{
  "url": "https://openlegislation.uk/preservatives-in-food-scotland-regulations-1989/schedule-5/part-I/paragraph-5",
  "json_url": "https://openlegislation.uk/preservatives-in-food-scotland-regulations-1989/schedule-5/part-I/paragraph-5.json",
  "legislation": "uksi/1989/581",
  "legislation_title": "The Preservatives in Food (Scotland) Regulations 1989",
  "legislation_url": "https://openlegislation.uk/preservatives-in-food-scotland-regulations-1989",
  "path": "schedule/5/part/I/paragraph/5",
  "kind": "paragraph",
  "number": "5",
  "heading": "Method of analysis",
  "text": "The analysis shall be carried out as follows—\n(a) Preparation and extraction: All the fruit in the sample for analysis is cut in half. Half of each piece of fruit is kept for quantitative determination of the residue of any biphenyl or 2-hydroxybiphenyl present. Pieces of peel are taken from the other halves to give a sample of about 80 g. These pieces are chopped, crushed in the mixer and placed in the 250 ml flask; to this is added 1 ml of 25 per centum hydrochloric acid and 100 ml dichloromethane. The mixture is heated under reflux for 10 minutes. After cooling and rinsing of the condenser with about 5 ml of dichloromethane, the mixture is filtered through a fluted filter. The solution is transferred to the evaporator and some anti-bumping granules are added. The solution is concentrated at reduced pressure at a temperature of 60C to a final volume of about 10 ml. If a rotary evaporator is used, the flask should be kept in a fixed position to avoid loss of biphenyl through the formation of a film of the product on the upper wall of the flask.\n(b) Chromatography: 30 g of silica gel and 60 ml of water are placed in a mixer and mixed for one minute. The mixture is then spread on to 5 chromatographic plates to form a layer approximately 0.25 mm thick. The plates covered with this layer are subjected to a stream of hot air for 15 minutes and then placed in an oven where they are kept for 30 minutes at a temperature of 110C.\nAfter cooling, the surface layer of each plate is divided into lanes, 2 cm wide, by parallel lines penetrating the silica gel down to the surface of the glass plate. 50 μl of the extract to be analysed are applied to each lane as a narrow band of contiguous spots approximately 1.5 cm from the lower edge of the plate. At least one lane is kept for the controls consisting of a spot of 1 ul (that is, 10 μg) of the standard solutions of biphenyl and 2-hydroxybiphenyl, one standard per lane. The chromatographic plates are developed in a mixture of cyclohexane and dichloromethane (25:95) in tanks previously lined with filter paper.\n(c) Detection and identification: The presence of biphenyl and 2-hydroxybiphenyl is shown by the appearance of spots in ultra-violet light (254 nm). The sodium biphenyl-2-yl oxide will have been converted to 2-hydroxybiphenyl during the extraction in an acid medium, and its presence cannot therefore be distinguished from that of 2-hydroxybiphenyl. The products are identified in the following manner—\n(i) biphenyl gives a yellow spot in daylight when sprayed with the TNF solution;\n(ii) 2-hydroxybiphenyl gives a blue spot when sprayed with the solution of 2,6-dibromo-p-benzoquinonechlorimine, followed by rapid passage through a stream of hot air and exposure to an ammonia-saturated atmosphere.",
  "extent": null,
  "status": null,
  "version": "current",
  "annotations": [],
  "outstanding_effects": [],
  "provenance": {
    "source": "legislation.gov.uk",
    "source_url": "https://www.legislation.gov.uk/uksi/1989/581/schedule/5/part/I/paragraph/5",
    "retrieved_at": "2026-10-29T15:46:06.805662+00:00"
  },
  "licence": "Open Government Licence v3.0",
  "licence_url": "https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/",
  "attribution": "Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives."
}