en 14663:2005

BRITISH STANDARD BS EN 14663:2005

Foodstuffs — Determination of vitamin B6 (including its glycosylated forms) by HPLC

The European Standard EN 14663:2005 has the status of a British Standard

ICS 67.050

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BS EN 14663:2005

This British Standard was published under the authority of the Standards Policy and Strategy Committee on 16 January 2006

© BSI 16 January 2006

ISBN 0 580 46982 4

National foreword

This British Standard is the official English language version of EN 14663:2005.

The UK participation in its preparation was entrusted to Technical Committee AW/-/3, Food analysis — Horizontal methods, which has the responsibility to:

— aid enquirers to understand the text;

— present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep UK interests informed;

— monitor related international and European developments and promulgate them in the UK.

A list of organizations represented on this committee can be obtained on request to its secretary.

Cross-references

The British Standards which implement international or European publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online.

This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.

Compliance with a British Standard does not of itself confer immunity from legal obligations.

Summary of pages

This document comprises a front cover, an inside front cover, the EN title page, pages 2 to 22, an inside back cover and a back cover.

The BSI copyright notice displayed in this document indicates when the document was last issued.

Amendments issued since publication

Amd. No. Date Comments

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EUROPEAN STANDARD

NORME EUROPÉENNE

EUROPÄISCHE NORM

EN 14663

December 2005

ICS 67.050

English Version

Foodstuffs - Determination of vitamin B6 (including itsglycosylated forms) by HPLC

Produits alimentaires - Dosage de la vitamine B6 (ycompris ses formes glycosylées) par CLHP

Lebensmittel - Bestimmung von Vitamin B6 (einschließlichglucosidisch gebundener Verbindungen) mit HPLC

This European Standard was approved by CEN on 26 October 2005.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Central Secretariat or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the officialversions.

CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATIONC OM ITÉ EUR OP ÉEN DE NOR M ALIS AT IONEUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: rue de Stassart, 36 B-1050 Brussels

© 2005 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.

Ref. No. EN 14663:2005: E

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EN 14663:2005 (E)

2

Contents Page

Foreword ..........................................................................................................................................................3

1 Scope ...................................................................................................................................................4

2 Normative references .........................................................................................................................4

3 Principle...............................................................................................................................................4

4 Reagents..............................................................................................................................................4

5 Apparatus ............................................................................................................................................9

6 Procedure ............................................................................................................................................9

7 Calculation.........................................................................................................................................11

8 Precision............................................................................................................................................12

9 Test report .........................................................................................................................................14

Annex A (informative) Precision data ..........................................................................................................15

Annex B (informative) Examples for suitable HPLC-conditions for the determination of vitamin B6 compounds........................................................................................................................................19

Annex C (informative) Examples for molar extinction coefficients ...........................................................20

Annex D (informative) Figures.......................................................................................................................21

Bibliography...................................................................................................................................................22

Figure

Figure D.1 — Standard substances and sample potato puree...................................................................21

Tables

Table 1 — Examples for molecular extinction coefficients of vitamin B6 compounds..............................7

Table A.1 — Precision data for Semolina with milk, powder......................................................................15

Table A.2 — Precision data for Potato puree,powder .................................................................................16

Table A.3 — Precision data for vegetables with ham (baby food) .............................................................17

Table A.4 — Precision data for multi vitamin drink.....................................................................................18

Table B.1 — Examples for suitable HPLC-conditions for the determination of vitamin B6 compounds ....................................................................................................................................................19

Table C.1 — Examples for molar extinction coefficients (E) of vitamin B6 compounds [3], [4] ..............20

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EN 14663:2005 (E)

3

Foreword

This document (EN 14663:2005) has been prepared by Technical Committee CEN/TC 275 “Food analysis - Horizontal methods”, the secretariat of which is held by DIN.

This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by June 2006, and conflicting national standards shall be withdrawn at the latest by June 2006.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

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EN 14663:2005 (E)

4

1 Scope

This document specifies a method for the determination of vitamin B6 in foodstuffs by high performance liquid chromatography (HPLC).

Vitamin B6 is the mass fraction of the sum of pyridoxine, pyridoxal, pyridoxamine including their phosphorylated derivatives as well as the β-glycosylated forms, calculated as pyridoxine.

This method has been successfully validated with semolina with milk (infant food), potato puree, vegetables with ham (convenient products) and a multi vitamin drink at levels from 0,034 mg/100 g to 1,21 mg/100 g.

2 Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

EN ISO 3696, Water for analytical laboratory use — Specification and test methods (ISO 3696:1987).

3 Principle

Pyridoxal, pyridoxamine and pyridoxine are extracted from food by acid hydrolysis and dephosphorylated and deglycosilated enzymatically using acid phosphatase and β-glucosidase.

The different derivatives of vitamin B6 (pyridoxal, pyridoxamine and pyridoxine) are separated by HPLC and quantified by fluorometric detection [1], [2].

4 Reagents

4.1 General

During the analysis, unless otherwise stated, use only reagents of recognised analytical grade and water of at least grade 1 according to EN ISO 3696, or double distilled water.

4.2 Di-potassium hydrogen phosphate, mass fraction w(K2HPO4 · 3 H2O) ≥ 99,9 %

4.3 Sodium acetate, without crystal water, w(CH3COONa) ≥ 99,0 %

4.4 Trichloroacetic acid (TCA), w(Cl3CCOOH) ≥ 99,0 %

4.5 Sodium acetate solution, substance concentration c(CH3COONa) = 2,5 mol/l

Dissolve 205 g of sodium acetate (4.3) in 1 l of water.

4.6 Post-column reagent (optional), K2HPO4 solution c(K2HPO4) = 0,15 mol/l

Dissolve 34,2 g of di-potassium hydrogen phosphate (4.2) in water, dilute to 1 000 ml, mix and degas.

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EN 14663:2005 (E)

5

4.7 Hydrochloric acid, c(HCl) = 1 mol/l

4.8 Hydrochloric acid, c(HCl) = 0,1 mol/l

4.9 Hydrochloric acid, c(HCl) = 0,2 mol/l

4.10 Sulfuric acid, c(H2SO4)= 1 mol/l

4.11 Light petroleum, boiling range of 40 °C to 60 °C

4.12 Acid phosphatase, from potatoes. Enzymatic activity approximately 5,3 U/mg1).

It is important that the enzyme used complies with the activity check 4.13.2, for further information see [2], [7].

4.13 Acid phosphatase solution

4.13.1 General

Dissolve/solubilise 60 mg of acidic phosphatase (4.12) in 10 ml of water in a beaker by stirring for 2 min. Prepare this solution on the day of analysis.

4.13.2 Activity check of Acid Phosphatase

Weigh 10 g of pork, 5 g of potato puree or 5 g of whole meal into a beaker, and extract with acid as described in 6.2.1. Add 1 ml of acid phosphatase solution (4.13.1) and optional 1 ml of β-glucosidase solution (4.15) to 12,5 ml of the extracted sample solution and mix. Incubate the solution at least 12 h or overnight at 37 °C with continuous stirring. Repeat this step with the double amount of acid phosphatase solution.

Determine the mass concentration of vitamins according to 6.6. The activity of the enzyme used is sufficient, if the resulting mass concentrations of vitamin B6 compounds in both sample solutions are equivalent. The chromatogram shall not show a peak arising from pyridoxamin phosphate.

NOTE For the interlaboratory test, the acid phosphatase from Sigma Nr P 37522) has been used.

4.14 ββββ-Glucosidase, from almonds. Enzymatic activity of approximately 3,2 U/mg.

It is important that the enzyme used complies with the activity check 4.15.2, for further information see [2], [7].

4.15 ββββ-Glucosidase solution

4.15.1 General

Dissolve/solubilise 100 mg of β-glucosidase (4.14) in 10 ml of water in a beaker by stirring for 2 min. Prepare this solution on the day of analysis.

1) U, this unit (often called the International unit or standard unit) is defined as the amount of enzyme which catalyses the transformation of 1 µmol substrate per minute under standard conditions.

2) This information is given for the convenience of users of this document and does not constitute an endorsement by CEN of the product named. Equivalent products may be used if they can be shown to lead to the same results.

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EN 14663:2005 (E)

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4.15.2 Activity check of ββββ-glucosidase

Weigh 10 g of pork, 5 g of potato puree or 5 g of whole meal into a beaker, and extract with acid as described in 6.2.1. Add 1 ml of acid phosphatase solution (4.13.1) and 1 ml of β-glucosidase solution (4.15.1) to 12,5 ml of the extracted sample solution and mix. Incubate the solution at least 12 h or overnight at 37 °C with continuous stirring. Repeat this step with the double amount β-glucosidase solution.

Determine the mass concentration of vitamin B6 compounds according to 6.6. The activity of the enzyme used is sufficient, if the resulting mass concentrations of vitamin B6 compounds in both sample solutions are equivalent. The chromatogram shall not show a peak arising from pyridoxamin phosphate.

NOTE For the interlaboratory test, the β-glucosidase from Sigma Nr G-0395 1) has been used.

4.16 Mobile phase for HPLC (Sulfuric acid, c(H2SO4)= 0,015 mol/l containing 0,005 mol/l TCA)

Dissolve 817 mg ± 5 mg of trichloroacetic acid (4.4) in 15 ml of 1 mol/l sulfuric acid (4.10), transfer into a 1 000 ml volumetric flask, dilute to the mark with water, mix and degas.

4.17 Silicon oil, for defoaming

4.18 Standard substances

4.18.1 General

Pyridoxamine (PM), Pyridoxal (PL) and pyridoxine (PN) can be obtained from various suppliers. The purity of the standards may vary, and it is therefore necessary to determine the concentration and purity (see 4.19.4 and 4.20.7).

4.18.2 Pyridoxamine (PM) dihydrochloride, w(C 8H12N2O2 · 2HCl) ≥ 98 %

4.18.3 Pyridoxal (PL) hydrochloride, w(C8H9NO3 · HCl) ≥ 98 %

4.18.4 Pyridoxine (PN) hydrochloride, w(C8H11NO3 · HCl ) ≥ 98 %

4.19 Stock solutions

4.19.1 Pyridoxamine (PM) stock solution, mass concentration ρ(PM) approximately 500 µg/ml

Dissolve 71,7 mg of pyridoxamine dihydrochloride (4.18.2) in a 100 ml volumetric flask in 0,1 mol/l HCl (4.8) and dilute to the mark with 0,1 mol/l HCl. The solution can be stored without any losses for up to one week at 4 °C or up to two months at -18 °C.

4.19.2 Pyridoxal (PL) stock solution, ρ(PL) approximately 500 µg/ml

Dissolve 60,9 mg of pyridoxal hydrochloride (4.18.3) in a 100 ml volumetric flask in 0,1 mol/l HCl (4.8) and dilute to the mark with 0,1 mol/l HCl. The solution can be stored without any losses for up to one week at 4 °C or up to two months at -18 °C.

1) This information is given for the convenience of users of this document and does not constitute an endorsement by CEN of the product named. Equivalent products may be used if they can be shown to lead to the same results.

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EN 14663:2005 (E)

7

4.19.3 Pyridoxine (PN) stock solution, ρ(PN) approximately 500 µg/ml

Dissolve 60,8 mg of pyridoxine hydrochloride (4.18.4) in a 100 ml volumetric flask in 0,1 mol/l HCl (4.8) and dilute to the mark with 0,1 mol/l HCl. The solution can be stored without any losses for up to one week at 4 °C or up to two months at – 18 °C.

4.19.4 Concentration tests

Pipette 1 ml of stock solutions of pyridoxamine (4.19.1), pyridoxal (4.19.2) and pyridoxine (4.19.3) respectively in a 50 ml volumetric flask and dilute to the mark with 0,1 mol/l HCl (4.8). Measure the absorbance of the solutions in a 1 cm quartz-cell against 0,1 mol/l HCl at the maximum wavelength using UV-spectrometry (see Table 1).

Calculate the mass concentration of each vitamin B6 compound, ρi, using the molar extinction coefficient as given in equation (1):

FVMA

i

ii ×××=

ερ (1)

where:

ρi is the mass concentration of pyridoxamine, pyridoxal and pyridoxine respectively in microgram per millilitre stock solution;

A is the absorbance value of pyridoxamine, pyridoxal and pyridoxine solutions at the maximum wavelength λmax (see table 1);

εi is the molecular absorbance coefficient of PM, PL or PN at the appropriate pH as defined in table 1;

Mi is the molecular weight of PM, PL and PN respectively standard substances as defined in table 1;

V is the dilution factor, in this case V = 50;

F is the calculation factor of HCl free vitamin B6 compounds.

Use these mass concentrations to calculate the exact concentrations of 4.19.1 to 4.19.3 and 4.20.1 to 4.20.6.

Table 1 — Examples for molecular extinction coefficients of vitamin B6 compounds

Compounds Solvent λmax εi mmol-1cm-1

Mi g mol –1

F

PM . 2 HCla 0,1 mol/l HCl, pH ~1 292 8,2 241,1 0,698

PL . HClb 0,1 mol/l HCl, pH ~1 288 9,0 203,6 0,821

PN . HClc 0,1 mol/l HCl, pH ~1 291 8,6 205,6 0,823

a PM . 2 HCl = Pyridoxamine-dihydrochloride (4.18.2)

b PL . HCl = Pyridoxal-hydrochloride (4.18.3)

c PN . HCl = Pyridoxine-hydrochloride (4.18.4)

4.20 Standard solutions

4.20.1 Pyridoxamine (PM) standard solution I, ρ(PM) approximately 10 µg/ml

Dilute 2 ml of pyridoxamine stock solution (4.19.1) with 0,1 mol/l HCl (4.8) to 100 ml. Prepare freshly every day

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EN 14663:2005 (E)

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4.20.2 Pyridoxal (PL) standard solution I, ρ(PL) approximately 10 µg/ml

Dilute 2 ml of PL stock solution (4.19.2) with 0,1 mol/l HCl (4.8) to 100 ml. Prepare freshly every day

4.20.3 Pyridoxine (PN) standard solution I, ρ(PN) approximately 10 µg/ml

Dilute 2 ml of pyridoxine stock solution (4.19.3) with 0,1 mol/l HCl (4.8) to 100 ml. Prepare freshly every day

4.20.4 Pyridoxamine (PM) standard solution II, ρ(PM) approximately 1 µg/ml

Dilute 10 ml of standard solution I (4.20.1) with 0,1 mol/l HCl (4.8) to 100 ml. Prepare freshly every day

4.20.5 Pyridoxal (PL) standard solution II, ρ(PL) approximately 1 µg/ml

Dilute 10 ml of PL standard solution I (4.20.2) with 0,1 mol/l HCl (4.8) to 100 ml. Prepare freshly every day

4.20.6 Pyridoxine (PN)standard solution II, ρ(PN) approximately 1 µg/ml

Dilute 10 ml of pyridoxine standard solution I (4.20.3) with 0,1 mol/l HCl (4.8) to 100 ml. Prepare freshly every day

4.20.7 Check of chromatographic purity by HPLC

Purity of standard substances can be checked by HPLC as follows:

Inject appropriate volumes of PM, PL and PN standard solutions I (4.20.1, 4.20.2, 4.20.3) into the HPLC system and analyse as described in 6.4.

Calculate purity of the standard substances according to equation (2):

Bxx

Ri

ii +

×=

100 (2)

where

Ri is the purity of standard substance i in %;

xi is the peak area of standard substance i;

B is the sum of the peak areas of contaminating substances (without solvent peak).

The chromatographic purity of standard substances should be ≥ 98 %, otherwise take new standard substances or prepare new standard solutions.

4.21 Mixed calibration solution e. g. ρ(PM, PL, PN) = 0,1 µg/ml to 10 µg/ml

Pipette suitable volumes of PM, PL and PN stock solutions (4.19.1 to 4.19.3) or standard solutions (4.20.1 to 4.20.6) into a 20 ml volumetric flask, dilute with 0,1 mol/l HCl (4.8) to 6,5 ml, if necessary. Adjust to pH = 4,8 with 2,5 mol/l sodium acetate solution (4.5), and then adjust to pH = 3,0 with sulfuric acid (4.10), dilute with water to the mark and mix (calibration solutions). At least three calibration points are recommended. If necessary, the mixed calibration solutions may be diluted with mobile phase prior to HPLC injection.

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EN 14663:2005 (E)

9

5 Apparatus

5.1 General

Usual laboratory apparatus, glassware, and the following.

5.2 UV Spectrometer, capable of measurement of absorbance at defined wavelengths

5.3 Heating devices

Laboratory autoclave and oven or water bath, with stirring facilities, able to be controlled at 37 °C

5.4 High performance liquid chromatographic system

Consisting of a pump, sample injecting device, fluorescence detector with excitation and emission wavelengths set at 290 nm and 390 nm, respectively and an evaluation system such as an integrator, and optionally, a post column derivatisation device

5.5 HPLC-Column, e. g. reversed phase column, such as:

LunaTM RP C18, 5 µm1), particle size of 5 µm, diameter 4,0 mm, length 250 mm2). Other suitable examples are listed in Annex B

5.6 Filter device

Filtering of the mobile phase as well as of the test sample solution through a membrane filter, with e. g. a pore size of 0,45 µm, prior to use or injection will increase longevity of the columns

6 Procedure

6.1 Preparation of the test sample

Cut and homogenise the test sample. Grind coarse material with an appropriate mill and mix again. Measures such as pre-cooling have to be taken to avoid exposing to high temperature for long periods of time. After homogenising, analyse the sample immediately.

6.2 Preparation of the sample test solution

6.2.1 Extraction

6.2.1.1 General

For samples with a high fat content (> 25 %) it can be useful to remove fat e.g. by repeated treatment with light petroleum before the acid hydrolysis.

1) LunaTM is an example of a commercially available product, supplied by Phenomenex. This information is given for the convenience of users of this document and does not constitute an endorsement by CEN of the product named. Equivalent products may be used if they can be shown to lead to the same results.

2) Other particle sizes or column dimensions than specified in this document may be used. Separation parameters have to be adapted to such materials to guarantee equivalent results. The performance criterion for suitable analytical columns is the baseline resolution of the analytes concerned.

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EN 14663:2005 (E)

10

For treatment of foaming material the use of few drops of silicon oil (4.17) is recommended.

The pH of the extracted solution should be approximately 1. Otherwise it is advisable to reduce the sample weight or to use hydrochloric acid with higher concentration (e. g. 0,2 mol/l (4.9) or even 1 mol/l (4.7)).

6.2.1.2 Extraction of dry products (water content < 20 %, e. g. cereals, dried milk, dried vegetables)

Weigh 1 g to 10 g of the homogenised test sample (6.1) to nearest milligram into a 150 ml conical flask, add 50 ml of 0,1 mol/l hydrochloride acid (4.8), mix and check that the pH is approximately 1.

Heat in the autoclave (5.3) for 30 min at 120 °C, cool down subsequently to room temperature, transfer to a 100 ml volumetric flask and dilute with water to 100 ml (with the possible silicon layer above the mark), and mix.

Filter or centrifuge an aliquot (approximately 50 ml) of the acid treated sample solution at 3 000 g and transfer the upper layer into a sealable glass bottle (this is the sample extract solution).

6.2.1.3 Extraction of wet and liquid products (water content > 20 %, e. g. meat, vegetables, juices)

Weigh 2 g to 40 g of the homogenised sample (6.1) to nearest milligram into a 150 ml conical flask, add 10 ml of 1 mol/l hydrochloric acid (4.7), dilute with water to approximately 50 ml, mix and check that the pH is approximately 1.

Heat in the autoclave (5.3) for 30 min at 120 °C, cool down subsequently to room temperature, transfer to a 100 ml volumetric flask and dilute with water to 100 ml (with the possible silicon layer above the mark), and mix.

Filter or centrifuge an aliquot (approximately 50 ml) of the acid treated sample solution at 3 000 g and transfer the upper layer into a sealable glass bottle (this is the sample extract solution).

NOTE During autoclaving an interchange of the different forms of the vitamin can occur, e.g. via transamination. This has been observed especially in cooked meat or in samples with high amounts of free amino groups, see [2], [7].

6.2.2 Enzyme treatment and transformation steps

For food samples of animal origin (pork, milk, fish, etc) that do not contain β-glucosidically bounded pyridoxin, enzymatic treatment with β-glucosidase is not necessary. Laboratory experiences have shown that the results for total vitamin B6 contents of foods of animal origins analysed with or without applying β-glucosidase for enzymatic treatment were approximately the same [2], [7].

Pipette 12,5 ml of the sample extract solution from 6.2.1.2 and 6.2.1.3 into a 20 ml conical flask and adjust to pH of 4,8 ± 0,1 with sodium acetate solution (4.5). Add 1 ml of acid phosphatase solution (4.13) and 1 ml of β-glucosidase solution (4.15) and mix. Cover the conical flask and incubate the solution at least 12 h or overnight at 37 °C with continuous stirring.

After cooling to room temperature, adjust the pH-value to approximately 3 with sulfuric acid (4.10), transfer the adjusted solution quantitatively into a 20 ml volumetric flask and dilute to the mark with water. Shake and filter through a dry fluted paper filter, discarding the first 5 ml of filtrate. This sample test solution may be stored up to 3 days in a refrigerator at approximately 4 °C.

For the HPLC analysis, filter an aliquot (approximately 2 ml) through a membrane filter (5.6) and dilute, if necessary, with the mobile phase.

6.3 Preparation of reagent blind solution

Pipette 12,5 ml of 0,1 mol/l hydrochloric acid solution (4.8) into a 20 ml conical flask and adjust to pH = 4,8 ± 0,1 with 2,5 mol/l sodium acetate solution (4.5). Add 1 ml of acid phosphatase solution (4.13), 1 ml of β-glucosidase solution (4.15) and mix. Incubate the solution at least 12 h or overnight at 37 °C with continuous stirring.

After cooling to room temperature, adjust the pH-value to approximately 3 with sulfuric acid (4.10), transfer quantitatively into a 20 ml volumetric flask, dilute to the mark with water, shake and filter through a dry fluted paper filter, discarding the first 5 ml of filtrate.

For the HPLC analysis, filter an aliquot (approximately 2 ml) through a membrane filter (5.6) and dilute, if necessary, with the mobile phase.

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EN 14663:2005 (E)

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6.4 HPLC conditions

The separation performance of the HPLC system shall lead to a base-line separation of peaks obtained for PM, PL and PN and from all other substances from the sample.

The separation and the quantification have proven to be satisfactory if following experimental conditions are followed (see also figures in Annex B):

HPLC column: according to 5.5;

Mobile phase: according to 4.16;

Flow rate: 1,5 ml/min;

Injection volume: 1 µl to 50 µl;

Detection: Fluorescence: Excitation: 290 nm; Emission: 390 nm.

6.5 Identification

Inject the same suitable volumes of the sample test solution (6.2.2), reagent blind solutions (6.3) and mixed calibration solutions (4.21) into the HPLC system under the conditions described in 6.4.

Identify PM, PL and PN by comparison of the retention time of the individual peaks in the chromatograms obtained with the test sample solution, and with the standard test solution. Peak identification can also be performed by post column pH-shifting to higher values, e. g. pH = 6,6 using the postcolumn derivatization device (5.4) with a flow rate of 0,1 ml/min of postcolumn reagent (4.6). Detection is carried out with excitation at 330 nm and emission at 390 nm [2], [4], [5].

NOTE An increase of the pH-value using post-column reagent (4.6) results in a shift of the excitation wavelength to 330 nm. Additionally, the selectivity for some matrices is improved due to a decrease of some matrix peaks [2], [4], [5].

6.6 Determination

Inject the same suitable volumes of the standard solution as well as of the sample test solution into the HPLC-system under the conditions described in 6.4. To carry out a determination by external calibration, integrate the peak areas or peak heights and compare the results with the corresponding values for the standard substance.

7 Calculation

7.1 Base the calculation on a calibration graph, on corresponding programs of the integrator, or according equations (3) to (6):

1000100××= F

my

w i (3)

iii abxy += (4)

iii BPx −= (5)

1VVF = (6)

where

yi is the mass of PM, PL or PN in µg/20 ml sample test solution (6.2.2) determined by peak area or height using linear regression or calibration graphs;

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m is sample mass in gram;

bi, ai are the regression coefficients for PM, PL or PN calculated by linear regression on the basis of concentration and peak area in the calibration solutions;

ai is the y-value of the calibration graph for PM, PL and PN;

bi, is the gradient of the calibration graph;

xi is the corrected peak area of PM, PL or PN of the sample test solution;

Pi are the peak areas of PM, PL and PN of the sample test solution;

Bi are the peak areas of PM, PL or PN of the reagent blank test solution;

F is the quotient from equation (6);

w is the mass fraction of pyridoxamine (PM), pyridoxal (PL) or pyridoxine (PN) in milligram per 100 g sample;

V is the total volume of acid extract solution of sample (6.2.1.2), (6.2.1.3) in millilitre;

V1 is the volume of acid extract solution using for enzymatic treatment (6.2.2), in millilitre.

7.2 Calculate the mass fraction, w, of vitamin B6 as pyridoxine in mg/100 g of the sample using equation (7):

w = 1,006 wPM + 1,012 wPL + wPN (7)

where

wPM is the content of of pyridoxamine in mg/100 g of sample;

wPL is the content of of pyridoxal in mg/100 g of sample;

wPN is the content of of pyridoxine in mg/100 g of sample;

1,006 is the factor for PM to calculate as PN;

1,012 is the factor for PL to calculate as PN.

7.3 Report the result for vitamin B6 calculated as pyridoxine in mg/100 g.

NOTE If necessary to give the result as pyridoxine hydrochloride, use the conversion factor of 1,216. This conversion should be pointed out clearly in the report.

8 Precision

8.1 General

The precision data for the determination of vitamin B6 were established in an interlaboratory test according to ISO 5725 carried out by the former BgVV (Bundesinstitut für gesundheitlichen Verbraucherschutz und Veterinärmedizin, German Federal Institute for Consumer protection and veterinary medicine).

Details of the collaborative study on the precision of the method are summarised in Annex A. The values derived from the interlaboratory tests may not be applicable to analyte concentration ranges and matrices other than given in Annex A.

The applicability and reliability of this method were also tested by other studies on different foods such as meat, fish, milk, vegetables, fruits and cereals [2], [3]. The analytical results were well reproducible and only relatively few interference peaks from food matrix, which can be separated easily, sometimes occurred. A very good correlation and linear regression between peak area and the concentration of PM, PL and PN

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respectively in the calibration solution is given. The relative standard deviations of total vitamin B6 content in a series of from three up to five routine determinations in different foods varied between 2 % and 6 %.

The recovery of PM, PL and PN added to food varied between 85 % to 105 % [2], [3]. Determination of total vitamin B6 by this method yielded distinctly higher values in foods of plant origin (containing glycosilated pyridoxine) than other methods without β–glucosidase treatment [2], [3], [7].

8.2 Repeatability

The absolute difference between two single test results found on identical test material by one operator using the same apparatus within the shortest feasible interval will exceed the repeatability limit r in not more than 5 % of the cases. The values are:

Semolina with milk, powder

Pyridoxamin x = 0,065 mg/100 g r = 0,008 Pyridoxal x = 0,080 mg/100 g r = 0,022 Pyridoxin x = 0,523 mg/100 g r = 0,067 Vitamin B6 x = 0,667 mg/100 g r = 0,084

Potato puree, powder


Vegetable with ham (baby food)


Multi vitamin drink

Pyridoxamin x = 0,004 mg/100 g r = 0,003 Pyridoxal x = 0,004 mg/100 g r = 0,003 Pyridoxin x = 0,374 mg/100 g r = 0,056 Vitamin B6 x = 0,380 mg/100 g r = 0,056 8.3 Reproducibility

The absolute differences between two single test results on identical test material reported by two laboratories will exceed the reproducibility limit R in not more than 5 % of the cases. The values are:

Semolina with milk, powder

Pyridoxamin x = 0,065 mg/100 g R = 0,035 Pyridoxal x = 0,080 mg/100 g R = 0,071 Pyridoxin x = 0,523 mg/100 g R = 0,151 Vitamin B6 x = 0,667 mg/100 g R = 0,193

Potato puree, powder

Pyridoxamin x = 0,163 mg/100 g R = 0,089 Pyridoxal x = 0,032 mg/100 g R = 0,022

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Pyridoxin x = 1,008 mg/100 g R = 0,314 Vitamin B6 x = 1,204 mg/100 g R = 0,369

Vegetable with ham (baby food)


multi vitamin drink


9 Test report

The test report shall contain at least the following data:

a) all information necessary for the complete identification of the sample;

b) reference to this document or to the method used;

c) date and type of sample procedure (if known);

d) date of sample receipt;

e) date of test;

f) results and the units in which the results have been expressed;

g) any particular points observed in the course of the test;

h) any operations not specified in the method or regarded as optional which might have affected the results.

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Annex A (informative)

Precision data

The existing data have been obtained by using the HPLC methods as outlined in Annex C. The precision data for the determination of vitamin B6 were established in an interlaboratory test according to ISO 5725 carried out by the former BgVV (Bundesinstitut für gesundheitlichen Verbraucherschutz und Veterinärmedizin, German Federal Institute for Consumer protection and veterinary medicine).

Table A.1 — Precision data for Semolina with milk, powder

Sample Semolina with milk, powder

Analyte Pyridoxamine Pyridoxal Pyridoxin Vitamin B6a

Year of collaborative study 2 000 2 000 2 000 2 000

Number of laboratories 11 11 11 11

Number of samples 5 5 5 5

Number of laboratories retained after elimination of outliers

10 10 10 10

Number of results retained 53 53 53 53

Mean value x , mg/100 g 0,065 0,080 0,523 0,667

Repeatability standard deviation sr, mg/100 g 0,003 0,008 0,024 0,030

Repeatability relative standard deviation RSDr, % 4,6 10,0 4,6 4,5

Repeatability value r (2,8 · sr), mg/100 g 0,008 0,022 0,067 0,084

Reproducibility standard deviation sR, mg/100 g 0,013 0,025 0,053 0,068

Reproducibility relative standard deviation RSDR, % 20,5 31,3 10,1 10,2

Reproducibility value R (2,8 · sR), mg/100 g 0,035 0,071 0,151 0,193

Recovery mean value, % 97,2 94,7 93,9

Recovery standard deviation, % 9 8,2 9,7

Number of results used for recovery calculation 23 20 23

a vitamin B6 = 1,006 pyridoxamine + 1,012 pyridoxal + pyridoxine

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Table A.2 — Precision data for Potato puree,powder

Sample Potato puree, powder




Number of samples 5(9) 5(9) 5(9) 5(9)


9 9 9 9


Mean value x , mg/100 g 0,163 0,032 1,008 1,204








Recovery standard deviation, % 9,4 7,4 9,9



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Table A.3 — Precision data for vegetables with ham (baby food)

Sample Vegetables with ham (baby food)




Number of samples 5(2) 5(2) 5(2) 5(2)


8 8 8 8


Mean value x , mg/100 g 0,043 0,009 0,047 0,107










a vitamin B6 = 1,006 pyridoxamine + 1,0 12 pyridoxal + pyridoxine

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Table A.4 — Precision data for multi vitamin drink

Sample Multi vitamin drink




Number of samples 5 5 5 5


10 10 10 10


Mean value x , mg/100 g 0,004 0,004 0,373 0,380





Reproducibility relative standard deviation RSDR, % 38,6 49 8,0 8,8






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4663

:200

5 (E

)

19

Ann

ex B

(in

form

ativ

e)

Ex

ampl

es fo

r sui

tabl

e H

PLC

-con

ditio

ns fo

r the

det

erm

inat

ion

of v

itam

in B

6 com

poun

ds

Tabl

e B

.1 —

Exa

mpl

es fo

r sui

tabl

e H

PLC

-con

ditio

ns fo

r the

det

erm

inat

ion

of v

itam

in B

6 co

mpo

unds

Lab

Sepa

ratio

n co

lum

n D

imen

sion

mm

× m

m

Tem

p.

°C

Mob

ile P

hase

Flow

ml/m

in

Det

ectio

n nm

EX

EM

Ret

entio

n tim

e m

in

PMb

PLc

PNd

1a

LUN

A R

P C

18, 5

µm

25

0 ×

4,0

30

H2S

O4 (c

= 0

,015

mol

/l) c

onta

inin

g TC

A (c

= 0

,005

mol

/l)

1,5

290

390

~ 3

~ 7

~11,

4

1b

LUN

A R

P C

18, 5

µm

25

0 ×

4,0

30

H2S

O4 (c

= 0

,015

mol

/l) c

onta

inin

g TC

A (c

= 0

,005

mol

/l)

and

post

col

umn

reag

ent:

K 2H

PO4 (c

= 0

,15

mol

/l)

1,5

0,5

330

390

~2,4

~6

,9

~11,

2

2 LU

NA

RP

C18

, 5 µ

m

250

× 4,

0 30

H

2SO

4 (c

= 0

,015

mol

/l) c

onta

inin

g TC

A (c

= 0

,005

mol

/l)

1,5

290

390

~ 3

~ 7,

9 ~

13,0

3 AQ

UA

C18

,5 µ

ma

Prec

olum

n: R

P C

18, 5

µm

250

× 4,

6

4,0

× 3,

0

30

H2S

O4 (c

= 0

,015

mol

/l) c

onta

inin

g TC

A (c

= 0

,005

mol

/l)

2,0

1,5

290

390

~ 2,

2

~ 2,

7

~ 4,

7

~ 5,

4

~ 6,

4

~ 6,

9

4 Li

Chr

osph

er 6

0 R

P C

8

Sele

ct B

, 5 µ

m

250

× 4,

0 30

H

2SO

4 (c

= 0

,03

mol

/l) c

onta

inin

g TC

A (c

= 0

,05

mol

/l),

0 m

in to

14

min

B: M

etha

nol,

14 m

in to

21

min

3,0

290

390

~ 2,

5 ~

4,8

~ 6,

1

5 N

ucle

osil

120

C18

, 5 µ

m

Prec

olum

n: R

P C

18

250

× 4,

0 ~

20

H2S

O4 (c

= 0

,015

mol

/l) c

onta

inin

g TC

A (c

= 0

,005

mol

/l)

2,0

290

390

~ 2,

0 ~

4,9

~ 7,

0

6 LU

NA

RP

C18

, 5 µ

m

250

× 4,

0 30

H

2SO

4 (c

= 0

,015

mol

/l) c

onta

inin

g TC

A (c

= 0

,005

mol

/l)

2,0

290

390

~ 2,

5 ~

6,3

~ 9,

2

7 LU

NA

RP

C18

, 5 µ

m

250

× 4,

0 30

H

2SO

4 (c

= 0

,015

mol

/l) c

onta

inin

g TC

A (c

= 0

,005

mol

/l)

2,0

290

390

~ 2,

8 ~

6,5

~ 11

,8

8 LU

NA

RP

C18

, 5 µ

m

250

× 4,

0 30

H

2SO

4 (c

= 0

,015

mol

/l) c

onta

inin

g TC

A (c

= 0

,005

mol

/l)

2,0

290

390

~ 2,

8 ~

6,9

~ 11

,4

9 Sp

heris

orb

80 O

DS-

2, 5

µm

25

0 ×

4,6

30

H2S

O4 (c

= 0

,015

mol

/l) c

onta

inin

g TC

A (c

= 0

,005

mol

/l)

2,0

290

390

~ 5,

5 ~

10,4

~

16,1

10

LUN

A R

P C

18, 5

µm

25

0 ×

4,0

30

H2S

O4 (c

=0,

015

mol

/l) c

onta

inin

g TC

A (c

= 0

,005

mol

/l)

and

post

col

umn

reag

ent:

K 2H

PO4 (

c =

0,15

mol

/l)

1,0

0,5

330

390

~ 6,

9 ~

17,9

~

28,4

a Ph

enom

enex

, 125

Å; b P

M =

Pyr

idox

amin

e, c P

L =

Pyr

idox

al, d P

N =

Pyr

idox

ine

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Annex C (informative)

Examples for molar extinction coefficients

Table C.1 — Examples for molar extinction coefficients (E) of vitamin B6 compounds [3], [4]

Compounds Solvent λλλλmax nm

E mmol-1cm-1

Mw g mol-1

Pyridoxine hydrochloride 0,1 mol/l HCl, pH approximately 1 290 8,6 205,6

Pyridoxine hydrochloride 0,1 mol/l phosphate buffer, pH 7 323,8 7,3 205,6

Pyridoxal hydrochloride 0,1 mol/l HCl, pH approximately 1 288 8,96 (9,0) 203,6

Pyridoxal-5’-phosphate 0,1 mol/l phosphate buffer, pH 7 388 5,02 247,1

Pyridoxamine dihydrochloride 0,1 mol/l HCl, pH approximately 1 292 8,2 241,1

Pyridoxamine dihydrochloride 0,1 mol/l phosphate buffer, pH 7 253 4,6 241,1

Pyridoxamine-5’-phosphate hydrochloride

0,1 mol/l phosphate buffer, pH 7 326 8,37 241,1

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Annex D (informative)

Figures

Key

LU fluorescence intensity

Figure D.1 — Standard substances and sample potato puree

Operating conditions:

HPLC column: according to 5.5;

Mobile phase: according to 4.16;

Flow rate: 1,5 ml/min;

Detection: Fluorescence: Excitation: 290 nm; Emission: 390 nm.

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Bibliography

[1] Bognár, A.: Bestimmung von Vitamin B6 in Lebensmitteln mit Hilfe der Hochdruckflüssig-Chromatographie (HPLC). Z Lebensm Unters Forsch A, 1985, 181: 200 – 205

[2] Bognár, A., Ollilainen, V.: Influence of Extraction on the Determination of Vitamin B6 in Food by HPLC. Z Lebensm Unters Forsch A, 1997, 204: 327 – 335

[3] Metzler, D. E., and Snell , E. E.: Spectra and Ionisation Constants of the Vitamin B6 - Group and Related 3-Hydroxypyridine Derivates. Journal of the American Chemical Society. 1955, 77: 2431 - 2437

[4] Bitsch, R., Möller, J., J Chromatogr., 1989, 463: 207 – 211

[5] Ollilainen, V.: HPLC Analysis of Vitamin B6 in Agricultural and Food Science in Finland. Department of Applied Chemistry and Microbiology University of Helsinki 1999. Vol. 8: No. 6: 515 – 619

[6] Bergaentzle, M., Arella, F., Bourguignon, J.B., Hasselmann, C.: Determination of vitamin B6 in foods by HPLC; A collaborative study. Food Chemistry, 1995, 52: 81 – 86.

[7] Ndaw, S., Bergaentzle, M., Aoude-Werner, D., Hasselmann, C.: Extraction procedures for the liquid chromatographic determination of thiamin Riboflavin and vitamin B6 in foodstuffs. Food Chemistry 2000, 71, 129 – 138.

[8] ISO 5725, Precision of test methods – Determination of repeatability and reproducibility for a standard test method by inter-laboratory tests 6)

6) ISO 5725:1986 is withdrawn and replaced by ISO 5725-1, ISO 5725-2, ISO 5725-3, ISO 5725-4 and ISO 5725-6, all edition 1994 as well as ISO 5725-5:1998.

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BS EN 14663:2005

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