Column:

Spherisorb 5 ODS (250*4.6 mm) chrompack (Bergen op Zoom, Netherlands)

Mobile phase:

A = acetonitrile

B = 0.067 M KH₂SO₄: 0.05% diethylamine H₂O

A = 60%; B = 40%; (1:1)

Wavelength:

UV: 240 nm

Flow:

1.2 ml/min

Injection volume:

100 ml

Retention time:

6.8 min

Reference solutions:

Freshly made before each new set of runs, with increasing concentrations from solution I to IV

Apparatus:

SP8800 ternary HPLC pump, a Spectra Physics UV detector 757 and an SP 4290 integrator (Spectra Physics)

Calibration curves

Ergometrine:

r = 0.9999

Methylergometrine:

r = 0.9999

Compound

Coefficient of variation (n =4/6) (%)

Concentration of free base (mg/tablet)

Inter-day (n=4)

Intra-day (n=6)

Ergometrine

147

1.2

1.73

Methyl- ergometrine

95

2.2

5.07

Column:

Spherisorb 5.0 ODS(250*4.6mm) chromopack

Mobile phase:

A: acetonitrile/H₂O 1:1

B: 0.1 M monobasicKH₂PO₄

buffer A = 55% ; B = 45%

Wavelength:

UV: 225 nm

Flow:

1.2 ml/min

Injection volume:

100 ml

Retention time:

6.7 min

Reference solutions:

Freshly made before each new set of runs, with increasing concentrations from solution I to IV.

Apparatus:

SP8800 ternary HPLC pump, a UV detector 757 and an SP 4290 integrator (Spectra Physics).

Calibration curves:

Oxytocin:

r = 0.9999

Desamino-oxytocin:

r = 0.9999

C Compound

Coefficient of variation (n =4/6) (%)

Concentration (IU/tablet)

Inter-day (n=4)

Intra-day (n=6)

Oxytocin

200

1.90

2.06

Desamino- oxytocin

50

3.19

1.96