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HomeSmall Molecules Analysis & QCAssay of Ibuprofen Esters & Impurities

Assay of Ibuprofen Esters & Impurities

Paul Lee, Jenna Milliken

MilliporeSigma Laramie, WY

INTRODUCTION

Ibuprofen, the active pharmaceutical ingredient in many brand-named products, is one of the most prolific APIs on the market and in our households. This application note describes an analysis of Ibuprofen-related compounds and impurities using an HPLC method similar to the compendial method described by the United States Pharmacopeia and European Pharmacopeia. The described ibuprofen assay method separates ibuprofen from various esters and intermediate impurities on the solid-core Ascentis® Express 90Å C18 column (USP L1) with 0.1% phosphoric acid in both water and acetonitrile as mobile phase. Due to the low absorbance maximum for ibuprofen at 220 nm, a slower gradient maximizes the separation and minimizes baseline drift.

Chemical structures of ibuprofen and ibuprofen-related impurities

Figure 1.Chemical structures of ibuprofen and ibuprofen-related impurities.

EXPERIMENTAL CONDITIONS

Column:

Ascentis® Express C18, 150 x 4.6 mm I.D., 2.7 µm (53829-U)

Mobile Phase:

[A] 0.1% phosphoric acid in water;

[B] 0.1% phosphoric acid in acetonitrile

Gradient:

Time (min)     %A     %B    

0                           48       52      

3                           48       52      

13                        15       85      

16                        15       85      

Flow Rate:

1 mL/min

Pressure:

194 bar (2814 psi)

Temperature:

Column: 30 °C
Autosampler: 12 °C

Detection:

DAD @ 220 nm, 254 nm

Injection:

7 µL

Samples

 

Diluent:

Acetonitrile and water (50:50)

Sample concentration:

Ibuprofen Standard - 0.4 mg/mL 

Resolution Solution - 0.07 mg/mL (each compound)

Results

Chromatogram of ibuprofen standard 0.4 mg/mL

Figure 2.Chromatogram of ibuprofen standard 0.4 mg/mL.

Chromatogram for Ibuprofen and its related impurities

Figure 3.Chromatogram for ibuprofen and its related impurities.

Peaks

Compound

Retention Time (min)

Relative Retention Time

Resolution to Preceding Peak

USP Tailing

λmax

1

1-(4-Isobutylphenyl)ethanol

5.224

0.92

-

1.07

220 nm                    

2

Ibuprofen

5.679

1.00

3.66

1.10

220 nm

3 | 4

2-Hydroxypropyl 2-(4-Isobutylphenyl)-propanoate)

7.212 | 7.517

1.27 | 1.32

11.70 (2.38)

1.39 | 1.03

220 nm

5

2-(4-Isobutyrylphenyl)propane

9.763

1.72

18.40

0.99

254 nm

6

Ethyl 2-(4-Isobutylphenyl)propanoate

12.696

2.24

24.19

0.99

220 nm

7

4-Isobutylstyrene

13.817

2.43

9.30

1.00

254 nm

8

Isopropyl 2-(4-Isobutylphenyl)propanoate

14.253

2.51

3.66

1.06

220 nm

9

1-Ethyl-4-isobutylbenzene

15.217

2.68

8.11

1.01

220 nm

Calibration and Linearity Data for Ibuprofen and its Related Compounds

 

Ibuprofen

2-(4-Isobutyrylphenyl)propane

2-Hydroxypropyl 2-(4-Isobutylphenyl)propanoate

Isopropyl 2-(4-Isobutylphenyl)propanoate

Concentration (μg/mL)

Mean Area

Mean Area

Mean Area

Mean Area

0.4

5.8

10.5

4.7

5.0

1.2

17.8

33.1

13.5

16.3

2.0

30.5

55.6

23.0

27.2

2.8

43.0

78.4

32.2

39.6

4.0

60.5

107.8

46.2

55.3

Std Error

0.31

1.28

0.15

0.47

STDEV

0.69

2.87

0.34

1.05

Slope

15.26

27.18

11.58

14.03

LOD (µg/mL)

0.14

0.32

0.09

0.22

LOQ (µg/mL)

0.46

1.05

0.30

0.75

 

1-Ethyl-4-isobutylbenzene

4-Isobutylstyrene

1-(4-Isobutylphenyl)ethanol

Ethyl 2-(4-Isobutylphenyl)propanoate

Concentration (μg/mL)

Mean Area

Mean Area

Mean Area

Mean Area

0.4

3.7

9.1

6.5

4.7

1.2

11.7

27.7

20.3

16.3

2.0

20.3

47.2

34.4

28.3

2.8

29.4

66.8

47.7

39.7

4.0

41.8

98.5

67.8

56.8

Std Error

0.28

0.91

0.24

0.23

STDEV

0.63

2.03

0.55

0.51

Slope

10.67

24.82

17.03

14.50

LOD (µg/mL)

0.18

0.25

0.10

0.11

LOQ (µg/mL)

0.59

0.82

0.32

0.35

 

Ibuprofen

2-(4-Isobutyrylphenyl)propane

2-Hydroxypropyl 2-(4-Isobutylphenyl)-propanoate)

Isopropyl 2-(4-Isobutylphenyl)propanoate

Concentration (μg/mL)

Mean Area

Mean Area

Mean Area

Mean Area

0.4

5.8

10.5

4.7

5.0

1.2

17.8

33.1

13.5

16.3

2.0

30.5

55.6

23.0

27.2

2.8

43.0

78.4

32.2

39.6

4.0

60.5

107.8

46.2

55.3

RSQ

0.9998

0.9987

0.9999 | 1.0000

0.9994

Concentration (μg/mL)

Mean Area

Mean Area

Mean Area

Mean Area

100

1516.8

3561.9 (125 µg/mL)

1138.5

1387.9

200

3193.9

7346.3 (250 µg/mL)

2377.4

2841.5

300

4612.4

10740.2 (375 µg/mL)

3567.0

4349.1

400

6202.9

13648.6 (500 µg/mL)

4767.7

5863.3

500

7493.0

-

5828.0

7123.3

RSQ

0.9983

0.9963

0.9993 | 0.9992

0.9990

Combined RSQ

0.9994

0.9988

0.9998 | 0.9998

0.9997

 

1-Ethyl-4-isobutylbenzene

4-Isobutylstyrene

1-(4-Isobutylphenyl)ethanol

Ethyl 2-(4-Isobutylphenyl)propanoate

Concentration (μg/mL)

Mean Area

Mean Area

Mean Area

Mean Area

0.4

3.9

9.1

6.5

4.7

1.2

11.7

27.7

20.3

16.3

2.0

20.3

47.2

34.4

28.3

2.8

29.4

66.8

47.7

39.7

4.0

41.7

98.5

67.8

56.8

RSQ

0.9994

0.9993

0.9999

0.9999

Concentration (μg/mL)

Mean Area

Mean Area

Mean Area

Mean Area

100

926.6

2011.4

1714.5

1537.4

200

1896.6

4321.2

3526.5

3212.7

300

2940.9

6568.6

5349.3

4748.2

400

3722.4

8838.6

7085.1

6012.3

500

4654.7

11273.2

8683.4

7672.4

RSQ

0.9973

0.9998

0.9993

0.9981

Combined RSQ

0.9992

0.9995

0.9998

0.9993

CONCLUSION

This method demonstrates excellent resolution for Ibuprofen and ibuprofen-impurities. But the stereochemical identification was not included in the scope of the analysis conducted (2-Hydroxypropyl 2-(4-Isobutylphenyl)propanoate comprises two diastereoisomers as synthesized).

The maximal range of linearity is approximately 500 µg/mL, particularly for 2-(4-Isobutyrylphenyl)propane and 4-Isobutylstyrene, which have strong absorption at 254 nm rather than 220 nm. The method enables ibuprofen to be separated from its impurities with excellent peak shape, with limits of quantification of 1 µg/mL or less.

See also Small Molecules Analysis & Quality Control (QC) for more information on other applications or use our chromatogram search.

See more chromatograms on ibuprofen here.

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