Instructions for using the spectrophotometer

Thread Content

Instructions for using the spectrophotometer: 1) Preheat the instrument. To ensure stable measurements, turn on the power switch and let the instrument warm up for 20 minutes. To prevent fatigue of the phototube, avoid continuous illumination. When preheating the instrument or when no measurement is being taken, the cuvette dark box cover should be opened to interrupt the light path. 　　2) Select the wavelength. According to the experimental requirements, rotate the wavelength adjuster so that the pointer indicates the desired monochromatic light wavelength. 　　3) Fixed sensitivity setting. Based on the light absorption of colored solutions, select an appropriate sensitivity to achieve an absorbance reading of 0.2–0.7. To this end, turn the sensitivity knob to fix it on a certain setting, so that it does not change during the experiment. The general measurement is set to level “1”. 　　4) Adjust the “0” point. Gently turn the potentiometer set to “0” so that the pointer on the gauge points exactly at a transmittance of “0” (at this point, the cover of the cuvette compartment is open, the light path is interrupted, and the phototube is not exposed to light). 　　5) Adjust T to 100%. Place the cuvette containing distilled water (or a blank solution or pure solvent) in the first slot of the cuvette holder; place colored solutions in the other slots. Gently close the lid of the cuvette dark box, and turn the light intensity regulator until the transmittance T reaches 100%, that is, until the pointer on the gauge points exactly at T=100%. 　　6) Measurement. Gently pull the cuvette holder rod to allow the colored solution to enter the light path; at this point, the pointer on the gauge indicates the absorbance A of that colored solution. After taking the reading, open the cuvette dark box lid. 　　7) Shut down. After the experiment, turn off the power supply, remove the cuvettes and wash them, and wipe the cuvette holders and dark box with soft paper. 　　Precautions: 1) To prevent phototube fatigue. When no measurement is being taken, the cuvette dark box cover must be opened to interrupt the light path, thereby extending the lifespan of the phototube. 　　2) Usage of the cuvette: ① When holding the cuvette, use your fingers only to grip the frosted side of it; do not touch the transparent side to avoid contamination. 　　②When cleaning cuvettes, they are generally first rinsed with water and then washed with distilled water. If the cuvette is contaminated with organic substances, it can be soaked in a hydrochloric acid-ethanol mixture (1:2) for a short time, and then rinsed with water. Cuvettes should not be washed with alkaline solutions or highly oxidizing detergents to avoid damage. Cuvets should not be cleaned with a brush either, to avoid damaging their light-transmitting surface. 　　After each experiment, the cuvette should be washed immediately. 　　③Wipe the water on the outer wall of the cuvette dry with lens paper or soft absorbent paper to protect the light-transmitting surface. 　　④When measuring the absorbance of a colored solution, it is essential to wash the inner wall of the cuvette several times with the colored solution itself, in order to avoid changing its concentration. Furthermore, when measuring the absorbance of a series of solutions, it is usually done in order from dilute to concentrated to reduce measurement errors. 　　⑤In actual analytical work, cuvettes with different thicknesses are typically used depending on the concentration of the solution, in order to keep the absorbance of the solution between 0.2 and 0.