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Calculate UV/RI Ratio for Composition Analysis

Source: R/step_sec_uv_ri_ratio.R
step_sec_uv_ri_ratio.Rd

step_sec_uv_ri_ratio() creates a specification of a recipe step that calculates the ratio of UV to RI detector signals at each elution point. This ratio is useful for detecting compositional heterogeneity in copolymers and conjugates.

Usage

step_sec_uv_ri_ratio(
  recipe,
  uv_col = NULL,
  ri_col = NULL,
  output_col = "uv_ri_ratio",
  min_signal = 0.01,
  smooth = TRUE,
  smooth_window = 5,
  role = NA,
  trained = FALSE,
  skip = FALSE,
  id = recipes::rand_id("sec_uv_ri_ratio")
)

Arguments

recipe

A recipe object.

uv_col

Name of the UV detector measure column.

ri_col

Name of the RI detector measure column.

output_col

Name for the output ratio column. Default is "uv_ri_ratio".

min_signal

Minimum signal threshold (as fraction of max) below which ratio is set to NA. Default is 0.01 (1%). Prevents noisy ratios in baseline.

smooth

Logical. Apply smoothing to the ratio? Default is TRUE.

smooth_window

Window size for smoothing (number of points). Default is 5.

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

The UV/RI ratio provides information about chemical composition across the molecular weight distribution:

$$Ratio(t) = \frac{UV(t)}{RI(t)} = \frac{\varepsilon \cdot c(t)}{(dn/dc) \cdot c(t) \cdot K}$$

Since concentration cancels out, the ratio reflects the relative detector response factors, which depend on chemical composition.

Applications:

  • Copolymer composition drift with molecular weight

  • Block copolymer characterization

  • PEGylation analysis (protein-PEG conjugates)

  • Detection of chemical heterogeneity

  • End-group analysis with UV labels

Interpretation:

  • Constant ratio: Uniform composition across MW

  • Increasing ratio with MW: More chromophore in higher MW species

  • Decreasing ratio with MW: Less chromophore in higher MW species

Note

Both UV and RI signals should be baseline-corrected and properly aligned (using step_sec_detector_delay()) before calculating the ratio.

See also

Other sec-composition: step_sec_composition()

Examples

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

# Calculate UV/RI ratio for copolymer
rec <- recipe(~., data = sec_copolymer) |>
  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_detector_delay(reference = "ri", delay_volumes = c(uv = 0.05)) |>
  step_sec_baseline() |>
  step_sec_uv_ri_ratio(uv_col = "uv", ri_col = "ri") |>
  prep()
} # }