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Measure the area under band of spectra

Source: R/area_under_band.R
area_under_band.Rd

Area under the band calculations are useful for quantifying spectral features. Specialized fields in spectroscopy have different area under the band regions of interest and their ratios that help with understanding differences in materials. Additional processing is typically required prior to calculating these values for accuracy and reproducibility.

Usage

area_under_band(x, ...)

# Default S3 method
area_under_band(x, ...)

# S3 method for class 'OpenSpecy'
area_under_band(x, min = NULL, max = NULL, na.rm = FALSE, index = NULL, ...)

Arguments

x

an OpenSpecy object.

min

a numeric value of the smallest wavenumber to begin calculation.

max

a numeric value of the largest wavenumber to end calculation.

na.rm

a logical value for whether to ignore NA values.

index

an optional character scalar naming a predefined area-under-band ratio. When supplied, min and max must both be omitted. Supported values are "carbonyl_index_saub", "carbonyl_index_pe", "hydroxyl_index_pe", "hydroxyl_index_pp", "carbon_oxygen_index_pe", and "carbon_oxygen_index_pp".

...

additional arguments passed to methods.

Value

A named numeric vector with one value per spectrum. Custom min/max calculations return the inclusive sum of intensities in that band. Named indices return the numerator-band sum divided by the denominator-band sum. An index is returned as NA when the shared wavenumber axis does not fully cover its required bands or its ratio is not finite.

Details

Named indices define band ratios only; they do not apply baseline correction, normalization, or other preprocessing. Compose those steps explicitly before calling area_under_band(). The preset definitions and intended materials are:

  • carbonyl_index_saub: 1650–1850 / 1420–1500 cm^-1; specified area-under-band carbonyl index used for polyethylene (PE) and polypropylene (PP).

  • carbonyl_index_pe: 1700–1770 / 1423–1495 cm^-1; PE.

  • hydroxyl_index_pe: 3021–3353 / 1467–1504 cm^-1; PE.

  • hydroxyl_index_pp: 3300–3400 / 952–986 cm^-1; PP.

  • carbon_oxygen_index_pe: 924–1197 / 2866–2987 cm^-1; PE.

  • carbon_oxygen_index_pp: 1000–1200 / 2885–2940 cm^-1; PP.

All bounds are inclusive. The function preserves signed intensities and does not clip negative values.

References

Almond J, Sugumaar P, Wenzel MN, Hill G, Wallis C (2020). Determination of the carbonyl index of polyethylene and polypropylene using specified area under band methodology with ATR-FTIR spectroscopy. e-Polymers, 20, 369–381. doi:10.1515/epoly-2020-0041 .

Campanale C, Savino I, Massarelli C, Uricchio VF (2023). Fourier transform infrared spectroscopy to assess the degree of alteration of artificially aged and environmentally weathered microplastics. Polymers, 15, 911. doi:10.3390/polym15040911 .

Author

Win Cowger

Examples

data("raman_hdpe")
#Single area calculation
area_under_band(raman_hdpe, min = 1000,max = 2000)
#> intensity 
#>     30213 
#Ratio of two areas. 
area_under_band(raman_hdpe, min = 1000,max = 2000)/area_under_band(raman_hdpe, min = 500,max = 700)
#> intensity 
#>  9.116777 
#A predefined ratio (requires spectra covering both bands)
area_under_band(raman_hdpe, index = "carbonyl_index_saub")
#> intensity 
#>  2.270178