Determination of sodium in margarine manufacture

Transcription

1 Titration Application Note H 124 Determination of sodium in margarine manufacture This Application Note describes the determination of the total sodium content of precursor solutions used in margarine manufacture. These solutions are mixed with food fats and oils to make margarine, and may contain sodium chloride and other salts of sodium and potassium, some of which may be added in the form of emulsifiers, stabilizers, antioxidants, vitamins, coloring agents, and flavorings. It is more efficient and costeffective for manufacturers to analyze (and, if need be, correct) the sodium content of these solutions rather than in the finished product. Traditionally, argentometric titrations have been used to estimate the sodium content of these solutions by analyzing for chloride, and assuming all sodium is derived from sodium chloride. Clearly, argentometric titration does not account for other sources of sodium present in the solution, and the use of potassium chloride as a partial replacement for sodium chloride in some formulations leads to a further source of error. The direct titration of sodium by thermometric endpoint titration (TET) accounts for all sodium present and is not subject to interference from potassium.

2 Titration Application Note H 124 Version 1 Principle Sodium ion reacts exothermically with aluminium ions in the presence of potassium and fluoride ions to form insoluble NaK 2 AlF 6 («elpasolite»). Aluminium must be in the Al 3+ ionic form. The reaction may be used for the quantitative determination of total sodium in various foodstuffs. Samples Randomly selected samples of aqueous margarine precursor solutions were provided by a food manufacturer. Sample preparation The samples required no special preparation. Configuration Basic equipment list for automated titration 814 USB Sample Processor Titrotherm Sample rack ml Thermoprobe HF resistant Sample beaker 75 ml Rod Stirrer Stirring propeller 104 mm Dosino Dosing unit 10 ml ETFE cylinder unit 10 ml 1 Dosing unit 5 ml tiamo * Acidified solutions of fluoride ion are used in this determination Solutions Titrant Analysis of samples c(al(no 3 ) 3 ) = 0.5 mol/l aluminium nitrate solution prepared in a solution of c(kno 3 ) = 1.1 mol/l potassium nitrate c(nh 4 F) = 40% (w/v) ammonium fluoride in deionized water. c(hcl) = ~1 mol/l hydrochloric acid (does not require standardization c(nacl) = 0.1 mol/l sodium chloride, for standardization of the c(al(no 3 ) 3 ) = 0.5 mol/l aluminium nitrate solution Between 0.5 and 2.5 g of sample is weighed into a clean, dry titration vessel to obtain a titration volume at the endpoint of between approximately 1 to 2.5 ml of titrant. The amount required may vary according to the formulation and may require some initial experimentation to obtain optimal sample masses for different solution formulations. The solution is diluted with 25 ml of c(hcl) = ~1 mol/l. Alternatively, 2 ml concentrated HCl and 25 ml deionized water may be used to dilute and condition the sample. The suspension is then titrated with standardized c(al(no 3 ) 3 ) = 0.5 mol/l solution after automated addition of 5 ml c(nh 4 F) = 40% (w/v) solution. Initial determination of reagent blank The blank determination is only required for the initial setup for analysis of this type of food product. Five separate titrations are performed on a sample regarded as typical by the analyst. For example, for a solution where the sodium content is approximately 1% (w/w), samples masses ranging from ~1 to ~2.5 g in roughly equal increments may be used. A regression analysis is performed on the results, with the x-axis denoting sample mass in g, and y-axis titration endpoint volumes in ml. Standardization of titrant Aliquots of 5, 10, 15, 20, and 25 ml of 0.1 mol/l c(nacl) are pipetted into titration vessels and diluted with deionized water to bring the volume to ~25 ml. To each vessel, 1 ml of concentrated HCl is added. The solutions are titrated under the same conditions as for the samples. A regression analysis is performed, with the amount of NaCl titrated (as mmol) plotted on the x-axis, and the volume of c(al(no 3 ) 3 ) = 0.5 mol/l in ml plotted on the

3 Titration Application Note H 124 Version 1 y-axis. The molarity of the Al3+ solution is calculated from the reciprocal of the gradient. A dedicated tiamotm program has been created to automatically perform this standardization. Parameters Basic experimental parameters Titrant dose rate (ml/min) ERC EP1 (exothermic) 8 Data smoothing («filter factor») Stirring speed (802 Rod Stirrer) Evaluation start (ml) 0.7 Damping until (ml) 0.7 Titration plot Blank determination Calculations % Na (w/w) = ((EP1 blank) C001 C )/C00 EP1 = endpoint in ml blank = titration blank, ml C00 = sample mass in g C001 = concentration of titrant in mol/l C002 = atomic mass of Na ( g/mol) Results Sample ID % Na (w/w) , , ± 0.01 (n = 5) , , 0, ± 0.01 (n = 8) Blank = y intercept = ml

4 Titration Application Note H 125 Determination of sodium in soy milk This Application Note describes the determination of the total sodium content in soy milk products. The methodology may also be applied to the determination of sodium in milk from cows, goats, and sheep. A standard addition technique is employed to permit the accurate and precise determination of sodium at relatively low levels.

5 Titration Application Note H 125 Principle Sodium ion reacts exothermically with aluminium ions in the presence of potassium and fluoride ions to form insoluble NaK 2 AlF 6 («elpasolite»). Aluminium must be in the Al 3 + ionic form. The reaction may be used for the quantitative determination of total sodium in milk products. For accurate and precise analysis, it is necessary to remove protein and lipids from the food. Trichloroacetic acid is used to denature the protein. The resultant curd is separated by filtration or centrifugation, and the whey or «serum» titrated for the sodium content. To enable the analysis of products with lower sodium contents, a fixed volume of standard sodium chloride solution is added. Subtraction of the titration volume of the standard sodium chloride solution alone allows determination of the sodium content. Samples Two soy milk products were purchased from a supermarket «Vitasoy» and «Nature s Soy». Sample preparation The products were well shaken before sampling. Configuration Basic equipment list for automated titration 814 USB Sample Processor Titrotherm Sample rack ml Thermoprobe HF resistant Sample beaker 75 ml Rod Stirrer Stirring propeller 104 mm Dosino Dosing unit 10 ml ETFE cylinder unit 10 ml 1 Dosing unit 5 ml tiamo * Acidified solutions of fluoride ion are used in this determination Solutions Titrant Analysis of samples c(al(no 3 ) 3 ) = 0.5 mol/l aluminium nitrate solution prepared in a solution of c(kno 3 ) = 1.1 mol/l potassium nitrate c(nh 4 F) = 40% (w/v) ammonium fluoride in deionized water. CCl 3 COOH trichloroacetic acid A.R. c(nacl) = 0.25 mol/l sodium chloride, for standardization of the c(al(no 3 ) 3 ) = 0.5 mol/l aluminium nitrate solution and use as a standard addition 100 ml of milk is pipetted into a 250 ml Erlenmeyer flask containing 12.0 g trichloroacetic acid and a magnetic spin bar. The flask contents are then stirred for five minutes. The curdled milk is then filtered through a fast filtering paper or centrifuged. A 25 ml aliquot of the filtrate or centrifugate is then titrated with standardized c(al(no 3 ) 3 ) = 0.5 mol/l solution after automated addition of 3 ml c(nacl) = 0.25 mol/l and 5 ml c(nh 4 F) = 40% (w/v) solution. Note that since the aliquot is taken from a solution whose original volume has been enhanced by the addition of the trichloroacetic acid; this volume increase has to be taken into account when calculating the effective volume of original milk actually titrated. It has been found experimentally that the dissolution of 12 g trichloroacetic acid in 100 ml water increases the volume of solution to 106 ml. Therefore, for example, a 25 ml aliquot of filtrate or centrifugate is equivalent to /106 = ml of milk. Initial determination of NaCl blank The blank determination is required when either a new standard solution of c(nacl) = 0.25 mol/l is prepared, or when a new batch of c(al(no 3 ) 3 ) = 0.5 mol/l titrant is prepared. Weigh 3.0 g trichloroacetic acid into a titration vessel and add 25 ml deionized water. Titrate with mixed c(al(no 3 ) 3 ) = 0.5 mol/l, c(kno 3 ) = 1.1 mol/l solution after automated addition of 3 ml c(nacl) = 0.25 mol/l and 5 ml c(nh 4 F) = 40% (w/v) solution. Perform this analysis in triplicate, and calculate the mean of the volume of titrant required to reach the endpoint. Save this value as a Common Variable CV.

6 Titration Application Note H 125 Standardization of titrant Prepare five titration vessels, each containing 25 ml deionized water and 3 g trichloroacetic acid. Aliquots of 2, 4, 6, 8, and 9 ml of c(nacl) = 0.25 mol/l are dispensed by a Dosino as part of an automated tiamo standardization program, which also adds 5 ml c(nh4f) = 40% (w/v) solution before the commencement of titration with mixed c(al(no 3 ) 3 ) = 0.5 mol/l, c(kno 3 ) = 1.1 mol/l solution. A regression analysis is performed automatically by tiamo to compute the strength of the Al solution. Titration plot Parameters Basic experimental parameters Titrant dose rate (ml/min) ERC EP1 (exothermic) -40 Data smoothing («filter factor») Stirring speed (802 Stirrer) Evaluation start (ml) 1 Damping until (ml) 1 Results Blank determination (titration of 3.0 ml c(nacl) = mol/l) : , , , ml Mean = ml Analysis of soy milks Na mg/100 ml Soy milk Nutrition information average value TET analysis Nature s Soy ± 0.2 (n = 7) Vitasoy ± 0.1 (n = 8)