Chemistry: analytical and immunological testing – Tracers or tags
Reexamination Certificate
2000-10-20
2001-11-06
Warden, Jill (Department: 1743)
Chemistry: analytical and immunological testing
Tracers or tags
C436S027000, C436S029000, C436S139000, C436S172000
Reexamination Certificate
active
06312958
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of marking liquids using at least two markers, wherein said markers absorb in the 600-1200 nm region of the spectrum and reemit fluorescent light and the absorption range of at least one marker overlaps with the absorption range of at least one other marker.
2. Description of the Related Art
The present invention further relates to a method for detecting markers in liquids marked by the method of the invention, which comprises using light sources which emit radiation in the absorption ranges of said markers and detecting the fluorescent light reemitted by said markers, at least one of said light sources emitting radiation in the overlapping absorption range of at least one marker with that of at least one other marker and the number of light sources being less than or equal to the number of markers.
The present invention further relates to liquids marked by the method of the invention.
It is frequently necessary to mark, or tag, liquids to allow their subsequent detection, for example in use, by means of suitable methods. This makes it possible, for example, to differentiate heating oil, which normally enjoys a favorable tax status, from the generally more highly taxed diesel oil, or to tag liquid product streams in large industrial plants, for example petroleum refineries, and to trace them thereby.
If the marking of the liquids is to be invisible to the human eye, it is necessary to resort to the use of markers which absorb and/or emit radiation outside the visible region of the spectrum. Owing to the extreme sensitivity of detection and the attendant possibility of achieving reliable marking with low levels of added marker, pride of place belongs here especially to markers which reemit the absorbed radiation as fluorescent light. This emitted radiation generally has a lower frequency than the absorbed radiation (STOKES radiation), less frequently the same frequency (resonance fluorescence) or even a higher frequency (ANTI-STOKES radiation).
Great economic importance attaches to the marking of hydrocarbons and hydrocarbon mixtures (e.g., various grades of diesel and gasoline motor fuels and of other mineral oils). Since these liquids usually themselves have high absorption and/or fluorescence in the region of the spectrum below about 600 nm, its is not surprising that the markers used absorb and/or fluoresce above about 600 nm.
Ideally, compounds useful as markers should therefore possess the following basic properties:
strong absorption in the 600-1200 nm region of the spectrum,
little or no absorption/fluorescence in the visible region of the spectrum,
strong emission of fluorescent light in the region of the spectrum which extends from about 600 to about 1200 nm,
give detectable emission levels of fluorescence when added to the liquid in question at less than 1 ppm by weight, and
adequate solubility in the liquid to be marked.
In addition, depending on the specific application requirements, compounds useful as markers may have to satisfy one or more of the following requirements:
miscibility with other markers and any other additives present (the marked and possibly additived liquids should also be miscible with each other),
adequate stability to the action of external conditions, e.g., temperature, light, moisture, etc., alone and dissolved in the liquid to be marked,
not be harmful to the environment in which they are used, e.g., internal combustion engines, storage tanks, etc., and
be both toxicologically and ecologically safe.
WO 94/02570 describes marking liquids by using markers having their absorption maximum within the range from 600 to 1200 nm and/or a fluorescence maximum within the range from 620 to 1200 nm selected from the group consisting of the metal-free and metal-containing phthalocyanines, the metal-free and metal-containing naphthalocyanines, the nickel-dithiolene complexes, the aminium compounds of aromatic amines, the methine dyes and the azulenesquaric acid dyes. It further describes a method essentially comprising detecting the fluorescent light of the marker present in the liquid, which marker absorbs radiation in the stated region of the spectrum. The cited reference also describes a detector for the marker. However, the simultaneous use of two or more markers is not explicitly mentioned.
U.S. Pat. No. 5,525,516 likewise describes a method for marking mineral oils with compounds which fluoresce in the NIR region. Substituted phthalocyanines, substituted naphthalocyanines and squaric or croconic acid derivatives are used as such markers. This U.S. Patent states in the description part (column 3, lines 35 to 40) that it is also within the scope of the invention described therein to mark one or more mineral oils not just with one, but also with two or more compounds which fluoresce in the IR region. It is further stated in this passage that these two or more compounds are selected so that they absorb IR radiation and/or reemit fluorescent light at wavelengths different enough from each other so as not to interfere with individual detection. Using the (then) state of the art detection equipment it is believed (column 4, lines 25 to 28) that such differences in absorption/fluorescence of as little as 20 nm in wavelength can be discerned. This reference explicitly rules out using markers having overlapping regions of absorption. What is more, it is pointed out (column 3, lines 41 to 44) that this or these fluorescent compound(s) should preferably absorb at wavelengths below 850 nm, since mineral oils absorb above this wavelength.
U.S. Pat. No. 5,525,516 further claims a method for identifying mineral oils which have been marked with one or more markers. The marked mineral oil, or the markers incorporated therein, are exposed to electromagnetic radiation within the range (absorption range) of 670-850 nm. But beyond that no further information is provided as to how to proceed when mineral oils have been marked with more than one marker.
U.S. Pat. No. 5,710,046 describes a method for tagging gasoline, again essentially by detecting an essentially metal-free fluorescent dye dissolved in the gasoline. An appropriately tagged gasoline is excited with radiation from a wavelength band of 600 to 2500 nm, the fluorescent light emitted by the dye in the wavelength band from about 600 to 2500 nm is detected, and the resulting detection signal is used to identify the tagged sample. This reference further describes at length the construction of a detector for detecting the fluorescent dyes in the tagged gasoline samples. However, the use of a plurality of markers (dyes) is not discussed.
If liquids, for example hydrocarbons and hydrocarbon mixtures (e.g., diesel and gasoline fuels and other mineral oils), from different sources or different manufacturers are to be marked, a multiplicity of different markers are required if only one marker is used per liquid. These different markers have to be sufficiently different in their absorption and/or fluorescence characteristics in order that the liquids may be identified with regard to their provenience and/or producer. Moreover, marking liquids with just one marker makes it easier for others to falsify unmarked liquids by adding the appropriate marker. This is of immense significance when chemically and qualitatively equivalent liquids carry different fiscal duties. An example are heating oil and diesel fuel.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to use two or more markers to mark liquids with a “fingerprint” signature which is difficult to reproduce.
We have found that this object is achieved by a method of marking liquids using at least two markers, wherein
said markers absorb in the 600-1200 nm region of the spectrum and reemit fluorescent light and
the absorption range of at least one marker overlaps with the absorption range of at least one other marker.
Preferably, markers are used whose respective maximum absorption wavelength is in the 600-1200 nm region of the spectrum.
DETAILED DESCRIP
Beck Karin Heidrun
Meyer Frank
Vamvakaris Christos
Wagenblast Gerhard
BASF - Aktiengesellschaft
Gakh Yelena G.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Warden Jill
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