<<Disclaimer: Verify this information before applying it to your situation.>>

A new test has recently become available for detection of gluten in foods.  This is not a home test, but one intended for manufacturers.  The detection limit is 3 ppm! So if you are told or read that gluten can only be measured to 20 ppm or even 10 ppm, that is no longer true.  This test also measures gluten from barley and rye, which was not true of some older tests.  I know that this new test is offered by FARRP (Food Allergen Research and Resource Program at the University of Nebraska), where it is the same price as the 10 ppm test, so it doesn't represent a greater expense.  Below is some information from the FARRP website, other links, and a pubmed abstract:

The Ridascreen Gliadin test is a sandwich enzyme immunoassay for the quantitative analysis of gliadins from wheat and corresponding prolamines from rye and barley in food. Gluten is the characteristic term for the protein mixture of glutelins and gliadins (prolamines) found in cereals. The proportion of glutelin to gliadin in the protein mixture is approximately the same

Ridascreen Gliadin (R7001)

  Detection limit: 1.5 ppm gliadine corresponding to 3 ppm (0.0003%) wheat gluten
  Sample preparation: Homogenization and extraction
  Incubation time: 1h 30 min 

Note: The gliadin test can detect gluten from wheat, rye and barley quantitatively with a detection limit of 3 ppm.

http://www.farrp.org/analysis.htm#assays
http://www.r-biopharm.com/

Innovative approach to low-level gluten determination in foods using a novel sandwich enzyme-linked immunosorbent assay protocol.

Valdes I, Garcia E, Llorente M, Mendez E.

Unidad de Gluten, Centro Nacional de Biotecnologia, Madrid, Spain.

OBJECTIVES: There is currently much call for a reliable enzyme-linked immunosorbent assay (ELISA) protocol for determining gluten in foods to serve as a basis for further Codex Alimentarius regulations. Given its ability to recognize the potential coeliac-toxic epitope QQPFP, which occurs repeatedly in alpha-, gamma- and omega-gliadins, hordeins and secalins, the monoclonal antibody R5 raised against a secalin extract may prove to be an essential tool for gluten analysis. This study was designed to develop a highly sensitive and specific sandwich ELISA to quantify low levels of wheat, barley and rye prolamins in foods for coeliacs. METHODS: Simple sandwich ELISA based on the use of a single monoclonal antibody (R5) as both the coating and detection was developed. A quantitative cocktail gluten-extraction procedure for heat-processed foods was also tested. RESULTS: R5-ELISA was able to identify gliadins, hordeins and secalins with assay sensitivities of 0.78, 0.39 and 0.39 ng/ml, respectively. The assay's detection limit was 1.5 ng gliadins/ml (1.56 ppm gliadins, 3.2 ppm gluten). The system proved insensitive to the non-coeliac-toxic cereals maize, rice and oats, and was non-cultivar-dependent. It was also able to detect gliadins and hordeins in unprocessed and heat-processed wheat- and barley-based products, and to estimate the gluten content of hydrolysed foods. CONCLUSION: We present a new generation of a robust sandwich R5-ELISA with good reproducibility (8.7%) and repeatability (7.7%). Its gluten-detection limit of 3.2 ppm is lower than the existing threshold of 20-200 ppm. The ELISA, which is equally sensitive to barley, wheat and rye prolamins, is compatible with the quantitative cocktail extraction procedure for heat-processed foods. Along with the cocktail procedure, the Working Group on Prolamin Analysis and Toxicity is currently evaluating an R5-ELISA system as proposed by the Codex Alimentarius Commission.

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