научная статья по теме DETERMINATION OF ENERGIZERS IN ENERGY DRINKS Химия

Текст научной статьи на тему «DETERMINATION OF ENERGIZERS IN ENERGY DRINKS»

ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2010, том 65, № 12, с. 1257-1263

ОРИГИНАЛЬНЫЕ СТАТЬИ =

УДК 543

DETERMINATION OF ENERGIZERS IN ENERGY DRINKS © 2010 Celina Pieszko, Irena Baranowska, Aneta Flores

Department of Analytical Chemistry, Silesian Technical University 7M. Strzody Str., 44-100 Gliwice, Poland Received 17.08.2009; in final form 05.05.2010

The method of UV/VIS derivative spectrophotometry for the determination of caffeine and B vitamins in energy drinks after solid phase extraction has been developed. Caffeine has been determined in the mixture with B2 vitamin with zero-crossing technique from the I derivative spectra = 266.8 nm), and B3 in mixture with B6 vitamin from the II derivative spectra (1 = 280.1 nm). Bi2 vitamin has also been determined in a three-component mixture with vitamins B3 and B6. Taurine in drinks has been determined from the basic spectra after derivatization with ninhydrin (1 = 570 nm).

Keywords: taurine, caffeine, B vitamins, derivative spectrophotometry.

Energy drinks are a source of energy, they improve mental and physical performance and liquidate fatigue. At the same time physicians warn about the side effects of many stimulants [1, 2]. The ingredients of most energy drinks are similar, the drinks are composed ofwater, sugar, acidity regulators (citric acid and sodium citrate) and carbon dioxide. The actual energizers are: caffeine, taurine and B vitamins like riboflavin, niacin, panthotenic acid, vitamins B6 and B12. The most common method of determination of the mentioned compounds is chroma-tography [3—8]. Spectrophotometry method was used for determination ofcaffeine in drugs [9—11]. For simultaneous determination of riboflavin (B2), pyridoxine (B6), nicotinamide (B3), caffeine and taurine in energy drinks a planar chromatography method was developed [12]. Also caffeine in energy drinks was determined using HPTLC—UV [13], GC-MS [14] and Raman spectrometry with Fourier transform [15].

In this work a method of derivative spectrophotometry has been used for the purpose of simultaneous determination of energizers in energy drinks.

EXPERIMENTAL

Reagents and materials. Standard solutions of caffeine (Sigma-Aldrich), vitamin B2, vitamin B3, vitamin B6, vitamin B12 (Merck) were all 0.1 mg/mL solutions in water. Materials for analysis were samples of energy drinks available on the market and produced by various companies. Ten different energy drinks were analyzed. Samples were stored in original cans in a refrigerator according to manufacturers' recommendations.

Spectrophotometry procedure. Spectrophotometric investigations were carried out on the Hewlett Packard UV/VIS spectrophotometer HP-8452A in 1 cm cells with integration time 1 s, AX 2 nm, accuracy of absor-bance scale 0.00001. Derivative spectra were calculated

step by step. Vlues of the first derivative were multiplied by 100. The wavelengths of zero — crossing points were found with 0.1 nm accuracy.

Sample preparation. Energy drinks were being degassed in an ultrasonic bath for 10 min 5 mL of the examined sample underwent solid phase extraction SPE in order to isolate analytes.

The eluate was collected up to a volume of 10 mL and examined by the method of UV/VIS spectrophotometry. Before determination ofcaffeine and taurine, 1 mL of the eluate was put into 10 mL volumetric flask and water was added to the graduation line. Standard solutions composed of taurine, caffeine and B vitamins underwent the same preparation procedure.

Solid phase extraction (SPE). J.T Baker Inc. set (Phillipsburg, USA) was used for the preliminary treatment of samples. SPE system was used to separate taurin from other compounds and caffeine from B vitamins (Baker Application Notes 2000). The SPE set was equipped with 3 mL sulfonic and phenyl columns.

Extraction in a sulfonic column:

Conditioning: 2 x 3 mL of methanol, followed with 2 x 3 mL ofwater

SPE ofenergy drinks: samples were applied to the sor-bent bed, rinsed with 2 x 2 mL of water

Elution: 2 x 2 mL of 0.1 M HCl and water was added up to a volume of10 mL

Extraction in a phenyl column:

Conditioning: 2 x 3 mL of methanol, followed with 2 x 3 mL ofwater

SPE ofenergy drinks: samples were applied to the sor-bent bed, rinsed with 2 x 2 mL of water

Elution: 2 x 3 mL of 1% water solution of acetic acid/acetonitrile

1258

PIESZKO и др.

70 ug/mL

-20 ug/mL

40 ug/mL

0

200 250 300 350 400 450 500 550 600 Wavelength, nm

450 500 550 600 650 700 750 800 Wavelength, nm

Fig. 1. Absorbtion spectrum of different concentrations of taurine after derivatyzation with nithidrine.

(3 : 7, v/v) and and water was added up to a volume of 10 mL.

RESULTS AND DISCUSSION

Methods of derivative spectrophotometry and zero order spectrophotometry were used to determine ener-gizers in energy drinks. Derivative spectrophotometry was used for determination of caffeine and B vitamins whereas taurine was determined from basic spectra after a reaction with ninhidrine. Analyses were carried out using synthethic samples which included caffeine, B vitamins and taurine. Preparation of samples was carried out in two steps: separation of taurine from the other ingredients and separation of caffeine from the mixture of B vitamins. Solid phase extraction on two sorbent beds (sulfonic and phenyl sorbens) was used. A sample containing taurine, caffeine and B vitamins was applied to a preconditioned sulfonic sorbent bed. Under the conditions described above taurine was retained on the sorbent bed. The solution containing caffeine and B vitamins, after being passed through the sulfonic sorbent, was applied to a preconditioned phenyl sorbent. Taurine was eluted from the sulfonic bed with 0.1 M HCl and put into reaction with ninhydrine. The absorption spectra were measured in the range 380—800 nm. Figure 1 shows taurine spectra for 3 different concentrations of analyte (20, 40 and 70 ^g/mL) after derivatization. The parameters of the calibration curve measured at 570 nm are shown in Table 1. Further analysis showed that caffeine and B2 vitamin are retained on the phenyl sorbent, and B3, B6 and B12 vitamins pass through this bed. Figure 2a shows an example of a zero order spectrum of the mixture of caffeine with B2 vitamin, and Fig. 2b shows the spectra of the remaining vitamins. Due to the fact that the zero order spectra have their absorption maxima at close wavelengths, derivative spectrophotometry was used for determination of these compounds. The possibility of determination of B2 vitamin in the mixture with caffeine from

200 250 300 350 400 450 500 550 600 Wavelength, nm

Fig. 2. a) The zero order spectra of caffeine and vitamin B2. b) The zero order spectra of vitamins B.

basic spectra at 440 nm was checked, however, the relative error in this method was more then 20%.

As Fig. 3 shows, caffeine can be determined at 266.8 nm with zero-crossing technique and B2 vitamin at 350.0 nm (baseline-to-peak) from the first derivative. Figure 4 shows that B3 and B6 vitamins can be determined in their mixture at 280.1 nm (B3) and 310.0 nm (B6) (second derivative spectra).

The parameters of the regression curve obtained by zero order spectrophotometry and derivative spectro-photometry are shown in Table 1. Calibration curves were prepared for the range of concentrations of compounds as they appear in real samples. The detection limit of the spectrophotometry method was expressed as LOD = = 3.3SDb/A, where A is slope of the corresponding calibration curve and SDb is the standard deviation of intercept. The LOD and LOQ = 3LOD varied from 0.03 to 0.5 and from 0.1 to 1.2 ^g/mL, respectively. The curves obtained by 9 points have in most cases high regression coefficients (0.999).

The results of determination of compounds in binary and ternary mixtures are shown in Tables 2 and 3, respectively. Table 2 shows the results of determination of caffeine and B2 vitamin in their mixtures from the I derivative spectra. B3 and B6 vitamins in their mixtures were determined from the II derivative spectra. These vitamins can be also determined from the I derivative spectra, but the error was more than 10%. The table also shows the

Ö-1.0 Q

-1.0 -2.0 -2.5 -3.0

Wavelength, nm

<D >

ce

<D 13

тз -0.0. й

2-0.10 -0.15 -0.20 -0.25

Wavelength, nm

Fig. 3. First derivative spectra of caffeine and vitamin B2.

Fig. 4. Second derivative spectra of vitamin B3 and vitamin B6.

Fig. 5. First derivative spectra of vitamins B.

SamPle Calibration

Recovery LOD SD(0)

Fig. 6. Ishikawa diagram presenting uncertainty contributions for the determination of energizers.

spectra of two-compound mixtures of B3 or B6 vitamins with B12 vitamin. B3 and B6 vitamins were determined from the I derivative spectra and B12 vitamin from the II derivative spectra. This method was checked for mixtures with a small and a large amount of examined compounds. In most cases the coefficient of variation was smaller than 10% and the confidence interval was not higher than 0.9.

The baseline-to-peak technique was used for determination of B12 vitamin in three-compound mixtures with B3 and B6 vitamins at 378 nm (Fig. 5), as well as B6 vitamin in the same mixture (k = 332.8 nm). The parameters of curves are shown in Table 1, and the results of determination of these compounds in Table 3. This Table also includes the calculated SD smaller than 0.4 for all compounds and the maximum confidence interval of 0.45 ^g/mL.

The developed method of derivative spectrophotom-etry was used for real samples (energy drinks). Ten samples of energy drinks were examined six times on account ofconformity ofthe content oftaurine, caffeine and B vi-

tamins to the details given on the labels. The real samples were prepared in the same way as standard samples. The results of determination are shown in Table 4. The samples contained caffeine in the range of27.6—33.8 mg/100 mL of a drink, B3 and B6 vitamins in the range of 3.4—7.6 and 0.3—1.9 mg/100 mL of a drink, respectively and taurine 210—419 m

Для дальнейшего прочтения статьи необходимо приобрести полный текст. Статьи высылаются в формате PDF на указанную при оплате почту. Время доставки составляет менее 10 минут. Стоимость одной статьи — 150 рублей.

Показать целиком