1. Marco Iammarino, Aurelia Di Taranto, Carmen Palermo*, Diego Centonze*
Polyphosphates in products of animal origin: validation of an analytical method based on ion chromatography with electrochemical conductivity detection
Marco Iammarino, Aurelia Di Taranto, Carmen Palermo*, Diego Centonze*
Istituto Zooprofilattico Sperimentale della Puglia e della Basilicata – Foggia, Italy
* Dipartimento di Scienze Agro-Ambientali, Chimica e Difesa Vegetale e BIOAGROMED, Università degli Studi di Foggia, Italy
INTRODUCTION
A class of condensation compounds of the phosphate ion, mainly used as stabilizer in food productions, is indicated by the term polyphosphates. Recently, some community Countries have communicated to the European Commission, by some alert notifications, the presence of these additives above the maximum admitted limits, in some products of animal origin, coming from third Countries. On the basis of these notifications, the Italian Ministry of Health has solicited the official control Organisms to develop an analytical method suitable for this kind of investigation, since the photometric technique (1) (2) was previously judged as inappropriate. In fact, it do not allow the identification and quantification of polyphosphates, but only the quantification of total phosphorus, resulting unspecific and giving overestimations in the case of presence of other additives containing phosphorus. Moreover, the problem of the specification of an appropriate natural phosphorus index for each class of animal origin products still exists. In this work an analytical method based on ion chromatography with electrochemical conductivity detection has been developed and validated for the direct determination of polyphosphates (diphosphate, trimetaphosphates - E450, triphosphates - E451 and tetrapolyphosphates - E452) in different matrixes of animal origin, in which these additives are typically used.
MATERIALS AND METHODS
The extraction of polyphosphates from the sample has been carried out by using ultra pure water; a simple filtration (0.20 µm) is enough to allow the HPIC injection. The analysis has been carried out by a HPIC system (Dionex, Sunnyvale, CA, USA) equipped with a GP50 quaternary gradient pump, an ASRS II ultra self regenerating suppressor and an electrochemical detector ED40 in conductivity mode. The chromatographic column was an IonPac AS11 250x2 mm (Dionex, Sunnyvale, CA, USA). An efficient separation of the four analytes studied (diphosphate, trimetaphosphate,
Table 1 – Validation parameters
triphosphate and tetrapolyphosphate) has been obtained by an optimized gradient elution with sodium hydroxide: 10 mM for 4 min, from 10 to 20.5 mM in 1 min, 20.5 mM for 2 min, from 20.5 to 45 mM in 1 min, 45 mM for 9 min, finally a re-equilibration at 10 mM for 2 min. The validation of the method has been performed in according to the Regulation (EC) No. 882/2004 (3). In order to evaluate the method performance parameters, some products of animal origin (processed meats, cheeses and fish), spiked with polyphosphates, have been analyzed.
RESULTS AND DISCUSSION
The optimized gradient guarantees a good separation of the four analytes investigated. The
developed method results specific for all the matrixes tested. The main parameters of valida- A B C
Figure 1 – Comparison of chromatograms relevant to real samples with and without polyphosphates, as declared on the food label: Cooked ham (A), Processed cheese (B), Codfish (C).
tion (see recovery, precision and accuracy in Tab.1) result in compliance with EC regulation (3). In figure 1 some chromatograms obtained from the analyses of real samples with and without polyphosphates, as declared on the food label, are reported. The comparison of the amount reported on the label with the results obtained by the proposed method has allowed to rule out a possible natural degradation of the polyphosphates in the sample, which guarantees the absence of false negative responses. Besides, the results obtained by a national inter-laboratory proficiency test (-1 < z-score obtained < +1), which has been carried out in 2006 and 2007 on shrimps and fish, and in 2008 on fish and processed meats, show the absolute method reliability for the official control of the products of animal origin.
CONCLUSIONS
The analytical method developed and validated in this work, for the determination of polyphosphates in products of animal origin, has been proved precise and accurate by the validation. It is selective, rugged, and applicable to various food matrixes (processed meats, cheeses and fish). Finally, it results very simple and rapid with respect to other technique, allowing the resolution of the phosphorus index problem encountered with the photometric method.
References
(1) Svoboda, L.; Schmidt, J. J. Chromatogr. A 1997, 767, 107. (2) Bernini, R.; Picconi, F.; Iacovacci V.; Principi C.; Abballe F. Industrie Alimentari – XL 2001, nov
(3) European Commission, Regulation No. 882/2004, april 2004, G.U.C.E., L 165,