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Calculate Copolymer Composition from Detector Signals

Source: R/step_sec_composition.R
step_sec_composition.Rd

step_sec_composition() creates a specification of a recipe step that calculates the weight fraction of components in a copolymer or blend using UV and RI detector signals with known response factors.

Usage

step_sec_composition(
  recipe,
  uv_col = NULL,
  ri_col = NULL,
  component_a_uv,
  component_a_ri,
  component_b_uv,
  component_b_ri,
  output_col = "composition_a",
  min_signal = 0.01,
  clip = TRUE,
  role = NA,
  trained = FALSE,
  skip = FALSE,
  id = recipes::rand_id("sec_composition")
)

Arguments

recipe

A recipe object.

uv_col

Name of the UV detector measure column.

ri_col

Name of the RI detector measure column.

component_a_uv

UV response factor for component A (extinction coefficient in mL/(mg*cm) or relative units).

component_a_ri

RI response factor for component A (dn/dc in mL/g or relative units).

component_b_uv

UV response factor for component B.

component_b_ri

RI response factor for component B.

output_col

Name for the output composition column. Default is "composition_a". Contains weight fraction of component A (0-1).

min_signal

Minimum signal threshold (as fraction of max) below which composition is set to NA. Default is 0.01.

clip

Logical. Clip composition values to [0, 1] range? Default is TRUE.

role

Role for generated columns.

trained

Logical indicating if the step has been trained.

skip

Logical. Should the step be skipped when baking?

id

Unique step identifier.

Value

An updated recipe with the new step added.

Details

For a two-component system, the detector signals are:

$$UV = \varepsilon_A \cdot c_A + \varepsilon_B \cdot c_B$$ $$RI = (dn/dc)_A \cdot c_A + (dn/dc)_B \cdot c_B$$

where c_A and c_B are the concentrations of components A and B.

The weight fraction of component A is calculated by solving this system:

$$w_A = \frac{R_{obs} - R_B}{R_A - R_B}$$

where R_obs is the observed UV/RI ratio, and R_A, R_B are the ratios for pure components (e/dn/dc).

Common Applications:

  • Styrene-acrylate copolymers (styrene is UV-active)

  • Block copolymers with different chromophore content

  • PEGylated proteins (protein at 280nm, PEG is UV-transparent)

  • Polymer blends with known compositions

Example Response Factors:

  • Polystyrene: UV (254nm) ~ 1.0, dn/dc ~ 0.185

  • PMMA: UV (254nm) ~ 0.01, dn/dc ~ 0.084

  • PEG: UV (280nm) ~ 0, dn/dc ~ 0.135

  • Proteins: UV (280nm) ~ 1.0, dn/dc ~ 0.185

Note

Response factors must be in consistent units. The absolute values don't matter as long as the ratios are correct for pure components.

See also

Other sec-composition: step_sec_uv_ri_ratio()

Examples

if (FALSE) { # \dontrun{
library(recipes)
library(measure)

# Styrene-MMA copolymer composition
rec <- recipe(~., data = copolymer_data) |>
  step_measure_input_long(ri_signal, location = vars(elution_time), col_name = "ri") |>
  step_measure_input_long(uv_signal, location = vars(elution_time), col_name = "uv") |>
  step_sec_baseline() |>
  step_sec_composition(
    uv_col = "uv",
    ri_col = "ri",
    component_a_uv = 1.0,    # Styrene (UV-active)
    component_a_ri = 0.185,  # Styrene dn/dc
    component_b_uv = 0.01,   # MMA (weak UV)
    component_b_ri = 0.084,  # MMA dn/dc
    output_col = "styrene_fraction"
  ) |>
  prep()
} # }