Paracetamol raw material used as a standard for the establishment of identifying comparison to the samples was procured from Farmason Pharmaceuticals (Gujarat, India), Distilled water used for dilution and sample preparation was from Kim Pharma laboratory (Kinshasa, D. R. Congo); and different brands used to conduct the study were purchased from legal distributors officially established in the Democratic Republic of the Congo. And in this work, we identified them as P1, P2, P3, P4 and P5.

Following instrumentations and apparatus helped to conduct this research: a Gram precision® Serie SV analytical balance to weigh analytical materials and samples, a UV/vis Spectrophotometer branded Genesis 10S UV-vis spectrophotometer to perform analytical essay and compounds identification. All pharmaceutical tests (hardness, friability, tablets disintegration, tablets dissolution) were performed using Sotax™ type apparatus for each parameter evaluation, volumetric flasks, measuring cylinders, mortar, pestle, Whatman N°4 filter paper and glass funnel.

We identified five Paracetamol brands, marketed in the Democratic Republic of the Congo from their local grossest (legal distributors) mostly based in Kinshasa. About 50 tablets per brand were registered for analytical purposes. And we have checked and noted all information for each one as the name of the manufacturer, the manufacturer location, batch number, manufacturing and expiring dates. To keep the manufacturer information confidential, we used codes to identify brands and for all of them, we used the letter P as Paracetamol, followed by a number as 1, 2, etc. to express the chronological order of collection.

After that collection, products were all kept under the same conditions before and during the analytical process to avoid every difference that can be related to an unregistered procedure on their manipulation.

Several analytical techniques can be used for Paracetamol determination from different matrixes which can be biological or pharmaceutical mixtures. In plasma, for example, Acetaminophen is currently estimated using spectrometric methods such as ultraviolet (UV) or separative methods combined with a good detection system like the gas-liquid chromatography (GLC) or high-performance liquid chromatography (HPLC) [10]. But in this research work, exclusively focused on the determination of pharmaceutical forms in particular tablet forms, we have only used ultraviolet spectrophotometry as an analytical method either in the identification of Paracetamol or for its quantification in brands under study.

To assess the quality and performance of the batches of a brand in comparison with one another, different tests should be taken. And this is the case with Paracetamol tablets, which were submitted to compendial and non compendial tests to establish a formal comparison based on the analysis of studied parameters.

These tests include weight uniformity, hardness and diameter, friability, disintegration time and dissolution test [11].

This examination includes the entire performed tests for the determination of different Paracetamol brands under this study:

• Identification test:

The quantity of Paracetamol powder obtained after crushing tablets is weighted for each brand sample. This is to contain about 500 mg of Paracetamol accurately weighted. That powder is placed in 10 ml of ethanol and filtered. After evaporation and drying, the residue was collected and mixed with 10 ml of water and 0.5 ml FeCl₃ 2%. A blue color appearance reveals the presence of Paracetamol. The obtained results for each studied brand will be presented below in this work.

• Paracetamol assay:

Several methods can be used to operate for Paracetamol quantification and most of them are costly and expensive for quality control purposes in the context of our countries because of the equipment and sophisticated apparatus they can request. However, the least expensive methods to perform that determination are revealed to be less sensitive with a lack of precision for serious quality studies [15].

In this research study, we used a sensitive, accurate and affordable method that required a low-cost reagent as a solvent for the dilution of the sample. The Paracetamol was assayed by UV spectrophotometry with all the collected brand samples and we present below different steps of the operating procedure.

1) The mean weight was determined for each brand sample using the weighted sum of twenty tablets divided by twenty.

2) We crushed ten tablets among twenty and weighted the powder quantity containing accurately 150 mg of Paracetamol from each brand.

3) We transferred into different 200 ml volumetric flasks all the five samples and labeled them.

4) In each volumetric flask, we added 50 ml of sodium hydroxide 0.1M and 100ml of distilled water.

5) The mixture was sonicated for fifteen minutes to dissolve Paracetamol in solution then we completed the volume with water to the gauge.

6) We filtered each solution into a clean beaker, and then we diluted each sample with distilled water until we obtained 7.5 µg/ml for every sample.

7) After UV spectrophotometer calibration, we started reading for determination of Paracetamol absorbance at 257 nm into a glass cuvette and we repeated the same operation for five brands, trice per sample and then we calculated the concentration using the Beer-Lambert formula and expressed it in percentage according to the British Pharmacopoeia 2008, H. M. Stationary Office, London, 2008, Vol. 3, pp 2968.

Notice that the UV spectra were determined for each Paracetamol brand and this was done trice per brand to observe the absorption curve as we present the below. It was done by running the apparatus between 200 and 400 nm on samples collected three times for each brand to observe the allure.

As stated above, this was to determine the weight uniformity and to establish the weights’ variation expressed in percentage. The following figure and table give the tablets’ weights and their variation according to the weighting manipulation for all the five brands under this study (Figure 2).

Each brand corresponds to a color and for each of them, there are twenty similar histograms giving an allure of the weight variation during the weighting operation of twenty tablets. Below this figure, we present a synthetic table giving all the weights values per unit of the tablet weighted, the weight variation and the corresponding variation expressed in percentage (Table 1).

w. mean = weight mean; D = variation; D in % = variation in percentage; mg = milligram and W/Unit = weight per unit (individual tablet weight).

The following table gives the statistical analysis of the weight uniformity test with all the five studied brands (Table 2).

This test allowed us to decide on the dissolution of tablets after administration by measuring the necessary time they take before complete disaggregation. It is an important test that helps to predict the absorption process. The following histogram and table show us graphically how the disintegration time varies between brands and the related figures in terms of disintegration time (Figure 3).

As we can see in Figure 2, the disintegration times related to Paracetamol brands under study showed good performance as the time did not exceed the reference fixed into the Pharmacopoeia and that time varied with a brand like P4 that disintegrated completely after 480 seconds or 8 minutes and was the highest time read for this test since other brands performed less than that duration. P3 gave a low figure in terms of disintegration time among all the samples under study.

The disintegration time of tablets from the five brands varied between 57 seconds to 480 seconds (8 minutes) leads us to conclude that all the brands are satisfied with the test according to the International pharmacopoeia, as their results are acceptable since that disintegrating time should not exceed 15 minutes (900 seconds), while studied samples performed the test along 8 minutes for the most lasting brand, as all the remaining samples did it during a time interval less or equal to 282 seconds (Table 3).

SD: standard deviation and RSD: relative standard deviation.

This test allowed us to predict the crushing strength of tablets from each of the five brands using the hardness tester. We considered the test as a failure if the tablets are outside of 39.23 N (4 Kgf) - 118 N (12 Kgf) intervals. The table below gives hardness values for each of the five brands.

Tables 4-8 shows that two Paracetamol brands, P4 and P5, have hardness values that fitted the referential standard according to that test. But differently, brands P1, P2 and P3 did not satisfy the conformity criterion as shown respectively their hardness figures 127.7, 155 and 124.4 Newton.

The tablets were placed in a Sotax™ friabilator and subjected to the tumbling actions at 50 rotations per minute for five minutes. After that, they were taken to be the time no granule on the apparatus mesh. The following table presents the rate of loss after the friability test established after tablets weighting by comparison to their weights before.

Tables 9-13 shows that all the branded samples had good friability valuable less than 1% as the first brand gave 0.4385%, the second 0.2037%, the third gave 0.7075% and the fourth 0.0787%. Only the fifth brand gave an exceeding value out of the acceptance value which is 1%. This last sample gave the wrong value (mean value of 1.687% as friability) that was above the acceptable figure according to the international pharmacopoeia given above.