Is food allergen analysis flawed? Health and supply chain risks and a proposed framework to address urgent analytical needs.

Food allergy is an increasing problem for those affected, their families or carers, the food industry and for regulators. The food supply chain is highly vulnerable to fraud involving food allergens, risking fatalities and severe reputational damage to the food industry. Many facets are being pursued to ameliorate the difficulties including better food labelling and the concept of thresholds of elicitation of allergy symptoms as risk management tools. These efforts depend to a high degree on the ability reliably to detect and quantify food allergens; yet all current analytical approaches exhibit severe deficiencies that jeopardise accurate results being produced particularly in terms of the risks of false positive and false negative reporting. If we fail to realise the promise of current risk assessment and risk management of food allergens through lack of the ability to measure food allergens reproducibly and with traceability to an international unit of measurement, the analytical community will have failed a significant societal challenge. Three distinct but interrelated areas of analytical work are urgently needed to address the substantial gaps identified: (a) a coordinated international programme for the production of properly characterised clinically relevant reference materials and calibrants for food allergen analysis; (b) an international programme to widen the scope of proteomics and genomics bioinformatics for the genera containing the major allergens to address problems in ELISA, MS and DNA methods; (c) the initiation of a coordinated international programme leading to reference methods for allergen proteins that provide results traceable to the SI. This article describes in more detail food allergy, the risks of inapplicable or flawed allergen analyses with examples and a proposed framework, including clinically relevant incurred allergen concentrations, to address the currently unmet and urgently required analytical requirements. Support for the above recommendations from food authorities, business organisations and National Measurement Institutes is important; however transparent international coordination is essential. Thus our recommendations are primarily addressed to the European Commission, the Health and Food Safety Directorate, DG Santé. A global multidisciplinary consortium is required to provide a curated suite of data including genomic and proteomic data on key allergenic food sources, made publically available on line.

Key comparison BIPM.RI(I)-K3 of the air-kerma standards of the NIST, USA and the BIPM in medium-energy x-rays.

A key comparison has been made between the air-kerma standards of the NIST, USA and the BIPM in the medium-energy x-ray range. The results show the standards to be in agreement at the level of the standard uncertainty of the comparison of 3.8 parts in 103, except at 250 kV where the difference is 1.5 times the standard uncertainty. The results are analysed and presented in terms of degrees of equivalence, suitable for entry in the BIPM key comparison database.

Honey authenticity: the opacity of analytical reports-part 2, forensic evaluative reporting as a potential solution.

The analytical techniques applied to verify honey authenticity are multifaceted and often result in complex data rich certificates of analysis that are open to interpretation and may be opaque to stakeholders without specialist knowledge. In these cases, the drawing of an independent overarching opinion is challenging. Two questions arise: (Q1) Is it acceptable to report interpretation, particularly if it is adverse, without exhibiting the supporting data? (Q2) How may a valid overarching opinion on authenticity be derived from a large, partially conflicting, dataset? To Q1, it is demonstrated that full disclosure of the data used in interpretation is mandatory. To Q2 it is proposed, with worked examples, to adopt 'evaluative reporting'; a formalised likelihood ratio thought process used in forensic science for evaluation of findings and their strength assessment. In the absence of consensus on techniques for honey authenticity adoption of reporting conventions will allow objective assessments of reports, with equity to all and provide a better basis to identify and address fraud.

Honey authenticity: the opacity of analytical reports - part 1 defining the problem.

The composition of honey, a complex natural product, challenges analytical methods attempting to determine its authenticity particularly in the face of sophisticated adulteration. Of the advanced analytical techniques available, only isotope ratio mass spectrometry (IRMS) is generally accepted for its reproducibility and ability to detect certain added sugars, with nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS) being subject to stakeholder differences of opinion. Herein, recent reviews of honey adulteration and the techniques to detect it are summarised in the light of which analytical reports are examined that underpinned a media article in late 2020 alleging foreign sugars in UK retailers' own brand honeys. The requirement for multiple analytical techniques leads to complex reports from which it is difficult to draw an overarching and unequivocal authenticity opinion. Thus arose two questions. (1) Is it acceptable to report an adverse interpretation without exhibiting all the supporting data? (2) How may a valid overarching authenticity opinion be derived from a large partially conflicting dataset?

Determination of consensus k Q values for megavoltage photon beams for the update of IAEA TRS-398.

The IAEA is currently coordinating a multi-year project to update the TRS-398 Code of Practice for the dosimetry of external beam radiotherapy based on standards of absorbed dose to water. One major aspect of the project is the determination of new beam quality correction factors, k Q , for megavoltage photon beams consistent with developments in radiotherapy dosimetry and technology since the publication of TRS-398 in 2000. Specifically, all values must be based on, or consistent with, the key data of ICRU Report 90. Data sets obtained from Monte Carlo (MC) calculations by advanced users and measurements at primary standards laboratories have been compiled for 23 cylindrical ionization chamber types, consisting of 725 MC-calculated and 179 experimental data points. These have been used to derive consensus k Q values as a function of the beam quality index TPR20,10 with a combined standard uncertainty of 0.6%. Mean values of MC-derived chamber-specific [Formula: see text] factors for cylindrical and plane-parallel chamber types in 60Co beams have also been obtained with an estimated uncertainty of 0.4%.

Diaphragm correction factors for free-air chamber standards for air kerma in x-rays.

At present, only a correction factor for photon transmission, k(l), is systematically applied for the entrance diaphragm of free-air chamber standards for air kerma. In the present work, the Monte Carlo code PENELOPE is used to re-evaluate k(l) for the BIPM standards and new correction factors are calculated for photon scatter and for fluorescence production in the diaphragm. An additional effect arising from electrons emitted from the diaphragm is shown to be significant at the highest photon energies. The results for the radiation qualities used for international comparisons give a combined diaphragm correction factor k(dia) = 0.9980(3) for the BIPM medium-energy standard at 250 kV. This is significantly different from the factor k(l) = 0.9996(1) in use at present and it might be concluded that differences are likely to exist for all free-air chamber standards. The effect of using a conical taper at the downstream edge of the diaphragm is shown to be negligible for these radiation qualities.

Air-kerma determination using a variable-volume cavity ionization chamber standard.

A graphite-walled cavity ionization chamber of modular design and variable volume has been used to determine the air-kerma rate in the reference 60Co field at the BIPM. The chamber can be configured in five sizes. High-accuracy mechanical measurements of the volume of the air cavity were made for each configuration using a co-ordinate measuring machine. Ionization current measurements were made for each configuration and corrected for the effects of ion recombination and diffusion, stem scatter and chamber orientation. Monte Carlo calculations of cavity dose were made to evaluate the correction factors kwall and kan. A reproducibility of the ionization current per mass of 1.5 parts in 10(4) was achieved on the repeated assembly of each configuration. The results show an air-kerma rate determination that increases with volume, the total change being around 8 parts in 10(4). When analysed differentially, the air-kerma rate relative to the BIPM standard is Kdiff/KBIPM = 1.0026(6). A detailed uncertainty budget is presented. Possible reasons for the observed behaviour are discussed that might have consequences for all existing standards for air-kerma.

A new approach to the determination of air kerma using primary-standard cavity ionization chambers.

A consistent formalism is presented using Monte Carlo calculations to determine the reference air kerma from the measured energy deposition in a primary-standard cavity ionization chamber. A global approach avoiding the use of cavity ionization theory is discussed and its limitations shown in relation to the use of the recommended value for W. The role of charged-particle equilibrium is outlined and the consequent requirements placed on the calculations are detailed. Values for correction factors are presented for the BIPM air-kerma standard for 60Co, making use of the Monte Carlo code PENELOPE, a detailed geometrical model of the BIPM 60Co source and event-by-event electron transport. While the wall correction factor k(wall) = 1.0012(2) is somewhat lower than the existing value, the axial non-uniformity correction k(an) = 1.0027(3) is significantly higher. The use of a point source in the evaluation of k(an) is discussed. A comparison is made of the calculated dose ratio with the Bragg-Gray and Spencer-Attix stopping-power ratios, the results indicating a preference for the Bragg-Gray approach in this particular case. A change to the recommended value for W of up to 2 parts in 10(3) is discussed. The uncertainties arising from the geometrical models, the use of phase-space files, the radiation transport algorithms and the underlying radiation interaction coefficients are estimated.

Comparison of the NIST and BIPM Standards for Air Kerma in Medium-Energy X-Rays.

A comparison has been made of the air-kerma standards for medium-energy x-rays of the National Institute of Standards and Technology (NIST) and the Bureau International des Poids et Mesures (BIPM). The comparison involved a series of measurements at the BIPM and the NIST using the air-kerma standards and three NIST reference-class transfer ionization chamber standards. Reference beam qualities in the range from 100 kV to 250 kV were used. The results show the standards to be in reasonable agreement within the combined standard uncertainty of the comparison of 0.37 %, although a significant trend with radiation quality is observed and the possible sources discussed.

R50 as a beam quality specifier for selecting stopping-power ratios and reference depths for electron dosimetry.

For electron beam reference dosimetry in radiotherapy, it is shown that by choosing the reference depth as dref = 0.6R(50)-0.1 cm, where R50 is the half-value depth in centimeters, the Spencer-Attix water-to-air stopping-power ratio at dref is given by (Llp)airw = 1.2534 - 0.1487 (R50)0.2144. This is derived from data for (Llp)airw obtained from realistic Monte Carlo simulations for 24 clinical beams. The rms deviation of this expression from the Monte Carlo calculations is 0.16%, with a maximum deviation of 0.26%. This approach fully takes into account the spectral differences between real electron beams of the same R50 and allows an absorbed-dose calibration at a standards laboratory to be easily and accurately transferred to a reference clinical beam. Using a single parameter to specify (Llp)airw, rather than the two parameters (R50 and depth) needed when the reference depth is chosen as the depth of dose maximum, has the potential to greatly simplify electron beam dosimetry protocols and allows the use of a similar formalism for photon and electron beam dosimetry. For use in converting a depth-ionization curve into a depth-dose curve, a somewhat less accurate but general expression for (Llp)w(air) as a function of R50 and depth is presented.

Ion recombination corrections for the NACP parallel-plate chamber in a pulsed electron beam.

The NACP electron chamber is one of three parallel-plate chambers recommended for use in the UK. Measurements with this chamber type have indicated a problem in determining the recombination correction. This is due to a variation of the ionization current I with polarizing voltage V which deviates from the accepted Boag theory. It is shown that there is a chamber-dependent threshold voltage below which the NACP chamber follows the Boag theory. Above this voltage the chamber should be used with caution, although it is still possible to correct for the dependence of the chamber response on the dose per pulse. The existence of such deviations from theory demonstrates the usefulness of the 1/I against 1/V plot and the limitations of the Boag two-voltage analysis. Values for the initial recombination and the coefficient of general recombination are measured for several NACP chambers. It is shown that from these one can derive a value for the effective plate separation and the collector radius of each chamber. Differences in the behaviour of NACP chambers manufactured by Scanditronix and Dosetek are discussed and the implications of free-electron collection are considered.

A new method to determine ratios of electron stopping powers to an improved accuracy.

A new method is presented to determine the ratio of electron stopping powers which is effective in the transfer of absorbed dose from one medium to another. The method involves an accurate measurement of the electron range in each of the media combined with a full Monte Carlo simulation of each experimental geometry. For the specific case of graphite and water, the uncertainty attainable is estimated to be around +/- 0.5% at the 95% confidence level, which is approximately a factor of three better than the best methods currently in use.

Review: Amplification reactions; origins and definitions-progress and present status.

Amplification reactions provide a chemical means of enhancing the sensitivity of an analytical measurement. This review describes the various types of amplification reactions currently available, proposes a systematic classification scheme for them and also provides a comprehensive account of amplification reactions for a wide variety of analytes.

Identification of some polyatomic inorganic anions as their diphenyliodonium salts by infrared spectroscopy and interpretation of the spectra.

The main features of infrared spectra of the diphenyliodonium salts of some polyatomic anions are reported and interpreted, and their application in qualitative analysis discussed.

Use of basic dyes in the determination of anions, particularly as a means of determining antimony, thallium, and gallium.

The use of xanthene, triphenylmethane and other basic dye cations as reagents for the determination of anions is reviewed. Elements and anions determined include Sb, Tl, Ga, Au, Te, In, Zn, Ta, Hg, Re, Sn, U, Os, B, Cr, Ag, ClO(4)(-), PO(4)(-), SO(4)(2-) and NO(3)(-). Difficulties encountered in developing satisfactory procedures involving basic dyes are discussed. Procedures for the purification and analysis of basic dye samples are outlined.

Masking of iron with fluoride in the extractive atomic-absorption spectrometric determination of chromium in steel.

Chromium in steel is determined by oxidation to dichromate, extraction into methyl isobutyl ketone from 1-3 M hydrochloric acid, and atomic-absorption measurements on the extract. The interference of iron in the atomic absorption is eliminated by using fluoride to keep the iron(III) in the aqueous phase in the extraction step.

Application of free-radical chromogens to determination of nitrite and nitrate ions by EPR spectrometry.

Various azines and substituted phenylene diamines are oxidized by the nitrite ion to give stable radicals in an autocatalytic reaction. This finding has now been developed into highly sensitive methods for nitrite determination by EPR spectrometry. Thus, when the reagent is phenothiazine, the detection limit for nitrite is 0.012 ppm, the relative standard deviation at 0.05 ppm is 1.9%, and the analytical range is 0-1.5 ppm. With N,N,N',N'-tetramethyl-p-phenylenediamine as the reagent, the corresponding values are 0.025 ppm, 2.6%, and 0-1.3 ppm. Nitrate can be determined after prior reduction to nitrite. A mixture of nitrite and nitrate ions can also be quantitatively analysed. The EPR methods were applied to the determination of the nitrite and nitrate contents of prepacked cooked ham and of soft-spreading cheese. The results agreed well with those obtained by ISO and AOAC standard methods for these samples. ca*|Author for correspondence.

Analytical aspects of organo-P, As, Sb, S, Se, Te and Sn(IV) (onium) cations.

Reactions and the analytical applications of tetraphenyl-phosphonium, -arsonium and -stibonium, triphenylmethylarsonium, triphenyl-sulphonium, -selenonium and -telluronium and triphenyltin cations with oxy-anions, and halo- and thiocyanato-anionic complexes are surveyed.

Elimination of nitrate interference in the trace détermination of sulphate as hydrogen sulphide.

The microdetermination of sulphate by reduction to hydrogen sulphide, determined colorimetrically as Methylene Blue, is subject to interference from nitrate ion. This interference is eliminated by adding zinc acetate and igniting samples at 320 degrees for one hr.

The luminescence properties of some anti-inflammatory and antipyretic drugs.

Twenty anti-inflammatory and antipyretic drugs have been examined for their fluorescence and phosphorescence characteristics, and conditions established for detection of fourteen of them at trace levels.