Spectrophotometic determination of Lorazepam in pharmaceutical tablets using batch and reverse flow injection methods

Figures & data

Fig. 1 Chemical structure of lorazepam.

Fig. 2 Manifold employed for RFIA-Spectrophotometric determination of LOR by reaction with MBTH and FeCl₃, where: IV, injection valve; RC, reaction coil; P, peristaltic pump; FC, flow cell; D, detector; W, waste.

Table 1 Analytical features of the procedures developed for the estimation of LOR.

Parameter	Batch procedure	RFIA procedure
Regression equation	y = 0.0166x + 0.1268	y = 0.0015x + 0.1008
Linear range (μg mL^−1)	2–40	25–400
Correlation coefficient (R^2)	0.9965	0.9996
Limit of detection (s/n = 3) (μg mL^−1)	0.614	2.287
Limit of quantification (μg mL^−1)	2.047	7.624
Reproducibility %	<0.321	<0.913
Average of recovery, %	101.165	99.560
Through-put (sample per hour)	6	26

Fig. 3 Schematic representation of the proposed reaction mechanism.

Fig. 4 Absorption spectra of the green colored product obtained from the reaction of 25 µg/mL of LOR with MBTH/ferric chloride measured against the reagent blank. The reagent blank was measured against distilled water. (For interpretation of the references to color in this figure caption, the reader is referred to the web version of this article.)

Fig. 5 Effect of the volume of reagent (MBTH 0.02 M) and oxidant (FeCl₃ 2% V/V).

Fig. 6 Effect of order of addition.

Fig. 7 Job method.

Table 2 Determination of LOR^* in presence of common interferences by batch method.

Excipient (250 μg/mL)	Found LOR, μg/mL	Recovery ± SD, %^**
Poly vinyl pyrrolidone	25.19	100.76 ± 0.36
Lactose	25.32	101.28 ± 0.22
Talc	25.22	100.88 ± 0.13
Magnesium stearate	25.46	101.84 ± 0.08
Total (contains all previous excipients)	26.09	104.36 ± 0.17

* Present 25 μg/mL of LOR.

** Average of five determinations.

Fig. 8 Effect of concentration of reagent.

Fig. 9 Effect of concentration of oxidant.

Fig. 10 Effect of reaction coil length.

Fig. 11 Effect of total flow rate.

Fig. 12 Effect of sample volume.

Table 3 Optimum conditions for the determination of LOR.

Variable	Studied range	Optimum values
Concentration of FeCl3 (% v/v)	1–10	8
Concentration of MBTH (M)	0.005–0.05	0.04
Reaction coil (cm)	50–200	80
Total flow rate (mL/min)	0.6–4.2	0.6
Injected reagent volume (µL)	75–200	150

Table 4 Accuracy and precision of the proposed methods.

Method	Conc. of LOR, μg/mL		RE%	Rec.%	RSD%^*
	Added	Found
Batch	15	15.18	1.20	101.20	0.32
	30	30.34	1.13	101.13	0.31
RFIA	100	99.47	−0.53	99.47	1.89
	250	249.13	−0.35	99.65	0.91

* Average of four determinations.

Table 5 Application of the proposed and official methods to the determination of LOR in different dosage forms.

Dosage form	Proposed methods								Official method [19]
	Batch				RFIA
	Conc. (µg/mL)		Rec. (%)^*	RSD (%)^*	Conc. (µg/mL)		Rec. (%)^*	RSD (%)c	Conc. (µg/mL)		Rec. (%)^*	RSD (%)^*
	Taken	Found			Taken	Found			Taken	Found
Lorativan® (2 mg)	10	10.28	102.80	0.11	75	75.49	100.65	0.56	10	10.23	102.30	0.75
	15	15.13	100.87	0.16	100	101.11	101.11	0.56	20	20.56	102.80	0.65
Lorazesam® (1 mg)	10	10.12	101.20	0.49	75	75.73	100.97	1.28	10	10.08	100.80	0.81
	15	15.30	102.00	0.25	100	101.35	101.353	0.55	20	20.53	102.65	1.45

* Average of five determinations.

Table 6 The statistical comparison between the current methods and standard method.

Dosage form	%Recovery ± SD^*
	Batch	RFIA	Official method
Lorazepam (pure form)	101.17 ± 0.05	99.56 ± 0.13	100.05 ± 0.23
Lorativan® (2 mg)	101.84 ± 1.37	100.88 ± 0.33	102.55 ± 0.35
Lorazesam® (1 mg)	101.60 ± 0.57	101.16 ± 0.27	101.73 ± 1.31
t (2.776)^**	0.123	1.027
F (19.000)^**	14.094	2.224

* For five determinations. Conc., concentration; RSD, relative standard deviation.

** Theoretical value.

USP (United States Pharmacopoeia, 30th revision); 2012.

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