Limit tests

Introduce the prescribed solution into a test-tube or dissolve the prescribed quantity of the substance to be examined in 14 mL of water R in a test-tube. Make the solution alkaline if necessary by the addition of dilute sodium hydroxide solution R, dilute to 15 mL with water R and add 0.3 mL of alkaline potassium tetraiodomercurate solution R. Prepare a standard by mixing 10 mL of ammonium standard solution (1 ppm NH4) R, 5 mL of water R and 0.3 mL of alkaline potassium tetraiodomercurate solution R. Stopper the test-tubes.

After 5 min, any yellow colour in the test solution is not more intense than that in the standard.

To 15 mL of the prescribed solution add 1 mL of dilute nitric acid R and pour the mixture as a single addition into a test-tube containing 1 mL of silver nitrate solution R2. Prepare a standard in the same manner using 10 mL of chloride standard solution (5 ppm Cl) R and 5 mL of water R. Examine the tubes laterally against a black background.

After standing for 5 min protected from light, any opalescence in the test solution is not more intense than that in the standard.

Introduce into the inner tube of the apparatus (see Figure 2.4.5.-1) the prescribed quantity of the substance to be examined, 0.1 g of acid-washed sand R and 20 mL of a mixture of equal volumes of sulfuric acid R and water R. Heat the jacket containing tetrachloroethane R maintained at its boiling point (146 °C). Heat the steam generator and distil, collecting the distillate in a 100 mL volumetric flask containing 0.3 mL of 0.1 M sodium hydroxide and 0.1 mL of phenolphthalein solution R. Maintain a constant volume (20 mL) in the tube during distillation and ensure that the distillate remains alkaline, adding 0.1 M sodium hydroxide if necessary. Dilute the distillate to 100 mL with water R (test solution). Prepare a standard in the same manner by distillation, using 5 mL of fluoride standard solution (10 ppm F) R instead of the substance to be examined. Into two glass-stoppered cylinders introduce 20 mL of the test solution and 20 mL of the standard and 5 mL of aminomethylalizarindiacetic acid reagent R.

After 20 min, any blue colour in the test solution (originally red) is not more intense than that in the standard.

To 10 mL of the prescribed solution add 0.1 g of disodium tetraborate R. Adjust the solution, if necessary, to pH 8.8 to pH 9.2 using dilute hydrochloric acid R or dilute sodium hydroxide solution R. Shake with 2 quantities, each of 5 mL, of a 1 g/L solution of hydroxyquinoline R in chloroform R, for 1 min each time. Allow to stand. Separate and discard the organic layer. To the aqueous solution add 0.4 mL of butylamine R and 0.1 mL of triethanolamine R. Adjust the solution, if necessary, to pH 10.5 to pH 11.5. Add 4 mL of the solution of hydroxyquinoline in chloroform, shake for 1 min, allow to stand and separate. Use the lower layer for comparison. Prepare a standard in the same manner using a mixture of 1 mL of magnesium standard solution (10 ppm Mg) R and 9 mL of water R.

Any colour in the solution obtained from the substance to be examined is not more intense than that in the standard.

To 200 mL of water R add 0.1 g of hydroxylamine hydrochloride R, 10 mL of ammonium chloride buffer solution pH 10.0 R, 1 mL of 0.1 M zinc sulfate and about 15 mg of mordant black 11 triturate R. Heat to about 40 °C. Titrate with 0.01 M sodium edetate until the violet colour changes to full blue. To the solution add the prescribed quantity of the substance to be examined dissolved in 100 mL of water R or use the prescribed solution. If the colour of the solution changes to violet, titrate with 0.01 M sodium edetate until the full blue colour is again obtained.

The volume of 0.01 M sodium edetate used in the second titration does not exceed the prescribed quantity.

The methods described below require the use of thioacetamide reagent R. As an alternative, sodium sulfide solution R1 (0.1 mL) is usually suitable. Since tests prescribed in monographs have been developed using thioacetamide reagent R, if sodium sulfide solution R1 is used instead, it is necessary to include also for methods A, B and H a monitor solution, prepared from the quantity of the substance to be examined prescribed for the test, to which has been added the volume of lead standard solution prescribed for preparation of the reference solution. The test is invalid if the monitor solution is not at least as intense as the reference solution.

Dissolve the prescribed quantity of the substance to be examined in water R and dilute to 10 mL with the same solvent or use 10 mL of the prescribed solution. Add 2 mL of a 200 g/L solution of citric acid monohydrate R and 0.1 mL of thioglycollic acid R. Mix, make alkaline with ammonia R and dilute to 20 mL with water R. Prepare a standard in the same manner, using 10 mL of iron standard solution (1 ppm Fe) R.

After 5 min, any pink colour in the test solution is not more intense than that in the standard.

Determine the lead by atomic absorption spectrometry (2.2.23, Method II).

To 100 mL of the solution prepared and, if necessary, neutralised as prescribed add 4 mL of sulfomolybdic reagent R3. Shake and add 0.1 mL of stannous chloride solution R1. Prepare a standard in the same manner using 2 mL of phosphate standard solution (5 ppm PO4) R and 98 mL of water R. After 10 min, compare the colours using 20 mL of each solution.

Any colour in the test solution is not more intense than that in the standard.

ZTo 10 mL of the prescribed solution add 2 mL of a freshly prepared 10 g/L solution of sodium tetraphenylborate R. Prepare a standard in the same manner using a mixture of 5 mL of potassium standard solution (20 ppm K) R and 5 mL of water R.

After 5 min, any opalescence in the test solution is not more intense than that in the standard.

All solutions used for this test must be prepared with distilled water R.

Add 3 mL of a 250 g/L solution of barium chloride R to 4.5 mL of sulfate standard solution (10 ppm SO4) R1. Shake and allow to stand for 1 min. To 2.5 mL of this suspension add 15 mL of the prescribed solution and 0.5 mL of acetic acid R. Prepare a standard in the same manner using 15 mL of sulfate standard solution (10 ppm SO4) R instead of the prescribed solution.

After 5 min, any opalescence in the test solution is not more intense than that in the standard.

Ignite a suitable crucible (for example, silica, platinum, porcelain or quartz) at 600 ± 50 °C for 30 min, allow to cool in a desiccator over silica gel or other suitable desiccant and weigh. Place the prescribed amount of the substance to be examined in the crucible and weigh. Moisten the substance to be examined with a small amount of sulfuric acid R (usually 1 mL) and heat gently at as low a temperature as practicable until the sample is thoroughly charred. After cooling, moisten the residue with a small amount of sulfuric acid R (usually 1 mL), heat gently until white fumes are no longer evolved and ignite at 600 ± 50 °C until the residue is completely incinerated. Ensure that flames are not produced at any time during the procedure. Allow the crucible to cool in a desiccator over silica gel or other suitable desiccant, weigh it again and calculate the percentage of residue.

Determine the nickel by atomic absorption spectrometry (2.2.23, Method II).

Heat a silica or platinum crucible to redness for 30 min, allow to cool in a desiccator and weigh. Unless otherwise prescribed, evenly distribute 1.00 g of the substance or the powdered herbal drug to be examined in the crucible. Dry at 100 °C to 105 °C for 1 h and ignite to constant mass in a muffle furnace at 600 °C ± 25 °C, allowing the crucible to cool in a desiccator after each ignition. Flames should not be produced at any time during the procedure. If after prolonged ignition the ash still contains black particles, take up with hot water, filter through an ashless filter paper and ignite the residue and the filter paper. Combine the filtrate with the ash, carefully evaporate to dryness and ignite to constant mass.

For vaccines for human use, prepare a 1 in 10 dilution of the vaccine to be examined. For bacterial toxoids for veterinary use, prepare a 1 in 25 dilution of the vaccine to be examined.

To 1 mL of the dilution, add 4 mL of water R and 5 mL of acetylacetone reagent R1. Place the tube in a water-bath at 40 °C for 40 min. Examine the tubes down their vertical axes. The solution is not more intensely coloured than a standard, prepared at the same time and in the same manner, using 1 mL of a dilution of formaldehyde solution R containing 20 µg of formaldehyde (CH2O) per millilitre, instead of the dilution of the vaccine to be examined.

This chapter describes the general approach for the determination of elemental impurities in medicinal products or substances for pharmaceutical use. As the chemical composition of the considered samples and the specification limits for the element(s) of interest vary considerably, it is not possible to describe all suitable sample preparation and measurement methods. Therefore, any method that fulfils the requirements described in this chapter may be used.

The results of the analysis are acceptable only if the system suitability has been demonstrated by a suitable test. Before the initial use of a method, the analyst must ensure that the method is appropriate for the samples and instruments used. This is accomplished by applying a validation procedure to methods not described in the individual monograph or by a system suitability test for methods which are described in the monograph. Decision trees for the choice of the sample preparation and the measurement procedures are presented in Figures 2.4.20.-1 and 2.4.20.-2.

The test for foreign oils is carried out on the methyl esters of the fatty acids contained in the oil to be examined by gas chromatography (2.2.28).

Examine by gas chromatography with static head-space injection (2.2.28).

The test is intended for the determination of residual ethylene oxide and dioxan in samples soluble in water or dimethylacetamide. For substances that are insoluble or insufficiently soluble in these solvents, the preparation of the sample solution and the head-space conditions to be employed are given in the individual monograph.

Head-space gas chromatography (2.2.28).

Examine by atomic absorption spectrometry (AAS) (2.2.23), inductively coupled plasma-atomic emission spectrometry (ICP-AES) (2.2.57), or inductively coupled plasma-mass spectrometry (ICP-MS) (2.2.58).

The nickel is determined using atomic absorption spectrometry (2.2.23, Method I).

Thin-layer chromatography (2.2.27).

Solvent mixture: anhydrous ethanol R, water R (10:90 V/V).

Test solution. The preparation to be examined.

Reference solution. Dissolve 0.86 g of tetrabutylammonium hydroxide R in the solvent mixture and dilute to 100 mL with the solvent mixture. Dilute 1 mL of the solution to V with the solvent mixture, V being the maximum recommended dose in millilitres.

Plate: TLC silica gel plate R; use a polyester plate.

Mobile phase:

–mobile phase A: concentrated ammonia R, methanol R (10:90 V/V);

–mobile phase B: concentrated ammonia R, methanol R (0.5:100 V/V).

Use either mobile phase A or mobile phase B. The choice of mobile phase depends on the matrix (for example, mobile phase B is suitable for preparations stabilised with ascorbate). Spiking experiments can be done to verify the suitability of the mobile phase and to show that the sample matrix has no influence on the results.

Application: 2 µL.

Development: over 4/5 of the plate.

Drying: at 50 °C for maximum 30 s.

Detection: place 0.5 g of iodine R at the bottom of a chromatographic tank; close the tank and heat it with a stream of hot air (about 60-80 °C) until it is filled with pink vapour; place the plate in the tank; leave the plate in contact with the iodine vapour for 1 min; withdraw the plate.

System suitability:

–the chromatogram obtained with the reference solution shows a clearly visible spot.

Limit:

–tetrabutylammonium: any spot due to tetrabutylammonium is not more intense than the corresponding spot in the chromatogram obtained with the reference solution (2.6 mg/V).