สารบัญ

Thai name น้ำมันมะนาวฝรั่ง (NAMMAN MA-NAO FA-RANG)

Category  Pharmaceutic aid (flavouring agent).

        Lemon Oil is the volatile oil obtained by expression from the outer part of the fresh pericarp of the ripe or nearly ripe fruit of Citrus × limon (L.) Osbeck (Family Rutaceae).  It contains not less than 3.5 per cent w/w of aldehydes, calculated as citral, C₁₀H₁₆O. 

Origin of plant Lemon Oil-yielding plants are native to South Asia, particularly northwestern and northeastern India, and other parts of Asia. 

Constituents  Lemon Oil contains monoterpenes, predominantly limonene, citral, β-pinene, γ-terpinene, coumarins (e.g., citropten and 5-geranyloxy-7-methoxycoumarin), and furanocoumarin such as bergamottin, byakangelicin, and psoralen.

Description  Pale yellow or greenish yellow liquid, visibly free from water; odour, that of lemon.

Packaging and storage  Lemon Oil shall be kept in well-filled, tightly closed containers, protected from light, and stored at a temperature not exceeding 25°.

Identification  Carry out the test as described in the “Thin-Layer Chromatography” (Appendix 3.1).
     Standard solution Dissolve 10 mg of citropten and 50 µL of citral in toluene and dilute to 10 mL with the same solvent.
     Test solution  Mix 1 mL of the sample with 1 mL of toluene.
     Adsorbent  Silica gel F254.
     Mobile phase  Ethyl acetate and toluene (15:85). Application  Apply 10 µL each of Standard solution and Test solution as 10-mm bands.
     Development and drying  Dry the developed plate in air.
     Detection A  Examine the plate under ultraviolet light (254 nm).
     Results A  When examined under ultraviolet light (254 nm), the test solution shows a light blue fluorescent band due to citropten in the middle of the chromatogram, a quenching band due to citral in the upper third of the chromatogram, corresponding in colour and R_f to the bands shown by the standard solution.  There are also quenching bands of byakangelicin and psoralen derivative lower than the citropten band, in the lower third of the chromatogram; a dark blue band of 5-geranyloxy-7-methoxycoumarin in the middle of the chromatogram above the citropten band and a quenching band of bergamottin above the citral band, in the upper third of the chromatogram.
     Detection B  Examine the plate under ultraviolet light (366 nm).
     Results B  When examined under ultraviolet light (366 nm), the test solution shows a bright violet-blue fluorescent band due to citropten in the middle of the chromatogram, a quenching band due to  citral in the upper third of the chromatogram, corresponding in colour and R_f to the bands shown by the standard solution.  There are also an orange band of byakangelicin and a yellow fluorescent band of psoralen derivative lower than citropten band, in the lower third of the chromatogram; a bright blue fluorescent band of 5-geranyloxy-7-methoxycoumarin above the citropten band, in the middle of the chromatogram; a yellow fluorescent band of bergamottin above the citral band, in the upper third of the chromatogram.

Weight per millilitre  0.850 to 0.856 g (Appendix 4.9).

Refractive index  1.473 to 1.476, at 20° (Appendix 4.7).

Optical rotation  +57° to +70°, at 20° (Appendix 4.8).

Assay  Carry out the method for the “Determination of Aldehydes” (Appendix 7.9), using 10 g, omitting the toluene and using a volume, not less than 7 mL, of hydroxylamine in ethanol (60 per cent) TS that exceeds by
1 to 2 mL the volume of 0.5 M potassium hydroxide in ethanol (60 per cent) VS required.  Each mL of 0.5 M potassium hydroxide in ethanol (60 per cent) VS is equivalent to 76.73 mg of C₁₀H₁₆O.