Unit 10: Mini Project 2 - Practice Quiz

1 What does TLC stand for?

2 What is the main purpose of TLC profiling of egg lipids?

3 What is commonly used as the stationary phase in lipid TLC?

4 What is the mobile phase in a TLC experiment?

5 Where should an egg lipid sample be applied on a TLC plate?

6 Why should the sample spot be small and concentrated?

7 What causes lipid components to move different distances on a TLC plate?

8 In general, a compound that travels farther on a TLC plate has a higher:

9 What does the value compare?

10 Which equation represents the TLC retention factor?

11 What is the solvent front?

12 Why is the solvent front marked immediately after development?

13 What is one reason to run egg samples from different sources on the same TLC plate?

14 If two egg samples produce spots at similar positions, what may this suggest?

15 What is a lipid standard used for in TLC?

16 Why are organic solvents often used to extract lipids from egg samples?

17 What should be avoided when applying a sample to a TLC plate?

18 Why should the baseline be drawn with a pencil rather than a pen?

19 What is one common way to make separated lipid spots visible?

20 What does a difference in the number of TLC bands between egg sources indicate?

21 What is the main purpose of using TLC when comparing lipids extracted from eggs of different sources?

22 A lipid extract produces a spot with an value of . If the solvent front traveled , how far did the spot travel?

23 Why should the origin line be drawn with a pencil rather than a pen?

24 Two egg extracts produce spots at the same value in the same solvent system. What is the most appropriate conclusion?

25 Why are reference lipid standards useful when analyzing egg lipid extracts by TLC?

26 A sample spot remains at the origin while the solvent front moves normally. Which explanation is most likely?

27 What is the likely effect of applying an excessively large volume of egg lipid extract to the TLC plate?

28 If the solvent level is above the sample application line at the start of development, what problem can occur?

29 Why should the developing chamber be covered during TLC separation?

30 An egg extract gives three spots, while another gives five spots under identical TLC conditions. What does this observation suggest?

31 Why should all egg extracts be spotted at the same distance from the bottom of the TLC plate?

32 A spot travels while the solvent front travels . What is the spot's value?

33 In a relatively nonpolar solvent system, which component would generally travel farther on a silica TLC plate?

34 What is the main reason for drying the TLC plate before visualizing or staining it?

35 If two nearby lipid spots merge into one broad band, which adjustment would most directly improve separation?

36 Why is it important to analyze egg samples from different sources on the same TLC plate when possible?

37 A spot has an value greater than . What is the most likely cause?

38 Why should the solvent front be marked immediately after removing the TLC plate?

39 A lipid spot is faint but appears at the same position in replicate samples. What is the best interpretation?

40 Which observation would provide the strongest evidence that two egg sources have different lipid profiles?

41 Two egg-lipid extracts are analyzed on silica TLC plates using the same solvent system. A phospholipid standard has an Rf of 0.18, while one sample contains a spot at Rf 0.19 and another at Rf 0.42. What is the most defensible interpretation?

42 The solvent front traveled 7.5 cm. A lipid spot traveled 3.0 cm in one lane and 2.7 cm in a replicate lane. What conclusion is best supported?

43 A lane containing an egg extract shows a broad streak from the origin through the middle of the plate instead of discrete spots. Which corrective action is most appropriate first?

44 A student compares egg sources using separate TLC plates. The same phospholipid standard has Rf values of 0.21, 0.28, and 0.34 on the three plates. What is the best experimental response?

45 Two egg extracts produce spots at nearly identical Rf values, but one spot is much darker after staining. Which interpretation is scientifically justified?

46 A sample lane contains a spot at the same Rf as a cholesterol standard and a second spot just below it. What is the most appropriate conclusion?

47 In a normal-phase silica TLC system, a less-polar neutral lipid generally travels farther than a more-polar phospholipid. What mechanism best explains this pattern?

48 A solvent chamber was not equilibrated before development, and solvent levels differed slightly between lanes. Which effect is most likely?

49 An egg extract shows no visible lipid spots, but the positive control is clearly detected. The extract was prepared with a solvent that does not efficiently recover neutral lipids. What is the strongest conclusion?

50 A lipid spot appears at the origin in every sample lane but not in the solvent blank. Which explanation is most plausible in a normal-phase system?

51 Three egg sources yield phospholipid spot intensities of 80, 160, and 240 arbitrary units, but different extract volumes were spotted. Which comparison is most appropriate?

52 A sample spot has an Rf of 0.50, while standards for lipid A and lipid B have Rf values of 0.48 and 0.52. What is the best identification strategy?

53 A sample was spotted before the pencil origin line had fully dried after marking. Several lanes show diffuse lower bands. What is the likely consequence?

54 A source-specific spot appears only after chemical derivatization, while the untreated plate showed no visible band. How should this result be reported?

55 A blank solvent lane develops a faint spot at the same Rf as a major sample spot. What should be done before attributing that spot to egg lipids?

56 Egg samples from two sources show different ratios of phospholipid to neutral-lipid spot intensities. However, one source was extracted from yolk and the other from whole egg. What is the primary limitation?

57 The solvent front is irregular, rising 6.0 cm on one side and 7.0 cm on the other. How should Rf values be calculated for spots on the plate?

58 A researcher wants to claim that one egg source has a unique lipid not found in the others because a faint spot appears only in that source. Which additional evidence is most important?

59 Two egg extracts have equal total lipid mass applied, but one produces severe streaking and the other gives sharp bands. Which factor should be investigated first?

60 A sample spot and a standard spot have the same Rf in one solvent system, but their co-spot produces a broadened or asymmetric band. What does this most strongly suggest?