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RI Detector Processing for SEC

Source: R/step_sec_ri.R
step_sec_ri.Rd

step_sec_ri() creates a specification of a recipe step that processes refractive index (RI) detector signals for SEC analysis, including application of dn/dc (refractive index increment) values.

Usage

step_sec_ri(
  recipe,
  measures = NULL,
  dn_dc = NULL,
  dn_dc_column = NULL,
  instrument_constant = 1,
  output_col = NULL,
  role = NA,
  trained = FALSE,
  skip = FALSE,
  id = recipes::rand_id("sec_ri")
)

Arguments

recipe

A recipe object.

measures

Character vector of RI detector column names to process. If NULL, will look for columns containing "ri" in the name.

dn_dc

Refractive index increment (mL/g). Can be:

  • A single numeric value applied to all samples

  • NULL to skip dn/dc normalization (signal remains in detector units)

dn_dc_column

Character name of a column containing sample-specific dn/dc values. Overrides dn_dc if provided.

instrument_constant

RI detector instrument constant. Default is 1.0 (no adjustment). This converts raw detector response to refractive index units.

output_col

Name for the output column. Default is to modify in place.

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 refractive index (RI) detector is the most common concentration detector in SEC/GPC. The detector response is proportional to the product of concentration and dn/dc:

$$RI_{signal} = K \times c \times (dn/dc)$$

where:

  • K is the instrument constant

  • c is the concentration (mg/mL)

  • dn/dc is the refractive index increment (mL/g)

Common dn/dc values (in water at 25°C, 633 nm):

  • Polystyrene in THF: 0.185 mL/g

  • PMMA in THF: 0.084 mL/g

  • PEG in water: 0.135 mL/g

  • Proteins: ~0.185 mL/g

  • DNA: ~0.170 mL/g

See also

Other sec-detectors: step_sec_concentration(), step_sec_dad(), step_sec_dls(), step_sec_intrinsic_visc(), step_sec_lals(), step_sec_mals(), step_sec_rals(), step_sec_uv(), step_sec_viscometer()

Examples

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

# Apply fixed dn/dc value
rec <- recipe(~., data = sec_triple_detect) |>
  step_measure_input_long(ri_signal, location = vars(elution_time), col_name = "ri") |>
  step_sec_ri(dn_dc = 0.185) |>
  prep()

# Use sample-specific dn/dc from a column
rec <- recipe(~., data = sec_triple_detect) |>
  step_measure_input_long(ri_signal, location = vars(elution_time), col_name = "ri") |>
  step_sec_ri(dn_dc_column = "dn_dc") |>
  prep()
} # }