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The analytical performance of the newly proposed laser-based photoacoustic spectroscopy (LPAS) and colorimetric method for quantification of anthocyanin (E163) in commercially available hard boiled candies are compared to that of the spectrophotometry (SP). Both LPAS and colorimetry are direct methods that unlike SP do not require the extraction of the analyte or some additional sample treatment. Results indicate that LPAS and colorimetry are both suitable for quickly screening content of anthocyanin in hard boiled candies. The correlation between the two methods and spectrophotometry is linear with R2 = 0.9989 for LPAS and R2 = 0.9570 for colorimetry.

A relatively novel approach for easy and quick determination of rutin in buckwheat grain is suggested. The rutin content of the grain in seven common buckwheat (Fagopyrum esculentum) and six Tartary buckwheat (Fagopyrum tataricum) varieties was investigated by means of UV photoacoustic spectroscopy and HPLC as reference method. The lowest content was found in ‘Botan’ and ‘Bamby’ varieties, while the highest values were obtained in the variety ‘Emka’. Rutin content in grain of all Tartary buckwheat varieties was two orders of magnitude higher than in the other varieties. Rutin content in F. esculentum ranges between 9 and 36 mg/100 g dry weight as compared to 921 to 2 132 mg/100 g dry weight in F. tataricum. The UV photoacoustic spectroscopy data show rather good correlations of R2=0.977 and R2=0.980 with values obtained by HPLC data for all measured samples. Therefore, UV photoacoustic spectroscopy can be a cheap and quick method for determining rutin content in buckwheat grain.

Background Photoacoustic spectroscopy (PAS) is a tool for the rapid and non-destructive identification of materials even without contact. In recent years, there have been several works concerning the applicability of PAS in food analytical measurements. The intention of this work is to identify whether there is a correlation between total carotenoid and the b-carotene content of pumpkin and squash measured by high-performance liquid chromatography (HPLC), spectrophotometry (SP) and PAS. Methods lCrown prince F1r, lVeenas F1r, lAtlas F1r and lApollo F1r (SAKATA) were used as experimental materials. The samples were measured in a fresh state and in a lyophilised condition with HPLC, SP and PAS. Results The results of SP show that total carotene content varies according to the species and variety. Lyophilisation resulted in lower, although varying carotene content compared to the raw form. Typical PA spectra of pumpkins were determined (300n550 nm), normalized to the carbon black powder. At 17 Hz the amplitude and carotene content shows direct proportionality in the range investigated. Photoacoustic (PA) signal and carotenoid content of pumpkin samples gave a linear correlation (R2 = 0.9821). Conclusions The measurement of PA spectra gives reliable information about the total carotene content of pumpkin and squash samples. These findings may allow the use of PAS as a fast tool for the carotenoid determination in squashes and give the possibility of instead for the results to be used for the evaluation of squash varieties currently used for industrial processing in functional food development.

Carotenes, found in a diversity of fruit-containing foods, are important sources of antioxidants; a good example is apricot jam. In the study described in this paper, both the total carotenoid content (TCC) as well as the content of $$\upbeta $$ -carotene in six different apricot jams were quantified using traditional (UV–VIS) spectrophotometry (SP), high-performance liquid chromatography (HPLC), laser photoacoustic spectroscopy (LPAS), and the optothermal window (OW) method. Unlike SP and HPLC, LPAS and the OW methods require the minimum of sample preparation and only a one time calibration step which enables practically direct quantification of the TCC. Results were verified versus data obtained with SP as the reference technique. It was shown that LPAS and the OW method (at 473 nm) provide satisfactory results with $$R^{2}=0.9884$$ and 0.9766 for LPAS and OW, respectively.

Laser photoacoustic spectroscopy (PAS) and colorimetry have been used to rapidly and accurately determine the content of fat-free cocoa solids in dark chocolates. Both techniques are inexpensive and require only a one-time calibration step versus a method capable of absolute concentration measurement (for example HPLC). Once the response of PAS and/or colorimetry has been obtained, the content of fat-free cocoa solids in dark chocolates can be determined directly (i.e. without any sample preparation including the process of extraction) from the calibration curves and the experimentally measured microphone signal (in PAS studies) and colorimetric indices L* and ΔE* (in colorimetric investigations). Both colorimetric indices and PA signals correlate positively with the content of fat-free cocoa solids. The correlation is highly linear over a wide concentration range (25–50 %).

Photopyroelectric (PPE) methods belong to the class of photothermal techniques and provide the means for determining some thermal properties of foods in a relatively fast and simple way. In particular, the inverse variant of the photopyroelectric method, abbreviated IPPE, was used here to determine thermal effusivity (also called heat penetration coefficient) of the sour cream and mayonnaise as a function of their fat content. In the sour cream the latter varied from 12 to 31 g/100 g as compared to 27 to 80 g/100 g range in mayonnaise; for both samples the effusivity decreased linearly with the increasing fat content. Each additional gram of fat in 100 g sour cream or mayonnaise resulted in 11.13 and 12.11 Ws1/2m-2K-1 drop in effusivity. Good agreement between the experimentally obtained data and the calculated effusivity was observed if both, the composition and the thermal properties of individual constituents of sour cream were known.

The performance of the newly proposed laser-based optothermal window (OW) method and colorimetry for quantification of trans -lycopene in 10 watermelon homogenates has been evaluated. Reverse phase HPLC served as an established reference method. Both, OW and colorimetry are direct methods as they, contrary to the HPLC, obviate the need for extraction, which leaves homogenization of the sample as the only preparatory step prior to the analysis itself. The evaluation of analytical performance of each method leads to the conclusion that the OW method and colorimetry are both suitable for quick screening of the trans -lycopene concentration of red-fleshed watermelon homogenates. Linear correlation is highest ( R = 0.917) for the laser-based OW method. This detection concept offers an additional but very unique advantage. By virtue of the operational principle of the OW method, it is possible to avoid the effect of saturation, a phenomenon known to cause difficulties when interpreting data collected by other analytical methods.

Carotenes found in a diversity of fruits and vegetables are among important natural antioxidants. In a study described in this paper, the total carotenoid content (TCC) in seven different products derived from thermally processed tomatoes was determined using laser photoacoustic spectroscopy (LPAS), infrared lock- in thermography (IRLIT), and near-infrared spectroscopy (NIRS) combined with chemometrics. Results were verified versus data obtained by traditional VIS spectrophotometry (SP) that served as a reference technique. Unlike SP, the IRLIT, NIRS, and LPAS require a minimum of sample preparation which enables practically direct quantification of the TCC.

The availability of thermo-physical data of foods and their constituents is of general importance to food industry. The thermal effusivity e is one among the relevant thermodynamical quantities. The latter is normally calculated from the relationship e = (κρc)½, where c is specific heat, ρ is the density, and κ is the thermal conductivity. The necessity for performing the time consuming independent measurements of these three quantities is the major reason that the existing database with effusivity of foods is not very wide. This paper describes the application of the inverse photopyroelectric (IPPE) technique that allows the determination of effusivity from a single measurement. This approach was used to directly measure thermal effusivity of fresh egg yolk, egg white, and white/yolk blends. In addition, thermal effusivity of rehydrated egg powders (white, yolk, and the whole egg powder) has been measured and compared to that of the fresh hen egg. In case of the egg white, effusivity of rehydrated egg powders was practically the same as that of the fresh egg. However, the difference in effusivity between fresh egg yolk and rehydrated egg yolk, and between the blend of fresh egg and the rehydrated whole egg power was significant. Finally, thermal effusivity of rehydrated egg yolk, egg white, and the whole egg powder was determined as a function of dilution factor.

Photoacoustic (PA) spectroscopy in the ultraviolet and visible was demonstrated to be a suitable tool for direct determination of total phenolic content in red sorghum flours. The PA spectra obtained feature two characteristic peaks: the first centered at 285 nm is due to the aromatic amino acids, while the second one at 335 nm is associated with the total phenolic content. The outcome of the PA study was compared with the results obtained by a conventional, tedious Folin-Ciocalteau chemical method. Statistical analysis indicates no significant difference between the two methods used in this study.

The concept of OW (with 632.8 nm He–Ne laser), combined with colorimetry based on a reaction of anthrone-sulphuric acid, was proposed as a new tool for determination of lactose in raw milk. Data obtained from various milk samples by OW colorimetry were compared to those acquired from the MilkoScan analyser; the correlation between the two methods is high.

Carotenoids are important antioxidants found in various foods including those for nutrition of infants. In this investigation, the total carotenoid content (TCC) of nine different commercially available baby foods was quantified using colorimetric index a * obtained via reflectance colorimetry (RC) and by laser photoacoustic spectroscopy (LPAS) at 473 nm. The latter requires a minimum of sample preparation and only a one time calibration step which enables practically direct quantification of TCC. Results were verified versus UV–Vis spectrophotometry (SP) as the reference technique. It was shown that RC and LPAS (at 473 nm) provide satisfactory results for a *, R 2 = 0.9925 and R 2 = 0.9972, respectively. Other color indices do not show a correlation with TCC. When determining the TCC in baby foods containing tomatoes, it is necessary to select a different analytical wavelength to compensate for the effect of lycopene’s presence in the test samples.

Cocoa is a very important ingredient in the food industry and largely consumed worldwide. In this investigation, colorimetry and photoacoustic spectroscopy were used to directly assess the content of cocoa powder in cakes; both methods provided satisfactory results. The calibration curve was constructed using a series of home-made cakes containing varying amount of cocoa powder. Then, at a later stage, the same calibration curve was used to quantify the cocoa content of several commercially available cakes. For self-made cakes, the relationship between the PAS signal and the content of cocoa powder was linear while a quadratic dependence was obtained for the colorimetric index $$L^*$$ (brightness) and total color difference ( $$\Delta E^*$$ ).

Photoacoustic spectroscopy (PAS) and reflectance colorimetry are suggested as new tools for the analysis of total carotenoids in lyophilized apricot powders. The data obtained by these two techniques from seven apricot cultivars were compared to those acquired by spectrophotometry and high-performance liquid chromatography (HPLC). Best correlations were found between the total carotenoid (TC) content (obtained by VIS spectrophotometry: 1.2–3.4 mg per 100 g of fresh mass) and colorimetric index a* (a* represents the redness of the investigated sample), as well as either argon-ion laser- or xenon-lamp-based PAS. In all three cases linear correlations were comparable. However, according to the sensitivity and precision data, expressed via limit of detection (LOD) and measurement repeatability, the Xe-lamp-based PAS is a preferred approach, followed by colorimetric index a* and Ar-ion laser PAS. Both PAS methods exhibit practically the same Pearson's correlation coefficient (R=0.987 and R=0.991) values. Nevertheless, residual sum of squares (RSS) and residual standard deviation of the linear regression (sy/x) differ markedly. For Xe-lamp-based PAS these parameters were much lower than in the case of Ar-ion laser PAS. Likewise, analysis imprecision amounted to relative standard deviation (RSD) of 1–3 % for Xe-lamp PAS and 2–6 % for Ar-ion laser PAS. On the other hand, as expected, the calibration sensitivity achieved for the PAS signal induced by an Ar-ion laser at 481 nm was substantially higher than that of a Xe-lamp at 470 nm. Nevertheless, according to much lower sy/x, the corresponding LOD for Xe-lamp PAS was still two times lower than that of Ar-ion-based laser PAS (0.59 vs. 1.10 mg per 100 g). Unlike this, Ar-ion laser PAS showed more favourable instrumental precision and standard error of the weighed mean when compared to the Xe-lamp PAS (0.1–0.6 and 0.1–0.3 % vs. 0.5–8.0 and 0.4–1.7 %, respectively). As far as colorimetric indices are concerned, only a* proved to be analytically useful; excellent R but rather modest RSS and sy/x resulted in LOD value of 0.70 mg per 100 g and acceptable analysis imprecision of up to 3 %. The outcome of this research provides sufficient amount of evidence that analytical methods such as reflectance colorimetry and PAS without the use of any chemicals are feasible for reliable quantification of total carotenoids in freeze-dried apricot homogenates., Fotoakustična spektroskopija (PAS) i refleksna kolorimetrija predložene su kao nove metode određivanja udjela ukupnih karotenoida u liofiliziranom prahu marelice. Rezultati dobiveni ispitivanjem sedam kultivara marelice ovim dvjema tehnikama uspoređeni su s onima dobivenim konvencionalnom vidljivom spektrofotometrijom i tekućinskom kromatografijom visoke djelotvornosti (HPLC). Najbolje su korelacije dobivene između udjela ukupnih karotenoida (vidljivom je spektrofotometrijom utvrđen udjel od 1,2 do 3,4 mg u 100 g svježe mase) i kolorimetrijskog indeksa a* (parametar crvenila ispitanog uzorka), te metodom PAS s argonskim laserom ili ksenonskom lampom kao izvorom zračenja. U sva su tri slučaja dobivene usporedljive linearne korelacije. Međutim, s obzirom na osjetljivost i preciznost rezultata izraženih pomoću granice detekcije i ponovljivosti mjerenja, najboljom se pokazala metoda PAS sa ksenonskom lampom, zatim kolorimetrijski indeks a* i naposljetku metoda PAS s argonskim laserom. Obje su metode PAS imale podjednake Pearsonove koeficijente korelacije (R=0,987 i R=0,991). Ipak, rezidualna suma kvadrata (RSS) i rezidualna standardna devijacija linijske regresije (sy/x) značajno su se razlikovale. Za metodu PAS sa ksenonskom lampom ovi su parametri bili znatno manji nego za metodu PAS s argonskim laserom. Također, nepreciznost je metode izražena pomoću relativne standardne devijacije (RSD) bila od 1 do 3 % za metodu PAS sa ksenonskom lampom i od 2 do 6 % za metodu PAS s argonskim laserom. S druge je pak strane, kao što je i bilo očekivano, kalibracijska osjetljivost postignuta za signal PAS induciran argonskim laserom pri 481 nm bila znatno niža od one dobivene ksenonskom lampom pri 470 nm. Ipak, zahvaljujući bitno nižoj vrijednosti sy/x, granica detekcije metode PAS sa ksenonskom lampom (0,59 mg u 100 g) bila je dvostruko manja od one metode PAS s argonskim laserom (1,10 mg u 100 g). Nasuprot tomu, metoda PAS s argonskim laserom imala je bolju preciznost instrumenta (nepreciznost mjerenja od samo 0,1-0,6 %) i standardnu pogrešku ponderirane sredine (0,1-0,3 %), u usporedbi s metodom PAS sa ksenonskom lampom (0,5-8,0 % odnosno 0,4-1,7 %). Među kolorimetrijskim indeksima samo je indeks a* bio koristan za analizu; odlične vrijednosti R, ali skromne vrijednosti RSS i sy/x rezultirale su granicom detekcije od 0,70 mg u 100 g i prihvatljivom nepreciznošću mjerenja od najviše 3 %. Rezultati ovog istraživanja pokazuju da se analitičke tehnike, poput refleksne kolorimetrije i fotoakustične spektroskopije mogu primijeniti za pouzdano određivanje udjela ukupnih karotenoida u liofiliziranim homogenatima marelice, i to bez uporabe reagenasa.

The front configuration photopyroelectric method has been used to determine, in a nondestructive fashion, thermal effusivity of the yolk and the white of eggs of several bird species as well as of the blends of a single egg yolk and egg white (also called liquid eggs) of different avian eggs. Statistically significant differences in thermal effusivity of egg whites were observed in ten out of twenty-one comparisons made. However, in the case of egg yolks, the differences were observed in twenty among twenty-one comparisons carried out. These observations are related to a varying fat content of egg yolk and a large amount of water found in egg white. The effusivity of the blends prepared from yolks and eggs varies because the contents of the yolk and white in avian eggs differ., Za nedestruktivno određivanje toplinske efuzivnosti žumanjaka i bjelanjaka izdvojenih iz jaja nekoliko vrsta ptica, te smjese žumanjka i bjelanjka (tzv. tekuća jaja), upotrijebljena je fotopiroelektrična metoda. Od 21 ispitanog uzorka opažena je statistički značajna razlika u efuzivnosti bjelanjaka u 10 uzoraka, a žumanjaka u 20, što se povezuje s udjelom masti u žumanjku te velikim udjelom vode u bjelanjku. Efuzivnost smjese žumanjka i bjelanjka ovisi o udjelu žumanjka i bjelanjka u jajima.

The analytical performance of the newly proposed laser-based photoacoustic spectroscopy (PAS) and of optothermal window (OW) method for quantification of total anthocyanin concentration(TAC) in five sour cherry varieties is compared to that of the spectrophotometry (SP). High performance liquid chromatography (HPLC) was used to identify and quantify specific anthocyanins. Both, PAS and OW are direct methods that unlike SP and HPLC obviate the need for the extraction of analyte. The outcome of the study leads to the conclusion that PAS and OW are both suitable for quick screening of TAC in sour cherries. The correlation between the two methods and SP is linear with R^2 = 0.9887 for PAS and R^2 = 0.9918 for OW, respectively. Both methods are capable of the rapid determination of TAC in sour cherries without a need for a laborious sample pretreatment.

Rapid, quantitative information about the micronutrients (including beta carotene) in mango fruit is often desired. High performance liquid chromatography (HPLC) and spectrophotometry (SP), the two widely used methods in practice to quantify carotenoids, both require a time consuming and expensive extraction of a pigment prior to the analysis itself. This paper compares the performances of the three candidate methods for the assessment of beta carotene in twenty one different mango homogenates to that of the HPLC as an established standard technique. The extraction is imperative in neither of the methods: the laser based optothermal window (OW), the resonance Raman spectroscopy and the tristimulus colorimetry. For the quantitative analysis however the availability of the calibration curve is a necessity. All candidate methods and in particular OW technique (compact instrument, low cost and the ease of operation) hold promise for a rapid screening/quantitative assessment of beta carotene in mango fruit

The total carotenoid concentration (TCC) of several commercially available dried pastas prepared with or without eggs was assessed by means of the two wellestablished destructive approaches [spectrophotometry (SP) and high- performance liquid chromatography (HPLC)] and three non-destructive, direct (i.e., no sample preparation required) methods (resonance Raman spectroscopy, photoacoustic (PA) spectroscopy and colorimetry). The results obtained by the three direct methods correlate well with the TCC of investigated dried pastas assessed by SP and HPLC. The best linear correlation and detection limit were achieved for the PA method at 470 nm.

The combined use of a high power light emitting diode (LED) and the compact photoacoustic (PA) detector offers the possibility for a rapid (no extraction needed), accurate (precision 1.5%) and inexpensive quantification of lycopene in different products derived from the thermally processed tomatoes. The concentration of lycopene in selected products ranges from a few mg to several tens mg per 100 g fresh weight. The HPLC was used as the well established reference method.

The trans-lycopene content of fresh tomato homogenates was assessed by means of the laser photoacoustic spectroscopy, the laser optothermal window, micro-Raman spectroscopy, and colorimetry ; none of these methods require the extraction from the product matrix prior to the analysis. The wet chemistry method (high performance liquid chromatography) was used as the absolute quantitative method. Analytical figures of merit for all methods were compared statistically ; best linear correlation was achieved for the chromaticity index a^* and chroma C^*.

The concept of optothermal window (OW) (with 632.8 nm He‐Ne laser used as a radiation source), combined with copper soap based colorimetry, was proposed as a new analytical tool to determine total free fatty acid (FFA) content in thermally treated cooking oil. The results obtained were compared to those acquired by conventional spectroscopy; the correlation between the two methods is high for FFA concentrations exceeding 2 µmol/mL.

The concept of optothermal window (OW) detection was used for the first time to assess the color of several products (juice, puree, paste) derived from thermally processed tomatoes. Unlike traditional techniques that operate either in the reflectance or transmission mode, the method proposed here actually relies on indirect measurement of absorbance in optically opaque and scattering samples. Very good correlation between the magnitude of the OW signal and the color-related parameters [colorimetric index L* and tomato paste index (TPI)] was observed.

Photoacoustic (PA) spectroscopy in the visible wavelength region was shown to be suitable for a direct (no preparatory steps involved) quantification of sunset yellow (E110) colour in effervescent multi-vitamin tablets. Measurements on powdered tablets containing E110 were performed at 480 nm at which wavelength this synthetic colour shows appreciable absorbance. The PA data obtained were compared to the results acquired by diffuse reflectance spectroscopy and conventional spectrophotometry. Intrinsic simplicity, ease of sampling and rapid response were the most important advantages of the PA technique. In terms of sensitivity the performance of the three methods were comparable.

The UV-Vis photoacoustic (PA) spectroscopy was demonstrated suitable for sensitive, direct and non-destructive study of lignin in synthetic cellulose/xylan mixtures. The PA spectra recorded in the 250–550 nm wavelength range show no characteristic peak; however the amplitude of the PA signal tends to increase for higher contents of lignin in the mixture. The quantification of lignin in cellulose/xylan mixtures was accomplished by analysing PA signals obtained at 300 and 400 nm; the limits of detection (LOD) are 1.8% (at 300 nm) and 0.4% (at 400 nm).

Airborne particulates of either natural or anthropogenic origin constitute a significant portion of atmospheric pollution. Environmental xenobiotics, among which are polynuclear aromatic hydrocarbons (PAHs) and pesticides, often adsorb to aerosols and as such are transported through the atmosphere with the physicochemical properties of the aerosols determining the lifetime of these organic compounds. As an example, the resistance of some PAHs against the photolysis is explained by the effect of the aerosol's "inner filter" that reduces the intensity of incident light reaching the mineral particles. On the other hand, some constituents of the aerosols can act as catalytic and/or stoichiometric reagents in atmospheric reactions on the solid surfaces. In the study described here the photoacoustic (PA) spectroscopy in the UV-Vis was used to investigate natural and model aerosols. The PA spectra obtained from coal and wood ashes and of Saharan sand, all three representatives of airborne aerosols, provide the evidence for the existence of the "inner filter." Furthermore, valuable information about the different nature of the interaction between the model aerosols and adsorbed organics (e.g., PAH-pyranthrene and silica, alumina, and MgO) has been obtained. Finally, the outcome of the study conducted with powdered mixtures of chalk and black carbon suggests that the PA method is a candidate method for determination of carbon content in stack ashes.

The present study was designed to provide information about (i) the profile of carotene pigments and (ii) trace quantities of lycopene and β-carotene left in tomato purees. The ultrasensitive method comprising HPLC and thermal lens spectrometric (TLS) detection enabled us to detect as low as 0.3 and 1.1 ng ml−1 lycopene and β-carotene in puree extracts, respectively. Total concentration of β-carotene and lycopene (varying from 3 to 170 ng g−1) in the examined tomato purees may serve as an indicator of the carotene-specific antioxidative capacity of these products. Although conventional spectrophotometry can be used to rapidly assess the quality of products derived from tomatoes, a highly sensitive and selective method such as HPLC-TLS is needed for reliable analyses of samples such as, for example, those subjected to inappropriate storage and/or handling.

The He-Ne laser (632.8 nm) and the concept of optothermal window (OW), a variant of the open photoacoustic cell, were combined with the Folin-Ciocalteu colorimetry assay to quantitate phenolics in four red wines. The total polyphenolic content in selected red wines varied between 786 and 1630 mg/L gallic acid equivalent (GAE) as determined by OW-Folin-Ciocalteu colorimetry, which compares well to 778 and 1614 mg/L GAE obtained for the same wines by means of classical spectrophotometry. The originality and merit of OW colorimetry used here is that, unlike what is encountered in conventional spectrometry, no intermediate dilution step is required when total polyhenolics are determined in red wine. The precision, defined as the closeness to each other of 256 replicate readings of the OW signal, is generally better than 2%.

The extent of quality loss caused by enzymatic and nonenzymatic browning reactions in milk powders is usually assessed by the chemical methods, among which the determination of peroxide value (PV) is a widely used approach. In this paper, peroxide values obtained from deliberately oxidized (UV irradiation combined with the thermal stress) whole milk powders are compared to the results of photoacoustic spectroscopy (PAS) and diffuse reflectance spectrometry (DRS) in the ultraviolet and visible region. The same samples were also investigated by various methods in the near-infrared (NIR) region. The experimental data suggest a good degree of correlation between the PV and the PAS and DRS data collected at 335 nm.

A novel methodology is proposed to determine the amount of whey powder in a binary mixture containing whey and skimmed-milk powders. This new approach is based on measurement of the amplitude of the photoacoustic (PA) signal obtained when the mixture is exposed to a controlled thermal treatment; the latter was shown to affect the colour of the powder. The limit of detection for the whey powder adulterant was 2% by weight. The PA and reflectance spectra (in the visible region) of the mixtures were also compared.

CO laser infrared (IR) photoacoustic spectroscopy (PAS) at 1801 cm-1 was used to determine the content of carbonate in various soils. The PA signal is linearly proportional to the content of carbonate within the 0-30% (w/w) range; the 2% (w/w) limit of detection (LOD) is adequate for the application in practice.

SummaryPhotoacoustic and proton-induced X-ray emission measurements were performed on iron-enriched milk protein concentrates. The possibility of measuring Fe content by photoacoustic measurements in the visible region of the spectrum is discussed.

Optical absorption of LiF:Mg, Ti (TLD-100) as-received and annealed powders was investigated in the 300-700 nm range by photo-acoustic spectrometry (PAS). Near-logarithmic behaviour was found between 3 kGy and 1 MGy for the observed absorption peaks at 380, 444 and 547 nm. Optical bleaching properties were studied with white light and monochromatic irradiations at 254 and 366 nm. Fading characteristics were determined. It is shown that PAS is an appropriate tool for measuring doses on powders, especially in the high-dose range. Suggestions are made for extending the dose range to lower levels. In this way LiF TLD-100 powder may be used continuously from the mu Gy (by thermoluminescent methods) to the MGy (by PAS) range.

It is shown that under usual conditions the photothermal interferometric method may measure signal combinations originating from both photothermal deformation and changes of the complex dielectric constant.

It has been shown by Wetsel, Jr. and Spicer that, in the special case of nonlinear boundary conditions, the resolution of a thermal wave microscope increases with the square root of the detection frequency. Such a case offers no gain above the linear detection technique. In this paper we treat the more general situation in which bulk parameters are also nonlinear. It is shown that under these circumstances the nonlinear resolution is proportional to the detection frequency. Direct proportionality involves superior resolution in nonlinear imaging.