Method of detecting contaminants

The present invention relates to the identification of an infrared (IR) signal in the range of 1360 cm −1 to 2090 cm −1 and/or 2650 cm −1 to 3000 cm −1 , and/or 3700 cm −1 to 4400 cm −1 that can be used as an indicator of the presence of petroleum hydrocarbon. In a particular application, the invention provides a method for the detection of petroleum hydrocarbon in an environmental sample such as a soil, silt, sediment, rock, mineral or waste sample.

This application is the U.S. national phase of International Application No. PCT/AU2010/000804 filed on 25 Jun. 2010, which designated the U.S. and claims priority from Australian Provisional Patent Application 2009902946, titled “METHOD OF DETECTING CONTAMINANTS”, and filed on 25 Jun. 2009; and Australian Provisional Patent Application 2010900753, titled “METHOD OF DETECTING CONTAMINANTS”, and filed on 23 Feb. 2010.

The entire content of these applications are hereby incorporated by reference.

Most petroleum hydrocarbon substances are derived from crude oil and, typically, comprise a mixture of short and medium length hydrocarbon compounds. The less volatile components of petroleum hydrocarbons can become environmental contaminants; they may remain in the environment for extended periods and become toxic to wildlife, flora and/or humans. Such contaminations are usually difficult, if not impossible, to observe visually unless gross contamination has occurred. Therefore, methods for the rapid and/or simple detection of petroleum hydrocarbons in the environment (ie as may be found in soils, sludges and waterways) are desirable for monitoring environmental contamination and/or assessing a site. For example, methods for the rapid detection of petroleum hydrocarbons are particularly useful in assessing or monitoring contamination of coastal land following off-shore oil spills.

For instance, with high urban growth, city fringes are gradually encroaching on areas that were formerly disused and/or predominantly industrial in nature. These sites present usable and valuable property for the further growth and development of many industrialised cities. However, many such sites have been contaminated by petroleum hydrocarbon leakage from their previous industrial uses, and some have been exposed to these recalcitrant materials time and time again. While these sites hold great potential, the environmental protection guidelines of most industrialised countries set safety standards for the minimum acceptable concentration of petroleum hydrocarbons in soils or other environmental matrices. Thus, to be placed in order for non-industrial reuse (eg residential or light-industrial uses), the amount of petroleum hydrocarbon on these sites must be reduced to acceptable levels for their intended future use. While many options are available for the treatment of contaminated sites, a significant portion of the time and costs involved in treating these sites is consumed in the monitoring of petroleum hydrocarbon. This is particularly true of the more sustainable remediation treatment techniques.

In addition, causing an environmental contamination event can be considered as a serious offence with hefty penalties applicable to entities that flagrantly cause serious contamination. In these instances, regulators must rely on time-intensive and costly techniques to monitor the contamination event, with the delay in testing time, in turn, causing a delay in possible action to control the severity of the event.

Such testing situations typically involve the testing of numerous soil samples involving the extraction and quantification of contaminant components, which is generally time consuming and labour intensive. For example, for the analysis of total petroleum hydrocarbons (TPHs) in soil, testing is usually carried put via supercritical fluid extraction of the TPH components from the soil samples followed by the quantitative analysis of the TPH either by gas chromatography-flame ionisation detection (GC-FID) and/or gas chromatography-mass spectrometry (GC-MS). GC-MS is particularly suitable for the quantitative analysis of the more volatile components of TPHs (ie compounds in the C6 to C10 carbon chain range), but often utilises a purge and trap method where a heated purge gas is used to introduce the TPH components to the GC column; a procedure that, alone, may take up to twenty minutes per sample. For the less volatile components of TPH (ie compounds in the C10 to C36 range), detection in soil or sediment samples can potentially be achieved by the direct extraction of the contaminants using a solvent such as methylene chloride, following sample sonication, and introduction of the TPH components to a GC column for GC-MS analysis or analysis by Fourier Transform (FT) IR transmission (Sadler and Connell, 2003). However, these techniques, although they potentially provide accurate results, can be time consuming and labour intensive. Moreover, none of these methods, which necessarily involve the use of sensitive equipment, are particularly suited to the direct on-site analysis of contaminants such as petroleum hydrocarbon.

Accordingly, a rapid and/or simple method for detecting the presence of contaminants, and particularly TPH components, in a site could provide significant cost advantages (ie in terms of reduced testing costs and/or the avoidance of delays in test results leading to productivity losses), and/or other advantages of rapid response, such as the capacity to undertake preventative measures to prevent further contamination and/or to limit contaminant spread.

Infrared (IR) spectrometry techniques represent a possible alternative approach to supercritical fluid extraction and gas chromatography analyses of site contaminants. IR spectrometry distinguishes between chemical compounds by detecting the selective absorption of different IR wavelengths by chemical bonds; thus, every compound present in a sample being analysed, that is IR active, has a unique IR “spectral signature” enabling its identification and potential quantification. IR spectrometry-based techniques, such as diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy with partial least-squares (PLS) chemometrics have been employed in agricultural soil analysis for the detection of organic carbon, exchangeable cations, air-dry moisture and clay content (Janik and Skjemstad, 1995; Reeves et al., 1999; and Cozzolino and Moron, 2003). For example, IR spectrometry has been used as a predictor of oil yield from oil shale minerals (Adams et al., 2005). However, these prior art techniques do not address the complexities associated with the qualitative or quantitative analysis of contaminants such as petroleum hydrocarbon in non-uniform and/or complex mixtures such as soil, sediment, rock or mineral samples. These difficulties arise because the spectral peaks typically attributable to petroleum hydrocarbon contaminants may also arise from the presence of naturally-occurring organic matter (NOM) and/or be masked by other factors in such non-uniform or complex samples. For example, using DRIFT, where the radiation penetrates only a short distance (a few tens of micrometers), quartz (as sand) and kaolinite clays can give particularly strong MIR spectral signatures which canvas a result, cause very weak spectral peaks to appear amplified while stronger spectral peaks may be distorted or disappear due to total “mirror” type of reflectance of the IR radiation.

The present invention is directed at IR spectrometry-based methods for detecting petroleum hydrocarbon contaminants in an environmental sample, particularly a soil, silt, sediment, rock, mineral or waste sample, which may overcome one or more of the problems associated with the prior art.

All publications, mentioned in this specification are herein incorporated by reference. Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in any country before the priority date of each claim of this application.

In a first aspect, the present invention provides for the use of an infrared (IR) signal in the range of 1360 cm −1 to 2090 cm −1 and/or 2650 cm −1 to 3000 cm −1 and/or 3700 cm −1 to 4400 cm −1 , as an indicator of the presence of petroleum hydrocarbon.

In a second aspect, the present invention provides a method for the detection of petroleum hydrocarbon in a sample comprising the steps of:

(i) subjecting the sample to infrared (IR) radiation, and (ii) detecting an IR signal in the range of 1360 cm −1 to 2090 cm −1 and/or 2650 cm −1 to 3000 cm −1 and/or 3700 cm −1 to 4400 cm −1 ;

wherein detection of said IR signal indicates the presence of petroleum hydrocarbon in said sample.

FIG. 1 shows the spectra of reference soil minerals, representing the most common soil minerals, by FT-IR spectroscopy. Arbitrary absorbance units are indicated on the y-axis and the frequency as wavenumber (cm −1 ) is indicated on the x-axis;

FIG. 2 shows the spectrum of NOM extracted from a reference soil sample;

FIG. 3 shows regions of the FT-MIR (2500 cm −1 to 4000 cm −1 ) and FT-NIR (4000 cm −1 to 5000 cm −1 ) spectra of diesel and crude oil in sand. Diesel is shown by the broken and crude oil in the solid line;

FIG. 4 ( a ): provides NIRS6500 vis-NIR transmittance spectra of hydrocarbon liquids (diesel, crude oil, n-hexane, iso-octane, chloro-hexadecane, and n-octanol) in a 1 mm quartz cuvette and (b): provides NIRS6500 vis-NIR transmittance (1 mm quartz cuvette) versus FT-NIR mirror (mirror transflectance) spectra of crude oil;

FIG. 5 provides FT-NIR mirror (mirror transflectance) spectra of hydrocarbon liquids (diesel, crude oil, n-hexane, iso-octane, chlororhexadecane, and n-octanol) in a 1 mm quartz cuvette. Insets show zoomed, spectral regions comprising alkyl peaks;

FIG. 6 shows a comparison of NIRS6500 vis-NIR transmittance (upper), FT-NIR mirror (transflectance) (middle) and FT-NIR DRIFT (lower) spectra of crude oil;

FIG. 7 shows the FT-MIR spectrum of sandy soil (solid line) and 1% crude oil adsorbed onto reference sandy soil (broken line);

FIG. 8 shows the FT-MIR spectra of 1% crude oil adsorbed onto reference soils comprising (a) smectite, (b) kaolinite, (c) carbonate and (d) illite;

FIG. 9 shows a side-by-side comparison of the FT-IR spectra of crude oil adsorbed onto soil minerals from a 1% solution of crude oil in cyclohexane in the 2500 cm −1 to 5000 cm −1 range. Kaolinite is shown as diff-Cka, illite is shown as diff-Cil, sand is shown as diff-CS, smectite is shown as diff-Sm, and carbonate is shown as diff-CCO 3 ;

FIG. 10 shows the spectra of quartz particles of varying sizes with 1% diesel sorbed: (a) shows the spectra prior to correction and (b) shows the baseline corrected spectra of samples of 1000-600 μm diameter particle size (S1), 600-500 μm diameter particle size (S2), 500-300 μm diameter particle size (S3), 300-212 μm diameter particle size (S4), 212-106 μm diameter particle size (S5) and 106-63 μm diameter particle size (S6);

FIG. 11 shows spectra of reference sandy soil with varying proportions of smectite wherein 1% diesel is absorbed to the soil: (a) shows the spectra prior to correction and (b) shows baseline corrected spectra of 0:1 pure smectite (1QS), 1:4 sand to smectite (2QS), 1:1.5 sand to smectite (3QS), 1:0.67 sand to smectite (4QS), 1:0.25 sand to smectite (5QS) and 1:0 pure sand (6QS);

FIG. 12 shows a summary of the effect of particle size and clay proportion on 1% diesel spectral intensity: (a) shows the effect of sand particle size and (b) shows the effect of smectite (ie clay) in quartz (ie sand); and

FIG. 13 provides an illustration depicting a range of soil particle variability distributions: (a) illustrates the effect of inter- and intra-particle variability by clay aggregates, sand, grains, carbonate and NOM on discrete particles and particle surfaces; (b) illustrates the effect of a diesel film coating on the surface of sand particles; (c) illustrates the effect of diesel sorbed throughout clay aggregates; and (d) illustrates the effect of clay and diesel coating on the surface of sand particles.

Present methods for the detection of petroleum hydrocarbon in an environmental sample, such as a soil, silt, sediment, rock, mineral or waste sample, require the partial or complete extraction of the hydrocarbon compounds from the sample, which can be time consuming and labour intensive. It is therefore desirable that alternative methods be developed which allow for the detection of petroleum hydrocarbon directly from an environmental sample (ie such that extraction steps are avoided), however this is complicated by the typical presence of naturally-occurring materials such as NOM which may mask or hide characteristic signals of TPH components that might otherwise be useful for petroleum hydrocarbon detection. The present applicant has, however, identified previously unrecognised IR signals (eg characteristic IR absorption peaks) which can be used to indicate the presence of petroleum hydrocarbon in an environmental sample. The signals appear to be substantially unaffected by the presence, of similar chemical groups on other naturally-occurring materials that may commonly be found in environmental samples.

The IR signals that are identified herein as being useful in determining the presence of TPH are in the mid-infrared (MIR) and near-infrared (NIR) regions of the infrared spectrum and are attributed to fundamental, combination and overtone —C—H vibrations. This is in contrast to prior art techniques (eg. Zwariziger and Förster, 1998) that rely on spectra only acquired in the NIR region and, as such, rely only on overtones and combinations.

In a first broad aspect, the present invention provides for the use of an infrared (IR) signal in the range of 1360 cm −1 to 2090 cm −1 and/or 2650 cm −1 to 3000 cm −1 and/or 3700 cm −1 to 4400 cm −1 as an indicator of the presence of a petroleum hydrocarbon.

The term “petroleum hydrocarbon” as used herein in relation to an environmental sample, such as a soil, silt, sediment, rock, mineral or waste sample is to be understood to refer to substances comprising one or more hydrocarbon compounds considered to form a component of the group known as “total petroleum hydrocarbon” (TPH). Such substances include crude oil or substances derived from crude oil (eg petroleum products) and typically comprise C6 to C30 hydrocarbon compounds including a —CH 3 (methyl) terminus.

The term “infrared signal” or “IR signal” as used herein in relation to IR radiation or IR spectrometry of spectra, is to be understood to refer to any indicator of absorbance and/or reflection of IR radiation. For example, in IR spectroscopy, an IR signal may comprise an absorbance or reflection peak in the IR spectrum. Reference herein to an IR signal at a specific wavenumber (eg 2850 cm −1 ) is intended to include many wavenumbers over a range, centred ion a signal at that particular wavenumber.

As used herein, all infrared intensities are expressed as absorbance units (A) wherein, A=Log Reflectance −1 and all frequencies are expressed as wavenumbers (cm −1 ).

Preferably, the use of the present invention is intended for the detection of petroleum hydrocarbon in an environmental sample such as a soil, silt, sediment, rock, mineral or waste sample.

Common soils, sediments, wastes or other environmental matrices often comprise naturally-occurring materials (NOMs) that may cause interference in performing IR spectrometry for petroleum hydrocarbon. In particular, these NOMs may mask or hide characteristic signals of petroleum hydrocarbon by, for example, giving a very strong IR signal that masks weaker IR signals (such as the weak IR absorption peak characteristic of TPH) or otherwise introduces “spectral noise” preventing the differentiation or identification of indicative peaks.

For instance, soil minerals can give strong IR signals in regions of the MIR and NIR; for example, strong IR absorption peaks below 2000 cm −1 , particularly in the region of 1100 cm −1 and 1000 cm −1 , are apparent in soil samples comprising quartz (ie sand) and kaolinite clays due to the presence of silicate (—SiO 2 ) structures in these substances and the consequent Si—O stretching vibration. In addition, the presence of clays such as smectite, illite and kaolinite can cause a strong IR signal in the 3690 cm −1 to 3620 cm −1 region due to clay lattice Al—OH vibrations, and further, any water absorbed into the clay structures can result in the generation of broad IR absorption peaks in the region from 3500 cm −1 to 3300 cm −1 . Moreover, the —OC—NH groups of any proteins that may be present in a sample create an IR signal near 1680 cm −1 and 1530 cm −1 , while the presence of other types of NOM bearing carboxylate (COO—) groups or carboxyl (—COOH) groups can be apparent from strong IR signals (at 1600 cm −1 and 1400 cm −1 and near to 1720 cm −1 , respectively. Also, carbonate (—CO 3 ) groups, generate characteristic IR signals in the regions in and near 2980 cm −1 to 2870 cm −1 , 2600 cm −1 to 2500 cm −1 and 1810 cm −1 , with the main —CO 3 peak apparent near 1375 cm −1 . These peaks overlap with several regions, mainly the 2900 cm −1 to 2800 cm −1 spectral region, where peaks resulting from the presence of alkyl groups (such as —CH 3 of petroleum hydrocarbon compounds) may also be found. For example, characteristic IR absorption peaks for alkyl groups are observed in the 2950 cm −1 to 2850 cm −1 region near 2955 cm −1 (—CH 3 ), 2931 cm −1 and 2856 cm −1 (—CH 2 ) (corresponding overtone peaks for these vibrations can be seen in the NIR at 4388 cm −1 , 4329 cm −1 and 4256 cm −1 ), however due to the potential interference caused by strong IR signals from NOM-derived alkyl groups and/or carbonate groups, it has not been previously considered possible to use one or more peaks in these regions as a reliable indicator of the presence of petroleum hydrocarbon in complex mixtures such as soil.

The use of the present invention is based upon the surprising finding that petroleum hydrocarbon compounds generate characteristic IR signals at or near 1380 cm −1 , 2690 cm −1 , 2730 cm −1 , 2830 cm −1 , 2850 cm −1 , 2870 cm −1 , 2950 cm −1 , 4164 cm −1 , 4256 cm −1 , 4329 cm −1 and/or 4388 cm 1 , particularly signals at or near 2730 cm −1 , 2830 cm −1 , and 2870 cm −1 . These “TPH-sensitive peaks” can be used to detect TPH even in the presence of naturally-occurring materials commonly found in environmental samples such as soil samples which might otherwise have been expected to confound the detection of petroleum hydrocarbon by an IR spectrometry-based method. For example, these “TPH sensitive peaks” can be used in the presence of carbonate (—CO 3 ) peaks detectable in the 2600 cm −1 to 2500 cm −1 and 2980-2870 cm −1 . These carbonate signals partly overlap with TPH alkyl peaks in the 2950-2850 cm −1 range.

However, as will be appreciated by persons skilled in the art, some variation in the exact location of the “TPH-sensitive peaks” can be anticipated depending upon, for example, the IR spectrometry equipment used and/or variation in the physical characteristics of the sample submitted for analysis. Indeed, many IR spectrometers may show some instability between scans of the same sample and nonetheless provide adequate stability for performing petroleum hydrocarbon analysis. Further, persons skilled in the art will recognise that some variation in the exact location of a reported peak will often be observed upon the repetition of IR analyses. Thus, the use of the present invention utilises specific IR signals in the mid-infrared (500-4000 cm −1 ) and near-infrared ranges (4000-7500 cm −1 )

In some embodiments, the present invention utilises IR signals in the range of 2700 cm −1 to 2950 cm −1 . In some embodiments, the present invention utilises IR signals in the range of 2690 cm −1 to 2760 cm −1 , preferably in the range of 2710 cm −1 to 2750 cm −1 . In specific embodiments, the use of the present invention utilises an IR signal at or near 2730 cm −1 .

In some other embodiments, the present invention utilises the an IR signal in the range of 2830 cm −1 to 2870 cm −1 . In some embodiments, the invention utilises an IR signal in the range of 2810 cm −1 to 2890 cm −1 , more preferably in the ranges 2810 cm −1 to 2850 cm −1 and/or 2850 cm −1 to 2890 cm −1 . In some specific embodiments, the present invention utilises IR signals at or near 2830 cm −1 and 2870 cm −1 . These signals are the wings of a peak at or near 2850 cm −1 and, therefore, in some other embodiments, the use of the present invention utilises and IR signal over this range centred on a peak near 2850 cm −1 .

In some other embodiments, the present invention utilises an IR signal in the range of 2670 cm −1 to 2710 cm −1 , more preferably in the range of 2680 cm −1 to 2700 cm −1 . In specific embodiments, the use of the present invention utilises and IR signal at or near 2690 cm −1 .

In some other embodiments, the present invention utilises and IR signal in the range of 4150 cm −1 to 4180 cm −1 , more preferably in the range of 4160 cm −1 to 4170 cm −1 . In specific embodiments, the use of the present invention utilises and IR signal at or near 4164 cm −1 .

In some other embodiments, the present invention utilises at least one IR signal at or near 4256 cm −1 , 4329 cm −1 and/or 4388 cm −1 .

The IR signals may be used alone or in combination to determine the TPH concentration in a sample. For example, we have found that for lower concentration ranges (eg. 0-1,500 mg/kg) use of the IR signals at or near 2830 cm −1 and 2870 cm −1 provides a model that is improved relative to the model obtained using only the IR signal at 2730 cm −1 over the same concentration range.

In a second aspect, the present invention provides a method for the detection of petroleum hydrocarbon in a same comprising the steps of:

(i) subjecting the sample to infrared (IR) radiation; and (ii) detecting an IR signal in the range of 1370 cm −1 to 2090 cm −1 and/or 2650 cm −1 to 3000 cm −1 and/or 3700 cm −1 to 4400 cm −1

wherein detection of said IR signal indicates the presence of petroleum hydrocarbon in said sample.

Preferably, step (i) comprises subjecting the same to IR radiation spanning almost the entire IR region of the electromagnetic spectrum (ie at least 450 cm −1 to 7800 cm −1 ). Alternatively, where, for example, the method utilises a portable or relatively basic IR spectroscopy equipment, it may be preferable to subject the sample to mid-infrared (MIR) radiation (ie 500 cm −1 to 4000 cm −1 ), or near-infrared (NIR) radiation (ie 4000 cm −1 to 7800 cm −1 ), or optionally a combination of MIR radiation and NIR radiation.

The methods described herein may find application, for instance, for the detection of petroleum tank leakage, particularly where tanks may be stored underground and wherein leakage detection presents a practical difficulty, and for the detection of petroleum hydrocarbons in dredge materials and other mixed wastes, such as industrial wastes.

The methods used herein may also find application in oil and gas exploration in which rapid detection of petroleum hydrocarbons in rock, mineral, silt or sand can be used as a rapid indicator of an area requiring further, detailed exploration.

Step (i) may be conducted directly on the sample (ie without any pre-processing or pre-treatment of the sample), however, for some samples such as soil, sediment, rock, mineral or waste samples, it may be preferred to crush or grind and/or sieve the sample prior to exposure to the IR radiation, so as to eliminate large particles and/or to ensure substantial uniformity in sample particle sizes. Further, for many solid samples, the surface characteristics of the particles within a sample may contribute to the “spectral definition” of the sample. If has, however, been found that if the sample is subjected to crushing or grinding, there can be a decrease in the baseline absorbance. Accordingly, for some samples, it may be preferred that before subjecting the sample to IR radiation, the sample is pre-processed to produce a sample comprising particles measuring less than 500 μm, more preferably, less than 200 μm, and most preferably, less than about 63 μm.

Further, it has been found that on certain particle surfaces, the presence of water or other solvents may “mirror” the IR radiation thereby causing distortion and/or the amplification of minor IR signals. Therefore, for some samples, it may be preferred, particularly when IR absorbance spectroscopy is used, to dry the sample prior to subjecting the sample to IR radiation. Drying the sample is preferably conducted in air at a temperature of less than 40° C. so as to avoid the volatilisation of modification of petroleum hydrocarbon. More preferably, the drying of the sample is conducted at ambient temperature.

Moreover, for some samples, it may be preferred to mix in a known amount of a diluent, such as an alkali halide (eg KBr) or fine clay, so as to achieve a substantially uniform baseline absorbance. It has been observed that the IR signal of petroleum hydrocarbon may be reduced by the presence of clay particles in the sample. It is suspected that clays and other porous media effectively shield the hydrocarbon from the IR radiation (which can only penetrate the sample to a depth of about 5 μm to 20 μm) through the absorption of the petroleum hydrocarbon within the solid particle. Soil particle size distribution may therefore need to be taken into consideration as a confounding factor.

In some embodiments, the IR signal to be detected in step (ii) is in the range of 2650 cm −1 to 3000 cm −1 .

In some embodiments, the IR signal to be detected in step (ii) is in the range of 2700 cm −1 to 2950 cm −1 , more preferably 2670 cm −1 to 2780 cm −1 , more preferably still in the range of 2690 cm −1 to 2760 cm −1 , and even more preferably still in the range of 2710 cm −1 to 2750 cm −1 . Most preferably, the IR signal to be detected is at or near 2730 cm −1 . We have found that the IR signal at 2730 cm −1 can be used across a wide range of TPH concentrations (eg from 0 to about 33,000 mg/kg).

In some embodiments, the IR signal to be detected in step (ii) is in the range of 2810 cm −1 to 2890 cm −1 , more preferably in the ranges 2810 cm −1 to 2850 cm −1 and/or 2850 cm −1 to 2890 cm −1 . Most preferably, the IR signal to be detected is at or near 2830 cm −1 and/or 2870 cm −1 .

In some embodiments, the IR signal to be detected in step (ii) is at or near 2950 cm −1 .

In some other embodiments, the IR signal to be detected in step (ii) is in the range of 1360 cm −1 to 2090 cm −1 , more preferably in the ranges 1360 cm −1 to 2000 cm −1 . Most preferably, the IR signal to be detected is at or near 1380 cm −1 .

In some other embodiments, the IR signal to be detected in step (ii) is in the range of 2670 cm −1 to 2710 cm −1 , more preferably in the range 2680 cm −1 to 2700 cm −1 . Most preferably, the IR signal to be detected is at or near 2690 cm −1 .

In some other embodiments, the IR signal to be detected in step (ii) is in the range of 4150 cm −1 to 4180 cm −1 , more preferably in the range 4160 cm −1 to 4170 cm −1 . Most preferably, the IR signal to be detected is at or near 4164 cm −1 .

The method of the present invention may be performed using, standard IR spectroscopy apparatus. Further, the scanning methodology utilised in the standard IR spectroscopy apparatus may be optimised for use with the method of the present invention by, for example, adjusting the scanning duration and resolution (eg optimised methods may involve scanning for 60 seconds in the range from 4000 cm −1 to 500 cm −1 (2500 nm to 20000 nm) at a resolution of 8 cm −1 , followed by repeat scans adjusted for a frequency and/or resolution above and/or below these values). Optimisation of the scanning methodology may also involve carrying out background reference scans, for instance, using silicon carbide (SiC) discs, gold or potassium bromide (KBr) designated with a reflectivity of 1. Advantageously, the method of the present invention may be performed using a portable DRIFT MIR spectrometer, optionally with some limited NIR capabilities included. A portable DRIFT MIR spectrometer may be used for in-situ scanning of soils. We have found that spectra obtained using a hand-held DRIFT MIR spectrometer are very similar to spectra obtained using lab-based instruments. As such, the method of the present invention may be used to rapidly generate data and, potentially, produce a spatial map of the soil TPH content over an area.

In embodiments comprising detecting an IR signal in the range of 2700 cm −1 to 2760 cm −1 , the method may further comprise:

(iii) detecting an additional IR signal in the range of 1000 cm −1 to 2700 cm −1 and/or 2760 cm −1 to 6000 cm −1 .

The identification of the additional IR signal may provide a stronger indication of the presence of petroleum hydrocarbon in the sample. For example, —CH 3 IR absorption peaks in range of 2845 cm −1 to 2965 cm −1 , their overtone peaks in the 4375 cm −1 to 4395 cm −1 range and/or the 5860 cm −1 to 5875 cm −1 range, or their deformational peaks in the 1355 cm −1 to 1395 cm −1 range may be used to confirm the 2700 cm −1 to 2760 cm −1 IR signal, as may the 2730 cm −1 overtone peak in the 2650 cm −1 to 2700 cm range and/or the 3700 cm −1 to 4400 cm −1 range. These signals may be used in combination with the 2700 cm −1 to 2750 cm −1 IR signal, for instance, to provide a benchmark for providing a semi-quantitative assessment of TPH. Alternatively, they may be used to normalise the 2700 cm −1 to 2760 cm −1 IR signal. Further, ethyl (—CH 2 CH 3 ) IR absorption peaks in the 2930 cm −1 to 2845 cm −1 range and/or 2845 cm −1 to 2865 cm −1 range and/or their overtone peaks in the 4245 cm −1 to 4265 cm −1 , 4320 cm −1 to 4340 cm −1 , 4345 cm −1 to 4365 cm −1 , 5685 cm −1 to 5695 cm −1 , 4295 cm −1 to 4305 cm −1 and/or 5795 cm −1 to 5805 cm −1 ranges, may also be used to, for example, account for the effect of NOM. Further, the main —CO 3 IR absorption peak in the 1370 cm −1 to 1380 cm −1 range, and/or its overtone peaks in the 1805 cm −1 to 1810 cm −1 range, the 2600 cm −1 to 2500 cm −1 range, and/or the 2980 cm −1 to 2870 cm −1 range, may be used to eliminate the interference.

The method of the present invention may be suitable for the detection of petroleum hydrocarbon in a liquid or aqueous sample (ie without the need to dry the sample to a solid form). This can be achieved by, for example, utilising mirror reflection techniques (ie transflectance techniques) to overcome the difficulty of specular reflectance distortions that may otherwise be experienced using DRIFT. Thus, for example, the detection of petroleum hydrocarbon in materials in wet or damp conditions, need not be delayed by the requirement to transport samples off-site for drying.

The method of the present invention may also be suitable for providing a semi-quantitative assessment of TPH in a sample. For example, the method may be operated so as to provide an indication of the presence or absence of TPH above or below a significant threshold point. That is, the method may be operated to provide an assessment of whether a sample includes TPH at a level above or below a regulatory limit (eg. 10,000 mg/kg or parts per million by weight of TPH). This may be achieved by for example, including step (iii) in the method. The assessment may be achieved using, for example, software to aid in the automation of TPH determination (eg to perform a calculation of whether a sample includes TPH at a level above or below a significant threshold point). Further, such software may be used to combine data from IR signals in the 2700 cm −1 to 2760 cm −1 range with those in the 1000 cm −1 to 2700 cm −1 and/or 2760 cm −1 to 6000 cm −1 ranges.

For instance, in the treatment of petroleum hydrocarbon contaminated soils, existing techniques that are used to monitor the progress of treatment (such as GC techniques) require that samples be prepared off-site and prior to analysis, usually by time consuming and lengthy solvent extraction processes. Further, analyses must be performed on a representative number of samples from the site. The process of monitoring petroleum hydrocarbon treatment or remediation efforts can be a time consuming and expensive process with delays in analysis, in turn, causing costly delays in site redevelopment (eg. contracting equipment on standby while awaiting analytical results) or re-use (eg. lost income from residential tenants).

In addition, techniques such as GC analysis do not differentiate between NOM content, which is normally present at a concentration of <5% in Australian soils and sediments (Rayment & Higginson, 1992), from total petroleum hydrocarbon content. Therefore, it is probable that many previous false positive results have resulted in conducting unnecessary petroleum hydrocarbon treatment measures whilst delaying site redevelopment.

Further, false positive results may be observed in the detection of NOM from interference by TPH in measured samples. Thus, the present methods for detecting petroleum hydrocarbon in a sample may be used to improve current IR methods for the dejection of NOM in samples, particularly for NOM analysis in agricultural applications. The present methods may be used to reduce or eliminate interference from current methods which fail to distinguish between TPH and NOM, or the “TPH specific” signal may be combined with known NOM analyses, such as known IR analyses, to more accurately predict NOM content in a sample.

Similarly, the present methods for the rapid, on-site and/or specific detection of petroleum hydrocarbons may be applied in other settings, such as oil or petroleum exploration. Detritus is a common source of NOM frequently found in substantial amounts in the vicinity of oil or petroleum reservoirs. The presence of detritic films on the surface of core samples taken for the purpose of oil or petroleum exploration pose significant difficulties in the specific detection of petroleum hydrocarbon by conventional techniques, such as GC techniques. Thus, the present methods may provide for the rapid and/or specific detection of petroleum hydrocarbon for the characterisation of a core sample.

Thus, in the present methods the sample may be a core sample. Methods for extracting core samples from environmental matrices such as soil, sediment or rock in terrestrial or aquatic environments, are well known in the art. The core sample may be directly subjected to IR radiation, for instance an IR beam may scan the entire length or circumference of the exterior surface of a core sample or an IR beam may scan one or more specific sections of the core sample. For instance, a scan may be taken at 10 cm intervals along the length of the core sample.

Alternatively, the core sample or a portion thereof may be subjected to crushing or grinding. Crushed or ground samples may, optionally, be sieved. The core sample or a portion thereof may be pre-processed to comprise particles measuring less than 500 μm, more preferably, less than 200 μm, and most preferably, less than about 63 μm.

The present methods may therefore be used for identifying the location of oil or petroleum hydrocarbon reservoirs and/or characterising the oil or petroleum reservoirs of a known location.

The present methods may be integrated into a detection apparatus specifically adapted for the detection of petroleum hydrocarbon in environmental matrices. That is, the detection apparatus may be a handheld device suitable for performing petroleum hydrocarbon detection in-situ, ie without the need to remove the sample from the site, or alternatively, it may be a portable device suitable for the ex-situ detection of petroleum hydrocarbons on-site, for instance in a mobile laboratory. The detection apparatus may be adapted for on-site applications by miniaturisation and/or stabilisation of the spectrometer. This may be achieved, for example, by limiting the source of IR radiation in a detection apparatus to the transmission of IR radiation in a limited range comprising the 1360 cm −1 to 2090 cm −1 and/or 2650 cm −1 to 3000 cm 1 , and/or the 3700 cm 1 to 4400 cm −1 range and/or by limiting the detection or an IR signal to a limited range comprising the 2650 cm −1 to 3000 cm −1 and/or 3700 cm −1 to 4400 cm −1 ranges.

Further, a detection apparatus adapted for the detection of petroleum hydrocarbon in environmental matrices may comprise software and hardware required to perform an analysis of the IR signal and to make a determination as to the presence and/or absence of petroleum hydrocarbon within predetermined confidence limits. The analysis may, optionally, comprise the software and hardware required to perform a semi-quantitative analysis. This may be used to determine whether the sample exceeds a predetermined threshold limit, for example the threshold may be set at a regulatory limit (eg 10,000 mg/kg TPH) to indicate whether the sample falls above or below the acceptable limit. A detection apparatus of this type has many applications, including for in-soil leak detection around tanks and pipes.

The present invention is hereafter further described by way of the following non-limiting examples and accompanying figures.

The use of infrared reflectance spectroscopy with PLS chemometrics to predict TPH in materials with widely variable mineralogy should preferably overcome difficulties associated with an overlap of TPH peaks by carbonate peaks, an overlap of TPH peaks by natural organic matter peaks, and the variable sorption into different minerals due to particle size, as this may lead to variable signal strength and detection limits for different types of environmental matrices. The results obtained in this example show that the PLS method may be used to model the relationship between TPH signal strength and concentration by taking into account sample composition or matrix type. The inclusion of spectral signatures from quartz in the PLS X-variable data, or otherwise providing a way for the PLS model to differentiate between sorption onto quartz and sorption onto other environmental materials, may further improve TPH prediction. Moreover, the disproportionate spectra reflectance from large sand grains may be reduced by eliminating particle size effects. It was observed that even a small amount of a clay material can dramatically reduce the TPH spectral intensity, and that this effect plateaus at about 50% clay. The plateau effect may be exploited by mixing all samples with a known weight of a diluent such as an alkali halide (eg KBr) or even fine clay. This would have the effect of covering the sand grains with a shielding agent and also sorbing some of the surface TPH film into this fine material.

The examples also show that infrared signals near 2730 cm −1 , 2830 cm −1 , 2870 cm −1 , 1380 (˜1360-1380) cm −1 , 2950 cm −1 , 4164 cm −1 and 4330 cm −1 may be used to differentiate between natural and petroleum derived hydrocarbons.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

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