regular maintenance ensures the longevity and accuracy of the spectrophotometer.
Troubleshooting:
The manual provides a comprehensive troubleshooting guide for common issues, including:
- Inoperative Instrument: Check power connections, power outlet, voltage setting, and internal fuse. If the fuse is blown or an electronic component is defective, an authorized service engineer should be contacted.
- Inability to Set 100%T (0.000A): Ensure the cuvette adapter is in the sample compartment. Check for blocked light beams due to misaligned holders or shutters. If the lamp is old, defective, or misaligned, it may need replacement or adjustment as per the bulb replacement instructions. Defective electronic components require an authorized service engineer.
- Inability to Set 00.0%T: Check the sample holder and ensure the sample holder shutter is closed. Defective electronic components require an authorized service engineer.
- Incorrect Transmittance to Absorbance Correlation: Check sample preparation and analytical procedures. Defective electronic components require an authorized service engineer.
- Digital Display "Frozen" or Unresponsive to Sample Concentration Changes: If the concentration reading is "frozen," change the MODE from C to F, T, or A and then back to C to restart the measurement procedure. Check the sample procedure and wavelength setting. Insufficient sample volume or stray sample preparation vapors can also cause issues; ensure cuvettes are filled adequately and samples are prepared away from the instrument with proper ventilation. Bubbles or particles in the solution should be checked. Defective electronic components or loose wiring require an authorized service engineer.
- Instrument Drift and Noise: Insufficient warm-up time, significant temperature changes, or improperly adjusted/old/defective lamps can cause drift and noise. Ensure the lamp is properly installed and adjusted. Unstable power supply or defective/dirty detector/electronic components require an authorized service engineer.
- Incorrect Readings Obtained: This can be due to insufficient sample volume, wrong wavelength setting, failure to blank (0A/100%T), or failure to set 0%T. Check analytical procedures, wavelength setting, and wavelength accuracy. Stray sample preparation vapors or bubbles/particles in solution should also be addressed. If the instrument is out of electronic calibration, an authorized service engineer should be contacted.
The UNICO 1200 Series Spectrophotometer is designed for reliable performance in a laboratory setting, with clear instructions for both routine operation and maintenance to ensure accurate and consistent results.
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