CMB_LAB_PEREZ_merged Identification of Biomolecules PDF

Name: Perez, Jelai E. Section: CAS 02 502A LABORATORY EXERCISE Identification of Biomolecules Introduction: Our physical bodies are essentially a collection of common and exotic chemicals. Many of these chemical...

Name: Perez, Jelai E. Section: CAS 02 502A LABORATORY EXERCISE Identification of Biomolecules Introduction: Our physical bodies are essentially a collection of common and exotic chemicals. Many of these chemicals are simple inorganic combinations such as sodium chloride, hydrochloric acid, molecular oxygen, and carbon dioxide. Most chemicals comprising our bodies are larger, more complex organic molecules. The biochemical reactions that are occurring constantly within our cells synthesize new, larger molecules or decompose larger molecules into smaller pieces. Anabolism is a term used for all the synthesis reactions occurring at any time; Catabolism is a term that refers to all the decomposition reactions occurring at any time. Metabolism is a term that refers to ALL the reactions that might be occurring in the body. While our bodies can metabolize a wide variety of organic molecules, the vast majority belong to three major groups: carbohydrates, lipids and proteins. We can perform simple tests to identify some of these molecules by adding indicators to a solution to be tested. A change in color, or other physical characteristic usually indicates the presence of a particular chemical. You will perform each of the above tests on a “positive” and a “negative” solution (the “negative” is usually water). After completing the test you will see both the positive and negative results for each kind of molecule above.. Objective: The purpose of this experiment is to determine the presence of Biomolecules. Materials: -Fruit Juice -Egg white -Starch -Cooking oil -Distilled Water -Hot water bath -Test tubes in a test tube stand -1 bottle of Benedict’s Solution -1 bottle of Iodine Solution -Ethanol -2,6-dichlorophenol-indophenol (DCPIP) -1 test tube brush -1 test tube tong Lugol’s Iodine Solution Ingredients a. Iodine powder = 5 grams. b. Potassium iodide = 10 grams. c. Distilled water = 100 mL. Lugol’s Iodine Solution Preparation 1. Dissolve the potassium iodide in the distilled water. 2. Add iodine crystals slowly and keep shaking the container (test tube) until these are dissolved. 3. Filter the resulting solution. 4. This is the stock solution. 5. For the working solution: 1. Dilute the stock solution 1:5 with deionized distilled water. 6. You can use this working solution for 2 to 3 weeks and make a new working solution. Biuret Solution Ingredients a. Copper sulfate (CuSO4) solution b. Sodium potassium tartrate c. Sodium hydroxide (NaOH) or potassium hydroxide (KOH) solution d. Distilled water  Biuret Solution Preparation 1. Dissolve 1 gram of CuSO4 crystals in 100 mL of distilled water. 2. Add 1.2 grams of sodium potassium tartrate to the mixture. (it stabilizes the Cu+2 ions) 3. Dissolve 10 grams of NaOH pellet in 90 mL of distilled water to make a 10% NaOH solution. 4. Add 10 mL of the 10% NaOH solution to 100 mL of 1% CuSO4 solution. Benedict’s Solution Ingredients a. Anhydrous sodium carbonate = 10 g b. Sodium citrate – 1.73 g c. Copper(II) sulfate pentahydrate = 1.73 g d. Distilled water = 100 ml Benedict’s Solution Preparation 1. Measure 1.73 grams of copper sulfate (CuSO4), 1.73 grams of sodium citrate (Na3C6H5O7), and 10 grams of anhydrous sodium carbonate (Na2CO3) (or 27 grams of sodium carbonate decahydrate (Na2CO3.10H2O)) 2. Put all the measured chemicals in a volumetric flask of 1000 mL. 3. Pour distilled water up to 100 mL marking. 4. Dissolve all the components properly by shaking gently. Ethanol Emulsion Solution Ingredients a. Ethanol 95% = 2 ml b. Distilled Water= 2 ml Indications for Positive Test: A. Complex carbohydrates (starches). Iodine causes a solution containing starch to turn dark blue to black. The more starch there is the darker the color. B. Proteins (and polypeptides) Biuret solution causes a protein solution to turn pink or violet. C. Reducing Sugars. Benedict's solution causes these sugars to turn green, yellow, orange or red when heated to boiling. The color of a positive reaction depends on how much sugar is present (green indicates low levels; red high sugar levels) D. Lipids (fats). Ethanol Emulsion causes a solution containing fats to develop white emulsion. Test Procedures: 1. Starches a. Add a 1 ml of the liquid samples to a dry test tube. b. Add 1 ml of Lugol’s iodine to each of the test tubes c. Shake the tube side to side smoothly to mix. d. Record the reaction as either “+” or “-“ in the table below 2. Proteins a. Add 1 ml of the liquid samples to a dry test tube. b. Add 1 ml of Biuret solution to each test tube c. Shake the tube side to side smoothly to mix. d. Record the reaction as either “+” or “-“ in the table below 3. Sugars: a. Add 1ml of the liquid samples to a dry test tube. b. Add 1 ml of Benedict’s solution to each test tube c. Place both test tubes in a boiling water bath at your table for about 2-3 minutes d. Shake the tube side to side smoothly to mix. e. Record the reaction as either “+” or “-“ in the table below 4. Fats: a. Add 1 ml of the liquid samples to a dry test tube. b. Add 1 ml of ethanol c. Add 1 ml of distilled water and shake it thoroughly d. Record the reaction as either “+” or “-“ in the table below. Cleanup and Disposal a. Discard all solutions into the sink with the water running. b. Clean test tubes with soap and water and return it to your lab table. c. Make sure the hot plate is turned off and unplugged before you leave. Observation: Put a (+) in the table for a positive result and a (–) for a negative result. Experimental Results [+/-] SAMPLE STARCH PROTEIN REDUCING FAT SUGAR FRUIT JUICE - - + - EGG WHITE - + - - POTATO + + + - COOKING OIL - - - + DISTILLED WATER - - - - 1. Which sample contains Starch? What is your evidence? What is the mechanism of the test reaction? - Potato, the sample turns blue-black when Lugol’s solution is added. The Lugol’s Iodine solution involves iodine and potassium iodide solution, which reacts with the polysaccharide chains of starch, particularly the helical structure of amylose, forming a blue-black complex. 2. Which sample contains Protein? What is your evidence? What is the mechanism of the test reaction? - Egg white, the sample turns purple/violet when Biuret reagent is added. The Biuret test detects peptide bonds, the copper ions in the Biuret reagent form a complex with the peptide bonds in the protein, turning the solution purple/violet. 3. Which sample contains Reducing Sugar? What is your evidence? What is the mechanism of the test reaction? - Fruit juice, the sample turns bright orange to brick-red when heated with Benedict’s solution. Benedict’s test involves reducing sugars reacting with copper sulfate in Benedict’s reagent, reducing it to copper oxide, which precipitates out as a bright orange to brick-red solid. 4. Which sample contains Fat? What is your evidence? What is the mechanism of the test reaction? - Oil, The presence of fat is confirmed if a milky or cloudy emulsion forms when the sample is mixed with ethanol and then water. Fats dissolve in ethanol; when water is added, the ethanol mixes with the water, causing the fats to precipitate out as tiny droplets, forming a cloudy emulsion, which indicates the presence of fat. 5. Each test included a sample that was just water. Why is it important to include a water-only sample for each test? - A water-only sample acts as a control. It helps ensure that the reactions observed in the other samples are due to the substances being tested and not contaminants or procedural errors. By showing no reaction, it validates the results of the actual samples. 6. Were there any sources of error? If so, explain how they could have influenced your data. - Potential sources of error include contamination of glassware or cuvettes, inconsistent reagent concentrations, and human errors such as incorrect  handling or measurement, which could lead to inaccurate results like false positives/negatives or unreacted samples. Conclusion: Through these tests, we identified that the potato contains starch, egg white contains protein, fruit juice contains reducing sugars, and oil contains fat. Including a water-only sample ensures the accuracy of the results by providing a baseline, while recognizing potential sources of error helps us refine our techniques for more reliable data. Documentation  LABORATORY EXERCISE Microscopy AT A GLANCE Conducts simulations that covers the general structures of various cell types OBJECTIVES At the end of this exercise the student should be able to: 1. Define resolving power, field of view, depth of field (focus), working distance 2. Name the parts of the microscope describe the function of each. 3. Use, clean and store the microscope using the techniques describe in this lab. 4. Calculate the total magnification of a lens system if the power of the ocular and objective lens is given. 6. Make a simple dry mount of a specimen. SKILLS Gathering (simulating), analyzing (identifying patterns), interpreting (identifying cause and effect, inferring) KEYWORDS Wet mount, Microscope, resolving power, magnification, depth of field, working distance INTRODUCTION Only objects 0.1mm and larger can be visualized by the human eye. Because most microorganisms are much smaller than 0.1mm, a microscope must be utilized in order to directly observe them. In general, the diameter of microorganisms ranges from 0.2 - 2.0 microns. A light microscope, which uses light as a source of illumination, will be employed in this lab. There are several types of light microscopes. The type used in this course is a brightfield microscope, where the specimen appears darker against a bright background. BASIC PRINCIPLES Resolving Power- ability of a lens system to separate fine detail Resolution- smallest resolvable distance between two objects Field of View- the circular viewing area of a lens system. Depth of Field- the vertical distance (thickness) of the specimen that is in sharp focus. Working distance- the distance between the objective lens and specimen when the specimen is in focus  Parts of the light microscope 1. Arm and base. All other parts of the microscope are attached to the arm or base. 2. Mechanical stage: The platform on which the microscope slide rests and the clamping device that secures the slide. 3. Mechanical stage control knobs (x-y control knobs): These knobs, under the stage, move the stage front to back and the slide from side to side. 4. Lamp (illuminator). The lamp on/off switch is located on the base. The light intensity can be adjusted with this on/off switch. The lamp should be adjusted to a medium level at the start of viewing. The lamp or illuminator usually has a blue filter that rests on the light housing or under the condenser. 5. Iris diaphragm: adjusts the amount of light reaching the specimen. It is adjusted with a thin, black lever under the stage. It has a dramatic effect on the contrast observed in the specimen and may need to be adjusted frequently. 6. Lens systems: There are three lens systems: the eyepieces (ocular), the objectives (four), and the condenser. 1) Eyepieces (ocular): Magnification of 10X. The eyepieces are held rather loosely in the eyepiece tubes. Never remove the eyepieces from the eyepiece tubes. A rubber eye shield should be on the top of each eyepiece. The width between the eyepieces should be moved until a full circle (the viewing field) is visible with both eyes simultaneously. 2) Objectives: There are four objectives: 4X (red), 10X (yellow), 40X (blue), and 100X (white, oil immersion objective). The objectives are attached to a rotating nosepiece (nose turret). The total magnification is calculated by multiplying the ocular magnification and the magnification of the objective in use. 3) Condenser: The condenser is located directly beneath the stage. It gathers and conducts the light to the specimen. Although it can be raised and lowered with the condenser adjustment knob, the condenser should remain at its highest position. 7. Focusing knobs: located on both sides of the microscope. The larger, inner coarse adjustment knob moves the stage up and down much faster and farther than the smaller, outer fine adjustment knob. The coarse adjustment knob is used ONLY with the low power (4X, 10X) objectives. When focusing under the 40X or 100X objective, ONLY use the fine adjustment, never the coarse adjustment. 8. Nosepiece: Holds the objective lenses Refer to each of the following procedures every time the microscope is used. VI. Preparation for viewing 1. If you have not done so, carefully remove a scope from the cabinet and set it on your lab bench. Remove the dust cover. Check that no parts are loose or missing. Immediately contact the instructor if parts are missing or anything is wrong with the scope. 2. Plug in microscope. Be sure the electrical cord is not dangling off of the lab bench or is not entangled. 4. Use the coarse adjustment knob to move the stage to its lowest level. 5. Cleaning the microscope. Clean all objective lenses with lens paper and, if necessary, liquid lens cleaner. Place a small amount of liquid lens cleaner on the swab. Use a fair amount of pressure to clean the lens. Dry the lens with a different swab. Use different swabs for each lens. Do not use liquid lens cleaner on the eyepieces. Dust on the eyepieces, or elsewhere, may be removed using the blower brush. NEVER remove any parts. 6. Before use, clean all slides, top and bottom, with Kimwipes. Place a coverslip over the specimen on the slide. Do not use a coverslip if viewing prepared slides. 7. Adjust the condenser to its highest level. Turn on the lamp. Adjust the on/off switch to a low/medium light level. 8. Rotate the nosepiece until the 4X objective clicks into place. 9. Place the slide on the stage so that it is held within the slide holder clamping device. The slide must lie flat on the stage. Using the mechanical stage knobs, position the slide so that the specimen is in the exact center of the light coming through the condenser. 10. While looking through the eyepieces, adjust the width between the eyepieces until a single, circular field is seen simultaneously with both eyes. 11. If problems are encountered during viewing, repeat the procedure. If problems persist, review the Common Problems section at the end of this document.  Viewing the specimen under the 4X, 10X, and 40X objectives 1. Always start with a low power objective (4X or 10X) clicked into place. The lowest power objectives have the largest field of view (a larger portion of the slide can be seen), making it easier to initially find the specimen. 2. Be sure to bring the stage to its lowest point with the coarse adjustment knob. In other words, the stage should be as far away from the objective as possible. 3. Light control Light intensity is a essential aspect of microscopy. For optimal viewing, the light must be adjusted at each magnification. Perform the following steps to adjust the light. Always adjust the light while looking through the eyepieces. a. Adjust the light intensity switch that turns the lamp on. Begin at a low/medium level. b. The entire viewing area (field) must be filled with light. c. Locate the thin, black iris diaphragm lever under the stage. Adjust this lever to a medium/low light level. The iris diaphragm will need to be adjusted as magnifications increase. 4. Under low power, SLOWLY focus with the coarse adjustment knob until the specimen comes into view. Adjust the light as instructed as needed. Many specimens are very small and may look like specks at this magnification. If the stage moves too quickly, you may go past the specimen without seeing it. 5. Refine the image with the fine adjustment knob and by adjusting the light. 6. Important! Before switching to the next objective, move the slide so that the desired specimen is located in the center of the field (circular viewing area). 7. SIGNIFICANT POINTS WHEN FOCUSING UNDER THE 4X,10X, AND 40X OBJECTIVES! a. Always start with a low power objective (4X or 10X). After making appropriate observations, rotate the nosepiece until the next objective clicks into place. Do not skip objectives. b. Do not move the stage up or down before rotating the nosepiece to the next objective. When properly focused, there is no need to adjust the objective's distance from the stage before increasing the magnification. c. DO NOT USE THE COARSE ADJUSTMENT KNOB WHEN FOCUSING UNDER THE 40X OBJECTIVE! ONLY USE THE FINE ADJUSTMENT KNOB! d. Before increasing the magnification, always move the slide so that the desired specimen is located in the center of the field. e. Remember to adjust the light each time the magnification is changed if the area observed is too dark.  Name: Jelai Perez Section: CAS 02 502A Microscopy Lab Experiment Letter "e". 1. Prepare a dry mount using the letter "e" as the specimen. Place the preparation with the letter "e" on stage so that you can read the letter "e" as in the previous sentence. 2. Study the slide under 40X, 100X, and 400X (total magnification). What observation did you make when you looked at the "e" for the first time? - Under 40X magnification, the "e" is a clear, identifiable letter with defined corners. At 100X magnification, the finer features of the ink and paper texture become apparent, showing a more complex structure. Under 400X magnification, the "e" is even more detailed, with the ink's fibers and any defects visible, converting the basic letter into a complex landscape. Draw and label the letter "e" after focusing with different magnifications Total Magnification:  3. Define resolution. 4. List two instances when the coarse adjustment knob is never used. - When focusing under high power magnification. - When using the oil immersion objective. 5. When should the lenses be cleaned? What is the correct way to clean them? - Lenses should be cleaned regularly before and after use with lens paper or a microfiber cloth, using gentle circular motions to avoid scratches. 6. List two common problems associated with using the microscope and how you would go about solving it. - Blurry images: Use the fine adjustment knob for precise focusing and ensure the slide is properly placed on the stage. - Insufficient light: Check the light source and adjust the diaphragm to increase brightness.  LABORATORY EXERCISE Cell Structure & Function AT A GLANCE Conducts simulations that covers the general structures of various cell types OBJECTIVES 1. Explain the difference between prokaryotic and eukaryotic cells and be able to distinguish each type under the microscope. 2. Compare and contrast animal and plant cells and be able to distinguish each type under the microscope. 3. Identify the following structures on the slides and explain the functions of each: plasma membrane, cytoplasm, nucleus, nucleolus, cell wall, and plastids (including chloroplasts and amyloplasts). 4. Examine the diversity in cell size and shape. 5. Properly prepare and view wet mount slides under the microscope. SKILLS Gathering (simulating), analyzing (identifying patterns), interpreting (identifying cause and effect, inferring) KEYWORDS Wet mount, Microscope, cell organelles, nucleus, In today’s lab you will be examining a variety of different cell types using the compound microscope. All cells have certain common features, including a fluid-filled cytoplasm surrounded by a plasma membrane, DNA (genetic material) and ribosomes (for protein synthesis). Some cells, including the prokaryotes, fungi, plants, and certain protists, also have a cell wall that lies outside the plasma membrane and functions in protection and structural support. Biologists recognize two major categories of cell types – the prokaryotes and the eukaryotes. Prokaryotes lack a membrane-bound nucleus, have few or no organelles and are smaller than eukaryotes. Prokaryotes include organisms in the Domains Bacteria and Archaea. Organisms in Domain Eukarya (protists, plants, fungi and animals) have eukaryotic cells. These cells have a membrane-bound nucleus that houses their DNA and contain extensive internal organelles (“little organs”) that perform specific functions. As you complete this lab, note the size and structural differences between the prokaryotic and eukaryotic cells you observe.  A tremendous amount of diversity exists within each category of cells. Differences occur in size, shape, and presence and number of various organelles and other structures. Each cell’s structure correlates with its specific function. You will be examining several different plant and animal cell types to explore eukaryotic cell diversity. Plant cells have a cell wall composed of cellulose and a large central vacuole that stores water, pigments and wastes. Various plastids are also present, which produce or store various products. Chloroplasts perform photosynthesis, using light energy to produce carbohydrates. Other plastids include the amyloplasts, which store starch. Animal cells lack cell walls, plastids, and a central vacuole, but share many other common organelles with plants, including mitochondria, the endoplasmic reticulum, Golgi apparatus and cytoskeleton. Most of these shared structures will not be visible in the slides we examine today. Plant Cells – Epidermal Leaf Peel Prepare a leaf peel of available plant using the following method: 1. Obtain a clean slide and a cover slip. 2. Break off a portion of a plant leaf and make a small nick on bottom surface of the leaf with a razor blade. Use forceps to gently pull up a portion of the epidermis. (It should be very thin and mostly transparent). 3. Place the peeled leaf on the slide and add one drop of water to the surface. 4. Holding the cover slip at an angle on the edge of the drop of water, slowly lower the cover slip down on top of the water. There should be minimal air bubbles if done correctly. 5. Gently wipe the bottom of the slide before loading it on the microscope if any water has escaped the cover slip. Examine the leaf peel at scanning, low and high power. Note the shape of the cells, the cell wall and the chloroplasts. What is the function of these structures? - Examining a leaf peel under a microscope at different magnifications might reveal important details. The cells' rectangular shape allows them to be packed tightly, improving their capacity to absorb light. The cell wall provides structural support and protects the cells. Photosynthesis, which converts light energy into chemical energy that fuels the plant, relies heavily on green structures known as chloroplasts. These structures work together to provide the environment for the plant to grow, thrive, and perform photosynthesis. You will also see paired, distinctly shaped cells known as guard cells scattered on the surface of the leaf. Guard cells surround and control the opening of pores called stomata (singular: stoma) on the leaf surface that allow gas exchange. Are the stomata on your specimen open or closed? Can you see chloroplasts in the guard cells?  Draw a few of the plant cells in the space below, labeling the cell wall, cytoplasm, and chloroplasts. Total Magnification ____________ Plant Cells – Potato Potatoes are modified underground stems used for carbohydrate storage. Starch is stored in organelles called amyloplasts, which will be visible under the microscope after staining the potato with iodine. Prepare a stained wet mount of a potato using the following method: 1. Obtain a clean slide and a cover slip. 2. Using a scalpel cut a very thin slice of a potato and place on the slide. 3. Add a drop of iodine solution and apply the cover slip as described above. Examine the potato tissue at scanning, low and high power. Iodine stains the starch a purple or blue-black color. Note the cell shape and the presence of amyloplasts. Are chloroplasts present? Why? - Under different magnifications, you will observe the potato cells' distinctive shape and the presence of amyloplasts stained purple or blue-black by iodine. Chloroplasts are not present because potatoes, being underground storage organs, don’t perform photosynthesis, which is the primary function of chloroplasts. Instead, they store starch in amyloplasts. Draw a few potato cells in the space below, labeling the cell wall, cytoplasm, and amyloplasts. Total Magnification ____________ Animal Cells – Human Cheek Cells The tissue that lines your cheeks contains multiple layers of flattened cells that are constantly sloughing off as you eat and drink. The layered nature of these cells serves to protect the underlying tissue against this abrasion. New cells are constantly being produced in the lower layers to replace those that are lost. Prepare a cheek smear slide of your own cells using the following method: 1. Obtain a clean slide and a cover slip. 2. Gently rub the inside of your cheek with a toothpick and smear the collected fluid onto the slide. Discard the toothpick in the trash. 3. Add a drop of dilute methylene blue stain to the slide and cover with the cover slip. View the slide at scanning, low and high power. Note the cell shape, plasma membrane, cytoplasm, and nucleus. Draw a few cheek cells in the space below, labeling the nucleus, plasma membrane and cytoplasm. Total Magnification ____________ **When you are finished with the cheek slide, place the cover slip in the glass disposal and put the slide in the container of bleach at the instructor bench.**  RIZAL TECHNOLOGICAL UNIVERSITY College of Arts and Sciences DEPARTMENT OF BIOLOGY NAME: PEREZ, JELAI E. SECTION: CAS 02 502A Activity 1. Answer the following essay questions 1. What Is a Spectrophotometer? - A spectrophotometer is an analytical instrument used to measure the intensity of light as a function of its wavelength. It quantitatively assesses how much a chemical substance absorbs light by measuring the intensity of light passing through a solution. The device provides insights into the molecular composition and concentration of substances in a sample. It’s crucial in fields ranging from chemistry and biology to industrial applications, allowing for the identification and quantification of various compounds. 2. Name the parts of the spectrophotometer and identify their function. - Light Source: Emits a continuous spectrum of light. Common sources include tungsten lamps (visible light) and deuterium lamps (UV light). - Monochromator: Disperses the light into its component wavelengths and allows selection of a specific wavelength of light to pass through the sample. It includes a diffraction grating or prism to separate the light. - Sample Holder (Cuvette): A transparent container that holds the liquid sample. The material of the cuvette (usually quartz or glass) should be transparent to the wavelength of light being measured. - Detector: Captures the light after it passes through the sample and converts it into an electrical signal proportional to the light intensity. Common detectors are photodiodes or photomultiplier tubes.  - Display/Output: Shows the measurement results, either as a digital readout or connected to a computer for data processing and analysis. 3. How Does a Spectrophotometer Work? - The spectrophotometer operates by directing a beam of light from the light source through a monochromator, which isolates a specific wavelength. This monochromatic light then passes through the sample in the cuvette. As the light interacts with the sample, some of it is absorbed while the rest passes through. The transmitted light reaches the detector, which measures its intensity. The difference between the incident light and the transmitted light indicates the absorbance or transmittance of the sample. The resulting data helps determine the concentration of the substance within the sample based on the Beer-Lambert law. 4. What Is a Spectrophotometer Used For? - Spectrophotometers are versatile tools used across various domains: Quantitative Analysis: Determining the concentration of a solute in solution by measuring absorbance. Kinetics Studies: Monitoring the progress of a chemical reaction over time by measuring changes in absorbance. Protein and Nucleic Acid Analysis: Assessing the purity and concentration of biomolecules in biochemistry. Quality Control: Ensuring the consistency and quality of products in industries like pharmaceuticals and food. Environmental Monitoring: Detecting pollutants in water, air, and soil samples. Colorimetry: Measuring the color of solutions, often used in textile and paint industries. 5. How did you determine which wavelength was absorbed at the highest level? How is this process useful in determining the identity of a molecule? - To determine the wavelength with the highest absorbance, you perform a spectrum scan of the sample by measuring its absorbance across a range of wavelengths. The peak absorbance indicates the wavelength at which the sample absorbs the most light. This peak is significant because each compound has a unique absorbance spectrum, acting as a molecular fingerprint. Identifying the peak absorbance helps in determining the identity of the molecule, as well as quantifying its concentration within the sample. 6. How do you clean a cuvette? - Proper cuvette cleaning is essential for accurate spectrophotometric measurements: Rinse the cuvette with the solvent or solution you will be using, to prevent contamination from previous samples. Use a lint-free cloth or air dry to avoid scratches on the cuvette surfaces. For stubborn residues, use a mild detergent solution followed by thorough rinsing with distilled water. Avoid touching the optical surfaces with your fingers to prevent smudging. Store cuvettes in a dust-free environment when not in use to maintain their cleanliness.