Domain: Engineering — Food and Bioprocess Engineering
Target concept: Detection of Vitamin B2 (Fluorometric Method)

Video generation prompt: Place 2 mL of milk sample into a quartz cuvette and measure it under a UV-Vis spectrophotometer at a wavelength of 445 nm.

Evaluation guide:
(i) Target concept: Fluorescence-based detection of riboflavin in milk requires selective 445 nm blue-light excitation of the native fluorophore in a transparent, non-fluorescent container under controlled optical geometry.
Minimum mechanism: Riboflavin must be present in milk; quartz must transmit 445 nm blue-violet light without self-fluorescence; the excitation source must be spectrally centered at 445 nm (visible blue light, not UV); emission must originate solely from liquid volume and cease when excitation stops.
(ii)Storyline: [Phase 1] Empty quartz cuvette shown in hand → [Phase 2] Milk sample dispensed into cuvette (liquid fills defined volume) → [Phase 3] Cuvette inserted smoothly into spectrophotometer compartment → [Phase 4] Instrument activated (lid closed / button pressed) → [Phase 5] Yellow-green fluorescence appears *only* within liquid column, synchronized with beam onset → [Phase 6] Fluorescence vanishes immediately upon removal or deactivation. All phases maintain fixed viewpoint, consistent lighting, and unbroken spatial continuity; fluorescence must not precede beam activation or persist beyond it.

Manual:
Experimental Procedure
1. Place 2 mL of milk sample into a clean quartz cuvette.
2. Insert cuvette into UV-Vis spectrophotometer sample compartment.
3. Set wavelength to 445 nm and activate the excitation source.
Observation of Experimental Phenomena
Milk sample emits visible yellow-green fluorescence exclusively while irradiated at 445 nm inside the spectrophotometer.
Summary of Experimental Principles
Vitamin B2 (riboflavin) is naturally fluorescent; excitation at 445 nm (visible blue light, not UV) induces emission in the yellow-green region (~520–530 nm), enabling quantitative detection via fluorometry.

Prompt Grounding rubric:
level_1: The quartz cuvette, the 2 mL milk sample, or the spectrophotometer is missing entirely, is replaced with the wrong container (e.g., a glass test tube or beaker), or the milk-placement action is never shown at all.
level_2: The cuvette and milk are both shown but at least one is misrepresented: the cuvette is opaque, tinted, or visibly scratched rather than optical-grade quartz, the sample looks like clear water instead of milk, or the cuvette is never inserted into the spectrophotometer's sample compartment (it is left beside the instrument or held in hand).
level_3: A transparent, smooth-walled quartz cuvette holds an opaque white-to-pale-yellow milk sample filling roughly half to two-thirds of its height, and the cuvette sits inside the spectrophotometer's sample compartment; the exact 2 mL fill volume and 445 nm wavelength setting are not explicitly displayed, but the cuvette, milk, and instrument are all present and correctly arranged relative to one another.
level_4: Everything in the 3-point level holds, and in addition the cuvette's uniform wall thickness and high optical clarity mark it clearly as quartz (no meniscus distortion), the milk is rendered as an opaque white or pale-yellow liquid (never transparent or blue-tinted), and the spectrophotometer shows a numeric display or an aligned beam path with no extra glassware, droppers, or unrelated lab items in frame.
level_5: Everything in the 4-point level holds, and in addition the milk column height is visually consistent with a 2 mL fill in a standard 10 mm-pathlength quartz cuvette, the spectrophotometer's compartment lid is shown closed with its beam-on indicator or numeric readout active, and there is no ambiguity about which object is the cuvette, which liquid is the milk, or when the insertion action occurs.

Scientific and Causal Correctness rubric:
level_1: The milk shows color or glow under ordinary room light with no excitation beam engaged, the cuvette glows without the 445 nm beam ever turning on, or a yellow-green tint is added artificially (e.g., a static overlay or lens-flare effect) rather than appearing as a response to excitation.
level_2: The milk in the cuvette looks transparent or plain pale yellow under ambient light and never develops fluorescence once the excitation beam activates, or fluorescence appears before the cuvette is inserted or continues after it is removed, or the glow seems to come from the cuvette walls rather than from the milk itself.
level_3: The milk sample develops visible yellow-green fluorescence only while seated inside the spectrophotometer's sample compartment and only while the 445 nm beam is indicated as active (beam-path illumination or an instrument status light is visible); the glow is confined to the liquid itself, not to the surrounding air or cuvette walls.
level_4: Everything in the 3-point level holds, and in addition the fluorescence color stays a consistent yellow-green (never shifting to orange, red, or cyan), the brightness is even across the liquid column with no dark patches or bright spots, no glow leaks onto the compartment walls, the operator's hand, or the background, and the fluorescence stops as soon as the cuvette is removed or the beam is switched off.
level_5: Everything in the 4-point level holds, and in addition the fluorescence turns on only after both the cuvette is seated and the beam is engaged, and turns off together with cuvette removal or beam deactivation with no delay or leftover glow; the yellow-green emission is visually distinguishable from the blue-violet color of the excitation light itself, matching riboflavin's known ~520-530 nm emission response to 445 nm excitation.

Spatiotemporal Consistency rubric:
level_1: The cuvette appears already inside the spectrophotometer with no insertion shown (a jump cut from empty to filled), the cuvette rotates or flips on its own between shots, or the room lighting or shadow direction switches with no connection to the beam turning on or off.
level_2: The hand-guided insertion of the cuvette into the compartment is jerky or skips frames rather than moving continuously, the milk's surface trembles or ripples while the cuvette is sitting still, or the beam-path illumination flickers on and off erratically or appears before the cuvette is fully seated.
level_3: The cuvette moves into the spectrophotometer's compartment in one smooth, continuous motion, the milk's surface stays level and undisturbed once the cuvette is at rest, and the only lighting change in the scene (the 445 nm beam turning on) happens right when the lid is closed or the activation button is pressed, with no warping of the cuvette or instrument body.
level_4: Everything in the 3-point level holds, and in addition the insertion motion keeps a steady pace with no sudden speed-ups or stops, the milk's meniscus keeps its normal curved shape throughout, the beam illumination stays confined to the cuvette's liquid column inside the compartment rather than spilling across the whole cavity, and no part of the cuvette or instrument is clipped or occluded inconsistently between frames.
level_5: Everything in the 4-point level holds, and in addition the cuvette stays centered on the beam axis in every frame, the spectrophotometer body and lab bench behind it show no drift or parallax as the camera holds its view, the beam-on lighting change is the only lighting change in the scene, and there is no ghosting, duplicated frames, or motion-blur artifact that breaks the natural inertia of the insertion motion.