Determination of Aspirin Content in Enteric-Coated Aspirin Tablets

Enteric-coated aspirin tablets are, as the name suggest, aspirin tablets that have been enterically coated. Enteric coating serves to prevent tablets from being broken down in the gastric environment, which serves to either protect the tablet content from the stomach, the stomach from the tablet content, or to specifically allow the tablet’s content to be released elsewhere in the system.

This report describes the method by which of the L-3000 HPLC System can be used to accurately and reliably determine the Aspirin content of enteric-coated aspirin tablets.

Aspirin Assay

The following equipment were used in the determination of aspirin content in enteric-coated aspirin tablets experiment: A 4-piece Dionamix HPLC system (Consisting of an L-3100 Solvent Organizer, an L-3220 Binary High-Pressure Gradient Pump, an L-3300 Autosampler, and an L-3500 UV/Visible Detector), a 5 µm, 4.6mmx250mm Dionamix Compass C18, a Millipore Milli-Q ultrapure water purification system, a Sartorius Germany BT 124S scale, a set of Eppendorf 10-100µL and 10-1000µL pipettes, and a Kunshan Ultrasound.

The experiment ran for 30 minutes, and was carried out under the following parameters: A flow rate of 1.0mL/min, an injection volume of 10µL, a detection wavelength of 276nm, and a column temperature of 30°C.

Mobile Phase

The mobile phase was prepared from a mix of acetonitrile, tetrahydrofuran, glacial acetic acid, and water, at a ratio of 20:5:5:70

Sample Preparation

Standard Curve Solutions

0.010g of the aspirin reference substance was added to a 5mL volumetric flask and mixed with a 1% glacial acetic acid methanol solution to produce a solution with a concentration of 2.0mg/mL (Stock Solution). 1mL of that solution was extracted and added to a 10mL volumetric flask and mixed with the aforementioned glacial acetic acid methanol solution to produce a solution with a concentration of 200µg/mL (Standard Solution (1)). This process was repeated with varying volumes added to 10mL volumetric flasks and mixed with 1% glacial acetic acid methanol solution to produce solutions with concentrations of 100µg/mL (2), 40µg/mL (3), 20µg/mL (4), and 10µg/mL (5).

Sample Solutions

20 enteric-coated aspirin tablets were weighed and ground down. 30mg of the powder (actual sample amount 29.600mg, equivalent to 10mg of aspirin) was added to a 100mL volumetric flask, dissolved in a 1% glacial acetic acid solution, and filtered with a 0.45µm organic phase filter (Enteric-Coated Aspirin Tablets Solution (1)). 30mg of the powder, added to a 100mL volumetric flask alongside 2mL of the Stock Solution, dissolved in a 1% glacial acetic acid methanol solution, and filtered with a 0.45µm organic phase filter (2).

System Suitability

Standard Solution (3) was injected. It was found to have a retention time of 7.200 seconds and a tailing factor of 1.038 with a column efficiency of 16994. The chromatogram of the aspirin reference substance can be seen on the right.

System Suitability Repeatability

Standard Solution (2) was injected 6 times. The qualitative and quantitative chromatogram of the aspirin reference substance can be seen on the left. A qualitative RSD% (n=6) of 0.144 and a quantitative RSD% (n=6) of 0.577 were calculated from the values below.

Name	Retention Time	Peak Area
Aspirin 100µg 1	7.193	295.337
Aspirin 100µg 2	7.200	290.560
Aspirin 100µg 3	7.210	294.770
Aspirin 100µg 4	7.217	294.148
Aspirin 100µg 5	7.213	293.863
Aspirin 100µg 6	7.220	294.466

Linear Range of the Standard Curve

Standard Solutions (5), (4), (3), (2), and (1) were successively injected once each, the chromatogram of which can be seen on the right

The standard curve of the aspirin reference substance can be seen on the left. The concentration range was found to be 10µg/mL - 200µg/mL, the regression equation Y = 3.04148 * X + 5.36948, and the correlation coefficient r = 0.9999

Quantification and Detection Limit

Single-point external standard was used to calculate the LOQ and LOD with the lowest concentration in the standard curve. Noise was cancelled via the ASTM method. The chromatogram of Standard Solution (5) can be seen on the right. With a concentration of 10mg/L, a peak height mAU of 3.169, a noise of mAU 0.030, the LOD (mg/L) S/N = 3 was calculated to be 0.283 and the LOQ (mg/L) S/N = 10 to be 0.944.

Sample Measurement Results

Sample 1 was injected, the chromatogram of which can be seen on the left. With a peak area of 324.129, a peak height of of 39.570, and a column efficiency of 17041, the ingredient content was calculated to be 27mg/tablet, using the content calculation formula below.

Vitamin B6 Content (mg/tablet) =
(AS + 5.36848) / 3.04148 / 1000 * 100 * 25 / 10
Where:
AS is the peak area of peak 1 of the enteric-coated aspirin tablet solution, and
MS represents the weighted mass of the enteric-coated aspirin tablet solution (1) (g)
MS is listed in the original appnote but is bizarrely not present in the formula

Sample Measurement Repeatability

Test solution (1) was injected was injected 6 times. The qualitative and quantitative chromatogram of the aspirin solution can be seen on the right. A qualitative repeatability RSD% (n=6) 0.073 and a quantitative repeatability of RSD% (n=6) of 0.234 were calculated from the values below.

Name	Retention Time	Peak Area
Aspirin Tablet 11	7.210	324.129
Aspirin Tablet 12	7.217	325.612
Aspirin Tablet 13	7.223	323.876
Aspirin Tablet 14	7.220	323.589
Aspirin Tablet 15	7.217	324.249
Aspirin Tablet 16	7.210	325.034

Rate of Recovery

Test Solution (2) was injected 3 times, the chromatogram of which can be seen on the left. Recovery rates were calculated from the formula below.

Rate of Recovery (%) =
[(AR + 5.36849) / 3.04148 - (AS + 5.36948) / 3.04148] / CA * 100%
Where:
AR is the peak area of the enteric-coated aspirin tablet solution after adding the aspirin standard substance,
AS is the average peak area of the enteric-coated aspirin tablet solution, and
CA is the concentration of aspirin standard solution added to the enteric coated aspirin tablet (µg/mL)

Of the three injections, the AR were given at 456.950, 457.371, and 458.092. All three shared an AS of 324.432, and a CA of 4000µg/mL, giving the calculated rate of recoveries as 108.9%, 109.3%, and 109.9%, with an average rate of recovery of 109.4%.

Conclusion

The L-3000 HPLC is capable of quickly and efficiently carrying out the enteric-coated aspirin tablet content experiment to a high degree of accuracy, and with good qualitative and quantitative repeatability.

This makes the Dionamix L-3000 HPLC system and method well suited to the needs of research scientists, quality control managers, industry regulators, and other similar roles that require a precise understanding of the content found within pharmaceutical tablets or similar.

Applicable to research and quality assurance processes, the HPLC system and method also delivers more accurate results than other methods, and is additionally quite versatile.